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Wavelength modulation spectroscopy: combined frequency and intensity laser modulation

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TLDR
A theoretical model of wavelength modulation spectroscopy that uses a laser diode on a Lorentzian absorption line and the effect of several modulation parameters on the detected signals is evaluated, confirming the relevance of the model.
Abstract
A theoretical model of wavelength modulation spectroscopy that uses a laser diode on a Lorentzian absorption line is presented. This theory describes the general case of a current-modulated semiconductor laser, for which a combined intensity and frequency modulation with an arbitrary phase shift occurs. On the basis of this model, the effect of several modulation parameters on the detected signals is evaluated. Experimental signals measured on an absorption line of CO2 by use of a 2-microm distributed-feedback laser are also presented and validate this analysis. These experimental results agree with the calculated signals, confirming the relevance of the model.

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Journal ArticleDOI

Wavelength modulation photoacoustic spectroscopy: Theoretical description and experimental results

TL;DR: In this paper, a theoretical description of photo-acoustic spectroscopy generated by wavelength modulation of a semiconductor laser source is reported for a Lorentzian absorption line, which describes the first and second-harmonic photoacoustic signals produced by a current-modulated semiconductor lens.
Journal ArticleDOI

Quartz─enhanced photoacoustic spectrophones exploiting custom tuning forks: a review

TL;DR: A detailed review on the design and realization of spectrophones exploiting custom quartz tuning forks (QTFs) aimed to applications of quartz-enhanced photoacoustic (QEPAS) trace-gas sensors is presented in this paper.
Journal ArticleDOI

A portable sensor for in-situ measurement of ammonia based on near-infrared laser absorption spectroscopy

TL;DR: In this paper, a portable laser sensor for trace ammonia (NH3) is developed based on near-infrared laser absorption spectroscopy, which is implemented by a system-on-chip based on field-programmable gate array.
Journal ArticleDOI

Compact and portable open-path sensor for simultaneous measurements of atmospheric N2O and CO using a quantum cascade laser.

TL;DR: A compact and portable open-path sensor for simultaneous detection of atmospheric N(2)O and CO has been developed with a 4.5 μm quantum cascade laser and an in-line acetylene gas reference cell allowing for continuous monitoring of the sensor drift and calibration in rapidly changing field environments.
Journal ArticleDOI

Enhanced near-infrared QEPAS sensor for sub-ppm level H2S detection by means of a fiber amplified 1582 nm DFB laser

TL;DR: In this paper, a power-boosted quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor is developed for sub-ppm H2S trace-gas detection in the near-infrared spectral region.
References
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Journal ArticleDOI

Frequency-modulation spectroscopy: a new method for measuring weak absorptions and dispersions.

TL;DR: A new type of wavelength-modulation laser spectroscopy is accomplished by utilizing an external phase modulator driven at radio frequencies large compared to the width of the spectral feature of interest.
Journal ArticleDOI

Second-harmonic detection with tunable diode lasers — Comparison of experiment and theory

TL;DR: In this paper, a series of experiments are carried out by current modulating a tunable diode laser, and slowly ramping the wavelength to scan weak absorption lines in gases at pressures ranging from 2 to 60 Torr.
Journal ArticleDOI

Frequency modulation and wavelength modulation spectroscopies:comparison of experimental methods using a lead-salt diode laser

TL;DR: Both of the FMS methods, which require modulating the laser at frequencies >/= 150 MHz, give relatively poor results due to inefficient coupling of the modulation waveform to the laser current, and the re ults obtained agree well with theory.
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