Overview

What do we do here?

Researchers in our group develop expertise in the production, characterization, and manipulation of near-infrared laser light pulses which are of extremely short duration. The focus of our research is studying the phenomena which result when these pulses are tightly focused to produce very high light intensities which are then used to illuminate various forms of matter. Since we are atomic and molecular physicists, we are primarily interested in interactions with gas-phase matter; however we are engaged in collaborations with other OSU research groups interested in using the femtosecond laser to study, for example, the photophysics of light-emitting polymers in liquid solution and within a solid matrix. In the past we have studied light-solid interactions in the context of understanding the plasma formation caused when even higher energy pulses interact with solid metallic surfaces, especially the production of short wavelength radiation arising from the cooling of these plasmas.

We are also presently interested in the application of femtosecond laser pulses to laser drilling and micromachining, as well as possible medical or other "real-life" applications. However, the overall thrust in our group is toward basic research into the pure physics of high-intensity laser-matter interactions.

The current focus of the majority of our research is the processes involved when a single atom is exposed to and ionized by high-intensity ultra-short laser pulses. To understand our approach to figuring out how atoms and molecules work (in layperson's terms), we refer you to the following joke:
Q: How does an atomic physicist tell what time it is?
A: He picks up a sledge hammer, smashes a clock to smithereens, then determines what time it was at the point of impact by putting all of the pieces back together.

How short is "ultra-short"?

Our laser pulses are typically around 120 femtoseconds (the temporal width measured at half of their peak power) in duration. One femtosecond is 10^-15 seconds, so 100 of them is about a tenth of a trillionth of a second. To get some feel for how short this is, consider that their are as many femtoseconds in one second as there are seconds in about 32 million years! One second is truly geologically long to our pulses. Another useful measure for comparison is the time scale for various atomic and molecular processes to take place. Here are some examples:

• The typical orbit time for an electron in a hydrogen atom is from around 10^-16 to 10^-14 seconds.


• The time between the vibrations of the nuclei in a hydrogen molecule (H₂) is around 10^-13 seconds.

Why is this stuff interesting?

Other than our favorite answer - "Because it is", there are other physically significant reasons. First, we study this for the same reason why most scientists choose to study science and to make it their careers. Pure curiosity. It is why some children (and adults) have an irresistible urge to take their toys apart. They want to figure out how it works, and a quick explanation is not good enough. They want to know how it really works. Being atomic and molecular physicists, we want to figure out exactly how atoms and molecules work. Now you might be saying, "Don't scientists already know how atoms and molecules work?" And the answer is, "Yes, ...well, sort of..." Scientists have a fairly good idea of how an atom behaves in a very calm or a normal environment, but if you place an atom in an extreme environment or even try to measure a single atom its behavior and characteristics will change dramatically. One of these extreme environments where an atom's behavior is not fully understood is when it is subjected to high-intensity laser light. Matter that is exposed to "normal" intensity light (that of a light bulb or sunlight) will absorb single photons and make some electronic transitions for atoms and molecules, and vibrational and rotational transitions for molecules. As you increase the intensity higher and higher, non-linear effects come into play and the properties and structure of the atom itself begin to change. How an atom responds and changes when exposed to light of this magnitude gives scientists a peek at how an atom really works.

The second reason why we find this stuff interesting is the excitement of reaching into the unknown and extending the knowledge base of how the universe around us works. What we study is an area of physics that is not completely understood. There are many more questions in this field than there are answers. Because of the mathematical complexity, physicists cannot explicitly describe the behavior and structure of any atom beyond the simplest one, hydrogen. For any other atom or molecule we have to rely on various models and approximation, albeit some work amazingly well. But, a unified, accurate, and well accepted model for the response and behavior of an atom in a high-intensity laser light field does not yet exist.

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