Diode laser spectrally fixed at an atomic absorption line

A simple all-optical technique for fixing the spectrum of the output from semiconductor laser at a chosen absorption atomic line is realized and studied. The technique, which is not of a laser locking type, uses a conventional diode laser without any influence on its operation. For implementation of the technique, the diode laser output is fed to a modified Michelson interferometer, and controllable disturbing of phase and amplitude correlation between the interfering beams in the two arms of the interferometer is achieved by frequency scanning through a contour of a reference absorption line of a substance introduced in one of the arms of the interferometer. It is shown both by experiment and theory that, under properly chosen conditions, the spectrum of the obtained light is fixed at the atomic line and has a linewidth comparable to the linewidth of the used absorption line.