What do I do?

I get asked the question a lot, what do I do? Now anyone who works in a scientific and technical field knows the problem with this question. And that is that half the time we don’t even know what we do!

For the short answer, I reply “I shoot [tag]lasers[/tag] at stuff”. But that doesn’t really say anything at all, does it?

For people with a little more technical knowledge, I might talk about how I make wire grids that are a tenth the width of your hair in the University of Alberta’s [tag]Nanofab[/tag] and then shoot them with lasers. But that’s still not really saying anything.
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Interest in physics

There was a bit of a weird call to the lab this morning. Someone was looking for my professor to ask him a couple questions he seemed curious about. I’ll have to paraphrase, but it went something like:

I’ve heard that the atom is something like 99% empty space, is that right? And also, would that be like our solar system, because I’ve heard it’s a lot of empty space too?

After I answered yes to these two questions (since I was a little taken aback by questions like this in the morning), he said thanks and hung up. My conclusion is he is just very interested in science, and I have to commend that.

But coming back to it, I want to go a little deeper into these questions.

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Re: Cosmic fingerprints pt. 2

Yesterday, I began a review of Perry Marshall’s Cosmic Fingerprints emails. Today I look at part 2: “Bird Droppings on my Telescope.

In this email, Marshall defends Big Bang Cosmology (which is nice, compared to some YECs).  He starts with the story of the discovery of the cosmic microwave background, one of the greatest discoveries of the past century.

Unfortunately, Marshall continues speaking.  He grabs a couple interviews with Robert Wilson (co-discoverer of the CMB):

Robert Wilson was asked by journalist Fred Heeren if the Big Bang indicated a creator.

Wilson said, “Certainly there was something that set it all off.  Certainly, if you are religious, I can’t think of a better theory of the origin of the universe to match with Genesis.”

Which is likely the good PR thing to say when cornered by an interviewer.  Scientists are known for being a bit sheepish with discussing religion, mainly since people who grant funding might look less favourably on someone who actively attacked the religious (especially forty years ago).

Continue reading Re: Cosmic fingerprints pt. 2

The basics of conductivity in metals

Currently my experiment involves determining the limits to a classical model for conductivity in metals.  So how do we model the conductivity of metals?

First, by conductivity, we are refering to the ability for current to pass through a material.  Current is moving charges, and the charges that are moving are either electrons (negative charges, which move in a direction opposite to the current – this is just the convention) or holes (positive charges, basically a place in the material where an electron no longer is).  Electrons and holes are known as charge carriers.

In metals the holes are basically stationary, and it is free electrons in the material that move around.  Now the ions (the atoms that are missing electrons) in the metal are very heavy (relative to the electrons), so they make up a background sludge while the electrons move essentially freely, like a gas through the material.

So if we treat the electrons as a free gas of particles against a background drag (caused by the electric attraction between the electrons and the ions), we have the Drude model of conductivity (invented in 1900, all equations will be ommited here but are available on the Wikipedia page).  Applying the classical laws of physics (Newton’s), we can find that the velocity of the electrons in a metal should be proportional to the mobility times the electric field magnitude.

Continue reading The basics of conductivity in metals

Terahertz vacuum

No, not a super-cool vacuum that picks up 1012 particles per second, but my normal terahertz spectroscopy setup under 10-5 Torr of pressure (equivalent to the high reaches of the Earth’s themosphere).

In today’s experiment I am probing wire grid polarizers.  Essentially wires of 200nm thick gold on a glass (fused SiO2) substrate that are 10 microns wide. The wires are separated by 10 microns gaps and vary in length from 5 millimetres to 10 microns long.

Since the wavelengths of the pulses I’m sending through are centred around 300 microns, this means at the extreme end of my devices I have subwavelength devices.

By doing terahertz time-domain spectroscopy on these samples, we should be able to figure out the limits for convential polarizers and determine whether (and where) the Drude model of conductivity breaks down.

The unfortunate part of today is that since the final sample mount isn’t finished for the vacuum chamber, which will attach to a cryostat, I have to break vacuum every time I want to move my sample and probe a different length of wire. The lucky part is vacuum is achieved in a mere 5 minutes.

So why use a vacuum for this experiment? Typically terahertz experiments are done in a nitrogen purged environment. The reason for purging (or vacuum) is that water is the sworn enemy of terahertz radiation. More specifically water molecules have several rotational modes that correspond to frequencies in the terahertz range. These modes absorb much of the incident radiation. Essentially terahertz radiation gets damped by damp air. By filling a chamber completely with nitrogen you eliminate most of the water vapour. Using a vacuum chamber accomplishes the same thing but is much cooler (and allows for a cryostat to be used inside as well).

This material is the work that I’ll be presenting at this year’s EngPhys/IEEE/Physics Undergraduate Research Symposium, which I worked to launch last year. After that I’ll hopefully take the work to CUPC.

Theory of Everything found?

Blogging on Peer-Reviewed Research See here and here; using the E8 mathematical structure, a man by the name of Garrett Lisi has proposed a new model of physics that basically explains the Standard Model and predicts a few new particles that the LHC may be able to detect next year. This sounds cool. Here‘s his paper. Oh also, since it uses only the geometry he did this without calculus!

Note: This is technically not peer-reviewed research yet, it has only been submitted online to a free online paper-publishing site, so holes may yet be found, or not.

CUPC 2007

This past weekend I attended the Canadian Undergraduate Physics Conference at Simon Fraser University in Vancouver (and Burnaby), British Columbia, and it was a hoot!

What tops my list is hearing the talk from Dr. Lene Hau who used Bose-Einstein Condensates to slow, stop, and even transport light!  This has gotten me interested in the entire field of BEC and atom trapping and I’m now in contact with Dr. Kirk Madison at UBC about a potential summer job in his lab next year (and maybe grad school after).

I must complain that the majority of the people I met from the University of Calgary were tremendous douchebags – and I don’t say that out of a school rivalry.  We listened to one of their talks (which wasn’t even that good), and midway through he insulted another university (over a plagiarism scandal that was likely unrelated to the paper he was referencing) and after he muttered that the audience was “boring” when they didn’t ask him any questions.  Another guy from their school was running through the hall on our floor and some chick yelled “you’re a nice guy, I just don’t want to fuck you” (or something to that extent), who also is rumoured to have gotten his funding cut for getting a tattoo when he was supposed to be presenting his poster (which was pretty abhorrent – ie. didn’t present anything expect what sounded like a dreamt up unresearched paradox, handdrawn, with links to pictures).  And even in talking with them they were just not nice.  We did meet one nice UofC Physics guy, so I don’t want to shame them all, just the majority of them.

As for the rest of the conference though, it was fantastic.  We saw TRIUMF and SFU Physics labs.  I presented and was later told by someone that he heard my talk was good – as in someone passed along good words about my talk.  Overall it was a great experience.

What is THz?

Terahertz radiation is electromagnetic radiation of frequencies between 10 GHz and 30 Thz (in the lab). THz = 1012 Hz This puts it in the far-infrared part of the spectrum with wavelengths (in case you can’t do the math) on the order of 100 microns.

This part of the spectrum is interesting because it lies in what’s known as the “THz gap” between traditional photonics and microwave technologies. Traditional electronics cannot switch fast enough to generate these pulses, and commercial lasers cannot generate that low of frequency of waves.

So how do we generate these waves? This is where ultrafast optics comes in. Using a technique called “modelocking” a standing wave is setup in a laser cavity and waves constructively interfere to create pulses with lengths on the order of femtoseconds (10-15 s). These pulses can then be amplified in a multi-pass system and set into a specific repetition rate (1080 Hz in my lab). Each ~100 fs pulse contains approximately 1/2 mJ. These pulses are then of high enough intensity to cause nonlinear effects in most materials. We now enter nonlinear optics land. When this light is incident on specific nonlinear crystals (in our case Zinc Telluride), a second order nonlinear effect called optical rectification occurs. This effect essentially creates a DC bias inside the crystal and current essentially flows through the crystal itself. This accelerating currents creates electromagnetic radiation in the THz regime.

THz pulses are interesting to study due to their absorption properties. Water is the primary absorber of these wavelengths, while plastics, papers, and fabrics have much lower absorption amounts. This allows for the application of techniques for THz imaging. For instance a THz wave can scan through clothes but gets absorbed by water or reflected by metal. This allows for the potential use of security scanning where police can essentially ‘see’ through a person’s clothes and determine if there are any weapons on them. The resolution is better than 1 mm, which is good enough to see most weapons. The following image shows a THz imaging scan:

THz imaging

There are several other ways to generate THz radiation (which I am presently working on a few), as well as many more applications (inlcuding THz-TDS). It is an exciting field that I am enjoying as I learn more about it.