Laser-Atom Interactions

What happens when high intensity laser light and matter interact?

Another question that has been asked (and answered) is "Why is the sky blue?" This question could be rephrased "What is it about the stuff in the atmosphere that makes the light coming from it blue?" It can be answered by considering what happens when light from the sun interacts with the atoms and molecules of gases in the earth's atmosphere.

In fact, the question of what happens when light interacts with a single atom or molecule has been and still is an active area of study in physics. At this point in our understanding of such phenomena, we know very, very well what happens in normal, "everyday" situations where the light is not very intense, or "bright". In such cases it turns out that the light has a very small effect on what happens inside the atoms or molecules themselves; that is to say it just sort of "tickles" them as it passes through, with the effect that they may absorb or scatter some of the light, but in such a way as to leave the optical properties of the material itself unchanged.

Light that is very intense, however, has the ability to modify the actual optical properties of the matter through which it propagates, which is the basis for the study of so-called "nonlinear optics". Nonlinear optical effects can account for a lot of interesting and exotic phenomena, for example, the ability of some crystals to change the color of a laser beam passing through them. On an atomic scale, the light no longer just "tickles" the atoms, it actually changes their structure in drastic ways. Such effects have been readily observable since the advent of lasers, which are capable of producing very intense light, due to their focusability and power.

By taking the intensity up a notch, we can observe what happens when the light is strong enough to actually tear the molecules or atoms apart, ripping electrons away from their nuclei or exploding molecules into smaller fragments. By doing so we actually create a new state of matter in the sense that its properties are dependent in equal proportion upon those of the matter being illuminated and the light being used to do so. We are able to reach the required intensities by using exotic lasers that are capable of producing pulses which last only tenths of trillionths of a second. Since the intensity of light is a measure of how much light energy can be delivered to how small a spot in how fast a time, by creating fast pulses we can reach focused intensities which are comparable to those, for example, on the surface of the sun. The study of the violent behavior that ensues is the focus of our research.