title: Water-vapor detection using asynchronous THz sampling.
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.
authors.affiliation: Innovative Scientific Solutions, Inc., 2766 Indian Ripple Road, Dayton, Ohio 45440-3638, USA. michael.brown@wpafb.af.mil
authors.forename: Michael S
authors.initials: MS
authors.lastname: Brown
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Fiechtner
authors.forename: J V
authors.initials: JV
authors.lastname: Rudd
authors.forename: David A
authors.initials: DA
authors.lastname: Zimdars
authors.forename: Matthew
authors.initials: M
authors.lastname: Warmuth
authors.forename: James R
authors.initials: JR
authors.lastname: Gord
mesh_terms: D000042:Absorption; D007834:Lasers; D013055:Spectrophotometry, Infrared / Q000295:instrumentation / Q000379:methods*; D013997:Time Factors; D014835:Volatilization; D014867:Water / Q000032:analysis* / Q000737:chemistry*
chemical_list: D014867:Water