1 trillion frames per second

[Eudaimonium]

Well after watching the video, I thought I'd clear up some points here because many of you seem to have misunderstood some stuff.

Firstly, it's not a trillion frames per second camera, it's a camera that can take a frame with exposure of a trillionth of one second - there's a difference.

The real life Rajesh Koothrapalli in the video explains that the video you've seen is composed of several gigabytes of data, acquired over several thousand shootings. Each frame is a shooting of one instance of experiment, just in different time. Think of it as a thillionth-second shot camera that needs to cool down before each use.


Second, Things:

How would there be a green reflection on top of the laser if the light had not yet traveled far enough to reflect back onto it?

Not to mention DPSS isn't nearly fast enough to produce a single pulse of light at that speed, let alone from a pointer.

That was just a photohopped picture to helo illustrate the point how their stuff works, not an actual picture. It's impossible to take an actual picture of a green laser bullet since semiconductors such as LEDs and laser diodes have a few nanoseconds of period before they actually start conducting said current, and are literally impossible to modulate as fast as is required to take a femtosecond photo. Besides you wouldn't see much anyway, laser beams are invisible at 1/200 second photography, let alone 1 femtosecond, without repeating the experiment a thousand times and taking picture each time and adding it to previous one.

 

[Things]

.. That's exactly what I said in my post, lol

It was a reply to Encap.

 

[Encap]

Yes, was me who bought the green laser photoshopped images hook , line , and sinker when looking at the lecture video quckly and not paying close attention. Thanks for the correction on that, Things. It made me go back for more and take a deeper look at the whole thing and Femto Photography---was interesting.

To me, the more interesting video is the you tube link I posted in post #16 which shows several volumetric propagation videos used in creating the illusion of a "bullet of light" traveling through the bottle based upon real data they aquired with their unique equipment set up and the mathmatical reconstruction techniques they employed.

They mention in the abstract on the Femto Photography, Camera Culture Group, MIT Media Lab web site:

"We have built an imaging solution that allows us to visualize propagation of light. The effective exposure time of each frame is two trillionths of a second and the resultant visualization depicts the movement of light at roughly half a trillion frames per second. Direct recording of reflected or scattered light at such a frame rate with sufficient brightness is nearly impossible. We use an indirect 'stroboscopic' method that records millions of repeated measurements by careful scanning in time and viewpoints. Then we rearrange the data to create a 'movie' of a nanosecond long event."

Interesting work!

 

[Things]

Yeah, it's actually quite a simple concept, as you could even do this with just a regular highspeed camera if you had a way of precisely triggering it at different times, but putting all the frames into order would be a royal pain in the @ss!

 

[Encap]

Yeah, the idea/concept is the same and you could do something that looks similar, perhaps

The problem with trying what they did with a regular high speed camera even if you could trigger it precisely at different times and could put all the frames in order is that light travels very fast (~1 foot in 1 nanosecond) and sampling light at these time scales is well beyond the reach of conventional sensors (fast video cameras have microsecond exposures).

In the Femto Photography web site FAQ discussion they mention that:
To observe photons (light particles) in motion requires a very different approach than conventional high speed cameras which use of a very short duration flash to 'freeze' the motion.

"the fastest electronic sensors have exposure time in nanoseconds or hundreds of picoseconds. To capture propagation of light in a tabletop scene we need sensor speeds of about 1 ps or one trillion frames per second. To achieve this speed we use a streak tube. The streak camera uses a trick to capture a one dimensional field of view at close to one trillion frames per second in a single streak image. To obtain a complete movie of the scene we stitch together many of these streak images. The resulting movie is not of one pulse, but is an average of many pulses. By carefully synchronizing the pulsed illumination with the capture of reflected light, we record the same pixel at the same exact relative time slot millions of times to accumulate sufficient signal."

What they developed a very clever way to get the images they got.

 

[FreeBee]

I just saw the video. It blew my mind. I actually wanted to post this here right away, then I thought hey let's use the search function. Turns out two threads already existed. I figured you guys would know about this.

Maybe one day this can be done in actual colour. That'd be so cool.