Scatterometer using a bidirectional ring laser

• DOI: 10.1016/j.optcom.2004.06.069
• Publication Date: 2004-07-09T15:09:41Z
• Authors: Rafael Quintero-T...; Martha Navarro; Mark Ackerman; Jean-Claude Diels
• Keywords: 0103 physical sciences; 01 natural sciences

Abstract A technique for the absolute measurement of very low-level scattering was developed using the locking frequency for the two counter-circulating beams in a mode-locked ring cavity. The locking threshold is a function of the scattering coefficient at the crossing of the bidirectional pulses and is measured through the beat note characteristics of the laser. Backscattering coefficients of 0.6 × 10−10 and 2.2 × 10−10 were measured for BK7 samples of scratch/dig quality of 10-5 and 40-20, respectively. A beat note bandwidth of 1 Hz, as has been observed with the unstabilized laser, corresponds to a sensitivity limit of an intensity backscattering of 10−15. Even smaller limits could be achieved by stabilization.