Methods of Cavity-Enhanced Laser Absorption Spectroscopy Using Microresonator Whispering-Gallery Modes
Theoretical analysis of, and experimental results using, chemical sensing techniques based on microcavity-enhanced optical absorption are presented. Two methods are described in detail, and several extensions and enhancements of these methods are discussed briefly. Both techniques involve novel applications of tunable diode laser absorption spectroscopy in which cavity enhancement is provided by a dielectric microresonator (<1 mm in diameter) with whispering-gallery modes (WGMs) excited by tapered-fiber coupling. The evanescent component of a WGM allows for interaction with the analyte. The first method is used for the detection of trace gases in the ambient air by measuring the coupling-fiber throughput as the laser scans in frequency. Centimeter effective absorption path lengths are measured, in agreement with theory. The second method employs the observation of thermal bistability to enable measurement of absorption due to a coating applied to, or molecules adsorbed on, the microresonator's surface. Absorption by the water layer on a fused-silica surface agrees with theory, and results for thermal accommodation coefficients and thin-film absorption are also presented.
KeywordsFree Spectral Range Accommodation Coefficient Tunable Diode Laser Coupling Loss Coupling Fiber
The following former and current students have made significant contributions to this work: Jeromy Rezac, George Farca, Siyka Shopova, Elijah Dale, and Deepak Ganta. Also contributing were these students and colleagues: Chuck Blackledge, Razvan Stoian, Michael Humphrey, Sarah Bates, Seth Koterba, Jiangquan Zhang, Brian Strecker, Donna Bandy, Bret Flanders, Lee Elizondo, Sitong Yuan, and Mike Lucas. This work was supported by the National Science Foundation under award numbers 0329924 and 0601362, by the Oklahoma Center for the Advancement of Science and Technology under award numbers AR022–052 and AR072–066, by the Oklahoma State Regents for Higher Education, and by ICx Nomadics, Inc.
- 5.Rosenberger, A. T.; Dale, E. B.; Ganta, D.; Rezac, J. P., Investigating properties of surfaces and thin films using microsphere whispering-gallery modes, In Laser Resonators and Beam Control X; Kudryashov, A. V.; Paxton, A. H.; Ilchenko, V. S., Eds.; Proc. SPIE 2008, 6872, 68720UGoogle Scholar
- 15.Westcott, S. L.; Zhang, J.; Shelton, R. K.; Bruce, N. M. K.; Gupta, S.; Keen, S. L.; Tillman, J. W.; Wald, L. B.; Strecker, B. N.; Rosenberger, A. T.; Davidson, R. R.; Chen, W.; Donovan, K. G.; Hryniewicz, J. V., Broadband optical absorbance spectroscopy using a whispering gallery mode microsphere resonator, Rev. Sci. Instrum. 2008, 79, 033106CrossRefGoogle Scholar
- 20.Rothman, L. S.; Rinsland, C. P.; Goldman, A.; Massie, S. T.; Edwards, D. P.; Flaud, J.-M.; Perrin, A.; Camy-Peyret, C.; Dana, V.; Mandin, J.-Y.; Schroeder, J.; McCann, A.; Gamache, R. R.; Wattson, R. B.; Yoshino, K.; Chance, K. V.; Jucks, K. W.; Brown, L. R.; Nemtchinov, V.; Varanasi, P., The HITRAN molecular spectroscopic database and HAWKS (HITRAN atmospheric workstation): 1996 edition, J. Quant. Spectrosc. Radiat. Transfer 1998, 60, 665–710CrossRefGoogle Scholar
- 21.von Klitzing, W.; Long, R.; Ilchenko, V. S.; Hare, J.; Lefèvre-Seguin, V., Tunable whispering gallery modes for spectroscopy and CQED experiments, New J. Phys. 2001, 3, 14.1–14.14Google Scholar
- 22.Farca, G., Cavity-Enhanced Evanescent-Wave Chemical Sensing Using Microresonators, PhD dissertation, Oklahoma State University, 2006 Google Scholar
- 26.Shopova, S. I., Nanoparticle-Coated Optical Microresonators for Whispering-Gallery Lasing and Other Applications, PhD dissertation, Oklahoma State University, 2007 Google Scholar
- 28.Il'chenko, V. S.; Gorodetskii, M. L., Thermal nonlinear effects in optical whispering gallery microresonators, Laser Phys. 1992, 2, 1004–1009Google Scholar
- 32.Rezac, J. P., Properties and Applications of Whispering-Gallery Mode Resonances in Fused Silica Microspheres, PhD dissertation, Oklahoma State University, 2002 Google Scholar
- 33.Carslaw, H. S.; Jaeger, J. C., Conduction of Heat in Solids, Clarendon, Oxford, 1959, Chap. IX, 230–254Google Scholar
- 35.Kennard, E. H., Kinetic Theory of Gases, McGraw-Hill, New York, NY, 1938, Chap. VIII, 291–337Google Scholar
- 37.Saxena, S. C.; Joshi, R. K., Thermal accommodation and adsorption coefficients of gases, In Vol. II-1 of McGraw-Hill/CINDAS Data Series on Material Properties; Touloukian, Y. S.; Ho, C. Y., Eds.; McGraw-Hill, New York, NY, 1981Google Scholar