Physicist Explains Lasers in 5 Levels of Difficulty | WIRED

I'm Donna Strickland I'm a professor at the University of Waterloo I study lasers and in particular I like really high intensity lasers so a laser is a way to get light to actually just be a single color going in a single direction all of the waves peaking at the same time so that the intensity can get very high today I've been challenged to explain lasers and high intensity lasers at five different levels from a child to a teenager to a college student to a graduate student and finally to a colleague of mine so I was told that maybe science is one of your favorite subjects at school is that right yes yeah have you actually studied light yet yes okay what have you learned so far about light so we learn how to like actually light up oh really Oh excellent well I'm somebody you'd like studies lasers so what do you think about lasers you know you haven't gotten to play with lasers so I brought one that's you know my friend's cat toy do you ever use a laser as a cat toy and one of the fun things people do with lasers the cat will try to grab that dot I'm sure what you have at home is a flashlight I brought a cute little one so the question is do you see any difference between what a flashlight does and what a laser does that's true the lace is just a dot and so the other thing to notice though is that this seems like when I shine it in your eyes I am sorry if I do but it seems awfully bright doesn't it and yet when you know you shine this down and you put the laser which one do you see easier laser so which one do you think's more powerful and yet it's not isn't that amazing yeah one of the things that lasers are great for is that it because of its a directed beam we can actually put that light where we want the light to go and sometimes we maybe just want to see something around a corner and you can't see it but with a laser you can actually and this is a smoky one so you can actually watch it go you see it actually bending the corner oh and that's because the light will go through this glass but when it hits that corner it has to bend and we actually sound laser beams down glass fibers the size of your hair yeah so this obviously is much bigger than our hair right so this is just a demonstration if you have a laser like this it actually bends and comes out I'm going to point it to you and you'll see it coming out the other end it hits these walls it has to go around and come out the other side you won't play so that's the first time you've seen a laser have you gotten to play with laser somewhere else I don't so you don't need a cat so I know have you ever gone to a grocery store and just scanned your objects over have you ever seen that maybe this is a little bit of a red light when you do that that's a laser we cut steel with them now we actually do surgery with lasers you know when some people have either scars or birthmarks that they don't want to see we can actually remove those with lasers now we've never seen a laser light show when they light up the sky with lasers it's almost like fireworks oh you got to say a shooting star well that's that's cool that's nature giving you the show there so what do you think about lasers I think they're fun and the next time you go to a grocery store take a peek at the red okay today we're here to talk about lasers so what do you think about lasers um I think they're pretty cool they show put in a lot of my favorite books and movies like Star Wars so just a bunch of different sci-fi movies and books do you know anything about lasers what makes the laser special kind of light all I really know is from like sci-fi books and movies and like the factory cutting lasers that they used to like cut steel and stuff did it even know maybe how to make a laser that it would be strong enough to cut steel no okay so one of the things about lasers is if you've ever seen a laser beam you know it's very directed like what are they made out of what does a laser made out of well really it's sort of the same thing as a light bulb right because people to beam so yeah it's a light bulb and there's a couple of mirrors now the light bulb has to be a little bit special it has to be a type of material that can store the energy in an excited state right it has to stay up there really energetic and sit there for a while so that when the light comes along it takes that energy and become stronger light and then the mirror sends it back and it does it again and again and again and between these two mirrors it makes the light come out in a nice beam in a laser it comes out as a single color they all come out with their waves at the same time every wave peaks at the same time which then makes it a giant wave and it's this giant wave that has a tremendous amount of power so it can do something like cutting steel but when you cut steel or if you're cutting this floor it's great it actually will absorb the light that's why the light you don't see it because the light isn't bouncing back or through it so I like to use demos to explain how my laser works so I've brought basically a hammer and a nail I'm sure you've probably hammered a nail before into a piece of wood but the question is if you asked yourself why it is that we hit the big end and it's the tiny end that we put on the piece of wood we would never pick up a hammer and hit the sharp hit the sharp end and hope this would go into the piece of wood because in to be center so can more easily just go in that's right it's all the same force that we apply up here goes all the way through but then it can only basically come out when it contacts the wood in that one tiny spot and so sometimes it's the force that you push something with but sometimes it is that force per unit area but sometimes it's not even the force per unit area because you know push down as hard as you can on that that and see if we can get it pushed in it doesn't really work does it so the laser needs ultimately thinks it needs well if titty centered it needs time to like actually penetrate and then it needs well it depends so if you're cutting steel you need to have the nail you need to have it concentrated all of the light not going in all directions but you need it into a smaller point as possible and for that we use a lens for a lens the lights coming down as a column you put in a lens it all focuses it down in the same way as the nail and then it starts cutting that steel okay so that's sort of force per unit area so it's kind of like a magnifying glass like get my good twice at lay it down to a point exactly you know sometimes you want to have all of your energy not just in a small area but in this small volume and so one of the other dimension is time or light but with light time and lengths are the same thing because light always travels at the speed of light exactly but if you send one second long light pulse out into the skies there the beginning of the pulse is actually two thirds of the way to the moon it's three hundred thousand kilometers long so now if you talk about light being concentrated that doesn't seem very concentrated the type of lasers I play with in my lab will be no thicker than this piece of paper so we take that energy that might be in three hundred thousand kilometers and we squeeze it all the way down into just this piece of paper and actually the beams are more the size of this piece of paper okay and so in my lab they would be flying pieces of paper like this would be flying through the sky but we can't see them because they don't come in our eyes they fly by us and they're infrared we like little concentrated beams of light exactly where and so now if we have light like that that we want a machine with I bring this funnel and so if we had a lens here the light was coming down so funnel sent into a spot so here would be my light coming from my laser no just be coming down down down down down hit a lens and we have to focus down but now all the light started out with this big of a spread so concentrated this much eventually it would be here more concentrated but by the end right at the focal spot that's when I get all of my light all of the energy has been squeezed down into fitting inside this piece of paper and that's why I say that I built a laser hammer because when this hits a piece of glass it just smacks those electrons right off the atoms and there's nothing else for them to do they have to fly away so can you tell me what you learned and maybe about the focusing of the light well what I learned is lasers they aren't like particles they're more like a super concentrated beam light that can be any color they get really concentrated and that's what makes them like play serious and that's why they cut things and break things because it just moves the electrons out of the way so do you think that lasers are fun enough to talk with your friends about her of course I'm gonna have to share something about my experience learning about lasers was an expert like you so you're a college student yes and what's your major I am an engineering physics major with a minor in math I'm in the 3-2 program for biomedical engineering excellent I got an engineering physics degree there you go something in common we're here today talking about lasers so have you had much exposure to lasers yet that's cool not yet I am really hoping that we will I think it's super interesting just the field in general because I really do enjoy examining all the calculations and being able to do a little bit more of the math side effect okay as opposed to the experimental side of it and seeing things okay so I'm much more I like to see the things happening so then the question is what's so special about making a light that's intense enough to actually possibly blow things out certainly we can blow atoms up with the laser hammer and the laser light comes in and just smacks the electron right off the atom and so the question really is is how do you make that back in the 70s and into the 80s I know that's a long time ago for you we had big energy lasers and we had short pulse lasers we couldn't have big energy short pulse lasers and actually it was my supervisor and I that figured the way around that and we got something called chirped pulse amplification have you heard of chirped pulse a awful fication by any chance vaguely well I brought a little bit of a prop to explain how chirps pulse amplification works our short pulses are made of different colors I've got a colored slinky here we probably could have called it stretched pulse amplification but that's kind of boring so we used the word chirped the word chirped comes around because birds chirp when the birds are singing the notes are actually changing audio frequency with time and that's a chirp the point is that when all the light is squeezed together like this it's a short pulse and that's when it's a hammer because all the light is now concentrated and you can imagine if this was coming along and also using a lens to focus it small than all of that light at the focal spot concentrate and so that was the laser hammer so we can't have that in the laser so the question is what could we do the fact that it's different colors and different colors because of dispersion travel different speeds inside material so we used a long fiber one point four kilometers of fiber but in fiber the red colors really haven't got that much in common with the glass atoms and so they spend very little time you know interacting and they travel fast the red is going to start traveling faster than the green faster than the blue and as you travel down the fiber next thing you know you have a long pulse and it's chirped from red at the beginning to blue at the back and so the frequencies go whoo okay so this is a chirped pulse and now it's a long pulse and so first this is what we did we chirped it we stretched him then we can safely amplify it because it's not all concentrated and after we amplify it then we use something called a compressor and we put all of the colors back together and it was back being short pulse but a high-energy pulse and to get that we really had what I like to call it laser hammer when this laser pulse goes inside it smacks those electrons right off the atom so the laser hammer that you were describing with other types of lasers and the one in the tripped is it's still the same premise well a lot of lasers and when lasers first came along there were only single color your cat to are below to be a singer color probably a red one and so that's just one color and one color means that it has to really be there for the whole time one color is one wavelength of light and so it's just one wave that goes on and on and on if you want a short pulse you actually have to have all the colors and if you can imagine at one point in time and I like to say it's like a conductor of an orchestra when you're listening to an orchestra warm up they sound terrible they're all playing their own notes but when the conductor conducts them they all play different notes but together it's beautiful music so we have something in a laser called a mo blocker and it's like the conductor and it says to go now and all the colors will start together but some colors are long wavelength and others are shorter so next thing you know you have peaks meeting valleys and they cancel each other and so the more colors you can bring in the faster that happens and the shorter the policy committees the necklace is something that was designed for my Nobel Prize it's sold at Nobel Museum and it is a chirped pulse so we've been talking a lot about lasers and applications what have you learnt about your pulses I learned that it all stretches which is super cool because red moves the fastest and so it kind of tugs around blue it really threw me off just how fast it's hard to imagine things happening that fast and I also learned how many of the things that I know are lasers and how many of the things that I've been looking for like the answers to it is in lasers so I understand you in grad school where I don't know why you and what he's studying I'm studying soft matter physics which in was the physics of squishies stuff we make micro swimmers in the laboratory and we drive them with a laser and what kind of laser to use we use a 10 watt laser it's a fiber laser do you know a lot about lasers or just about the laser that you use not about you just a little bit okay so this is about high intensity lasers no no how do you make them but what was really stopping them being made in both cases nonlinear optics you know we want to do something that requires a huge photon density application yes and so that's how come we came up with chirp false amplification so that we could stretch the pulse safely amplify it then compress it at the end and then we're ready to do whatever we want at the end so what do you think the main difference is between the continuous-wave laser that you have that runs at 10 watts and a chirped pulse amplifier I feel like the continuous laser delivers power to continuous rate whereas you want all that power to be delivered in a really really short time but with your amplification and so we get the power with a lot less energy because it's power is energy per unit time sorry we aren't depositing much energy in comparison yes can I just ask cos sure you are using the thermal process of it heating up but is have you ever had the opportunity to use a laser tweezers I have yeah we use optical tweezers to trap particles institution okay and and twirl the motors are not told the motors I know I haven't what you're over that okay so I was always curious how much further like what higher power can we go now so trip falsification took a sort of fun we were at ten to the twelve but when I was working the ten to the twelfth sort of sat on a football size field it was a kilojoule laser with a nanosecond pulse okay and we brought it down to something we'd call tabletop terawatt so it was the same terawatt but now it was one jewel in one picosecond so it could fit on a basic optical bench like you would have in your lab we were able to take that up to I think the record is right around somewhere between 10 to the 22 and 10 to the 23 watts per square centimeter so then and going forward one of the Holy Grails is can we reach ten to the twenty-nine watts per square centimeter so we saw six orders so we've gone from ten to the twelve to ten to the 23 so we've done you know eleven order so you think six isn't so much harder I have to tell you over time it's rolling over its we need another Nobel prize-winning idea but if we get out there that's where if you focus the intensity the energy in that volume is enough to break the vacuum we could probably use this to drive chemical reactions at a very very specific spot like if we wanted I get just a single cell in the body yes and and and maybe what do pump probe spectroscopy and watch the cell or to ionize it I mean I was thinking more on the lines of if we want to let's say destroy one cell like I do myself or something like that so that neighboring areas are not affected but just the cell thanks I don't know if people working on that because I'm not so much of the reticle field but I should look into that and see if that's a possibility so after hearing about high intensity lasers can you think about next time you go back to the lab and you're wondering how to do something in the love with lasers can you see how short pulses might help you I think short pulses might have been my experiment in the sense that if I Drive my swimmers with a continuous wave as opposed to a pulsed wave maybe a continuous wave would heat up the sample too much and a pulsed laser would deliver power exactly where I need it so that I could run my experiment from there maybe that's true thank you very much thank you nice to meet you hello Donna good to see you here with me so we go way back 1991 year I got married I moved across the country left my husband in New Jersey Sark with you at Livermore I remember very much and how hard it was to convince you to travel across the country and work at the lab and stay there and stay there I couldn't convince you to stay you could not get through this day though especially there long enough to make a big impression and get some good work done and I've been talking sort of starting with sort of what is a laser through linear optics nonlinear optics high intensity laser physics and saying that you know we're trying to get to that showing her limit of ten to the twenty-nine watts per square centimeter we're at about somewhere just shy of 10 to the 23 I think at this point but even if we get to 100 petawatts and focus that down to a wavelength we're not at ten to the twenty-nine yes so you're hoping to build the biggest laser yes at Rochester but we're still not going to get to the stronger limit isn't that right so just a little bit of back history again after you you know demonstrated CPA I was intrigued by how powerful could we make lasers and then how lasers are wonderful because you know they allow you to take energy and compress it in space and time so having high peak power and something it's been a motivator for me for a long time and so we at the University are making proposals to build 225 petawatt lasers maybe 30 petawatt lasers we'll use them to be able to get combined power of the over 10 to the 24 watts per square Center still far from the swinger limit but we have a trick we're going to use one of these petawatt lasers to make an electron beam and this electron beam will be relativistic we actually think we could make electron beam maybe even hundreds of GEB up to a TV which would be another nobel prize that's right you can do that go for it and then we will shine that laser onto that electron beam and the electrons bris frame we meet the swinger limit okay that's kind of cheating that's not getting to ten to the twenty nine if you do it with 100% efficiency that's all we need that's why I wanted that Nobel Prize because again if we're able to do this you know it's way as I can see today right I can see us doing it today by just exploiting it what we already know and take it to a limit then that would be a real motivator I think to be able to even take these texts needs further cheating is not the right exact word is taking advantage of relativity take advantage of all physics not just optical physics since that's why we want to do it this way we have to get into entertainment when is the high intensity laser gonna get into entertainment so then there's real money yes yes well we have started the photon torpedoes that's why what they actually knew what you were doing is if you ever seen a start though Star Trek had like science fiction no Star Trek had photon torpedoes and they show bursts of light about this long it was the same thing because if he's down a second pulse it how much energy it carried and you can see it but I'm what it was scattering off of but you could see it so it was a great thing so we can either cheat by doing laser accelerating and going into that rest frame yes and that's like you said we're stuck a little bit we're not up to that kind of acceleration so that would be a Nobel prize-winning possibly or we need going around and giving my talks now I show how her plateauing I showed how there was a plateau see PA raises it up but we're sort of started a plateau again and we need another Nobel Prize winning idea and so do you think it's on the horizon do you see anything out there that really says oh yeah that's that's a good way to go because we're going to have to get out to the x-rays right we can't we can't stay in the visual so actually I think you do there's a potential ways of doing it with optical or near optical radiation and you know there's been a lot of work done in the Defense Department officers of how do I combine laser beams together okay and make them act as a one coherent source so one of the things that we'll be doing with our two petawatts we're going to see if we can actually combine them into a 15 if you can do that you can begin to imagine doing this with many lasers many petawatt lasers of the scale we're talking about so one could possibly see an X want from that you know which I you know people have been able to combine tens of lasers together for a coherent source so you have to be able to phase lock them you have to be able to make them you know there fazes be exactly connected and related and be able as they propagate through all the different optical components whatever may be just and don't you think that's the process the entire Appetit it's because it's not like our beams are as perfect as we all like to think they are so it's right so you have to have so over the Aperture Science you have to have them phase-locked across the entire aperture which will be a great challenge and people done again with small lasers the laser will be trying to is about 40 centimeter aperture so we'll begin to start looking at this and actually wave fun control I mean be able to adaptive optics other ways which you can control the uniformity of the phase is something that's been developed in lots of ways now here for defense applications for science applications so we'll do our best to make use of all these technologies lasers I think have progressed so much just like the semiconductor business because there's such a market or there's so many different applications okay so there's a lot of us working around the world on these high intensity lasers and so what do you think the real fun is what do you see the real excitement being I remember when the laser was first demonstrated in 1960 what could we do with this we already got light now we can't live without lasers my cell phone that is in my pocket has billions of transistors how is that made with lasers you know all integrated circuitry is done with lasers actually now it's being using x-rays made from Blaser he didn't matter that came out of the laser fusion program so it is amazing the parallels and optics is used everywhere we're going to possibly take over from CERN and let's we'll just do high-energy physics no lasers we're looking at gravity waves with lasers we want to do black holes with lasers we want a machine with lasers we want to do medicine with lasers everywhere and now with the Nobel Prize people are hearing more about it so they know lasers are everywhere I couldn't agree with you more and you winning Nobel Prize has been an inspiration to lots of people only three women have won the Nobel Prize in Physics and only one educated in the United States and I use that every place ok and only one Canadian there you [Laughter] today was fun I got to explain the work I do at all levels it's always fun for me to talk to elementary school students because they bring such enthusiasm with a student who's already started to learn optics to a graduate student and finally my own colleague where we can really get into a huge conversation about what's the future of this field electronics was the technology for the 20th century and it brought us the transistor electrons don't move nearly as fast as light and so trust me photonics will take us where we want to go in this century [Music]

Channel: WIRED

Views: 725,445

Rating: 4.8769183 out of 5

Keywords: 5 levels, innovation, lasers, science & tech, science & technology, 5 levels lasers, laser expert, laser expert wired, wired lasers, lasers wired, difficulty, donna strickland, donna strickland wired, university of waterloo, waterloo, 5 levels of lasers, levels of wired, laser, laser experts, donna strickland lasers, lasers explained, how lasers work, laser explanation, explanation on lasers, lasers how they work, laser expert explains, lasers 5 levels, wired

Id: 3eTogq7rknQ

Length: 24min 37sec (1477 seconds)

Published: Mon Oct 28 2019

Reddit Comments

[u/Jarb0t]

Top comment: I failed her class in waterloo rip

[u/minecraftraytracing]

DAMN!

[u/shellderp]

now we have to use the lasers logo officially

[u/daga2222]

No idea what she was talking about after she explained to the kid

[u/[deleted]]

frick what does it say about me if i only understand the first one

[u/TheRealHamdullahpur]

Donna Strickland is the coolest.

[u/hippiechan]

Can someone give an ELI5 about the Schwinger Limit? I looked it up and I don't understand the significance. What does she mean when she says it "breaks the vaccum"?

[u/[deleted]]

Donna Strictland is a pocket full of sunshine

[u/rickjamesbeach]

it is lightshow. it is lightshow, jah.