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Water-Vapor Detection Using Asynchronous THz Sampling

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Abstract:

The use of a fiber-coupled terahertz (THz) transmitter/receiver pair for spectroscopic detection of water vapor is investigated. Transmission signals of an alumina cylinder demonstrate that the measurement approach can be applied in a windowless ceramic combustor. First, a conventional commercial transmitter/receiver pair is used to make measurements for frequencies to 1.25 THz. Water-vapor absorption is clearly evident within the alumina transparency window and is readily modeled using existing databases. A variety of data-acquisition schemes is possible using THz instrumentation. To assess signal-collection techniques, a prototype THz transmitter/receiver pair is then used with the asynchronous optical-sampling (ASOPS) technique to obtain asynchronous THz-sampling signals to 1 THz without the need for an optomechanical delay line. Two mode-locked Ti:sapphire lasers operating at slightly different repetition rates are used for pumping the transmitter and receiver independently to permit a complete time-domain THz signal to be recorded. The resulting repetitive phase walkout is demonstrated by collecting power spectra of room air that exhibit water-vapor absorption.

Keywords: ASOPS; ASYNCHRONOUS OPTICAL SAMPLING; TERAHERTZ TIME-DOMAIN SPECTROSCOPY; THZ-TDS; WATER VAPOR

Document Type: Research Article

DOI: http://dx.doi.org/10.1366/000370206776342670

Affiliations: 1: Innovative Scientific Solutions, Inc., 2766 Indian Ripple Road, Dayton, Ohio 45440-3638 2: Sandia National Laboratories, P.O. Box 969, Livermore, California 94550-0969 3: Picometrix, Inc., 2925 Boardwalk, Ann Arbor, Michigan 48104-6765; Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87123-1153 4: Picometrix, Inc., 2925 Boardwalk, Ann Arbor, Michigan 48104-6765 5: Picometrix, Inc., 2925 Boardwalk, Ann Arbor, Michigan 48104-6765; General Dynamics, P.O. Box 134008, Ann Arbor, MI 48113-4008 6: Air Force Research Laboratory, Propulsion Directorate, Wright-Patterson AFB, Ohio 45433-7251

Publication date: March 1, 2006

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