discover the fastest camera in the world

In “Extreme physics” published by Albin Michel, physicist Julien Bobroff led the investigation to offer us an overview of physics records. He immerses us in the world of the extreme, populated by extravagant machines and happy scientists. Discover an excerpt about the fastest camera in the world.

Illustration of how a camera works.
© Albin Michel

“It was a surreal, ecstatic moment!” The one who marvels like this is called Lihong Wang. A professor at the famous California Institute of Technology or Caltech, he has always been passionate about light, which his research group manipulates in a vacuum, in matter and even in the human body for medical applications.

He has many feats of arms to his credit, but perhaps his most dizzying feat took place in 2014. That year, he managed to design a record-breaking camera with two young colleagues.

Its principle is based on almost the same trick as the rotating mirror cameras that filmed the first atomic bombs. Instead of trying to scroll through a negative, the camera will instead send the images taken one after the other to different locations on a sensor. The image itself is captured with a simple lens, nothing but very mundane. Then, and this is the originality, it is transformed into electricity. Each of the grains of light that constitute it is converted into a small avalanche of electrons.

The scanning camera, better known to regulars by its American name, the “streak camera”, will use an electrical voltage of just a few volts to deflect the electrons upwards. The filmed image is thus found at the top of the sensor. Then the tension is suddenly reduced. Inevitably, the image arrives lower, then lower, and lower again. The images are found one after the other spread vertically over the entire sensor. All that remains is to separate them and reorder them to obtain a film, as Muybridge had done a century earlier. The electrical voltage regulates the rhythm.

In this ultra-fast camera, the image is sent to small mirrors then to a detector which transforms the photons into electrons.

Be careful though, if you go too fast, the images end up overlapping and the film becomes completely blurry. This is where Wang and his cohorts get an idea. They decided to encode the images by adding a few small black spots in QR code style, using cleverly positioned micro-mirrors.

From the blurry film that they recover, they just need to do… math. By spotting the black spots, they are able to calculate how to reprocess the images to obtain a sharp film, whatever the speed! Thanks to this trick, the incredible value of one hundred billion images per second is reached, yes, one image every hundredth of a nanosecond!

As the detector voltage decreases, the image shifts downward. Step by step, we can capture and break down a movement.

Filming the light…

So, what do we film with this? The answer is simple: nothing. Nothing happens fast enough. At such a pace, everything seems perfectly still… everything except light, the only phenomenon fast enough on our scale to see it move.

So, let’s go ahead and film the light, Wang said to himself. It sends out a small burst of red light using a pulsed laser. Then he takes blocks of ice, which he evaporates so as to materialize the passage of the laser. And there, before the amazed eyes of the small team, the video thus captured displays a small red puff which advances towards a mirror, bounces, and goes back in the other direction, at three hundred thousand kilometers per second. Wang recalls: “We would never have thought this possible. For the first time, humans were able to see light propagating in space in real time!”, an old fantasy that had already inhabited Galileo in his time …

The Caltech physicist did not stop there and decided to put to the test this good old geometric optics that he had been taught in high school, starting with the laws of Snell-Descartes.

These laws describe how light is deflected when it passes from one medium to another. The proof, look at your leg in a bathtub, you will see it clearly distorted, the water deflecting the light before it reaches your eye. Rather than a bathtub, Wang chose a piece of transparent resin which he placed in the path of the laser beam. As expected, the light is deflected, and as expected, it advances more slowly, another well-known law of electromagnetism.

As a final treat, the researchers send the laser into a fluorescent substance. A beautiful fluorescent red spot appears and goes out almost immediately, in just a few dozen picoseconds. In short, all the laws are well verified, but seeing them live for the first time is heartwarming. […]

A new world in slow motion

The Caltech team didn’t just use their camera to film the light. She also used it to observe our brains working. I’m hardly exaggerating, judge for yourself. When you hold your smartphone or computer right now, the sensation of touch is transmitted to your brain through your nervous system using small electrical signals. These signals travel along axons, a sort of extension of the neurons which will ensure the communication between the latter via synapses. They each measure only a few tens of micrometers in diameter and the electrical potentials circulate there at high speed.

Wang’s team, however, managed to film them and see for the first time the current propagating there live, at more than a hundred meters per second.

The latest progress to date is that Wang has slightly modified his “streak camera” by using laser pulses no longer just red but of all colors. He then managed to have each color arrive at a different time on the screen. At the end of the journey, an optical instrument, the diffraction grating, separates them horizontally: red goes to the left, blue to the right, etc. This separation is added to that along the vertical. The film of the events is now spread out in all directions, a real headache to reconstruct the scene.

But the researchers succeeded, which allowed them to film even faster, and not just a little: the new camera records more than two hundred thousand billion images per second, a record in all categories. Muybridge seems a bit outdated…

The Caltech “streak camera” is not the only one of its kind as it is part of a vast movement in the field of optics. In recent years, inventions and progress have accelerated tremendously. New visualization tools, once thought impossible, are being developed at a constant pace. This series of successes comes from the conjunction of three key factors: the appearance of new ultrafast pulse lasers, the invention of ever more efficient detectors, and the emergence of treatments mathematics innovative images. Everyone has their own invention: frequency coding, single photon detectors, single pixel cameras, quantum holography… […] We can finally follow, down to the picosecond, the propagation of shock waves during explosions, strange rogue waves in optics, or even chemical reactions “live”. We may be living in the golden age of imagery. […]

Exactly, what progress is to come? Now that we know how to see the fastest or most hidden phenomena, what new feats can we hope for? Always faster, ever more precise seem to be the key words.

Some people dream of one day filming the very structure of light, no longer just seeing the laser beam advance, but the electromagnetic wave that composes it oscillates live. Another promising horizon is to be found in quantum. In recent years, researchers have been able to take advantage of the quantum nature of photons to obtain better images. For example, we can design microscopes that visualize matter with exceptional resolution using pairs of entangled photons, or film an object without looking at it…

Cutting-edge optics, cutting-edge electronics, cutting-edge algorithms, a little quantum to season it all, here is now the winning cocktail for filming the invisible and its movements!