Scatterometer using a bidirectional ring laser

✍ Scribed by Rafael Quintero-Torres; Martha Navarro; Mark Ackerman; Jean-Claude Diels

• Publisher: Elsevier Science
• Year: 2004
• Tongue: English
• Weight: 391 KB
• Volume: 241
• Category: Article
• ISSN: 0030-4018
• DOI: 10.1016/j.optcom.2004.06.069

✦ Synopsis

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 À10 and 2.2 • 10 À10 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 À15 . Even smaller limits could be achieved by stabilization.