1 00:00:00,000 --> 00:00:19,579 *36c3 preroll music* 2 00:00:19,579 --> 00:00:23,100 Herald: So who is excited about photography or videography? 3 00:00:23,100 --> 00:00:28,320 *applaus* Herald: Yeah? The title of the talk kind 4 00:00:28,320 --> 00:00:35,790 of gives us gives it away. OK. We bet we are waiting for the last people to come in 5 00:00:35,790 --> 00:00:44,160 and take a seat. Last time, raise your hands if you have a free seat next to you. 6 00:00:44,160 --> 00:00:55,289 Every one of you coming in, look for raised hands and take your seat and then we will start. 7 00:00:55,289 --> 00:01:19,390 Yeah, very good. OK. Looks like the doors are finally closed. Okay, so the next talk 8 00:01:19,390 --> 00:01:26,899 on the second day is about ultrafast imaging. So many of you have done 9 00:01:26,899 --> 00:01:34,149 videography or photography. Have thought about exposure time, how fast you can do 10 00:01:34,149 --> 00:01:39,869 your photography. And some of your might have played with lasers and have built 11 00:01:39,869 --> 00:01:45,540 blinky stuff with it or have done scientific experiments and Caroline Will 12 00:01:45,540 --> 00:01:51,140 now show us what happens if we take those to combine them and take it to the 13 00:01:51,140 --> 00:01:58,849 extreme. Caroline is working at DESY since four years. She has not done her PhD and 14 00:01:58,849 --> 00:02:05,619 is now working in a group for theoretical fast modeling of inner workings of 15 00:02:05,619 --> 00:02:11,280 molecules and atoms. She is doing a computational work and working together 16 00:02:11,280 --> 00:02:16,709 with experimentalists to verify their observations, and now she is presenting 17 00:02:16,709 --> 00:02:22,310 the inner mechanics of what she is doing and how we can actually maybe photograph 18 00:02:22,310 --> 00:02:27,720 molecules by their forming. Applause! 19 00:02:27,720 --> 00:02:31,160 *applause* 20 00:02:31,160 --> 00:02:35,189 Caroline: Great. Yeah. Thank you very much for the introduction and thank you very 21 00:02:35,189 --> 00:02:40,170 much for having me here. I'm excited to see this room so full. So I'm going to 22 00:02:40,170 --> 00:02:44,680 speak today about an ultrashort history of ultrafast imaging. It's a really broad 23 00:02:44,680 --> 00:02:48,469 topic. And I'm just gonna present some highlights, some background. Before I 24 00:02:48,469 --> 00:02:53,860 start, I'd like to give you a few more few more words about myself. As we've already 25 00:02:53,860 --> 00:02:57,620 heard, I work at DESY, this is the DESY campus you see here and in the Center for 26 00:02:57,620 --> 00:03:03,280 Free Electron Laser Science, circle in orange. That's where I did my PhD. So this 27 00:03:03,280 --> 00:03:08,530 whole campus is located in Hamburg. This is probably also a familiar place to many 28 00:03:08,530 --> 00:03:15,260 of you. And now this year we are in Leipzig a bit further away for the 36th 29 00:03:15,260 --> 00:03:21,299 Congress. So I'd like to start with a very broad question. What is the goal of 30 00:03:21,299 --> 00:03:25,519 ultrafast imaging? And we've heard already that ultrafast imaging is related to 31 00:03:25,519 --> 00:03:31,550 photography. Now, as many of you know, when you take a picture, with a quite long 32 00:03:31,550 --> 00:03:36,389 exposure time, you see just a blurry image, for example, in this picture of a 33 00:03:36,389 --> 00:03:42,510 bowl of water. We can hardly see anything. It looks a bit foggy. But if we choose the 34 00:03:42,510 --> 00:03:47,019 correct exposure time, which in this case is 100 times shorter in the right picture 35 00:03:47,019 --> 00:03:51,250 than in the left picture, then we see a clear image and we can see dynamics 36 00:03:51,250 --> 00:03:55,959 unfold. So we have here, a drop of water that is bouncing back from the bowl and 37 00:03:55,959 --> 00:04:00,470 also some ripples that are forming on the surface of this bowl. This is only visible 38 00:04:00,470 --> 00:04:06,329 because we chose the right exposure time. And this is to me really the key of being 39 00:04:06,329 --> 00:04:13,230 successful in ultrafast imaging to take a clear picture of an object that is moving. 40 00:04:13,230 --> 00:04:17,130 But it's not enough to say take just a picture. So now imagine you're a sports 41 00:04:17,130 --> 00:04:20,680 reporter. You get these two pictures and you're supposed to write up what happened. 42 00:04:20,680 --> 00:04:25,660 So it's complicated. So the top picture is the start, the bottom pictures is the end. 43 00:04:25,660 --> 00:04:30,500 Just from these two pictures, it's hard to see. But if we see before picture, we can 44 00:04:30,500 --> 00:04:35,169 see very complex dynamics unfold. There are particles accelerating at high 45 00:04:35,169 --> 00:04:41,090 velocity *laughing* coming in from the back. And even particles we did not see in the first 46 00:04:41,090 --> 00:04:46,330 picture at all somehow are very relevant to our motion. And not only skiing races 47 00:04:46,330 --> 00:04:52,270 are very dynamic, but most processes in nature are also not static. This is true 48 00:04:52,270 --> 00:04:55,889 for everything we see around ourselves, but it's especially true for everything 49 00:04:55,889 --> 00:05:01,370 that is quite small in the microcosm. And in general, we can gain a lot more insight 50 00:05:01,370 --> 00:05:08,360 from time resolved images. So from ultra short movies. I'd like to show you the 51 00:05:08,360 --> 00:05:12,270 very first ultrafast movie that was ever taken. Or maybe even the first movie that 52 00:05:12,270 --> 00:05:19,960 was taken at all. This guy, Eadweard Muybridge lived in the 19th century. And 53 00:05:19,960 --> 00:05:24,770 very shortly after the invention of a photography method, he tried to answer the 54 00:05:24,770 --> 00:05:29,900 question does a galloping horse ever lift all of its feet off the ground? Why, it's 55 00:05:29,900 --> 00:05:34,460 running. To us, it may seem like not so important question, but in the 19th 56 00:05:34,460 --> 00:05:39,560 century, the horse was the main method of transportation, and horse races were very 57 00:05:39,560 --> 00:05:45,490 popular. So there was a lot of interest in studying the dynamics of a horse, and this 58 00:05:45,490 --> 00:05:50,259 process is too fast to see with the naked eye. But Muybridge implemented a stop 59 00:05:50,259 --> 00:05:55,040 motion technique where the horse as it is running, cuts some wires, that then 60 00:05:55,040 --> 00:06:00,129 trigger photographs. And with this he was able to take these twelve photographs of 61 00:06:00,129 --> 00:06:05,220 the horse in motion. That was published under this title in Stanford in the 19th 62 00:06:05,220 --> 00:06:10,080 century. And we see very clearly in the top row third picture and maybe also 63 00:06:10,080 --> 00:06:14,330 second picture that indeed the horse lifts all of its legs off the ground, which was 64 00:06:14,330 --> 00:06:20,170 a new insight at that time. And when we stitch all of these snapshots together, we 65 00:06:20,170 --> 00:06:24,860 have an ultra fast movie of a horse galloping, which might be seen as the 66 00:06:24,860 --> 00:06:31,259 first movie that was ever made in the history of mankind. Now, when I say 67 00:06:31,259 --> 00:06:35,550 ultrafast today, I'm no longer thinking about horses, but about smaller things and 68 00:06:35,550 --> 00:06:40,570 faster things. But let's go there, very gently. So the time scale that we are all 69 00:06:40,570 --> 00:06:44,909 familiar with that we can see with the naked eye is something of the order of 70 00:06:44,909 --> 00:06:50,150 seconds. So, for example, the acceleration of this cheetah, we can see with the naked 71 00:06:50,150 --> 00:06:56,349 eye. Now, if we zoom in on this motion, we see that there are muscles inside of the 72 00:06:56,349 --> 00:07:00,930 animal that are contracting as it is running. And this muscle contraction takes 73 00:07:00,930 --> 00:07:06,810 place within milliseconds. So that's a part of a thousand in one second. But we 74 00:07:06,810 --> 00:07:11,319 can go even smaller than that to the microsecond. So proteins inside of the 75 00:07:11,319 --> 00:07:17,180 muscles or in any biologic matter fold and unfold on a timescale of microseconds. 76 00:07:17,180 --> 00:07:22,509 That's already a part in a million of a second. Now going even smaller, to 77 00:07:22,509 --> 00:07:29,080 nanoseconds there's certain dynamics that take place within these proteins, for 78 00:07:29,080 --> 00:07:34,091 example, of how they dissolve in water. But the timescale that I'm interested in 79 00:07:34,091 --> 00:07:38,969 today is the femtosecond. It's even faster than that it's the timescale where 80 00:07:38,969 --> 00:07:44,539 individual atoms move in molecules as shown in this animation. Now a 81 00:07:44,539 --> 00:07:49,199 femtosecond is very short. It's a part in a million of a billion of a second, or as 82 00:07:49,199 --> 00:07:55,039 we physicists like to call it, ten to the minus 15 seconds because it's easier to 83 00:07:55,039 --> 00:08:01,689 spell *laughing* to us. We can - to us - , we can go even faster than that. The time scale of 84 00:08:01,689 --> 00:08:05,389 electronic motion and in molecules would be an attosecond. I'm just mentioning it 85 00:08:05,389 --> 00:08:12,340 here because we don't stop at molecules, but nature is even faster than that. But 86 00:08:12,340 --> 00:08:15,030 for the purpose of this talk, I will mainly focus on processes that take place 87 00:08:15,030 --> 00:08:21,741 within the femtosecond. So within ten to the minus fifteen seconds. Now, this time 88 00:08:21,741 --> 00:08:26,410 scale is something that is not really related to what we think about in everyday 89 00:08:26,410 --> 00:08:31,150 life. But there are certain processes in chemistry, biology and physics that are 90 00:08:31,150 --> 00:08:36,419 really fundamental and that start at this time scale. Just to give you an idea how 91 00:08:36,419 --> 00:08:42,070 short a femtosecond is, the width of a human hair is about 100 micrometer. It's 92 00:08:42,070 --> 00:08:47,130 shown here in an electron microscopic picture. And for light at the speed of 93 00:08:47,130 --> 00:08:53,750 light, it takes only thirty femtoseconds to cross the hair. So that's how fast a 94 00:08:53,750 --> 00:08:58,950 femtosecond is. And even although this timescale is so short, there are many 95 00:08:58,950 --> 00:09:03,730 important processes that start here, I'd like to mention, just two of them. The 96 00:09:03,730 --> 00:09:07,630 first one is vision in our eyes and our retina there sits a molecule called 97 00:09:07,630 --> 00:09:13,660 rhodopsin, that is shown here to the left. And when light hits rhodopsin, it starts 98 00:09:13,660 --> 00:09:18,870 to isomorphise, which is a fancy word for saying it changes its shape. And this 99 00:09:18,870 --> 00:09:24,760 transmits, in the end, electrical impulses to our brain, which enables us to see. And 100 00:09:24,760 --> 00:09:28,850 this very first step of vision takes only two hundred femtoseconds to complete. But 101 00:09:28,850 --> 00:09:33,060 without it, vision would not be possible. Another very fast process that is 102 00:09:33,060 --> 00:09:39,649 fundamental in nature is photosynthesis, where plants take light and CO2 and 103 00:09:39,649 --> 00:09:45,740 convert it to other things, among them oxygen. And the very first excitation 104 00:09:45,740 --> 00:09:53,110 where light hits the plant and it starts to make all this energy available. That 105 00:09:53,110 --> 00:09:56,690 also takes less than one hundredth femtoseconds to complete. So really the 106 00:09:56,690 --> 00:10:01,930 fundamental questions of life lie at this timescale. And I'd like to just mention 107 00:10:01,930 --> 00:10:06,820 that all of these processes are not only very fast, but they also take place in 108 00:10:06,820 --> 00:10:11,540 very small objects, that are of a size of a few atoms to nanometers, which makes it 109 00:10:11,540 --> 00:10:15,480 also hard to observe because we cannot see them with the naked eye or with standard 110 00:10:15,480 --> 00:10:22,240 microscopes. Now, we've seen already that it's important to choose the right 111 00:10:22,240 --> 00:10:28,190 exposure time to get a clear image of something that's moving, but the kind of 112 00:10:28,190 --> 00:10:32,510 method that we need for taking such a photograph of something that is moving 113 00:10:32,510 --> 00:10:37,220 depends a lot on the timescale. So for stuff that is moving within seconds or 114 00:10:37,220 --> 00:10:43,459 fractions of a second, we can see that with the naked eye, we can use cameras to 115 00:10:43,459 --> 00:10:48,180 resolve faster motion, very much like Muybridge did with the very first camera. 116 00:10:48,180 --> 00:10:53,500 Today, of course, we can go much faster to maybe a few microseconds. With very fancy 117 00:10:53,500 --> 00:10:57,230 cameras called opto-electronic street cameras - i won't go into detail here - we 118 00:10:57,230 --> 00:11:01,560 can go down to picoseconds. So we are already very close to the motion of 119 00:11:01,560 --> 00:11:06,899 molecules, but we are not quite there yet. The timescale that we want to investigate 120 00:11:06,899 --> 00:11:11,060 is a femtosecond. So really a time timescale of molecular motion and 121 00:11:11,060 --> 00:11:16,550 electronics are not fast enough to reach this timescale. So we need something new. 122 00:11:16,550 --> 00:11:21,380 And fortunately, we can create light pulses that serve as to say flashes, but 123 00:11:21,380 --> 00:11:26,199 take snapshots of our moving molecules with femtosecond time resolution and light 124 00:11:26,199 --> 00:11:31,970 pulses can be made so short. So in the following, I'm going to show you a bit 125 00:11:31,970 --> 00:11:37,550 more detail on how we can use these ultra short light pulses to take snapshots of 126 00:11:37,550 --> 00:11:43,699 moving molecules. The first method that I would like to briefly show you is X-Ray 127 00:11:43,699 --> 00:11:49,120 diffraction, where we have an ultra short pulse, an X-Ray pulse coming in. It hits a 128 00:11:49,120 --> 00:11:54,899 sample shown here in the red bubbles. That's essentially a molecule that that we 129 00:11:54,899 --> 00:12:01,541 just place in the beam and it produces a so-called diffraction pattern that we can 130 00:12:01,541 --> 00:12:07,829 then record on a screen. Now, the whole process is quite complicated. So I like to 131 00:12:07,829 --> 00:12:15,420 just sketch the very basics of it. We see here X-Ray radiation hitting a crystalline 132 00:12:15,420 --> 00:12:23,040 sample here to the left and the sample is excited, starts to radiate X-Ray back and 133 00:12:23,040 --> 00:12:29,199 on the right we can see the X-Rays leaving the sample again. They will interfere and 134 00:12:29,199 --> 00:12:34,670 we can record this pattern on the screen. So this is what we see here in this 135 00:12:34,670 --> 00:12:42,570 visualization to the right. With this, we can feed a reconstructionalgorithm that 136 00:12:42,570 --> 00:12:47,110 allows us to transform back our diffraction pattern that we've seen here 137 00:12:47,110 --> 00:12:53,570 for for in this case a bio molecule. We can reconstruct from that the image as it 138 00:12:53,570 --> 00:13:00,899 was in real space. So this is some protein, I believe. X-ray diffraction is 139 00:13:00,899 --> 00:13:09,149 very nice for resolving small structures with atomic detail. Another method how we 140 00:13:09,149 --> 00:13:15,560 can take snapshots using ultra short pulses, that I would like to briefly 141 00:13:15,560 --> 00:13:20,830 introduce is absorption spectroscopy. Now you may know that light contains several 142 00:13:20,830 --> 00:13:27,540 colors. For example, you've surely have held a prism in hand, and the prism can 143 00:13:27,540 --> 00:13:32,130 break white light up into all the colors of a rainbow, that we can see with the 144 00:13:32,130 --> 00:13:38,149 eye. Now we can do the same with X-Ray pulses. Then we cannot see the colors 145 00:13:38,149 --> 00:13:44,410 anymore. So just let's just stick with a prism here. When we place a molecule in 146 00:13:44,410 --> 00:13:49,200 front of all these colors, the molecule will block certain colors. That's quantum 147 00:13:49,200 --> 00:13:56,920 mechanics. You just have to believe it or learn about it in long studies. So the 148 00:13:56,920 --> 00:14:03,110 molecule is placed in front of all these colors. And to be right, the absorption 149 00:14:03,110 --> 00:14:08,110 spectrum is recorded and the parts of the spectrum that are very bright correspond 150 00:14:08,110 --> 00:14:14,480 to the colors that have been blocked by the molecule. And this is a very nice 151 00:14:14,480 --> 00:14:19,089 technique to investigate ultra short dynamics, because where these lines are 152 00:14:19,089 --> 00:14:24,880 located is characteristic of the chemical elements that we find in the molecule. For 153 00:14:24,880 --> 00:14:28,760 example, if we use X-Ray radiation for this specific molecule, that I've shown 154 00:14:28,760 --> 00:14:33,810 here lysine, that's not so important which molecule it is. We have three different 155 00:14:33,810 --> 00:14:39,269 atoms in this molecule that are important carbon, nitrogen and oxygen and they 156 00:14:39,269 --> 00:14:43,880 absorb at very different colors so we can keep them apart when we take the spectrum. 157 00:14:43,880 --> 00:14:49,120 But not only that, we can take the spectrum at a later time when the molecule 158 00:14:49,120 --> 00:14:54,420 has moved around a bit and we will see that the colors, the position of the lines 159 00:14:54,420 --> 00:14:59,829 have changed a tiny bit. So it's really not much and I accelerated it already in 160 00:14:59,829 --> 00:15:06,070 this visualization quite a bit. But with experimental methods, we can resolve this. 161 00:15:06,070 --> 00:15:11,420 And this allows us to then trace back to how the molecule was moving in between 162 00:15:11,420 --> 00:15:16,889 when we took these two snapshots. There are many more methods that you can use to 163 00:15:16,889 --> 00:15:21,820 take ultrafast images. So we call them probe signals because we probe the 164 00:15:21,820 --> 00:15:26,889 ultrafast motion of a molecule with such an ultra short pulse. For example, we can 165 00:15:26,889 --> 00:15:33,009 record photo electrons or we can record fragments of a molecule and many more. But 166 00:15:33,009 --> 00:15:37,519 I won't go into further detail here because this is not an exhaustive list of 167 00:15:37,519 --> 00:15:42,320 methods that we can use. I'd rather like to show you how we can take molecular 168 00:15:42,320 --> 00:15:47,709 movies so how we can combine all these ultrashort pulses to in the end film a 169 00:15:47,709 --> 00:15:55,050 molecule in action. Now we've already seen in the movie of the horse that we need to 170 00:15:55,050 --> 00:16:00,990 stitch several snapshots together and then we have a full picture, full motion of a 171 00:16:00,990 --> 00:16:06,740 molecule. So we just like to do the same, but ten to the 15 times faster, should not 172 00:16:06,740 --> 00:16:13,029 be too difficult, right? So we use our ultra short pulse. First ultrasound parts 173 00:16:13,029 --> 00:16:17,980 that we use as a trigger, parts that sets off the motion and the molecule. This 174 00:16:17,980 --> 00:16:22,410 defines us a certain time zero in our experiment and makes it sort of repeatable 175 00:16:22,410 --> 00:16:28,300 because we always start the same kind of motion by giving it a small hit and now 176 00:16:28,300 --> 00:16:34,870 it's just moving around. So we wait for a certain time, a time delay and then come 177 00:16:34,870 --> 00:16:40,940 in with a probe pulse. The probe pulse takes a snapshot of a molecule. This goes 178 00:16:40,940 --> 00:16:45,320 to some detector, goes to a kind of complicated reconstruction method that we 179 00:16:45,320 --> 00:16:51,709 just execute from our screen. And with this, we reconstruct a snapshot of a 180 00:16:51,709 --> 00:16:56,850 molecule. But this is only one snapshot and we want a whole movie. So we need to 181 00:16:56,850 --> 00:17:02,240 repeat this process over and over again by shining and more and more probe pulses. 182 00:17:02,240 --> 00:17:08,040 And this will create more and more snapshots of a molecule. And in the end, 183 00:17:08,040 --> 00:17:12,209 we could stitch all of these together and we would arrive at the same image that you 184 00:17:12,209 --> 00:17:18,430 see in the in the middle where the molecules is happily moving around. There 185 00:17:18,430 --> 00:17:24,790 is one little problem: The probe pulse typically destroys the molecule. This is 186 00:17:24,790 --> 00:17:28,500 very different. This is very different from taking pictures of a horse. The horse 187 00:17:28,500 --> 00:17:36,289 normally survives. *laughting* So the probe pulse destroys the molecule. It just goes away. 188 00:17:36,289 --> 00:17:41,830 So for each of these snapshots we need to use a new molecule. So we typically have a 189 00:17:41,830 --> 00:17:47,970 stream of samples that is falling from the top to the bottom in our experiment. And 190 00:17:47,970 --> 00:17:51,690 then we have to carefully align two pulses a trigger pulse and a probe pulse that 191 00:17:51,690 --> 00:17:57,610 come together and take a snapshot of this molecule. And of course, we have to find a 192 00:17:57,610 --> 00:18:03,120 method on how to make identical molecules available in - Yeah - you see, there's a 193 00:18:03,120 --> 00:18:07,860 lot of complications with doing these experiments that I'm completely leaving 194 00:18:07,860 --> 00:18:15,090 out here. So now we want to take a molecular movie and we know that we want 195 00:18:15,090 --> 00:18:19,700 to have ultra short pulses to do so. But I didn't tell you yet what kind of light 196 00:18:19,700 --> 00:18:24,750 source we need. So there are many light sources all around us. We have here lights 197 00:18:24,750 --> 00:18:29,450 from lamps. I have a light in my laser pointer with light from the sun. But we 198 00:18:29,450 --> 00:18:35,380 need quite specific light sources to take these snapshots of molecular motion. We've 199 00:18:35,380 --> 00:18:37,970 already established that we want ultrashort pulses because else we cannot 200 00:18:37,970 --> 00:18:44,260 resolve femtosecond dynamics, but for the proper kind of wavelength that we need I 201 00:18:44,260 --> 00:18:47,980 would like to quickly remind you of the electromagnetic spectrum that you've 202 00:18:47,980 --> 00:18:54,090 probably seen at some point in high school. So, so light, as you see here in 203 00:18:54,090 --> 00:18:58,970 the bottom picture is an electromagnetic wave that comes in different wavelengths. 204 00:18:58,970 --> 00:19:05,440 They can be quite long as in the case of radio waves to the very left. Then we have 205 00:19:05,440 --> 00:19:08,470 the region of visible light shown here as the rainbow that we can perceive with our 206 00:19:08,470 --> 00:19:14,270 eyes. And then we have wavelengths that are too short to see with our eyes. First, 207 00:19:14,270 --> 00:19:18,880 UV radiation, that gives us a tan in the summer if we leave our house and then we 208 00:19:18,880 --> 00:19:25,400 have X-ray radiation, soft and hard X-ray radiation that have atomic wavelength. So 209 00:19:25,400 --> 00:19:30,570 the wavelength is really on the order of the size of an atom. So what kind of 210 00:19:30,570 --> 00:19:37,080 wavelength do we need to study ultra short dynamics - ultra fast dynamics? We can 211 00:19:37,080 --> 00:19:43,321 first think about what kind of wavelength we need when we want to construct an ultra 212 00:19:43,321 --> 00:19:49,600 short pulse. I've drawn here two pulses to the left, a slightly longer pulse to the 213 00:19:49,600 --> 00:19:53,980 right, a shorter pulse. And now if you think about squeezing the left parts 214 00:19:53,980 --> 00:19:58,610 together such that it becomes shorter and shorter, you see visually that the 215 00:19:58,610 --> 00:20:03,890 wavelength also needs to shrink. So we need shorter wavelengths for the shorter 216 00:20:03,890 --> 00:20:10,350 the pulse we want to make. So this will be located somewhere here in this region of 217 00:20:10,350 --> 00:20:15,450 the electromagnetic spectrum. And another important thing that we need to keep in 218 00:20:15,450 --> 00:20:21,250 mind is if we want to take pictures by X-ray diffraction, we are limited, so we 219 00:20:21,250 --> 00:20:27,429 can only resolve structures that are about the same size as the wavelength we used to 220 00:20:27,429 --> 00:20:31,919 take our diffraction image. So if we want to take a picture of something with atomic 221 00:20:31,919 --> 00:20:37,549 resolution, our wavelength needs to be of atomic size as well. And this places us in 222 00:20:37,549 --> 00:20:47,169 the region of X-Rays drawn here, that have a wavelength of less than a nanometer. So 223 00:20:47,169 --> 00:20:51,510 we can establish that we want small wavelengths in general. We have two 224 00:20:51,510 --> 00:20:55,840 additional requirements that would just touch upon very briefly. First, we need 225 00:20:55,840 --> 00:21:01,460 very brilliant pulses because the pulses are so short, we need to have a lot of 226 00:21:01,460 --> 00:21:06,760 light in the short pulse. You can think about taking a picture in a dark room with 227 00:21:06,760 --> 00:21:12,270 a bad camera. You won't see anything. So we need very bright flashes of light. 228 00:21:12,270 --> 00:21:16,159 Another requirement is we need coherent laser light. So we cannot just use any 229 00:21:16,159 --> 00:21:20,130 light, but it needs to have certain properties like laser light. 230 00:21:20,130 --> 00:21:25,110 Unfortunately, the lasers that you can buy commercially do not operate in the region 231 00:21:25,110 --> 00:21:29,110 of the electromagnetic spectrum that we are interested in. So we need to come up 232 00:21:29,110 --> 00:21:34,830 with something new. And I will show you how we can generate ultra short pulses 233 00:21:34,830 --> 00:21:39,380 both in the laboratory where we can generate pulses that are very short and 234 00:21:39,380 --> 00:21:46,650 extend up to maybe the soft X-ray region. And another method to generate ultra short 235 00:21:46,650 --> 00:21:53,380 pulses is at free electron laser sources, where we can go really to the hard X-Ray 236 00:21:53,380 --> 00:21:59,480 regime. But first I'd like to go to the laboratory. So in the laboratory, it's 237 00:21:59,480 --> 00:22:03,380 possible to generate an ultrashort pulse by using a process that's called high 238 00:22:03,380 --> 00:22:08,201 harmonic generation. In high harmonic generation we start off of a high 239 00:22:08,201 --> 00:22:13,470 intensity pulse, that's a red pulse coming in from the left, which which is focused 240 00:22:13,470 --> 00:22:19,350 in a gas cell. And from there, it generates new frequencies of light. So the 241 00:22:19,350 --> 00:22:24,770 light that comes out is no longer red, but it's violet, blue. We cannot see it with 242 00:22:24,770 --> 00:22:27,980 the naked eye. So that's an artist's impression of how high harmonic generation 243 00:22:27,980 --> 00:22:33,470 works. Before going into more detail about why this method is so good at producing 244 00:22:33,470 --> 00:22:38,770 ultra short pulses, I'd like to mention that this is only possible because we have 245 00:22:38,770 --> 00:22:44,120 the high intensity driving pulses, the red laser pulses available. This goes back to 246 00:22:44,120 --> 00:22:47,270 work by Donna Strickland and Gerard Mourou, who were awarded the Nobel Prize 247 00:22:47,270 --> 00:22:54,950 in the year 2018 in physics for this work that has been done in the 80s. Now we're 248 00:22:54,950 --> 00:22:59,690 coming to the only equation of his talk, which is this equation that relates the 249 00:22:59,690 --> 00:23:07,500 energy width and the time duration of a ultra short pulse. By the law of fourier 250 00:23:07,500 --> 00:23:13,150 limits we cannot have pulses that are very short in time and at the same time very 251 00:23:13,150 --> 00:23:17,700 narrow in energy. But we need to choose one. So if we want to have policies that 252 00:23:17,700 --> 00:23:23,640 are very short in time like the pulse that I've shown here on the bottom, that is 253 00:23:23,640 --> 00:23:26,669 actually only two hundred fifty attoseconds long, so even shorter than a 254 00:23:26,669 --> 00:23:33,059 femtosecond, then we need to have a very broad width in energy. And this means 255 00:23:33,059 --> 00:23:37,450 combining a lot of different colors inside of this pulse. And this is what makes high 256 00:23:37,450 --> 00:23:41,580 harmonic generation so efficient at creating ultra short pulses, because the 257 00:23:41,580 --> 00:23:47,419 spectrum that the colors that come out of high harmonic generation are shown here 258 00:23:47,419 --> 00:23:52,080 and they really span a long width. So we get a lot of different colors with about 259 00:23:52,080 --> 00:23:57,669 the same intensity. And you can think of it like putting them all back together 260 00:23:57,669 --> 00:24:04,990 into one attosecond pulse. That is very short in time. This method has really made 261 00:24:04,990 --> 00:24:08,950 a big breakthrough in the generation of ultra short laser pulses we see here a 262 00:24:08,950 --> 00:24:15,300 plot of a time duration of laser pulses versus the year, and we see that since the 263 00:24:15,300 --> 00:24:23,520 invention of the laser, here in the mid 60s, there was a first technological 264 00:24:23,520 --> 00:24:28,920 progress and shorter and shorter pulses could be generated. But then in the 80s, 265 00:24:28,920 --> 00:24:34,399 there was a limit that had been reached of about five femtoseconds, I believe. And we 266 00:24:34,399 --> 00:24:39,710 could not really go farther than that and only with high harmonic generation, that 267 00:24:39,710 --> 00:24:45,419 sets in here shortly before the year 2000, we were able to generate pulses that are 268 00:24:45,419 --> 00:24:51,760 of a femtosecond duration. So that really touch the timescale of molecular motion. 269 00:24:51,760 --> 00:24:57,200 The current world record is a pulse, that is only 43 attoseconds long, established 270 00:24:57,200 --> 00:25:02,289 in the year 2017. So that's really the timescale of electrons and we can do all 271 00:25:02,289 --> 00:25:06,649 sorts of nice experiments with it where we directly observe electronic motion in 272 00:25:06,649 --> 00:25:12,470 atoms and molecules. This is all very nice, but it has one limitation: We cannot 273 00:25:12,470 --> 00:25:17,169 go to hard X-rays, at least not right now. So high harmonic generation cannot produce 274 00:25:17,169 --> 00:25:23,000 the kind of very short wavelengths that we need in order to to do X-ray diffraction 275 00:25:23,000 --> 00:25:29,429 experiments with atomic resolution. So if we want to have ultra short pulses that 276 00:25:29,429 --> 00:25:35,730 have X-Ray wavelengths, we need to build right now very complex, very big machines, 277 00:25:35,730 --> 00:25:43,080 the so-called free electon lasers. Now, this would be a specific light source that 278 00:25:43,080 --> 00:25:48,059 can produce ultra short pulses with X-ray wavelengths in itself. The X-Ray 279 00:25:48,059 --> 00:25:52,720 wavelengths is not so new. We know how to take X-ray images for about one hundred 280 00:25:52,720 --> 00:25:58,910 and thirty years and already in the 50s. Rosalind Franklin, who is looking at a 281 00:25:58,910 --> 00:26:05,110 microscope here, was able to take a picture of DNA, an X-ray diffraction 282 00:26:05,110 --> 00:26:11,880 pattern of a DNA double helix that was successful in revealing the double helix 283 00:26:11,880 --> 00:26:19,370 structure of our genetic code. But this is not a time resolved measurement. So think 284 00:26:19,370 --> 00:26:24,650 of it as you have a molecule that is in crystalline form, so it's not moving 285 00:26:24,650 --> 00:26:32,480 around and we can just take an X-ray image of it, it's not going anywhere. But if we 286 00:26:32,480 --> 00:26:36,860 want - if we want to take a picture of something that is moving, we need to have 287 00:26:36,860 --> 00:26:43,400 very short pulses. But we still need the same number of what we call photons, light 288 00:26:43,400 --> 00:26:48,890 particles. Or think of it as we need more brilliant X-ray flashes of light than we 289 00:26:48,890 --> 00:26:55,140 could obtain before. And there was very nice technological development in the past 290 00:26:55,140 --> 00:27:01,690 50 years or so, where we were able to go from the X-ray tube to newer light sources 291 00:27:01,690 --> 00:27:07,260 called Synchrotron, and today, free electro lasers that always increase the 292 00:27:07,260 --> 00:27:12,180 peak brilliance in an exponential way. So we can take really brilliant, really 293 00:27:12,180 --> 00:27:17,270 bright X-ray flashes right now. I cannot go into the details of all of that, but I 294 00:27:17,270 --> 00:27:21,350 found a very nice talk from two years ago, but actually explains everything from 295 00:27:21,350 --> 00:27:28,590 Synchrotron to FELs still available online if you're interested in this work. And as 296 00:27:28,590 --> 00:27:32,110 always, if something is failing scaling exponentially, most of you will be 297 00:27:32,110 --> 00:27:37,840 familiar with Moore's Law, that tells us about the exponential scaling of 298 00:27:37,840 --> 00:27:45,169 transistors. If something grows this fast, it really opens up a new series of 299 00:27:45,169 --> 00:27:49,299 experiments of new technological applications that no one has thought of 300 00:27:49,299 --> 00:27:55,600 before. And the same is true with free electron lasers. So I'm going to focus 301 00:27:55,600 --> 00:28:00,450 just on the most brilliant light sources for X-rays. Right now, the free electron 302 00:28:00,450 --> 00:28:06,230 lasers that are at the top right here of this graph have been around for maybe 10 303 00:28:06,230 --> 00:28:13,220 years or so. I cannot go into a lot of detail on how to generate ultrashort 304 00:28:13,220 --> 00:28:18,220 pulses with X-Rays. So I'd like to give you just a very broad picture of how 305 00:28:18,220 --> 00:28:23,909 this works. First, we need a bunch of electrons, that is accelerated to 306 00:28:23,909 --> 00:28:29,640 relativistic speed. This sounds very easy, but is actually part of a two kilometer 307 00:28:29,640 --> 00:28:35,490 long accelerator, that we have to build and maintain. Now we have this bunch here 308 00:28:35,490 --> 00:28:41,230 of electrons shown in red and it's really fast and now we can bring it into 309 00:28:41,230 --> 00:28:46,519 something that is called an undulator. That's a series of alternating magnets, 310 00:28:46,519 --> 00:28:52,270 shown here in green on blue for the alternating magnets. And you may remember, 311 00:28:52,270 --> 00:28:57,100 that when we put an electron, that is as a charged particle, into a magnetic field, 312 00:28:57,100 --> 00:29:02,820 the Lorence force will drive it away. And if you have alternating magnets, then the 313 00:29:02,820 --> 00:29:08,890 electron will go on a sort of wiggly path in this undulator. And the electron is a 314 00:29:08,890 --> 00:29:13,890 charged particle as it is wiggling around wherever it turns around, it will emit 315 00:29:13,890 --> 00:29:18,309 radiation, that happens to be in the X-ray region of the electromagnetic spectrum, 316 00:29:18,309 --> 00:29:23,260 which is exactly what we want. We can watch this little movie here to see a 317 00:29:23,260 --> 00:29:28,800 better picture. So this is the undulating seeing from the side. We now go inside of 318 00:29:28,800 --> 00:29:35,880 the undulator. We have a series of alternating magnets. Now the electron 319 00:29:35,880 --> 00:29:42,430 bunch shows up and you see the wiggly motion as it passes the different magnets. 320 00:29:42,430 --> 00:29:48,390 And you see the bright X-Ray flash that is formed and gets stronger and stronger as 321 00:29:48,390 --> 00:29:54,779 the electron bunch passes the undulator. So we need several of these magnet pairs to 322 00:29:54,779 --> 00:30:00,130 in the end, get the very bright X-Ray flash. And at the end of the undulator we 323 00:30:00,130 --> 00:30:06,240 dump the electron, we don't really need this electron bunch anymore and continue 324 00:30:06,240 --> 00:30:13,830 with a very bright X-Ray flash. This whole process is a bit stochastic in nature, but 325 00:30:13,830 --> 00:30:18,890 it's amplifying itself in because of the undulator. This is why the longer the 326 00:30:18,890 --> 00:30:29,020 undulator is, the more bright X-Ray flashes we can generate. This whole thing 327 00:30:29,020 --> 00:30:33,149 is kind of complicated to build, it's a very complex machine. So right now there 328 00:30:33,149 --> 00:30:37,740 are only very few free electron lasers in the world. First one in California called 329 00:30:37,740 --> 00:30:43,850 LCLS 1, currently being upgraded to LCLS 2. There are several in Europe. There's 330 00:30:43,850 --> 00:30:49,330 one in Switzerland, in Italy and Hamburg. So there's a Flash that does not operate 331 00:30:49,330 --> 00:30:54,559 in the hot X-ray regime, but was kind of first free electron laser. That's the most 332 00:30:54,559 --> 00:30:58,919 recent addition to the free electron laser zoo. It's the European XFEL also located 333 00:30:58,919 --> 00:31:04,399 in Hamburg. And then we have some of these light sources in Asia, in Korea, South 334 00:31:04,399 --> 00:31:10,730 Korea, Japan, and one currently under construction in Shanghai. I'd like to show 335 00:31:10,730 --> 00:31:15,740 you a bit more details about the European X-ray free electron laser, because it's 336 00:31:15,740 --> 00:31:23,980 closest to us, and at least closest to where I work. So the European XFEL is a 337 00:31:23,980 --> 00:31:30,049 three point four kilometer long machine that is funded by in total 12 countries, 338 00:31:30,049 --> 00:31:36,350 So Germany and Russia paying the most and then the other 10 countries also providing 339 00:31:36,350 --> 00:31:41,130 to the construction and maintenance costs. This machine starts at the DESY campus, 340 00:31:41,130 --> 00:31:47,340 but as shown here to the right of the picture. And then we have first an 341 00:31:47,340 --> 00:31:51,580 accelerator line for the electrons that it's already one point seven kilometers 342 00:31:51,580 --> 00:31:58,450 long and where we add electrons reach their relativistic speed. Then the 343 00:31:58,450 --> 00:32:04,600 undulate comes in, so the range of magnets where we X-Ray flashes are produced. The x 344 00:32:04,600 --> 00:32:09,330 X-Ray flashes then cross the border to Schleswig-Holstein, *laughter * shown here, on the 345 00:32:09,330 --> 00:32:16,450 other side in a new federal state. They reach the experimental hall. We have in 346 00:32:16,450 --> 00:32:21,049 total six experimental end stations at the European XFEL that provide different 347 00:32:21,049 --> 00:32:24,419 instrumentation, depending on which kind of system you want to study, you need 348 00:32:24,419 --> 00:32:30,960 slightly different instruments. And it's not only for taking molecular movies, but 349 00:32:30,960 --> 00:32:36,010 the XFEL is used, among others, for material science, for the imaging of bio 350 00:32:36,010 --> 00:32:40,950 molecules, for femtosecond chemistry, all sorts of things. So really wide range of 351 00:32:40,950 --> 00:32:46,580 applications. It's right now the the fastest such light source can take twenty 352 00:32:46,580 --> 00:32:51,580 seven thousand flashes per second, which is great because every flash is one 353 00:32:51,580 --> 00:32:56,110 picture. So if we want to take a lot of snapshots, if you want to generate a lot 354 00:32:56,110 --> 00:33:01,179 of data in a short time, it's great to have as many flashes per second as 355 00:33:01,179 --> 00:33:08,720 possible. And as you can imagine, it's kind of expensive since there are so few 356 00:33:08,720 --> 00:33:15,450 free electron lasers in the world to take measurements there. The complete price tag 357 00:33:15,450 --> 00:33:19,919 for constructing this machine, it took eight years and cost one point two billion 358 00:33:19,919 --> 00:33:25,580 euros, which may seem a lot, but it's the same amount that we spend on concert halls 359 00:33:25,580 --> 00:33:39,029 in Hamburg. *loud laughter applause* So kind of comparable. Now, when you factor in maintenance and so on, 360 00:33:39,029 --> 00:33:45,639 I think a minute of X-Ray beam at such an XFEL cost several thousands of tens of 361 00:33:45,639 --> 00:33:51,570 thousands of euros in the end. So getting measurement time is complicated and there 362 00:33:51,570 --> 00:33:56,710 are committees that select the most fruitful approaches and so on. So in order 363 00:33:56,710 --> 00:34:04,000 to not to waste or do taxpayers money. With this, I'd like to make a small 364 00:34:04,000 --> 00:34:08,020 comparison of the light sources that I've introduced now. So I introduced the 365 00:34:08,020 --> 00:34:12,810 laboratory light sources and the XFEL light source. In general, in the 366 00:34:12,810 --> 00:34:17,600 laboratory we can generate very short pulses of less than 100 attoseconds by now 367 00:34:17,600 --> 00:34:22,980 and in the XFEL we are limited to something about 10 femtoseconds right now. 368 00:34:22,980 --> 00:34:29,630 In terms of brilliance the XFELs can go to much more bright pulses, simply because 369 00:34:29,630 --> 00:34:32,960 they are bigger machines and high harmonic generation in itself is a kind of 370 00:34:32,960 --> 00:34:38,870 inefficient process. In terms of wavelength X-Ray free electron lasers 371 00:34:38,870 --> 00:34:42,620 enable us to reach these very short wavelengths with X-Rays, that we need to 372 00:34:42,620 --> 00:34:48,290 get atomic resolution of defractive images. In the laboratory we are a bit 373 00:34:48,290 --> 00:34:54,850 more limited to maybe the soft X-ray region. There's another important thing to 374 00:34:54,850 --> 00:34:59,890 keep in mind when we do experiments, that's the control of pulse parameters. So 375 00:34:59,890 --> 00:35:03,040 is every pulse that comes out of my machine the same as the one that came out 376 00:35:03,040 --> 00:35:08,520 of my machine before. And since the XFEL produces pulses by what is in the end, a 377 00:35:08,520 --> 00:35:13,630 stochastic process, that's not really the case. So the control of possible 378 00:35:13,630 --> 00:35:20,400 parameters is not really given. This is much better in the laboratory. And in 379 00:35:20,400 --> 00:35:23,280 terms of cost and availability, it would of course, be nice if we could do more 380 00:35:23,280 --> 00:35:29,620 experiments in the lab. Then at the XFEL simply because we XFEL ls so expensive to 381 00:35:29,620 --> 00:35:35,730 build and maintain and we have so few of them in the world. And you can see this 382 00:35:35,730 --> 00:35:41,840 tunnel here. It stretches for two kilometers or so, all packed with very 383 00:35:41,840 --> 00:35:53,260 expensive equipment. So I'd like to show you a brief example of what we can learn 384 00:35:53,260 --> 00:35:58,500 in ultrafast science. So this is a theoretical work that we did in our group. 385 00:35:58,500 --> 00:36:03,720 So no experimental data, but still nice to see. This is concerned with an organic 386 00:36:03,720 --> 00:36:09,730 solar cell. So we all know solar cells. They convert sunlight to electric energy 387 00:36:09,730 --> 00:36:14,480 that we can use in our devices. The nice thing about organic solar cells is that 388 00:36:14,480 --> 00:36:20,900 they are foldable, very lightweight, and we can produce them cheaply. The way that 389 00:36:20,900 --> 00:36:25,630 such a solar cell works is we have light shining in and at the bottom of the solar 390 00:36:25,630 --> 00:36:29,410 cell there sits an electrode that collects all the charges and creates an electric 391 00:36:29,410 --> 00:36:33,570 current. Now light creates a charge that somehow needs to travel down there to this 392 00:36:33,570 --> 00:36:42,000 electrode and in fact, many of these charges. So the important thing where we 393 00:36:42,000 --> 00:36:46,640 build such an organic solar cell is that we need a way to efficiently transport 394 00:36:46,640 --> 00:36:55,240 these charges. And we can do so by putting polymers inside. A polymer is just a 395 00:36:55,240 --> 00:36:59,670 molecule that is made up of two different or two or more different smaller 396 00:36:59,670 --> 00:37:05,100 molecules. And one such polymer, which should be very efficient at transporting 397 00:37:05,100 --> 00:37:10,170 these charges is BT-1T, that is shown here of a name is not so important, it's an 398 00:37:10,170 --> 00:37:15,080 abbreviation. Because in BT-1T when we create a charge at one end of a molecule 399 00:37:15,080 --> 00:37:20,180 here at the top, it travels very quickly to the other side of a molecule and you 400 00:37:20,180 --> 00:37:26,880 can imagine stacking several of these BT-1T or especially of the Ts together, 401 00:37:26,880 --> 00:37:31,170 putting it in this material. And then we have a very efficient flow of energy in 402 00:37:31,170 --> 00:37:41,880 our organic solar cell. So what we did was we calculated the ultrafast charge 403 00:37:41,880 --> 00:37:48,161 migration in BT-1T, shown here to the right. The pink thing is the charge 404 00:37:48,161 --> 00:37:53,570 density that was created by an initial ionization of the molecule. And now I show 405 00:37:53,570 --> 00:37:58,110 you the movie, how this charge is moving around in a molecule so you can see 406 00:37:58,110 --> 00:38:02,820 individual atoms moving, the whole molecules vibrating a bit. And the charge, 407 00:38:02,820 --> 00:38:10,570 if you look closely, is locating on the right half of a molecule within about 250 408 00:38:10,570 --> 00:38:16,780 femtoseconds. Now, we cannot observe this charge migration directly by looking at 409 00:38:16,780 --> 00:38:21,290 this pink charge density that I've drawn here, because it's at least for us, not 410 00:38:21,290 --> 00:38:26,151 experimentally observable directly. So we need an indirect measurement, an X-Ray 411 00:38:26,151 --> 00:38:30,050 absorption spectroscopy that I showed you in the beginning could be such a 412 00:38:30,050 --> 00:38:35,310 measurement. Because in the X-Ray absorption spectrum of BT-1T that I've 413 00:38:35,310 --> 00:38:41,030 shown here in the bottom left, we see distinct peaks depending on where the 414 00:38:41,030 --> 00:38:47,070 charge is located. Initially the charge is located at the top sulfur atom here and 415 00:38:47,070 --> 00:38:53,780 this molecule and we will see a peek at this color. Once the charge moves away to 416 00:38:53,780 --> 00:38:58,060 the bottom of a molecule to the other half, we will see a peak at the place 417 00:38:58,060 --> 00:39:02,680 where nothing is right now because the charge is not there. But if I start this 418 00:39:02,680 --> 00:39:09,600 movie, we will again see very fast charge transfer. So within about two hundred 419 00:39:09,600 --> 00:39:14,050 femtoseconds, the charge goes from one end to the molecule to the other end of a 420 00:39:14,050 --> 00:39:19,470 molecule. And it would be really nice to see this in action in the future XFEL 421 00:39:19,470 --> 00:39:25,720 experiment. But the process is very long. You need to apply for time at an XFEL. You 422 00:39:25,720 --> 00:39:29,850 need to evaluate all the data. So maybe a couple of years from now we will have the 423 00:39:29,850 --> 00:39:37,730 data available. Right now we are stuck with this movie, that we calculated. Now, 424 00:39:37,730 --> 00:39:43,590 towards the end of my talk, I'd like to go beyond the molecular movie. So I've shown 425 00:39:43,590 --> 00:39:47,860 you now how to generate the light pulses and an example of what we can study with 426 00:39:47,860 --> 00:39:53,540 these light pulses. But this is not all we can do: So when you think of a chemical 427 00:39:53,540 --> 00:39:58,420 reaction, you might remember high school chemistry or something like this, which is 428 00:39:58,420 --> 00:40:03,460 always foaming and exploding and nobody really knows what is going on. So a 429 00:40:03,460 --> 00:40:08,480 chemical reaction quite naturally involves molecular dynamics, for example, the 430 00:40:08,480 --> 00:40:13,180 decomposition of a molecule to go from here, from the left side to the right 431 00:40:13,180 --> 00:40:18,180 side, the molecules will somehow need to rearrange so all the atoms will have moved 432 00:40:18,180 --> 00:40:24,340 quite a bit. We've seen already how we can trigger these chemical reactions or these 433 00:40:24,340 --> 00:40:29,770 molecular motion that was part of a molecular movie. But it would be really 434 00:40:29,770 --> 00:40:34,430 cool if we could control the reaction with light. So the way to do this, it's not 435 00:40:34,430 --> 00:40:38,920 currently something that is possible, but maybe in the near future, would be to 436 00:40:38,920 --> 00:40:44,440 implement a sort of optimisation feedback loop. So we would record the fragments of 437 00:40:44,440 --> 00:40:48,970 our reaction, send it to an optimization routine that will also be quite 438 00:40:48,970 --> 00:40:53,620 complicated and will need to take into account the whole theory of how light and 439 00:40:53,620 --> 00:40:58,770 matter, interact and so on. And this optimization routine would then generate a 440 00:40:58,770 --> 00:41:03,800 new sequence of ultra short pulses and with this feedback loop, it might be 441 00:41:03,800 --> 00:41:10,100 possible to find the right pulses to control chemical reactions, taking into 442 00:41:10,100 --> 00:41:17,640 account the quantum nature of this motion and so on. Right now this is not possible. 443 00:41:17,640 --> 00:41:23,651 First, because the whole process of how we can generate these ultra short pulses is 444 00:41:23,651 --> 00:41:28,760 not so well controlled that we could actually implement it in such a loop. And 445 00:41:28,760 --> 00:41:33,000 also the step optimization routine is more complex than it looks like here in this 446 00:41:33,000 --> 00:41:39,490 picture. So this is something that people are working on at the moment, but this 447 00:41:39,490 --> 00:41:44,300 would be something like the ultra fast wishlist for next Christmas, not this 448 00:41:44,300 --> 00:41:49,710 Christmas. So we've succeeded in taking a molecular movie, but we would also like to 449 00:41:49,710 --> 00:41:55,270 be able to direct a molecular movie. So to go beyond just watching nature, but 450 00:41:55,270 --> 00:42:01,460 controlling nature because this is what humans like to best, * laughing* fortunately or 451 00:42:01,460 --> 00:42:06,230 unfortunately, it depends. So I'd like to just show you that this is really an ultra 452 00:42:06,230 --> 00:42:12,220 fast developing field. There's lots of new research papers every day, every week 453 00:42:12,220 --> 00:42:18,070 coming in, studying all sorts of systems. When you just take a quick and dirty 454 00:42:18,070 --> 00:42:22,820 metric of how important ultrafast science is this is the number of articles per year 455 00:42:22,820 --> 00:42:28,500 that mentioned ultrafast in Google Scholar, it's exponentially growing. At 456 00:42:28,500 --> 00:42:30,780 the same time, the number of total publications in Google Scholar is more or 457 00:42:30,780 --> 00:42:34,990 less constant, so the blue line here outgrows the green line considerably since 458 00:42:34,990 --> 00:42:45,070 about ten years. So what remains to be done? We've seen that we have light 459 00:42:45,070 --> 00:42:50,020 sources available to generate ultra short pulses, but as always, when you have 460 00:42:50,020 --> 00:42:55,540 better machines, bigger machines, you can take more fancy experiments. So it would 461 00:42:55,540 --> 00:43:00,580 be really nice to develop both lab based sources and free electron laser sources so 462 00:43:00,580 --> 00:43:06,360 that we can take more, more interesting, more complex experiments. Another 463 00:43:06,360 --> 00:43:10,060 important challenge, that's what people in my research group where I work are working 464 00:43:10,060 --> 00:43:16,750 on is to improve theoretical calculations because I did not go into a lot of detail 465 00:43:16,750 --> 00:43:21,730 on how to calculate these things, but it's essentially quantum mechanics and quantum 466 00:43:21,730 --> 00:43:26,530 mechanics skales very unfavorably. So going from a very small molecule like the 467 00:43:26,530 --> 00:43:32,490 glycene molecule here to something like a protein is not doable. Simply, it cannot 468 00:43:32,490 --> 00:43:38,100 compute this with quantum mechanics. So we need all sorts of new methodology to - 469 00:43:38,100 --> 00:43:45,100 Yeah - to better describe larger systems. We would in general like to study not only 470 00:43:45,100 --> 00:43:49,410 small molecules and not only take movies of small molecules, but really study large 471 00:43:49,410 --> 00:43:55,710 systems like this is the FMO complex, that is a central in photosynthesis or solid 472 00:43:55,710 --> 00:44:01,410 states that are here shown in this crystal structure simply because this is more 473 00:44:01,410 --> 00:44:07,790 interesting for biological, chemical applications. And finally, as I've shown 474 00:44:07,790 --> 00:44:13,460 you, it would be cool to directly control chemical reactions with light. So to find 475 00:44:13,460 --> 00:44:20,810 a way how to replace this mess with a clean light pulse. With this, I'm at the 476 00:44:20,810 --> 00:44:26,240 end. I'd like to quickly summarize femtodynamics, really fundamental in 477 00:44:26,240 --> 00:44:31,500 biology, chemistry and physics. So more or less, the origin of life is on this 478 00:44:31,500 --> 00:44:36,840 timescale. We can take molecular movies with ultrashort laser pulses and we can 479 00:44:36,840 --> 00:44:41,650 generate these pulses in the laboratory or add free electron lasers with different 480 00:44:41,650 --> 00:44:46,820 characteristics. And we would like to not only understand these ultra fast 481 00:44:46,820 --> 00:44:51,920 phenomena, but we would also like to be able to control them in the future. With 482 00:44:51,920 --> 00:44:54,160 this, I'd like to thank you for your attention and thank the supporting 483 00:44:54,160 --> 00:45:04,570 institutions here that funded my PhD work. 484 00:45:04,570 --> 00:45:10,820 *applause* 485 00:45:10,820 --> 00:45:17,380 Herald: Well, that was an interesting talk. I enjoyed it very much. I guess this 486 00:45:17,380 --> 00:45:23,450 will spark some questions. If you want to ask Caroline a question, please line up 487 00:45:23,450 --> 00:45:28,900 behind the microphones. We have three in the isles between the seats if you want to 488 00:45:28,900 --> 00:45:36,070 leave, please do so in the door here in the front. And until we get questions from 489 00:45:36,070 --> 00:45:39,570 the audience, do we have questions from the Internet? 490 00:45:39,570 --> 00:45:45,311 Signal angel: Yes. Big fat random user is curious about the design of the X-Ray 491 00:45:45,311 --> 00:45:48,460 detector. Do you have any information on that? 492 00:45:48,460 --> 00:45:56,030 Caroline: That's also very complex. I'm not a big expert in detectors. At this 493 00:45:56,030 --> 00:45:58,460 point, I really recommend watching the talk from two years ago, that explains a 494 00:45:58,460 --> 00:46:05,140 lot more about the X-Ray detectors. So what I know about the X-Ray detector is 495 00:46:05,140 --> 00:46:09,990 that it's very complicated to process all the data because when you have 27000 496 00:46:09,990 --> 00:46:16,370 flashes of light, it produces, I think terabytes of data within seconds and you 497 00:46:16,370 --> 00:46:21,030 need to somehow be able to store them and analyze them. So there is also a lot of 498 00:46:21,030 --> 00:46:24,190 technology involved in the design of these detectors. 499 00:46:24,190 --> 00:46:30,060 Herald: Thank you. So the first question from microphone 2 in the middle. 500 00:46:30,060 --> 00:46:34,110 Microphone 2: So my question is. Herald: Please go close to the microphone. 501 00:46:34,110 --> 00:46:38,860 Microphone 2: My question is regarding the synchronization of the detector units when 502 00:46:38,860 --> 00:46:45,030 you're pointing to free electron laser so you can achieve this in synchronization. 503 00:46:45,030 --> 00:46:50,700 Caroline: This is also very complicated. It's easier to do in the lab. So you're 504 00:46:50,700 --> 00:46:54,800 talking about the synchronization of essentially the first pulse and the second 505 00:46:54,800 --> 00:47:00,540 pulse. Right. So in the lab, you typically generate the second pulse from part of the 506 00:47:00,540 --> 00:47:05,310 first pulse. So you have a very natural alignment, at least in time of these two 507 00:47:05,310 --> 00:47:10,190 pulses. The X-ray free electron lasers have special timing tools that allow you 508 00:47:10,190 --> 00:47:16,830 to find out how much is the time delay between your two pulses. But it's true 509 00:47:16,830 --> 00:47:21,520 that this is complicated to achieve and this limits the experimental time 510 00:47:21,520 --> 00:47:25,860 resolution to something that is even larger than the time duration of the 511 00:47:25,860 --> 00:47:30,540 pulses. Herald: So now next question from 512 00:47:30,540 --> 00:47:35,930 microphone number 3. Microphone 3: Yes, i remember in the 513 00:47:35,930 --> 00:47:42,810 beginning, you explained that your measuring method usually destroys your 514 00:47:42,810 --> 00:47:49,700 molecules. That's a bit of a contradiction to your idea to control. *laughing* 515 00:47:49,700 --> 00:47:59,090 Caroline: In principle, yes. But, so in the case of control, we would like to use 516 00:47:59,090 --> 00:48:04,650 a second pulse, that does not destroy the molecule. But for example, at least 517 00:48:04,650 --> 00:48:11,140 destroys it in a controlled way, for example. *loud laughter* So there's a difference between 518 00:48:11,140 --> 00:48:15,250 just blowing up your molecule and breaking apart a certain part, but yet that we are 519 00:48:15,250 --> 00:48:19,770 interested in. And that's what we would like to do in the control case. So we 520 00:48:19,770 --> 00:48:24,490 would like to be able to to control, for example, the fragmentation of a molecule 521 00:48:24,490 --> 00:48:30,230 such that we only get the important part out and everything else just goes away. 522 00:48:30,230 --> 00:48:34,430 Microphone3: Thank you. Herald: So then another question for 523 00:48:34,430 --> 00:48:39,240 microphone 2 in the middle. Microphone 2: So thank you for the talk. I 524 00:48:39,240 --> 00:48:44,470 was interested in how large structures or molecules can you imagine with this lab 525 00:48:44,470 --> 00:48:48,520 contributions and with this XFEL thing? Caroline: Sorry. Can you repeat? 526 00:48:48,520 --> 00:48:54,790 Microphone 2: So how large molecules can you imagine in this laboratory with this 527 00:48:54,790 --> 00:48:59,120 high harmonic measures? Caroline: So how large is not really the 528 00:48:59,120 --> 00:49:05,630 fundamental problem? People have taken snapshots of viruses or bigger bio 529 00:49:05,630 --> 00:49:11,870 molecules. If you want to - the problem is rather how small can we get? So yeah, to 530 00:49:11,870 --> 00:49:16,370 take pictures of a very small molecule. Currently we cannot take a picture of an 531 00:49:16,370 --> 00:49:21,780 individual small molecule, but what people do is they create crystals of a small 532 00:49:21,780 --> 00:49:25,260 molecule, sticking several of them together and then taking images of this 533 00:49:25,260 --> 00:49:30,371 whole crystal for single particles, I think right now about the scale of a virus 534 00:49:30,371 --> 00:49:34,180 nanometers. Microphone 2: Thank you. 535 00:49:34,180 --> 00:49:38,190 Herald: OK. Do we have another question from the Internet? 536 00:49:38,190 --> 00:49:43,740 Signal Angel: We have. So this is concerning your permanent destruction of 537 00:49:43,740 --> 00:49:49,450 forces, I guess. How do you isolate single atoms and molecules for analysing between 538 00:49:49,450 --> 00:49:55,860 the different exposures? Caroline: Yes, excellent question. So 539 00:49:55,860 --> 00:50:01,440 molecules can be made available in the gas phase by - so if you have them in a solid 540 00:50:01,440 --> 00:50:08,030 somewhere and you heat that up, they will evaporate from that surface. This is how 541 00:50:08,030 --> 00:50:11,760 you can get them in the gas phase. This, of course, assumes that you have a 542 00:50:11,760 --> 00:50:15,940 molecule, that is actually stable in the gas space, which is not true for all 543 00:50:15,940 --> 00:50:22,450 molecules. And then the, the hard thing is to align all three things. So the pump 544 00:50:22,450 --> 00:50:27,540 pulse, the probe pulse and the molecule all need to be there at the same time. 545 00:50:27,540 --> 00:50:32,600 There are people doing whole PhD theses on how to design gas nozzles that can provide 546 00:50:32,600 --> 00:50:37,670 this stream of molecules. Signal Angel: So you basically really 547 00:50:37,670 --> 00:50:41,190 having a stream coming from a nozzle? Caroline: Yes. 548 00:50:41,190 --> 00:50:43,300 Signal Angel: It's a very thin stream, I guess. 549 00:50:43,300 --> 00:50:47,620 Caroline: Yes. Signal Angel: Then you're exposing it like 550 00:50:47,620 --> 00:50:49,990 in a regular interval. Caroline: And of course you try to hit as 551 00:50:49,990 --> 00:50:56,180 many molecules as possible. So this is especially important when you do pictures 552 00:50:56,180 --> 00:50:59,760 of crystallized molecules because crystallizing these molecules is a lot of 553 00:50:59,760 --> 00:51:04,480 work. You don't want to waste like 99 percent that just fall away and you never 554 00:51:04,480 --> 00:51:07,990 take snapshots of them. Signal Angel: Thanks. 555 00:51:07,990 --> 00:51:10,990 Herald: So another question from microphone 3. 556 00:51:10,990 --> 00:51:18,810 Microphone 3: How do you construct this movie? I mean, for every pulse to have a 557 00:51:18,810 --> 00:51:25,240 new molecule and for every molecule is oriented differently in space and has 558 00:51:25,240 --> 00:51:31,190 different oscillation modes. How do correlate them? I mean, in the movie, I 559 00:51:31,190 --> 00:51:35,100 mean, every molecule is different than the previous one. 560 00:51:35,100 --> 00:51:41,400 Caroline: Yes. Excellent question. That's, So first, what people can do is align 561 00:51:41,400 --> 00:51:48,430 molecules. So especially molecules that are more or less linear. You can force 562 00:51:48,430 --> 00:51:55,410 them to be oriented in a certain way. And then there's also a bit of a secret in the 563 00:51:55,410 --> 00:52:00,220 trigger pulse that first sets off this motion. For example, if this trigger pulse 564 00:52:00,220 --> 00:52:04,600 is a very strong proto ionization, then this will kill off any sorts of 565 00:52:04,600 --> 00:52:08,910 vibrational states that you have had before in the molecule. So in this sense, 566 00:52:08,910 --> 00:52:12,840 the trigger parts really defines a time zero, that should be reproducible for any 567 00:52:12,840 --> 00:52:17,950 molecule that shows up in the stream and the rest is statistics. 568 00:52:17,950 --> 00:52:23,580 Microphone 3: Thank you. Herald: So there's another question on 569 00:52:23,580 --> 00:52:27,070 microphone 3. Microphone 3: Are there any pre pulses or 570 00:52:27,070 --> 00:52:31,420 ghosts, You need to get rid of? Caroline: Sorry. Again. 571 00:52:31,420 --> 00:52:36,550 Microphone 3: You have to control pre pulses or ghosts during this effect for 572 00:52:36,550 --> 00:52:39,560 measurement. Caroline: That I'm not really sure of, 573 00:52:39,560 --> 00:52:42,090 since I'm not really conducting experiments, but probably. 574 00:52:42,090 --> 00:52:49,510 Herald: And another one from the middle, from microphone 2 please. 575 00:52:49,510 --> 00:52:55,430 Microphone 2: I suppose if you apply for experimentation time at the XFEL laser, 576 00:52:55,430 --> 00:53:02,000 you have to submit very detailed plans and time lines and everything. And you will 577 00:53:02,000 --> 00:53:07,950 get the time window for your experiment, I guess. what's going to happen if you're 578 00:53:07,950 --> 00:53:13,760 not completely finished within that time window? Are they easy possibilities to 579 00:53:13,760 --> 00:53:19,180 extend the time or are they do they just say, well, you had your three weeks, 580 00:53:19,180 --> 00:53:23,120 you're out apply in 2026? Caroline: Yeah, I think it's a regular 581 00:53:23,120 --> 00:53:26,930 case, that you're not finished with your experiments by the time your beam time 582 00:53:26,930 --> 00:53:31,870 ends. That's how it usually goes. It's also unfortunatly not free weeks, but it's 583 00:53:31,870 --> 00:53:38,531 rather like 60 hours delivered in five shifts of twelve hours. So, yeah, you 584 00:53:38,531 --> 00:53:43,250 write a very detailed proposal of what you would like to do. Submit it to a panel of 585 00:53:43,250 --> 00:53:50,620 experts, both scientists and technicians. So they decide, is it interesting enough 586 00:53:50,620 --> 00:53:54,980 from a scientific point of view and is it feasible from a technical point of view? 587 00:53:54,980 --> 00:54:00,320 And then once you are there, you more or less set up your experiment and do as much 588 00:54:00,320 --> 00:54:06,490 as you can. If you want to come back, you need to submit an additional proposal. So, 589 00:54:06,490 --> 00:54:10,590 yeah, I think most experimental groups try to have several of these proposals running 590 00:54:10,590 --> 00:54:15,490 at the same time, so that there is not a two year delay between your data 591 00:54:15,490 --> 00:54:21,070 acquisition. But yes. No possibility to extend. It's booked already for the 592 00:54:21,070 --> 00:54:27,890 complete next year. The schedule is fixed. Herald: So I don't see any more people 593 00:54:27,890 --> 00:54:33,060 queuing up. If you want to pose a question, please do so now. In the 594 00:54:33,060 --> 00:54:35,460 meantime, I would ask the signal angel if there's another question from the 595 00:54:35,460 --> 00:54:38,240 Internet. Signal Angel: I have a question about the 596 00:54:38,240 --> 00:54:44,650 dimensions of all those machines. The undulator seems to be rather long and 597 00:54:44,650 --> 00:54:48,910 contain a lot of magnets. Do you have an idea how long it is and how many of those 598 00:54:48,910 --> 00:54:55,221 electromagnets are in there? Caroline: Yeah. Sorry, I didn't mention 599 00:54:55,221 --> 00:54:57,221 it. It's about, I think one hundred and seventy meters long in the case of the 600 00:54:57,221 --> 00:55:03,390 European XFEL. I'm not sure about the dimension of the individual magnets, but 601 00:55:03,390 --> 00:55:09,100 it's probably also in the hundreds of magnets, magnet pairs. 602 00:55:09,100 --> 00:55:16,080 Herald: So is there more - excuse me, there is a question on the microphone 603 00:55:16,080 --> 00:55:20,350 number 3. Microphone 3: Yeah. Hi. It's regarding the 604 00:55:20,350 --> 00:55:22,350 harmonic light. Herald: Please go closer to the 605 00:55:22,350 --> 00:55:24,350 microphone. Microphone 3: The harmonic light generator 606 00:55:24,350 --> 00:55:26,870 that you were showing at the very beginning, just before the one that won 607 00:55:26,870 --> 00:55:32,700 the Nobel Prize. And can you also produce light in the visible range? Or it has to 608 00:55:32,700 --> 00:55:38,050 be in the visible range? Caroline: The high harmonic generation? So 609 00:55:38,050 --> 00:55:43,160 in the in the visible range, you cannot create pulses that are so short that they 610 00:55:43,160 --> 00:55:50,960 would be interesting for what I'm doing. The pulse that comes in is already quite 611 00:55:50,960 --> 00:55:54,791 short. So it's already femtoseconds long. They just convert it into something that 612 00:55:54,791 --> 00:56:01,850 is fractions of a femtosecond long. And yeah. In the indivisible range that's kind 613 00:56:01,850 --> 00:56:05,800 of a limit how short your pulse can be. Microphone 3: So it is not a good 614 00:56:05,800 --> 00:56:11,060 candidate for hyperspectral light source. We need another kind of technique, I 615 00:56:11,060 --> 00:56:16,360 guess. Caroline: Well, I mean you are kind of 616 00:56:16,360 --> 00:56:21,070 limited what short pulses you can generate with which wavelength. 617 00:56:21,070 --> 00:56:26,441 Microphone 3: Thank you. Herald: So again, a question to the Signal 618 00:56:26,441 --> 00:56:29,020 Angel. Are there more questions from the internet? 619 00:56:29,020 --> 00:56:34,590 Signal Angel: Yes I have another one about the lifetime of the molecules in the beam? 620 00:56:34,590 --> 00:56:39,800 How fast are they degrading or how fast are they destructed? 621 00:56:39,800 --> 00:56:44,290 Caroline: So probably the question is about how fast they are destructed before 622 00:56:44,290 --> 00:56:53,420 - so either before our pulses hit the molecule the molecules should be stable 623 00:56:53,420 --> 00:56:57,330 enough to survive in the gas phase from the point where they are evaporated until 624 00:56:57,330 --> 00:57:01,370 the point where the pump and the probe pulse come together, because otherwise it 625 00:57:01,370 --> 00:57:07,560 doesn't make sense to study this molecule in the gas phase. When the probe pulse 626 00:57:07,560 --> 00:57:12,690 hits and it flows apart, I guess pico seconds until the whole molecules ... 627 00:57:12,690 --> 00:57:21,780 Microphone 3: Like instantaneous. Herald: So I don't see any more questions 628 00:57:21,780 --> 00:57:26,040 on the microphones and we have a few minutes left. So if there are more 629 00:57:26,040 --> 00:57:30,030 questions from the Internet, we can take maybe one or two more. 630 00:57:30,030 --> 00:57:42,560 Signal Angel: Give me a second. Herald: For people leaving already, please 631 00:57:42,560 --> 00:57:46,760 look if you have taken trash and bottles with you. 632 00:57:46,760 --> 00:57:52,390 Signal Angel: So this one very, very technical question. How do you compensate 633 00:57:52,390 --> 00:57:58,210 the electronic signal that the electronic signal reaction is probably slower than x 634 00:57:58,210 --> 00:58:05,240 ray or light or spectrum changes at one moment or at one particular moment, that 635 00:58:05,240 --> 00:58:10,170 was interesting to analyze. I do not understand the question, though. 636 00:58:10,170 --> 00:58:13,240 Caroline: I think I understand the question, but I don't have the answer 637 00:58:13,240 --> 00:58:16,860 because again, I'm a - that's the problem of speaking to a technical audience, you 638 00:58:16,860 --> 00:58:23,710 get a lot of these very technical question. Yeah. The data analysis is not 639 00:58:23,710 --> 00:58:32,810 instantaneous. So the data is transported somewhere safe in my imagination. And then 640 00:58:32,810 --> 00:58:37,180 taken from there. So this data analysis does not have to take place on the same 641 00:58:37,180 --> 00:58:41,330 timescale as the data acquisition, which I guess is also because of the problem that 642 00:58:41,330 --> 00:58:47,530 was mentioned in the question. Herald: I might interrupt here. Maybe it's 643 00:58:47,530 --> 00:58:55,680 also about the signal transmission, like the signal rising of the signal of the 644 00:58:55,680 --> 00:59:01,900 electrical signal transmissions. Because this would probably require bandwidths of 645 00:59:01,900 --> 00:59:06,680 several megahertz, gigahertz, I don't know, to transport these very fast 646 00:59:06,680 --> 00:59:09,680 results. Caroline: Yeah. I think that's also a 647 00:59:09,680 --> 00:59:15,130 problem of constructing the right detector. That has been solved apparently 648 00:59:15,130 --> 00:59:20,690 because they can take these images. *laughter* Herald: And on the other hand, we have 10 649 00:59:20,690 --> 00:59:28,760 gigabit either nets. So we get faster and faster electronics. More questions from 650 00:59:28,760 --> 00:59:39,921 the Internet? Does not look like it, also the time is running out. So let's thank 651 00:59:39,921 --> 00:59:42,760 Caroline for her marvelous talk. *Applause,* *final music* 652 00:59:42,760 --> 01:00:13,000 subtitles created by c3subtitles.de in the year 2019. Join, and help us!