Determination of phase fluctuations of a Highly-Stabilized laser by the analysis of photon echo decay functions

The simple 2-pulse echo as a prototype of coherent spectroscopy offers the unique possibility for a recall of past time parameters. This feature is utilized in the optical frequency domain for the realization of a phase comparator, equivalent to an optical interferometer of approximately 10 km variable path length difference. The measured autocorrelation time of the optical field is a convenient absolute measure of the frequency stability of the laser field and has been tested in the 10–100 kHz line width range.