Elimination of residual amplitude modulation in tunable diode laser wavelength modulation spectroscopy using an optical fiber delay line

Arup Lal Chakraborty, Keith C. Ruxton, W. Johnstone, Michael Lengden, K. Duffin

Research output: Contribution to journalArticle

43 Citations (Scopus)

Abstract

A new fiber-optic technique to eliminate residual amplitude modulation in tunable diode laser wavelength modulation spectroscopy is presented. The modulated laser output is split to pass in parallel through the gas measurement cell and an optical fiber delay line, with the modulation frequency / delay chosen to introduce a relative phase shift of pi between them. The two signals are balanced using a variable attenuator and recombined through a fiber coupler. In the absence of gas, the direct laser intensity modulation cancels, thereby eliminating the high background. The presence of gas induces a concentration-dependent imbalance at the coupler's output from which the absolute absorption profile is directly recovered with high accuracy using 1f detection.
Original languageEnglish
Pages (from-to)9602-9607
Number of pages6
JournalOptics Express
Volume17
Issue number12
DOIs
Publication statusPublished - Jun 2009

Keywords

  • pressure
  • temperature
  • frequency
  • gases

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