Phase-sensitive laser detection by frequency-shifted optical feedback

For further interferometric application on diffusive target, the phase fluctuation of a solid-state laser submitted to frequency shifted optical feedback is analyzed both theoretically and experimentally. As a drawback of the laser high sensitivity to optical feedback, the phase fluctuations induced by a strong phase-amplitude coupling noise are several orders of magnitude higher than the standard interferometric phase noise induced by the laser frequency width (Schawlow-Townes limit). Nevertheless, by sending a few milliwatts output power microchip laser beam on a diffusive target with an effective reflectivity of 10⁻⁹, a target displacement precision of 0.1 Å∕√Hz has been experimentally determined.