Highly reflective mirrors have been widely used in high power lasers, laser gyros, and gravitational-wave detection, etc. However, reliable measurement of high reflectivity (R>99.99%) is difficult. In this paper a novel optical feedback cavity ring-down technique (OF-CRD) by re-injecting the strong optical feedback from the ring-down cavity (RDC) into the oscillator cavity of a Fabry-Perot diode laser is developed for the ultra-high reflectivity measurement. The laser line is narrowed and occasionally in resonance with one or more ring-down cavity modes. The amplitude of the RDC output signal is enhanced by a factor of over two orders of magnitude, compared with the conventional phase-shift CRD technique. Four pairs of cavity mirrors with different reflectivity are used to investigate the sensitivity and reproducibility of the OF-CRD technique. The accuracy is greatly enhanced from about 0.003% to 0.00003% as the reflectivity of cavity mirrors increases from about 99.8% to 99.996%. A folded RDC with cavity length of 70cm is constructed by inserting a planar test mirror into the linear RDC and the reflectivity of the test mirror is statistically determined to be 99.9526±0.0004%. The OF-CRD is simple, reliable, highly-sensitive and cost efficient.

Date Published: 30 December 2008
PDF: 10 pages
Proc. SPIE 7132, Laser-Induced Damage in Optical Materials: 2008, 71320U (30 December 2008); doi: 10.1117/12.804178

Published in SPIE Proceedings Vol. 7132:
Laser-Induced Damage in Optical Materials: 2008
Gregory J. Exarhos; Detlev Ristau; M. J. Soileau; Christopher J. Stolz, Editor(s)