ABSTRACT
L asers have impacted our lives in a countless number of ways. Today they are found everywhere-in computer hard disk drives, CD players,
grocery store scanners, and in the surgeon’s kit. In research laboratories, almost everyone uses lasers for one reason or another. However, the greatest impact of lasers in physics has been in high-resolution spectroscopy of atoms and molecules. To see this, consider how spectroscopy was done before the advent of lasers. You would use a high-energy light source to excite all the transitions in the system, and then study the resulting emission “spectrum” as the atoms relaxed back to their ground states. This is like studying the modes of vibration of a box by hitting it with a sledgehammer and then separating the resulting sound into its different frequency components. A more gentle way of doing this would be to excite the system with a tuning fork of a given frequency. Then by changing the frequency of the tuning fork, one could build up the spectrum of the system. This is how you do laser spectroscopy with a tunable laser-you study the absorption of light by the atoms as you tune the laser frequency, and build up a resonance curve as you go across an atomic absorption.
