The semiconductor lasers in use today are on one hand, prized, and highly praised, for their small size, light weight, longevity and
energy-efficiency, -and on the other, criticized for their susceptibility to frequency-fluctuations brought about by changes in
temperature and driving current. Once this "wrinkle" is ironed out, semiconductor lasers will become the default light-sources, for
satellites' onboard interferometers. Our studies have been directed at stabilizing oscillation frequency to the atomic absorption line,
and using negative electrical feedback to the injection current. Frequency stabilization is accomplished, by either; a) applying direct
modulation to the semiconductor laser's driving current, or b) modulating the reference frequency, to obtain the error signal needed
for stabilization. In this instance, Faraday effect-based stabilization was used. This indirect oscillation frequency stabilization has no
discernable effect on spectra width, but, stability was no better than that observed in the system using the direct modulation.
When we compared Faraday effect- and direct modulation-based methods of stabilization, in order to uncover the root-cause of the
discrepancy, sensors picked up system noise, the source of which was heat generated by the heavy current applied to a magnetic coil
used to apply the Faraday effect. We also substituted a permanent magnet for the electromagnet.
The primary objective of the Decihertz Interferometer Gravitational Wave Observatory (DECIGO) mission is to detect and observe black holes' and galactic binaries' gravitational waves (GWs), at frequencies ranging from 10−2 to 101 Hz (from 0.1 to 100 s in averaging time). This low-frequency range is inaccessible to ground-based interferometers, due to unshieldable background noise and to the fact that ground-based interferometers are limited to a few kilometers in length. Our research is focused on efforts to stabilize semiconductor, Nd:YAG, and fiber lasers, for use as GW detectors' optical sources. In present-day and future detectors, frequency and phase noise may place certain limitations on sensitivity and stability. Our goal is primarily to design robust experiments. In this report, we compare existing methods: Faraday, Faraday peak, and saturated absorption spectroscopy. In these, the laser frequency is stabilized to Rb as an atomic frequency reference by a feedback-loop control system. From the frequency stability of these models, we can predict the characteristics of the three systems through dynamic stability analysis, by analyzing the dynamic Allan variance. We find the optical frequency stability, expressed as the Allan deviation (the square root of the Allan variance), to be 3.3×10−11, 2.9×10−12, and 1.2×10−12 in the respective methods.
Scientists throughout the world are seeking to enhance the capabilities of satellite-to-satellite tracking laser
interferometer-based optical systems used to measure the alterations in earth's gravitational field that indicate critical
changes in the environment. These systems must be able to measure infinitesimal fluctuations in the relative velocities of
two satellites, using a light source that oscillates at a level of frequency stability rated better than 10-13 in the square root
of the Allan variance. In our experiments, semiconductor laser frequency stabilization that typically requires a brief
direct modulation of the laser injection current to obtain an error signal, was accomplished using the Faraday effect of Rb
absorption lines. This effectively modulates the reference frequency of the stabilization system, i.e., the Rb absorption
line, by modulating the magnetic field applied to the Rb absorption cell, instead of the oscillation frequency of the laser
diode. Most recently, we used the Faraday method, in conjunction with a precision temperature controller. For present
purposes, we also use the PEAK method, to obtain the most accurate signal possible, comparing it with saturated
absorption spectroscopic readings, to determine the noise-source.
The primary objective of the Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) mission is to detect
and observe black holes' and galactic binaries' gravitational waves (GWs), at frequencies ranging from 10-2 to 101 Hz.
This low-frequency range is inaccessible to ground-based interferometers, due to unshieldable background noise, and
the fact that ground-based interferometers are limited to a few kilometers in length. Our research is focused on efforts to
stabilize semiconductor-, Nd:YAG- and fiber- lasers, for use as GW detectors' optical sources. In present-day- and future
detectors' frequency- and phase-noise may place certain limitations on sensitivity and stability. Our goals (shared with
scientists around the world) are; first, to design robust experiments that will measure a variety of noises (random-walk
FM, flicker-FM, white FM, flicker PM and white PM), in order to verify existing models, and second, to find ways to reduce sensitivity to spurious noise. Current models predict a variety of frequency- and phase-dependent noise slopes, but, a conclusive distinction between noise-models can only be made when the exact points at which the noises occurred are known. In order to increase the sensitivity of the experiment, the laser frequency is stabilized to an atomic-frequency-reference by a feedback-loop control system.