Resonant Absorption and Refraction

Optical resonance in atoms forms the basis for this workshop. Even though the effect is strictly a quantum one, it can be modeled semi-classically. Thus, the system exhibits all of the familiar features of a driven harmonic oscillator, including resonance and the associated phase shift. In this case, the phase shift can be observed interferometrically, and doing so provides an opportunity to cover several useful and interesting topics in experimental optics and atomic physics.

In this lab, participants will use a Teachspin laser-diode apparatus and a cell of Rubidium vapor to observe both the absorption and refractive index change of a gas as the frequency of the laser is passed through an atomic resonance. First, they will measure the absorption of the gas as a function of temperature and extract the latent heat of vaporization of atomic Rubidium using the Clausius-Clapeyron relation. Then they will place the cell in one arm of a Mach-Zender interferometer and, by observing the resulting fringe pattern, measure the change in index of refraction due to resonance. The absorption and index of refraction are fundamentally related through the Kramers-Kroenig relations, and we will cover some of the theory of this as well as the measurement technologies.