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

摘要

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 H2O near 1.4 mu m in a propane flame at 2 kHz (SNR = 200) and measurements of CH4 near 1.65 mu m (SNR = 20 to 1500) at stand-off distances of 15 cm and 10 m, respectively. The fraction of photons collected ranged from 104 to 1 parts per million at stand-off distances from 10 cm to 10 m, respectively, and is similar for aluminum and paper reflectors. (C) 2016 Optical Society of America