Abstract. We describe a method of generating physical random numbers by means of a diode laser that has an extremely wide-band frequencynoise profile. Fluctuations in the laser frequency affect the intensity of the light transmitted through the optical frequency discriminator, detected thereafter as random fluctuations. This allows us to simultaneously generate 8 random bit streams, due to the parallel processing of 8-digit binary numbers sampled by an 8-bit analog-to-digital converter. Finally, we generated physical random numbers at a rate of 3 Gbit∕s, by combining one data stream with another stream that is delayed by 2 ms, by exclusive-OR.

A method of detecting gravitational-field variations using laser diodes is described. While the GRACE project is currently using the Doppler microwave system to measure the velocities of satellites flying in tandem, in the future, more advanced laser interferometry will be employed. It is hoped that we will be able to measure infinitesimal changes in their velocities, by using frequency-stabilized lasers rated at better than 10 -13 in the square root of the Allan variance (σ) for 1s < τ < 100s. As laser light sources, these devices will be notable for their compactness, energy efficiency, lightweight and high frequency-stability. This thesis describes the improved frequency stabilization obtained through the use of the magneto-optical effect of the Rb-D 2 absorption line, and the adaptation of the PEAK method, in order to obtain a precise control signal. The method allows us to modulate the reference frequency of the stabilization system (the absorption spectrum of the Rb-D 2 absorption line) by modulating the magnetic field applied to the Rb absorption cell, instead of the oscillation frequency of the laser diode. In so doing we are able to achieve a frequency stabilized laser diode (σ = 9 x 10 -12 ), while maintaining its linewidth, at an averaging time of 40s. In the next stage, we will test frequency-stabilized laser optical sources that are to be used in detecting and observing gravitational waves.

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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, using 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 -12 and 2.73× 10 -11 , respectively, in the square root of the Allan variance, by measuring the beat-note between two independently-stabilized laser diodes.

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