Doppler-free Laser Spectroscopy

This article discusses several experimental techniques with Doppler-free spectral resolution such as linear spectroscopy in collimated molecular beams and nonlinear spectroscopy in gas or vapor cells, using saturation spectroscopy, polarization spectroscopy, or multiphoton absorption. Optical cooling of atoms and molecules down to extremely low temperatures brings the Doppler width below the natural linewidth. Special double-resonance schemes enable stabilization of atomic collision pairs and sub-Doppler spectroscopy of molecules in very high-vibrational levels. Finally, some techniques with a resolution below the natural linewidth are discussed. Keywords: laser spectroscopy; molecular beams; saturation spectroscopy; polarization spectroscopy; multiphoton spectroscopy; Doppler width