Dense Atomic Vapors

Steve Cundiff studies the behavior of dense atomic vapors at temperatures ranging from 300-800 °C. In his group’s initial experiments, researchers directed two or three excitation laser pulses into dense vapors of potassium atoms (³⁹K). The group used a reflection cell to study the signal beam generated by coherent interaction between the excitation pulses in the vapor. This method is similar to using a stroboscope, which uses pulses of ordinary light to make tennis balls appear stationary as they fly through the air. One major goal of this and subsequent experiments is to test an 1873 prediction of a fundamental interaction of light (known as the Lorentz-Lorenz shift) with a dense ensemble of oscillators. The Cundiff group’s results suggest that the interactions are more complicated than Hendrik Lorentz predicted more than 130 years ago.

The first set of experiments showed that the first laser pulse synchronized resonance frequencies of the emitted light from the K atoms (i.e., created coherence); additional pulses gathered information about the dissipation of the coherence caused by atomic collisions. By varying the amount of time between pulses, the group monitored what occurred as atoms approached each other, collided, and flew apart. The group also studied the change of the decay rate of the signal with different laser powers.

In the latest set of experiments, the Cundiff group is using a transmission cell in a JILA MONSTR (Multidimensional Optical Nonlinear SpecTRometer) to perform two-dimensional Fourier-transform spectroscopy of the dense atomic vapor. The new technique is allowing the researchers to observe how a laser pulse interacts with the K atoms. It is also making it possible to discover new phenomena and investigate their properties. This research continues to shed light on the collision behavior of K atoms in a dense vapor.