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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.

We have succeeded, thus far, in stabilizing laser diode (LD) frequencies to Rb absorption lines, by means of negative electrical feedback. While the absorption lines were stable over the long term, the Doppler Effect's influence was evident, in broadened spectrum linewidth. To avoid the problem in subsequent tests, we used Rb-saturated absorption signals. In this work, we demonstrated potentials of two applications; one was as a reference signal source for estimation of other LD's frequency stabilization system, and the other was a light source for generation of THz radiation.­¬«W

The precise interferometric systems employed in today's artificial satellites require semiconductor lasers of the highest caliber. To this end, efforts to stabilize their oscillation frequencies and narrow spectrum line-widths continue relentlessly. While a number of different approaches have been tested, none have provided overall, long-term stability. Most recently, we employed a Doppler-free absorption line of Rb atoms, with a precision temperature controller and an improved laser mount. In this instance, relative optical frequency stability rated 9.07×10 -13 ≤σ(2,τ)≤7.54×10 -10 , in averaging time for 0.01s≤τ23s. By introducing an optical feedback, which narrows the laser's linewidth, we obtained improved frequency stability.

The precise interferometric systems employed in today's artificial satellites require semiconductor lasers of the highest callibur. But, one particularly large obstacle has stood in the way of their broad application; the stabilization of their oscillation frequencies. While a number of different approaches have been tested, none have provided overall, long-term stability. Most recently, we used a Doppler-free absorption line of Rb atoms with a precision temperature controller and an improved laser mount; in this instance, relative optical frequency stability rated 9.07×10 -13 ≤ σ(2,τ) ≤ 7.54×10 -10 , in averaging time for 0.01s ≤ τ ≤ 23s. Furthermore, we heated the Rb cell to up to 313K, in order to enhance the control signal and improve oscillation frequency stability.

The precise interferometric system s employed in today’s artificial satellites requi re semiconductor lasers of the highest calli bur. But, one particularly large obstacle has stood in the way of their broad application; th e stabilization of th eir oscillation frequen cies. While a number of different approaches have been tested, none have provi ded overall, long-term stability. Most recently, we used a Dopp ler-free absorption line of Rb atoms with a precision temperature controller and an improved laser mount; in this instance, relative optical frequency stability rated 9.07×10 -13 ”1 (2,2)—” 7.54×10 -10 , in averaging time for 0.01s”2” 23s. By introducing optical feedback, which narrows the laser’s linewidth, we obtained improved frequency stability. Keywords : semiconductor laser, oscillation frequency, stab ilization, Rb absorption line, optical feedback 1. INTRODUCTION The precise interferometric system s employed in today’s artificia l satellites require semiconducto r lasers of the highest stabi lity. But, one particularly large obstacle has stood in the way of their broad application; th e stabilization of th eir oscillation frequen cies. While a number of different approaches have been tested, none have provi ded overall, long-term stability. Most recently, we used a Dopp ler-free absorption line of Rb atoms with a precision temperature controller and an improved laser mount; in this instance, relative optical frequency stability rated 9.07×10

Laser interferometers detect gravitational waves with a degr ee of accuracy and efficiency unimaginable even a few years ago. The semiconductor lasers that are the primary light source for these devices are small, lightweight, durable and energy-efficient. On the downside, the devices currently available are still marked by broad oscillation spectra, and heightened sensitivity to fluctuations in injection current and /or ambient temperature. By applying a small sine wave to the injection current, we modulate the oscillation frequency. This frequency-modulated beam is introduced to the Avalanche photo diode through the Rb cell in the saturated absorption optical setup. The resulting signal and a reference signal are detected simultaneously and combined, to produce an error signal, which, when fed back to the injection current, stabilizes the diode’s oscillation frequency at 2.12 ™ 10 -12 9 1 (2,2) 9 5.88 ™ 10 -11 in the averaging time between 0.4s to 65s. An optical feedback method, which introduc es the laser beam reflected by a mirror or a grating to the semiconductor laser itself, is reported to narrow oscillation linewidth and improve frequency stability. We are now combining these two techniques to further improve frequency stability. Keywords : semiconductor laser, oscillation frequency, stab ilization, Rb absorption line, optical feedback