Share Email Print

Proceedings Paper

Tunable diode and fibre laser spectroscopy in the near-IR for measurement of gas parameters
Author(s): George Stewart; Walter Johnstone; Norhana Arsad; Kevin Duffin
Format Member Price Non-Member Price
PDF $14.40 $18.00
cover GOOD NEWS! Your organization subscribes to the SPIE Digital Library. You may be able to download this paper for free. Check Access

Paper Abstract

There has been much research performed in recent years on tunable diode laser spectroscopy for detection of gases such as methane, carbon dioxide, acetylene, etc., which possess near-IR absorption lines. To attain adequate sensitivity with weak near-IR lines, wavelength modulation spectroscopy with phase-sensitive detection is normally employed. However injection current modulation of diode lasers produces both wavelength and amplitude modulation, with a phase shift dependent on the modulation frequency. This results in residual amplitude modulation on the output and in distortion of the harmonic signals derived from the absorption line. These are important issues for calibration and where it is desired to accurately recover the line-shape function in order to make simultaneous measurements of gas concentration, pressure or temperature in industrial applications. Here we discuss how calibration-free measurements may be obtained with diode lasers and explore the implications for fibre laser based systems for spectroscopy which conventionally employ thermal or piezoelectric tuning of the wavelength. In particular, we consider modulation techniques which may be applied to ring fibre lasers which use un-pumped erbium fibre as a saturable absorber to prevent mode-hopping or to DFB fibre lasers which use a short cavity with a Bragg grating to ensure single mode operation.

Paper Details

Date Published: 28 April 2008
PDF: 10 pages
Proc. SPIE 7003, Optical Sensors 2008, 700319 (28 April 2008); doi: 10.1117/12.779976
Show Author Affiliations
George Stewart, Univ. of Strathclyde (United Kingdom)
Walter Johnstone, Univ. of Strathclyde (United Kingdom)
Norhana Arsad, Univ. of Strathclyde (United Kingdom)
Kevin Duffin, Univ. of Strathclyde (United Kingdom)

Published in SPIE Proceedings Vol. 7003:
Optical Sensors 2008
Francis Berghmans; Anna Grazia Mignani; Antonello Cutolo; Patrick P. Meyrueis; Thomas P. Pearsall, Editor(s)

© SPIE. Terms of Use
Back to Top