Influence of the wavelength-dependence of fiber couplers on the background signal in wavelength modulation spectroscopy with RAM-nulling

Arup Lal Chakraborty, Keith C. Ruxton, W. Johnstone

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


Recently a technique to optically eliminate the background residual amplitude modulation in 1f wavelength modulation spectroscopy was demonstrated, where perfect elimination throughout the scan range was not achieved due to the wavelength-dependence of couplers and that of the laser intensity modulation. This paper theoretically analyzes the technique and experimentally demonstrates that the elimination can be perfect for one of three possible experimental configurations, making this important for potential applications with some recently-developed laser sources. For the other configurations a non-zero background slope is predicted, experimentally verified, and the anomalous nature of signals is thereby explained. A common signal normalization method is devised that is independent of the signal slope, a fact that is important for industrial deployment of such systems.
Original languageEnglish
Pages (from-to)267-280
Number of pages14
JournalOptics Express
Issue number1
Publication statusPublished - 4 Jan 2010


  • tunable diode lasers
  • directional couplers
  • pressure
  • gases
  • temperature
  • depth
  • line

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