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Appl Opt. 2016 Jan 20;55(3):479-84. doi: 10.1364/AO.55.000479.

Fiber-coupled diode-laser sensors for calibration-free stand-off measurements of gas temperature, pressure, and composition.


A fiber-coupled near-infrared diode-laser sensor for stand-off measurements of gas temperature, pressure, and composition is presented. This sensor utilizes a fiber bundle with six multimode catch fibers surrounding one single-mode pitch fiber to transmit and receive backscattered laser light in a handheld transmitter/receiver. Scanned-wavelength-modulation spectroscopy with 1f-normalized 2f-detection and fast (80-200 kHz) wavelength modulation were used to provide calibration-free measurements and reduce the influence of spurious cavity noise formed by the overlapping transmitted and reflected laser light. Demonstrations include two-color measurements of temperature, pressure, and H(2)O near 1.4 μm in a propane flame at 2 kHz (SNR=200) and measurements of CH(4) near 1.65 μm (SNR=20 to 1500) at stand-off distances of 15 cm and 10 m, respectively. The fraction of photons collected ranged from 10(4) to 1 parts per million at stand-off distances from 10 cm to 10 m, respectively, and is similar for aluminum and paper reflectors.


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