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  • Translator: Joseph Geni Reviewer: Thu-Huong Ha

  • Doc Edgerton inspired us with awe and curiosity

  • with this photo of a bullet piercing through an apple,

  • and exposure just a millionth of a second.

  • But now, 50 years later, we can go a million times faster

  • and see the world not at a million or a billion,

  • but one trillion frames per second.

  • I present to you a new type of photography,

  • femto-photography,

  • a new imaging technique so fast

  • that it can create slow motion videos of light in motion.

  • And with that, we can create cameras that can look around corners,

  • beyond line of sight,

  • or see inside our body without an x-ray,

  • and really challenge what we mean by a camera.

  • Now if I take a laser pointer and turn it on and off

  • in one trillionth of a second --

  • which is several femtoseconds --

  • I'll create a packet of photons barely a millimeter wide.

  • And that packet of photons, that bullet,

  • will travel at the speed of light,

  • and again, a million times faster than an ordinary bullet.

  • Now, if you take that bullet and take this packet of photons

  • and fire into this bottle,

  • how will those photons shatter into this bottle?

  • How does light look in slow motion?

  • [Light in Slow Motion ... 10 Billion x Slow]

  • Now, the whole event --

  • (Applause)

  • Now remember, the whole event is effectively taking place

  • in less than a nanosecond --

  • that's how much time it takes for light to travel.

  • But I'm slowing down in this video by a factor of 10 billion,

  • so you can see the light in motion.

  • (Laughter)

  • But Coca-Cola did not sponsor this research.

  • (Laughter)

  • Now, there's a lot going on in this movie,

  • so let me break this down and show you what's going on.

  • So the pulse enters the bottle, our bullet,

  • with a packet of photons that start traveling through

  • and that start scattering inside.

  • Some of the light leaks, goes on the table,

  • and you start seeing these ripples of waves.

  • Many of the photons eventually reach the cap

  • and then they explode in various directions.

  • As you can see, there's a bubble of air

  • and it's bouncing around inside.

  • Meanwhile, the ripples are traveling on the table,

  • and because of the reflections at the top,

  • you see at the back of the bottle, after several frames,

  • the reflections are focused.

  • Now, if you take an ordinary bullet

  • and let it go the same distance and slow down the video --

  • again, by a factor of 10 billion --

  • do you know how long you'll have to sit here to watch that movie?

  • (Laughter)

  • A day, a week? Actually, a whole year.

  • It'll be a very boring movie --

  • (Laughter)

  • of a slow, ordinary bullet in motion.

  • And what about some still-life photography?

  • You can watch the ripples, again, washing over the table,

  • the tomato and the wall in the back.

  • It's like throwing a stone in a pond of water.

  • I thought: this is how nature paints a photo,

  • one femto frame at a time,

  • but of course our eye sees an integral composite.

  • But if you look at this tomato one more time,

  • you will notice, as the light washes over the tomato,

  • it continues to glow.

  • It doesn't become dark. Why is that?

  • Because the tomato is actually ripe,

  • and the light is bouncing around inside the tomato,

  • and it comes out after several trillionths of a second.

  • So in the future, when this femto-camera is in your camera phone,

  • you might be able to go to a supermarket

  • and check if the fruit is ripe without actually touching it.

  • (Laughter)

  • So how did my team at MIT create this camera?

  • Now, as photographers, you know,

  • if you take a short exposure photo, you get very little light.

  • But we're going to go a billion times faster than your shortest exposure,

  • so you're going to get hardly any light.

  • So what we do is we send that bullet --

  • that packet of photons -- millions of times,

  • and record again and again with very clever synchronization,

  • and from the gigabytes of data,

  • we computationally weave together

  • to create those femto-videos I showed you.

  • And we can take all that raw data and treat it in very interesting ways.

  • So, Superman can fly.

  • Some other heroes can become invisible.

  • But what about a new power for a future superhero:

  • To see around corners.

  • The idea is that we could shine some light on the door,

  • it's going to bounce, go inside the room,

  • some of that is going to reflect back on the door,

  • and then back to the camera.

  • And we could exploit these multiple bounces of light.

  • And it's not science fiction. We have actually built it.

  • On the left, you see our femto-camera.

  • There's a mannequin hidden behind a wall,

  • and we're going to bounce light off the door.

  • So after our paper was published in Nature Communications,

  • it was highlighted by Nature.com,

  • and they created this animation.

  • (Music)

  • [A laser pulse is fired]

  • (Music)

  • Ramesh Raskar: We're going to fire those bullets of light,

  • and they're going to hit this wall,

  • and because of the packet of the photons,

  • they will scatter in all the directions,

  • and some of them will reach our hidden mannequin,

  • which in turn will again scatter that light,

  • and again in turn, the door will reflect some of that scattered light.

  • And a tiny fraction of the photons will actually come back to the camera,

  • but most interestingly,

  • they will all arrive at a slightly different time slot.

  • (Music)

  • And because we have a camera that can run so fast --

  • our femto-camera -- it has some unique abilities.

  • It has very good time resolution,

  • and it can look at the world at the speed of light.

  • And this way, we know the distances, of course to the door,

  • but also to the hidden objects,

  • but we don't know which point corresponds to which distance.

  • (Music)

  • By shining one laser, we can record one raw photo,

  • which, if you look on the screen, doesn't really make any sense.

  • But then we will take a lot of such pictures,

  • dozens of such pictures, put them together,

  • and try to analyze the multiple bounces of light,

  • and from that, can we see the hidden object?

  • Can we see it in full 3D?

  • So this is our reconstruction.

  • (Music)

  • (Applause)

  • Now, we have some ways to go

  • before we take this outside the lab on the road,

  • but in the future, we could create cars that avoid collisions

  • with what's around the bend.

  • Or we can look for survivors in hazardous conditions

  • by looking at light reflected through open windows.

  • Or we can build endoscopes that can see deep inside the body around occluders,

  • and also for cardioscopes.

  • But of course, because of tissue and blood,

  • this is quite challenging,

  • so this is really a call for scientists

  • to start thinking about femto-photography

  • as really a new imaging modality

  • to solve the next generation of health-imaging problems.

  • Now, like Doc Edgerton, a scientist himself,

  • science became art --

  • an art of ultra-fast photography.

  • And I realized

  • that all the gigabytes of data that we're collecting every time,

  • are not just for scientific imaging.

  • But we can also do a new form of computational photography,

  • with time-lapse and color coding.

  • And we look at those ripples.

  • Remember:

  • The time between each of those ripples is only a few trillionths of a second.

  • But there's also something funny going on here.

  • When you look at the ripples under the cap,

  • the ripples are moving away from us.

  • The ripples should be moving towards us.

  • What's going on here?

  • It turns out, because we're recording nearly at the speed of light,

  • we have strange effects,

  • and Einstein would have loved to see this picture.

  • (Laughter)

  • The order at which events take place in the world

  • appears in the camera sometimes in reversed order.

  • So by applying the corresponding space and time warp,

  • we can correct for this distortion.

  • So whether it's for photography around corners,

  • or creating the next generation of health imaging,

  • or creating new visualizations,

  • since our invention,

  • we have open-sourced all the data and details on our website,

  • and our hope is that the DIY, the creative and the research communities

  • will show us that we should stop obsessing about the megapixels in cameras --

  • (Laughter)

  • and start focusing on the next dimension in imaging.

  • It's about time.

  • Thank you.

  • (Applause)

Translator: Joseph Geni Reviewer: Thu-Huong Ha

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