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

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.

Globetrotter Grady in Berlin

Despite the fact that pretty much no one else in the group was all that impressed by Berlin, I had a great time there and thought it was an amazing city. We only got to spend about four days there, and what little time we had was sometimes spent on pointless activities, but after all was said and done we got to do some pretty neat things.

We arrived at our hotel Thursday evening, and quickly discovered that it had communal showers in the grand European tradition. Sorry though I am to admit it, I am still a bit of a prude when it comes to such things, and spent an interesting and uncomfortable four days showering with large, talkative European men.

Thursday evening about five of us went to see a variety show at the Winter Garten on Potsdamer Strasse, which is this beautiful theater in the classic vaudeville style. Brass handrails, the flashing lights outlining the stage, employees in evening dress- the place had everything. The show was equally excellent, with a variety of gymnasts and so forth, and one really outstanding old school entertainer. That guy was pretty amazing. Let me tell you about him.

He comes out on the stage and starts chatting with us, dropping little jokes here and there that were really pretty clever- quite a few of them were plays on words that you wouldn't get unless you knew a little German and English, and he's dropping in references to American radio shows from the '30s. And while he's got his patter running, he's doing little tricks for us- a bit of juggling, a bit of balancing a top hat on his nose. Except he's not perfect; every once in a while he wouldn't quite catch the hat he was trying to flip from his foot to his head, or he'd miss a ball juggling, or something. But he was great fun to listen to, and everyone in the audience was like, "What a charming old man, I certainly don't expect him to pull off every trick flawlessly." So as he continues with his act, he pulls out a teacup and saucer. He balances the saucer on his foot, and flips it up and catches it on his head, and we're all like, "Yay! Good job!" Then he puts the teacup on his foot and flips it up, catching it on top of the saucer. So now we're all like, "Wow, that's pretty cool." Then he takes out another teacup and saucer (all while keeping up the banter) and does the same thing. And we're suitably impressed, but we're getting worried, because he keeps wandering around the stage with these teacups balanced on his head, and he's good, but he's not perfect, and they're rattling around a lot, and we don't want him to embarass himself by having them fall. So next he breaks out another teacup and saucer. Has a little trouble balancing them on his foot without letting the other fall off his head, but manages it. Flips the saucer up, and catches it. Flips the teacup up, it almost misses, the whole stack is wobbling, it almost falls, we gasp, but he manages to catch it. So now he has a stack of three teacups and three saucers balanced on his head, and we're impressed. Next he takes out a tea kettle.

Teacups rattling, he leans down and balances the tea kettle on his foot. We're all thinking, "Oh, come on man, you can do it. You're so old and funny, don't screw up now." He flicks his foot. The kettle flips up through the air and lands squarely on top of the stack, which doesn't even quiver.

The man was stringing us along the entire time. He knew exactly what he was doing, and had perfected the technique of making deliberate failures look like mistakes. The whole act, he was building a skeptical audience up to the point where they were completely empathizing with the performer. I have never seen anyone work the audience as well as he did.

On Friday, we had some tasty, tasty Brötchen for breakfast, and then piled on the bus for a "Grand Tour through the City." It was conducted by some random friend of Professor Klabes', and wasn't the greatest. Bus tours to begin with leave quite a bit to be desired, and the high point of this one was the moment when the guide said, "Oh, and by the way, that was the Brandenburger Tör we just passed, turn around quick and you might get a picture." Ah well. Friday afternoon we visited the Checkpoint Charlie museum, which is small and badly designed but very interesting. After that, I strongarmed a couple of people into visiting the Judisches Museum, which is an architectural marvel, and also a damn good museum, following which we wandered around the streets of Berlin and grabbed some dinner before taking the S-Bahn back to the hotel.

Other highlights of the trip included visiting the Pergamon Museum, and getting to see the opera Eugene Onegin. Now, Pergamon was a city in ancient Greece that built a huge altar to either Zeus or Athena, and it's been reconstructed inside this musuem. And when I say 'huge' there, I mean, seriously, you walk into the first room of this musuem and are dwarfed by this massive, wide set of steps leading up to the altar. It's just unbelievable. They also have just a shit-ton of other artifacts from antiquity, from several different areas of the world. The other things that really stick out in my mind are the Ishtar Gate and the Processional Way from Babylon. Babylon, folks. Now, keep in mind that these are building-size structures that have been reconstructed inside this musuem, and I didn't even come close to making it through the entire thing. If you should ever wake up one day and discover you're in Berlin, this is a good place to spend a week or so. And the crazy thing is that this is just one museum on this island in the middle of Spree River with something like four other world-famous museums on it.

Moving on, the last thing I wanted to mention was Eugene Onegin. The text is a poem written by Pushkin using an unusual rhyme scheme that has since become known as an Onegin stanza. The music was by Tchaikovsky. I won't pretend to know exactly what was going on, but the music was pretty, the staging was interesting, and after I got back to the states I read a little about the text, and it turns out it's got a fairly interesting history. Nabokov did a crazy translation of it that a lot of people hate. And interestingly enough, Douglas Hofstadter, the mathematician who wrote Gödel, Escher, Bach has also written a verse translation of Onegin. All this has convinced me to read it. Right after I get through the new Potter...

Charles Johnston's translation of Eugene Onegin

In conclusion, the most consistently amusing thing about the entire German trip was Herr Klabes. As proof positive, I submit this photo: