8.22.2005

Pulsed Laser Deposition

This summer after returning from Germany, I spent the rest of my time back at William & Mary doing research for one of my physics professors. One of the areas in which she does experiments is using ultrafast laser pulses to ablate or deposit materials. The basic idea is this: if you have a little chunk of some metal, say nickel, you can shoot it with a laser pulse. If this laser pulse is fast enough and powerful enough, it can actually excite the electrons in the metal so much that they vaporize and form a plasma plume that shoots off the surface of the metal. This is called laser ablation.

You can also repeat this process in quick succession using a laser that generates, say, 1000 pulses that each last for 150 nanoseconds. Each pulse will generate a plasma plume. Now, if you take some kind of substrate or gridwork and place it directly in front of the material, then whenever a plume shoots off the surface of the material, some of that vapor plume is going to recondense on the substrate. By using several thousands laser pulses, it's possible to build up a film of material that's only a few atoms thick. This is called pulsed laser deposition, and the sorts of films you generate are apparently useful in fields such as superconductor research.

Although the idea is pretty straightforward, the process itself becomes very complicated when you try to do one of these experiments in reality. There are a tremendous number of interactions that need to be considered- what kind of atmosphere should the experiment be conducted in, how should you set up the laser pulse so that it vaporizes the material without melting it, how do the characteristics of the plume change as you whittle away a hole where the laser is impacting, how do successive laser pulses interact with the gas from the previous plume, and so on. The work I did this summer was kind of a basic first step in coming up with a computational model for one of these experiments.

I spent the last few weeks of summer looking at how the temperature of the material is affected by the laser pulse. Mathematically, this is modeled with a system of differential equations by considering the temperature of the electrons in the material and the temperature of the lattice in which they are held to be two separate but related quantities; it's referred to as the two-temperature model. In very special, restricted cases, it's possible to solve this system analytically, but these solutions are not of much practical use. I put together a Mathematica notebook that numerically models the initial laser pulse as well as the period of time during which the heat diffuses throughout the material. Although this project was mostly a chance for me to learn a bit about using Mathematica, it was also an interesting twist on the classic heat diffusion boundary problem, as one side of the material is not held at a fixed temperature. The solution turns out to be using an "insulation" condition for that boundary, which amounts to setting the first derivative of the temperature function with respect to space equal to zero; this represents the fact that heat is not passing through that boundary; it's insulated. Although this wouldn't be strictly true in practice, we didn't get around to including heat loss to radiation in this model before college got rolling again.

Anyhow, for your viewing pleasure, below you can take a look at what I came up with, both as a Mathematica notebook if you've got the program, and as a pdf. If anything I've done would actually be of help to you on a project of your own, feel free to use whatever you find, but please, credit where credit is due. Additionally, if you have any suggestions for improving the code in this notebook, I would love to hear them.

>Mathematica Notebook
>Portable Document Format

8.08.2005

Comics

You may have noticed in the past few years that comics are getting quite a bit more press than they historically have- there have been any number of articles on the internet commenting on their wider-spread acceptance as 'serious' art, how the form has finally matured, and so on and so forth; the number of movies based on comics that have been made in the past five years also bears testament to this phenomena. Scott McCloud is probably the most well-known comic advocate, and has written extensively on the theory of comics, but it seems like these days everyone from literary journalists to college students is writing about the comic as a medium.

I won't make any claims about being a comic aficionado; I know next to nothing about their history, or the history of their acceptance in the mainstream. However, the result of seeing several writeups about comics and some comic-inspired movies was that I broke down and actually read a few of them. Now, right up front let's be clear on the fact that, when people talk about the comic as an art form, they're not usually thinking about X-Men or Batman. Not to say that those kinds of comics are bad; they are, in fact, excellent in the same way Harry Potter is excellent- entertaining, fun reads. As well-executed as they are, however, you probably wouldn't point to them as the vanguard of the 'new seriousness.' Comics (believe it or not) are just as capable as book or film of treating all manner of issues from the timeless coming-of-age story to discovering someone you love has cancer, and the infinitely nuanced way in which a story can be told through pictures is what makes these works so fascinating.

If you're interested in more wonderful background, certainly click on the things above. Although I'm certainly not well-read as far as comics go, here are the books that initially got, and held, my attention:

  • Hellboy- I'm a dork, right, so naturally I saw the Hellboy movie at some point. Although it's not one of the better comic-based movies, I was interested enough to check out the source material; it turns out a few of them are available online for free. Despite my undying hatred of H.P.Lovecraft, I'm a huge fan of the whole occult/folklorish kind of atmosphere this comic creates, and thoroughly enjoyed the two in the series I've picked up so far. This particular comic undoubtedly falls more in the Batman/X-Men category than that of Mom's Cancer, but it nonetheless stands out in my mind for its very sharp, distinctive artwork. Plus, like I said, it's a ton of fun to read.
  • Bone- This is a fairly well-known and respected comic from Jeff Smith, and despite being highly regarded by other comic artists, I was somewhat disappointed with it. It was initially published in several volumes over the course of a decade or so, and with the recent conclusion was collected into a one volume edition. The drawings themselves are consistently excellent, the characters are wonderfully well-developed, and the opening third of the series has an immediate charm; in all these respects, the series was a great read. For me what held it down was the plot, which becomes very Dungeons & Dragons-ish the farther into it you get. Much as I enjoy playing D&D, the sorts of stories you see in a game session are not the kind of thing you want to be reading. Tenuously connected plot points, the princess thought dead secretly living as the woodsman's daughter, a magic force permeating the world that an ancient evil seeks to corrupt- these are things I could have done without. It's won a whole stack of awards, though, so don't put too much stock in this opinion.
  • Flight- This is an anthology of short pieces, all drawn by up-and-coming webcomic artists. That may not sound too promising, but the collection is, in fact, really fantastic, and I hear that Vol. 2 is as well, though I haven't read it yet. Many of the stories in this book deal in some manner with flying, but not all of them- the book is really a showcase of artistic styles, some of which depart pretty drastically from what most people would consider "traditional comic," to very impressive effect. Relatedly, the guy who edits the Flight series (Kazu Kibuishi) also draws a monthly webcomic called Copper that has some of the best artwork you will see in a webcomic. His Daisy Kutter series has also won or been nominated for an award, something like that.

That's about it. I'm hoping to get into the Sandman series when I've got some cash, also Heavy Liquid by Paul Pope. And as far as honest-to-God syndicated comics go, Complete Calvin & Hobbes is hitting this Fall, and will rock. AND there's some comic-based movie called V for Vendetta coming out soon. I don't know a thing about the comic, but the movie is starring Hugo Weaving, and what he does in the movie is kick ass, so chances are it will be really good.

If any of you guys have recommendations or comments, you should, you know, leave a comment. But not if you have a remark. We don't truck with those here.