Phase-Conjugate External-Cavity Diode Laser

An external-cavity diode laser based on self-pumped phase-conjugate optical feedback is reported. An antireflection-coated diode laser is subjected to strong phase-conjugate feedback from a photorefractive Ce-doped BaTiO
₃
crystal. This provides narrow laser linewidth and good stability. Inherent linewidth of 25 kHz and relative frequency stability of 1.5times10
^-8
(at 100 s) are demonstrated. Due to phase-conjugate feedback, the laser is insensitive to mechanical drifts and misalignment of the feedback element