Mindbogling 20 billion fps camera to film a laser in flight by scientist.

We’ve all been spoiled by the fashylasers in science fiction to the point that the real thing can seem a little mundane. A laser, by definition, is tightly focused and all but invisible to the human eye. However, a team of physicists at Heriot-Watt University in Edinburgh, UK have managed to film a laser bouncing off mirrors with a new type of high-speed camera. It looks like something out of Star Wars, but it actually happened in real life.

Filming a laser pulse moving through air is no easy feat, and certainly no conventional camera was up to the task. So the team built their own, as really clever physicists sometimes do. Visualizing a laser as it moves through the air relies on exploiting the scattering of photons. You can get a feel for what’s going on in the video by shining a regular laser through smoke or water vapor. The light from the laser is scattered by the particulates in the air, which is why you can see it. You’re actually just seeing the photons split off from the focused beam.

The system devised by PhD student Genevieve Gariepy and colleagues at Heriot-Watt University is doing the same basic thing, but in air and much, much faster. Air scatters less light than fog or smoke would, so the camera used to capture the video below needed to be extremely sensitive. It’s composed of a 32×32 pixel grid of single-photon avalanche diode (SPAD) detectors. This type of CMOS sensor was chosen because it has high temporal resolution. That means the image data acquired by them can be accurately correlated with real life.
So how accurate is the SPAD camera system? It can has a temporal resolution of 67 picoseconds, or 0.000000000067 seconds. Looking at it another way, it can capture about 20 billion frames per second. That’s good enough to pinpoint a single photon within a few centimeters. When you’re talking about light, which is literally the fastest thing in the universe, that’s fantastically impressive. The camera is also tied into the laser emitter so it knows the exact time the pulse is produced.

The video of the laser bouncing shows a bit of haze around the beam, but that’s a consequence of the method used to capture it. Even though the SPAD camera is extremely sensitive, it still only picks up a few photons scattered from the beam. The video is actually a blending of 2 million pulses fired over the course of 10 minutes. The team simply had to combine all that image data and subtract the background. The result is the video you see above.

This was a pure research experiment to see if it was possible to visualize a laser in flight without interacting directly. Gariepy believes there could be practical experimental applications for a SPAD camera with high temporal resolution like this one. For example, observing the formation of plasma as ions are heated. This is, of course, in addition to it being used to create really, really cool videos.