World's Deepest-Penetration and Fastest Optical Cameras
I didn't know about all the new applications.
It was intriguing that I couldn't find any good brief info about how it works. Yes, the video mentions something about how it works, but doesn't teaches. I've seen a few years ago similar videos with femptosecond cameras, and always wrongly assumed that the principle is similar with that of a sampling oscilloscope, but that is NOT how it works.
The genius of it is that the whole video (like the one with the light passing through a bottle, or the illuminated figurines) is computed out of only one single flash. The video is not produced by taking repeated snapshots at each flash. It is one single flash and one photo, and from there, the time evolution of the light is reconstructed (computed). The movie is calculated, not filmed. At least this is how I understood it so far.
Following the research papers, the working principles of femptosecond cameras originate in some apparently unrelated concepts that were started during WWII, then developed in the following years to improve (chirped) radar and sonar technologies. At first it was about impulse stretching while keeping their shape (in analog domain).
Impulse stretching happens by passing the signal through a diffuser, then mixing the signal with a frequency chirp. By the chirp type, ascending or descending in frequency, the original pulse can be stretched or compressed in time while still keeping its shape. From there, it all went to building time lenses, or the opposite, to strongly sharpen wider pulses without destroying the vacuum tubes or the sonars, and so on. Stretched signals were required to extract more details from the echoes, while compressed signals were required to sharpen the pulses sent to make echoes. The sharper the sent pulses, the more precise the echoes.
Stretching is the first key concept, and from there there are many physics, RF, EE, optics and DSP tricks combined in making femptosecond cameras. I just hope I didn't get it all wrong, still digging.
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So far it was a fascinating journey down the rabbit hole, thanks for bringing up this subject!
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