is there a theoretical limit to the speed of a high speed camera?

Answer

Dear Paul,

I’m having some trouble with the concept of “filming a laser beam”. The laser beam itself is light. If you “film” the laser street, you actually film light from the laser beam that scatters (by small dust in the air, etc.) or reflects off objects. Just like the laser beam, this scattered or reflected light *also* travels at the speed of light.

Currently, semiconductor-based cameras exist that can film short sequences at 1 to 10 million frames per second. Special vacuum tube-based “streak cameras” can record short sequences of 100 million images per second. I estimate that even 10 billion images per second should be possible today.

There are two upper limits for this speed

1) the light receptor, usually a photodiode, Diodes as used in fiber optic connections can achieve time resolution much shorter than 1 picosecond, so, theoretically, a camera made up of pixels with these photodiodes >> could take 1E12 images per second.

2) the real problem is the amount of light. Full sunlight produces several million photons per second per pixel. Shooting 1E9 frames per second in such conditions, each pixel per frame sees an average of only 0.001 photons (ie: mostly nothing, and occasionally 1 photon). Obviously, even with the best possible pixels, this is unusable little.

A laser can be brighter than sunlight. But you need at least a few photons per pixel per image to have a meaningful image. The laser intensity *in the camera* must therefore be at least 1000 times greater than that of sunlight in order to record 1E9 images per second. Given that this concerns stray light, the laser beam itself must be many times larger. Not entirely impossible, but a formidable problem in terms of power dissipation.