A narrow linewidth semiconductor laser device has a semiconductor laser
and a low noise current source operatively connected to the laser with
the current source being adapted to prevent degradation of the laser's
frequency noise spectrum. An optical frequency discriminator provides an
error signal representative of the laser's optical frequency and a
control circuit has a feedback network that provides a frequency feedback
signal that is adapted to the frequency noise spectrum of the frequency
discriminator and to the laser's frequency noise spectrum and tuning
response. The control circuit also has a sequencer to automatically
enable frequency locking of the laser on the frequency reference of the
optical frequency discriminator. An enclosure encloses the frequency
discriminator to isolate the frequency discriminator from external
perturbations. The device provides an improved sub-kHz linewidth and a
high coherence while being compact, lightweight and highly reliable, as
well as being automatically operated.