life as a physicist : terahertz

Appropriately, it's already 2 weeks since I last wrote something down in my blog. And really, I made it a point and reward myself to pen down (not literally) my thoughts every forthnightly. I was busy preparing for exams and all that sort the last 2 weeks, finally had one (2 more to go!!) this morning...gone my good old days with Principle of Lasers and Mode-Locking! Okay, I am now going to write something about my research and project that I do for a living (LOL!) this year.

When we started to educate ourself with the physics of things around us, first thing we want to understand is how light behaves. Then, from there we start digging out dirt and all sort of yucky behaviors of light, term them with this and that theories. So we have established ourself with the notion that light is wave, that has this speed c (predicted by J.C Maxwell) constant all over the universe (interestingly, back in the 1900's lotsa people trying to disprove this--making measurement to prove the presence of the so called luminous ether wind. None succeed). Light as laymen see it is the only visible part of whole spectrum of LIGHT, lots of other regimes invisible to naked eyes with properties that some of us maybe familiar with today--microwave,x-ray--to name a few. So the part that I currently researching and do stuff in it is the TERAHERTZ waves, (tera meaning to the power of 12) or so called the sub milimeter regime. If you look closely on the light spectrum, it is squished in between UV (ultraviolet) and IR (infra-red) regime. It's pretty narrow, and hence hardly we've heard of it. The birth of THz around 10 years ago perhaps justify the fact that not so many reasearch done on it worldwide. Infact, googling through uni library catalogue only yields one reference book on it.

To start with, let me give you an overview of what actually this THz stuff is all about (although I know your middlename is Wikipedia-addict). With naked eyes, we cannot see it, the same as invisibility of microwave in a microwave oven. To see it, we need special eyepiece to make our eyes more sensitive to THz radiations. In my lab, I had the privilege of having a binocular that enable me to look at it. It appears green in color through that particular binocular. It's pretty awesome, in that I can view IR light that pump photoconductive semicondutor GaAs that produce the THz wave at the same time--red and green, like Christmas tree and Santa Claus. It's harder to produce than that of producing microwave and IR-waves, because as I said earlier it's only a narrow slab in between them. Tweaking by small amount either by factor of tens, we'll end up with microwave or IR. What makes THz waves stunning is that they don't give us human radiation effects at all, while maintaining that absorption power on water (like microwaves). I'm not too sure if it won't heat up things though, since setups in the lab only allow unidirectional flow of energy (unlike in spinning microwave oven), but so far I had THz waves goin through my lens collimators and samples for 8-10 hours a day, without fire drills turned on. I, together with Sam, a graduate student who's been working on the area for almost 2 years now, supervised by Leo, collaborating with Alexis, from ANU are all looking for ways to transmit this THz waves somewhere far (hopefully by meters :P), because like its neighbour microwave, they suffer attenuation passing through air due to the small content of water vapour in it.

So Alexis designs and fabricates samples of waveguides in OZ for THz transmission, and we run test on them here in NZ. Those are Zeonex waveguides that I've been testing on, designed from Silica-Strained-Model (used in optical telecommunication fiber) to transmit THz. It's pretty modest lengths that we've been covering so far--2cm and 4cm--yet the outgoing power from one end of the fiber measurement shows substantially reduced transmission. Only getting out 14% of input THz energy with 4cm so far, the outcomes urge for a more robust design of waveguides and new less-dispersive material as waveguides. I know it doesn't look as good yet, but I'm pretty confident I'm learning something from it, like how to be patience on the screwed results :P. Frankly speaking, the problem is not mine alone, that in many scientific community around the globe are also facing it. Recent journal article reports that with HDPE waveguides, their measurement limited to 1.5cm length and already transmission output around 18%. So, I would rank, and quoting Leo, we're pretty a step ahead of them. :P. To physicists, it's important to be a step ahead of the rest, but not more than that since that'll mean you'll get lost easily, and fall behind of the advancing team after they learnt your mistakes, as closely as I could remember from a lecture given years ago by Carl Wiemann, 2001 Nobel Laureate in Physics, here at my proud uni. I think that's pretty true, although the selfish flavour it adds makes me a little bit grumpy.

In that way, THz is pretty lagging behind, but the world has already started to earn benefits on THz imaging and scanning. From astronomical imagings, to chemical and image scannings, THz techniques had been so advanced that they're now making their way to commercial value in airport/luggage security checks, agricultural sectors and medical scannings (is said to soon replace x-ray). And perhaps, there are more to comes in the coming years. Looking back at the invention of lasers back in the 60s, the guys didn't know what to do with it, except excited that it works! But look at today, everywhere, almost instantaneously application of lasers! I'm optimistic, sooner or later, THz will gain popularity, just like lasers.

That's about it for my research project, and I'm enjoying it really, although some days it makes my hair tangled up. Come to think about it, I'm left with few months now to enjoy my days with physics people here at uni. I love them so much, especially my funny classmates and estranged phsycologist among us (hehe..). I love funny Leo and Sam, all the most for putting up with my why's and "explain again" cues. I may not be someone that they might remember in their careers later, but to me their invaluable comments and all pave my way deeper into physics, and truly grateful to have them. Even if physics is going to be harder than it is now later, I never regret taking it up, meeting all these wonderful people along. How will my life begin when my university days over, and I am sent back home end of this year? Have you had that feeling that you belong to this country, and you want so much to stay with it? My love for physics strengthen here in NZ, and I am falling for this country despite its ruralness. Maybe it's physics, or something else?