Five-year frequency stability of a Zeeman stabilized laser.

A five-year record of the lockpoint frequency of a Zeeman stabilized laser shows an observed drift rate of 0.3 +/- 0.5 MHz/yr following an initial drift of 5.7 +/- 2.2 MHz/yr in the first eighteen months of intermittent operation. A second Zeeman laser drifted at a rate of -0.8 +/- 1.0 MHz/yr over the last 2.5 yr; the frequency drift was -0.2 +/- 0.6 MHz/yr over the last 3.3y r. Empirical temperature correctionsto laser frequency measurements produce a slight variance reduction in the data but no effective bias in the drift estimates.

Optical fibers for measurement of earth strain.

We report on laboratory experiments on single-mode optical fibers for use in measuring earth strain. We have monitored the long-term stability of 25-m long tensioned fibers and found their rates of fractional change in optical path lengths to be no more than 2 x 10(-6)/yr. The optical temperature coefficients for several fibers whose physical lengths were held constant were found to be within 4% of 1.17 x 10(-5) apparent strain/ degrees C. The strain sensitivity (the ratio of observed optical path change to physical path change) was determined to be within 1% of 1.16 for all the fibers tested. Initial field tests indicate that fibers are suitable for earth strain measurements of moderate precision.