Wavelength-shifting phase-conjugate interferometry for distance measurements with an external-cavity laser diode

Laser-diode phase-conjugate interferometer with two self-pumped (cat) phase-conjugate mirrors instead of two ordinary mirrors is constructed for distance measurements over extended ranges. The measurement is based on frequency-modulated continuous wave techniques. An external-cavity laser diode (ECLD) is used as a light source in a phase-conjugate wavefront-matched interferometer. The interferometer is insensitive to spatially nonuniform phase distortion, but can only detect the spatially uniform phase change introduced by the displacement of one cat mirror. The error due to the nonlinear frequency chirping of an ECLD can be free from the reference interferometer of fixed arms with a known optical path difference.