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Attosecond Physics

Atto: the SI prefix for 10^-18. A prefix not commonly found in textbooks or courses, because there aren’t many quantities that are measured in atto-somethings.

The lab that I’m working in this summer, headed by Prof. Dr. Ferenc Krausz, does research in the field of attosecond physics. Essentially, they make the world’s shortest laser pulses to try to do really cool stuff, including high quality resolution of electronic processes in atoms and molecules.

When you want to look at a process (e.g. a chemical reaction), one way to do it is to shine laser pulses on it and see what is reflected and transmitted. The shorter the laser pulse, roughly speaking, the higher the resolution. In the case of certain electronic processes (e.g. the relaxation of an electron from a high energy state to a lower one), the timescales involved are so fast that you need avery short laser pulse to be able to resolve it. So short, in fact, that the laser pulse must be below a femtosecond (10^-15) in duration!

My group at MPQ pioneered a device known as the light field synthesizer which currently holds the Guiness World Record for the shortest laser pulse ever synthesized! What the synthesizer basically does is split a laser beam into constituent channels, ranging from infrared to ultraviolet, and sculpt these individual channels, recombining them at the end to create an extremely short laser pulse.

The field synthesizer. The colors are real, and not photoshopped!

It’s all really cool stuff, but what might not be as apparent is how much effort goes into such an experiment. Because the group at MPQ is pushing the boundaries of how short laser pulses can be, the equipment involved is absolutely massive. The entire group is around 150 people, and the many laboratories working on attosecond physics each utilize millions of Euros of technology! When talking to my PhD student mentor, he casually mentioned that their research was limited by creativity and drive, rather than funding. Coming from the USA, where grant-writing is much more common and funds are always limited, it’s a completely new concept to myself.

Anyway, I’m contributing a very small portion to the research going on at MPQ, since I’m only an undergraduate here for 12 weeks. My group is running some new experiments on extreme ultraviolet (EUV) radiation, and they need to know the spatial profile of the generated beam – essentially, what the laser beam cross section looks like. To do that, they need to have a beam profiler. The tricky part is that we can’t use a regular CCD camera, since EUV radiation is very intense and very weak, and won’t be picked up in that case. Instead, we’ll be using a microchannel plate (MCP) detector, which can detect few-photon signal and amplifies them in a sort of avalanche process. The whole experiment needs to be done in vacuum, since EUV radiation can ionize air and mess up the whole thing, and various other experimental considerations need to be taken into account (mainly the fact that there’s only one optical table and avery limited amount of space!).

What I’ll be working on for the next few weeks is designing the beam profiler in Autodesk Inventor, a 3d modeling software. Basically, I need to figure out how to arrange all the components in a way that fits with the rest of the experiment, and design the enclosure that will comprise the beam profiler. It sort of feels like art; at least for me, a person who can’t draw to save his life, this is the closest I’ll ever get. Since I’d never used a CAD software before, learning was fun, and I actually have a preliminary profiler ready! Now it’s just a matter of taking the design to the mechanic shop in the institute, where the technicians will tell me exactly how impossible and infeasible my design really is.

My (preliminary, rough, hesitant, possibly disastrous) profiler design.

And now, some Bavarian culture. At the cafeteria I had this for lunch:

At first glance, I thought I was eating meatballs for lunch. Turns out it’s actually a thing called Knödeln! What they are, are dumplings made out of potato or bread and usually served with a sauce. Here, it’s served with sauerkraut. According to one of my office mates, this is a very traditional Bavarian dish. It tasted pretty good!

Jonathan Liu