I’ve posted before on how liquid-crystal display (LCD) monitors emit polarized light (and can be birefringent), and some of the fun you can have with this, and everyone is probably familiar with other uses as well.

LCD’s don’t emit light by themselves; they rely on backlighting or on reflecting ambient light, which passes through a polarizer behind the display. In this short video we can see what happens with a calculator display when you take the top polarizer off:

We see nothing at all. The effect of the display is not visible to us, because we are not (very) sensitive to polarized light. When we put the polarizing screen in place, then we can see what’s happening — the display has a “zero” energized, which has a different polarization than the rest of the display and blocks the light that has passed through the display and been reflected and polarized. When we rotate the screen, the light is blocked from the rest of the display, and the light from the zero passes through. At an angle, light of each polarization makes it through, so you can’t see the digit at about 45º.

First the good: The website.

We have built an imaging solution that allows us to visualize propagation of light. The effective exposure time of each frame is two trillionth 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 nano-second long event.

Unfortunately, there’s also this video (or, more specifically, the first few seconds of this video), which I saw before finding their site.

We have built a virtual slow-motion camera where we can see photons, or light particles, moving through space.

Prof. Raskar has whipped out (and abused) his poetic license: you cannot literally see photons moving through space. You only know light is there if it scatters into your sensor — if it is light that simply goes by you/it, you would never know it’s there. If you shine a laser out into space, you don’t see that light — you only see light that scatters back to you. Unfortunately, by leading off with that sound bite, I fear everybody who sees the video is going to be repeating that line: OMG, we can see actual photons moving through space!

What they have recreated is a way to visualize the photons or a wavefront moving through space. Which is no small feat and is very cool.

And I just saw that Rhett has a post up about this, with some details of how it works, and is also repulsed by the sound-bite. I don’t have a huge problem with the trillion fps claim, because they are pretty clear that this is a virtual, post-processed effect, where you are sort of combining strobe and stop-action to give you the result, with the caveat that the stop-action is static — this generally wouldn’t work if anything were moving.