Ranging and interferometry with a frequency shifted feedback laser

Abstract

The potential advantages of chirped pulses for very precise measurement of distance, through frequency-domain ranging, has prompted consideration of frequency shifted feedback (FSF) lasers as sources of interferometer light. We here derive theoretical limitations to the spatial accuracy one can expect in such applications, by considering analytical expressions for the electric field emerging from a frequency shifted feedback (FSF) laser seeded by a CW laser whose finite bandwidth originates in phase fluctuations. We also consider consequences of fluctuations in cavity size. We show that, for surfaces flat within the laser footprint, such a system can provide the subwavelength accuracy of conventional interferometry but without dependence on material-dependent phase shifts. Although noise has been important for previous uses of FSF lasers in optical ranging and interferometry, we here show that a frequency modulated seeding laser can be used to better advantage than noise.