Ultrasensitive dual-beam absorption and gain spectroscopy: applications for near-infrared and visible diode laser sensors

Abstract

A dual-beam detection strategy with automatic balancing is described for ultrasensitive spectroscopy. Absorbances of 2 × 10(-7) Hz(-½) in free-space configurations and 5 × 10(-6) Hz(-½) in fiber-coupled configurations are demonstrated. With the dual-beam technique, atmospherically broadened absorption transitions may be resolved with InGaAsP, AlGaAs, and AlGaInP single-longitudinal-mode diode lasers. Applications to trace measurements of NO(2), O(2), and H(2)O are described by the use of simple, inexpensive laser and detector systems. Small signal gain measurements on optically pumped I(2) with a sensitivity of 10(-5) are also reported.

Extended Performance Handheld and Mobile Sensors for Remote Detection of Natural Gas Leaks

“…[1][2][3][4] The principles are straightforward: Gas molecules absorb energy at specific wavelengths in the electromagnetic spectrum. At wavelengths slightly different than these absorption lines, there is essentially no absorption.…”

“…This transmission system serves local distribution companies that operate some 500-1000 gate stations supplying roughly 132,000 surface metering and pressure regulation sites stationed along 1,000,000 miles of distribution pipeline terminating at 61,000,000 end-user customer meters. 1 Maintaining the security and integrity of this system is a continual process of searching for, locating, and repairing leaks.…”

Preparing to Measure the Effects of the NOxSIP Call— Methods for Ambient Air Monitoring of NO, NO2, NOy, and Individual NOzSpecies

“…Laser Sources or LEDs Allen et al 48 and Sonnenfroh and Allen 49 reported the application of single-longitudinal-mode, room-temperature semiconductor lasers operating in the visible and near IR spectra to in situ monitoring of NO 2 . They reported a system design that uses the relatively new balanced ratiometric detector, a novel electronic laser noise-canceling technique.…”

Faraday modulation spectrometry of nitric oxide addressing its electronic X^2Π−A^2Σ^+ band: II experiment

“…For robust implementation, it often uses Distributed Feedback Lasers (DFB) to address various overtone bands and incorporates Wavelength Modulation Spectrometry (WMS) for reduction of noise [16][17][18][19][20]. Although this technique is versatile and regularly used for detection of a number of species under various conditions [12][13][14][15][21][22][23][24][25][26][27], its detectability is not yet sufficient for in-situ detection of NO [28][29][30][31][32][33][34], primarily caused by a combination of low transition probabilities of the overtone bands in 3 the infrared (IR) region and a lack of reliable diode lasers producing light in the wavelength regions of these bands. In addition, the overtone bands are susceptible to spectroscopic interferences from concomitant species, which can hamper quantitative assessments.…”