COMPUTER-CONTROLLED NARROW-LINEWIDTH AND FREQUENCY-STABILIZED ALGAAS LASER SYSTEM WITH UNMODULATED OUTPUT

A narrow-linewidth semiconductor laser system at 780 nm wavelength was developed, with frequency locked to the saturation absorption resonance frerquency of rubidium (Rb-87). Optical feedback from an external Fabry-Perot cavity was employed to reduce the linewidth of the laser. The third derivative of the saturated absorption spectrum in Rb-87 was used as a frequency demodulator for frequency locking, for which the Zeeman modulation was employed to keep the output power and frequency unmodulated. The minimum of the square root of the Allan variance was 2.1 X 10(-12) at the integration time of 300 s. The full linewidth at half maximum of the field spectrum was measured to be narrower than 170 kHz. A computer-control program was developed for automatic frequency locking to the Rb-87 line.