Frequency-Stabilized Diode-Laser-Pumped Solid State Lasers: Optical Clocks of the Future

Monolithic diode-laser pumped solid state lasers1 are compact, reliable, and inherently-stable optical oscillators, providing nearly diffraction-limited beams with linewidths narrower than 10 kHz. While this linewidth is much narrower than that of most other lasers, the quantum-limited value is less than 1 Hz for an output power of 1 mW. However, the dependence of the cavity length and refractive index on the environment (temperature, acoustic vibrations, etc.), causes the lasing frequency to drift at a rate of several MHz per minute. External frequency stabilization can therefore improve the oscillator performance.