Continuous wave optical parametric oscillator for quartz-enhanced photoacoustic trace gas sensing |
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| Authors: | A.K.Y. Ngai S.T. Persijn I.D. Lindsay A.A. Kosterev P. Gro? C.J. Lee S.M. Cristescu F.K. Tittel K.-J. Boller F.J.M. Harren |
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| Affiliation: | (1) Life Science Trace Gas Facility, Molecular and Laser Physics, Institute for Molecules and Materials, Radboud University, P.O. Box 9010, 6500 GL Nijmegen, Netherlands;(2) Laser Physics and Nonlinear Optics Group, Faculty of Science and Technology, University of Twente, 7500 AE Enschede, Netherlands;(3) Department of Electrical and Computer Engineering, Rice University, Houston, TX 77005, USA |
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| Abstract: | A continuous wave optical parametric oscillator, generating up to 300 mW idler output in the 3–4 μm wavelength region, and pumped by a fiber-amplified DBR diode laser is used for trace gas detection by means of quartz-enhanced photoacoustic spectroscopy (QEPAS). Mode-hop-free tuning of the OPO output over 5.2 cm-1 and continuous spectral coverage exceeding 16.5 cm-1 were achieved via electronic pump source tuning alone. Online monitoring of the idler wavelength, with feedback to the DBR diode laser, provided an automated closed-loop control allowing arbitrary idler wavelength selection within the pump tuning range and locking of the idler wavelength with a stability of 1.7×10-3 cm-1 over at least 30 min. Using this approach, we locked the idler wavelength at an ethane absorption peak and obtained QEPAS data to verify the linear response of the QEPAS signal at different ethane concentrations (100 ppbv-20 ppmv) and different power levels. The detection limit for ethane was determined to be 13 ppbv (20 s averaging), corresponding to a normalized noise equivalent absorption coefficient of 4.4×10-7 cm-1 W/Hz1/2. PACS 42.55.Wd; 42.65.Yj; 42.62.Fi |
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