Saturated Absorption Spectroscopy

Saturated-absorption, or “Doppler-free,” spectroscopy is a widespread and useful tool for modern atomic physics. As the name suggests, it allows the effective removal of the Doppler broadening in absorption lines of an atomic vapor. The basic idea is to use counterpropagating “pump” and “probe” beams of the same frequency (generated by the same laser) to select for and probe only those atoms whose velocity component parallel to the beams is zero, i.e. those atoms moving at right angles to the laser beams. This allows us to do spectroscopy limited only by the natural linewidth of the atomic transitions, revealing features of the absorption lines that would otherwise be unobservable in a gas at room temperature.

In this lab, participants will use a Teachspin laser-diode apparatus and a cell of Rubidium vapor to learn how to do Doppler-free spectroscopy in hydrogen-like atoms. After learning the basics of diode lasers and saturated-absorption spectroscopy, they will calibrate the system using an asymmetric Michelson interferometer and measure the hyperfine splitting of the P3/2 levels of both 85Rb and 87Rb.