The present work discusses methods of stabilizing the frequencies of commercially-available laser diodes. Laser diodes are generally compact and long-lived. The frequency stability, which makes them ideal for onboard laser interferometer light-sources, in applications such as the satellite-to-satellite tracking systems used to verify fluctuations in earth's gravity field, which, in turn, indicate other critical changes in the environment, is the key characteristic of this work. We used the devices typically operating at 780nm, and their frequencies can be stabilized using either of two systems; one, employing the Doppler-free absorption line of Rb atoms and another, sing the Faraday effect of the Rb absorption line. In both cases, the use of the proper modulation frequency and amplitude improved frequency stability, overall, attaining 2.05×10<sup>-12</sup> and 2.73×10<sup>-11</sup>, respectively, in the square root of the Allan variance, by measuring the beat-note between two independently-stabilized laser diodes.
We report on the stabilization of a semiconductor laser's frequency, using Rb absorption lines. In order to improve overall frequency stability within our system, we adjusted the setup used in Rb- saturated absorption spectroscopy, and optimized modulation parameters such as modulation - frequency and -width, to more accurately detect the error signal. When we stabilized laser frequency using a Doppler-free absorption line of Rb atoms, a time-constant of 0.01sec, and a modulation frequency of 7.77kHz, relative optical frequency stability of 2.12×10<sup>-12</sup>≤σ(2,τ)≤5.88×10<sup>-11</sup> was achieved, in averaging time for 0.04s≤τ≤65s.
We report on the stabilization of a semiconductor laser’s frequency, using spectra-controlled etalon. As the spectra of an etalon are controlled by one of the Rb absorption lines, they provide highly stable reference frequencies in a broad frequency range. When we adapted the PEAK method to the etalon’s spectra and used a Doppler-free absorption line of Rb atoms as the control signal for the newest model of our system, relative optical frequency stability of 2.91x10<sup>-11</sup>≤σ(2,τ)≤3.72x10<sup>-10</sup> was achieved in averaging time for 0.04s≤τ≤100s.