Ranging with a frequency-shifted feedback laser using frequency-comb driven phase modulation of injected radiation

• Published in: Journal of physics. B, Atomic, molecular, and optical physics Atomic, molecular, and optical physics, 2022-09, Vol.55 (18), p.184001
• Main Authors: Kim, J I, Yatsenko, L P, Bergmann, K
• Format: Article
• Language: English
• Subjects: frequency-shifted feedback laser; laser ranging; phase modulation; seed laser
• ISSN: 0953-4075; 1361-6455
• DOI: 10.1088/1361-6455/ac8327

Theoretical and experimental data is presented for the application of an injection-seeded frequency-shifted feedback (FSF) laser for high accuracy ranging. Previous work discussed such a ranging scheme with a phase-modulated single-frequency laser where the phase modulation is done by an electro-optical modulator driven by a single frequency Ω which is swept over a certain bandwidth depending on the given experimental situation. In the present theoretical and experimental work, the phase modulation of the injection laser is done by a frequency comb with temporally fixed frequency components at intervals Ω d spanning a bandwidth adapted to the geometry of the object to be measured. It is shown that the superposition of such FSF radiation returning from the object and a reference surface on a detector leads to a train of sinusoidal pulses with an instantaneous frequency Ω inst in the radio-frequency range. The repetition rate of these pulses is Ω d and their duration is < 2 π / Ω d . The central result of this work is the observation that the path length difference between reference and object surface can be deduced from Ω inst , e.g. by frequency counting. The benefit of this approach lies in the fact that active frequency variation is not needed; all features of the entire system (FSF laser plus phase-modulated injected radiation) are constant in time. Proof-of-concept results using an FSF-laser ranging scheme based on a semiconductor laser are presented.