Accession Number : AD0815954

Title :   LASER MATERIAL (SPECTROSCOPY).

Descriptive Note : Rept. no. 4 (Final), 15 Jun-15 Dec 66,

Corporate Author : STANFORD UNIV CA MICROWAVE LAB

Personal Author(s) : Siegman, Anthony E.

Report Date : MAY 1967

Pagination or Media Count : 40

Abstract : MEASUREMENT OF LASER SHORT-TERM FREQUENCY FLUCTUATIONS: Detailed measurements have been made for the first time of the short-term frequency or phase fluctuations in stable single-frequency helium-neon lasers. These frequency fluctuations are the principal cause of the finite spectral width of laser oscillators. The fluctuations were measured by examining the beat notes between two essentially free-running lasers operating in a quiet stable environment. The average frequency of the beat was kept at a nominal 30 MHz center frequency by a slow AFC loop which did not affect the faster short-term fluctuations. Separate measurements were made of (a) the power spectral density of the 30 MHz beat note; (b) the mean-square accumulated phase jitter in the beat during intervals of varying length; and (c) the spectral density of the low-frequency output from a discriminator cented at 30 MHz. Results of the three separate measurement techniques were in good agreement, indicating a gaussian power spectral density for the laser oscillators, a mean-square phase jitter increasing quadratically with time, and a discriminator output spectrum varying as 1/f squared. The standard deviation of the gaussian laser spectrum was found to be sigma sub f is approx equal to 13 kHz, or a spectral purity better than three in 10 to the eleventh power. A full report on these measurements will appear in the IEEE Journal of Quantum Electronics in early 1967. Nd: YAG LASER SPECTRAL STUDIES: During the final period the amplitude fluctuations of the Nd:YAG laser were studied. These amplitude fluctuations, which were small compared to the steady-state level of the output power, were found to be of the form of damped sinusoids.

Descriptors :   (*GAS LASERS, FREQUENCY), SPECTRUM ANALYZERS, HELIUM, NEON, OSCILLATORS, NEODYMIUM, YTTRIUM COMPOUNDS, GARNET, AUTOMATIC FREQUENCY CONTROL, MEASUREMENT, BANDWIDTH.

Subject Categories : Lasers and Masers

Distribution Statement : APPROVED FOR PUBLIC RELEASE