Today was quite the whirlwind, after getting breakfast in the morning, I went off to a room that I hadn't been to before. Unfortunately, I thought it was somewhere else, so I ended up circling the conference center and coming back to the room right above the coffee shop. And this was after I had my morning coffee... sigh...
Anyway, there were a few gems of talks today. The first was a talk by Mark Foster on his work doing time lensing - essentially using an all fiber setup to shift the pattern in the spectrum of light into the time domain, and the time domain into the spectral domain. This is cool stuff because in telecom they have well developed methods for handling one type of signal but not the other, so by having an all fiber way of switching between the two makes it easy to modify either signal. This could lead to faster bandwidth with only minimal overhead. It turns out that you can use a similar method to do extra-precise analog to digital conversion by using a pulsed laser (which has very small timing jitter of about 5 fs, that's 5*10^-15 s) to do the sampling, then stretch the samples out a bit so that an electronic ADC can pick it up (these have timing jitter of about 100 fs). So you pick up a factor of 10-100 accuracy by this method.
The rest of the morning wasn't particularly my field, so I didn't get a lot out of it. Consequently I went off to The Tech Museum to have some fun, but also decompress and get my brain ready for more talks. I had a really good time there, and to do it justice, I think I'll make a separate post (with pictures).
By the time the afternoon rolled around, a few more talks popped up on my radar. First up was a talk by Eric Van Stryland's group on their work in seeding supercontinuum (SC) generation. I mentioned this briefly before, but the idea is that if you go through special optical fibers or, in this case, a krypton gas cell you can turn a short laser pulse of a few frequencies (about 100 nm bandwidth) into a longer pulse of many more frequencies (usually spanning the visible, from 400 nm (deep purple) to 800 nm (red) and even longer wavelengths). Since supercontinuum generation is the result from a plethora of nonlinear processes, you have to have very intense light to do it. Usually there is also a sharp turn on, from having no SC to having the SC by tuning the laser power very slightly. By seeding the supercontinuum, a process where you add a bit of light - his group used a pulse with 40,000 times less energy - to get the process started. Not only did they find it works, but it increases the amount of light you get out by a factor of 4 or so. They don't completely understand it yet, but this is a fantastic result, because having a bright light source that is continuously variable over such a broad range of spectrum really opens to door to many experiments, and is something I may be working on in the future.
Then there were two talks on biology and biological optics. I'm going to save the one by Nicholas Roberts on polarized vision in animals for a later post - this was the research on Mantis Shrimp being able to see circularly polarized light, but there's so much more than just that. Instead I'd like to focus on Hui Cao's work on mimicking nature's optics... and then doing better! You may have heard that butterflies have a wing scale pattern that has very fine microstructure, acting like a diffraction grating and giving them their wing iridescence. Well, it turns out that some birds, and for some colors, have a similar effect that colors their wings. However, while the butterfly wing will seem to change colors as you change viewing angle, this does not happen for the birds. This is a result of having local structure but no large scale structure in the bird wing. By making similar structures, they were able to re-create the effect in the lab. But if that were all it would hardly be entertaining. They went a step further, and placed what are known as quantum dots into their structures, these are small metallic spheres that emit different colors based on how big they are. When they hit this structure with light, it would preferentially amplify a certain frequency - they had created a laser! Hopefully the birds don't figure this one out.