Research Notebook: Light and matter

Matthew Edwards spends his weeks in the extreme light-matter interactions laboratory at Princeton University, chasing a phenomenon that happens in an attosecond.

There’s no reason for most of us to know what an attosecond is; it’s so small that humans can hardly comprehend it. Roughly 1018 attoseconds passed in the time it takes to say the word “attosecond.”

One of the only things that moves this fast is electrons around the nucleus of an atom, which is exactly what Edwards wants to see more clearly. That’s why he spends his time in the laboratory, tinted goggles pressed firmly over his eyes, meticulously adjusting the equipment to generate the next attosecond pulse.

“The time duration of these pulses is very short,” Edwards said. “That allows you to use it as a very fast camera more or less to taken an image of something that evolves very quickly…These are some of the fastest processes in nature.”

Matthew Edwards in the lab at Princeton University.

Edwards is working toward his doctorate in mechanical and aerospace engineering while studying the interactions between high-intensity lasers and matter. He did similar kinds of research as an undergraduate, studying how lasers can be used to better detect the properties of air around planes.

Now he’s working with lasers and the X-ray radiation generated when they hit a target, an area that has entirely different kinds of uses.

“There are some imaging applications, there are applications in something like measuring the structure of proteins. A lot of times when you talk about bright X-ray sources you’re trying to measure molecular structures at a very detailed level,” Edwards said.

For instance, electrons around a nucleus move so quickly that it’s hard for scientists to gain insight into their actual nature. The best they can do is use the information available to develop models that draw conclusions about an electron’s average behavior. Edwards hopes that some of the things he works on can lead to those models being refined.

“There are questions about some of the models and whether they’re right,” Edwards said. “They seem to be right, but you don’t really know until you measure them.”

These pulses, the things that capture electrons in their true state, are the output of a laser hitting a target after undergoing a complex series of alterations. Because the laser is so bright and so powerful, it can damage the equipment it runs through without these changes.

It essentially happens in three steps. First, the laser is diffracted through a grating, which means the energy of the beam hits the amplifier at slightly different times instead of all at once. Then, the amplifier increases the beam’s intensity in chunks. Finally, the beam is re-compressed back to its original form, striking the target with enough power to strip electrons away from the atom and accelerate them to near-light speed. This particle emits radiation in the form of the attosecond pulses Edwards wants to measure.

It takes a certain kind of dedication to revel in the perfection of this process. That commitment comes naturally to Edwards, who knows that there’s a wide gap between knowing the steps and being able to replicate it consistently, not to mention under different conditions. Practical possibilities will have to wait until that gap is bridged.

“We’re at the edge of what can be achieved with lasers today,” Edwards said. “There are a lot of fundamental questions that need to be answered before you can even think about applications.”

Still, Edwards is encouraged by the progress made on finding out the answers to some of those questions. Experiments like the ones Edwards does used to take up whole facilities that cost billions of dollars to build. The equipment Edwards needs to run his experiments is more in the range of millions of dollars. It can all fit on a couple of lab tables.

That kind of progress is significant for researchers, but it could be even more significant for hospitals.

“There are some types of surgery for treating cancer where you would want to use some of these large-scale facilities that accelerate particles to deposit energy and destroy particular areas of tissue,” Edwards said. “You can do that if you have an expensive facility. One possible application of this work is to make that a little less expensive.”

Of course, Edwards was quick to add the caveat that there’s no guarantee his work would lead to anything of the sort. If it did, it would only be after countless experiments by lots of people. He’s still excited by the possibilities, though.

“You’re discovering things that are new. You get to go into the laboratory and look for things that haven’t been seen or understood before. You get to try to find out something new about how the world works.”

“You know that if you get something that comes out (of the experiment), you’ve made a contribution that hopefully lasts for a while.”

This is the first story in a new series highlighting research being conducted by Princeton area graduate students and professors.