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Title: Optical re-injection in cavity-enhanced absorption spectroscopy

Abstract

Non-mode-matched cavity-enhanced absorption spectrometry (e.g., cavity ringdown spectroscopy and integrated cavity output spectroscopy) is commonly used for the ultrasensitive detection of trace gases. These techniques are attractive for their simplicity and robustness, but their performance may be limited by the reflection of light from the front mirror and the resulting low optical transmission. Although this low transmitted power can sometimes be overcome with higher power lasers and lower noise detectors (e.g., in the near-infrared), many regimes exist where the available light intensity or photodetector sensitivity limits instrument performance (e.g., in the mid-infrared). In this article, we describe a method of repeatedly re-injecting light reflected off the front mirror of the optical cavity to boost the cavity's circulating power and deliver more light to the photodetector and thus increase the signal-to-noise ratio of the absorption measurement. We model and experimentally demonstrate the method's performance using off-axis cavity ringdown spectroscopy (OA-CRDS) with a broadly tunable external cavity quantum cascade laser. The power coupled through the cavity to the detector is increased by a factor of 22.5. The cavity loss is measured with a precision of 2 × 10{sup −10} cm{sup −1}/√(Hz;) an increase of 12 times over the standard off-axis configuration withoutmore » reinjection and comparable to the best reported sensitivities in the mid-infrared. Finally, the re-injected CRDS system is used to measure the spectrum of several volatile organic compounds, demonstrating the improved ability to resolve weakly absorbing spectroscopic features.« less

Authors:
 [1]
  1. Los Gatos Research, 67 E. Evelyn Avenue, Suite 3, Mountain View, California 94041 (United States)
Publication Date:
OSTI Identifier:
22314439
Resource Type:
Journal Article
Journal Name:
Review of Scientific Instruments
Additional Journal Information:
Journal Volume: 85; Journal Issue: 9; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0034-6748
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; ABSORPTION SPECTROSCOPY; ACCURACY; CAVITIES; LASERS; LIGHT TRANSMISSION; MIRRORS; OPTICAL REFLECTION; ORGANIC COMPOUNDS; PERFORMANCE; PHOTODETECTORS; REINJECTION; SENSITIVITY; SIGNAL-TO-NOISE RATIO; VISIBLE RADIATION; VOLATILITY

Citation Formats

Leen, J. Brian, E-mail: b.leen@lgrinc.com, and O’Keefe, Anthony. Optical re-injection in cavity-enhanced absorption spectroscopy. United States: N. p., 2014. Web. doi:10.1063/1.4893972.
Leen, J. Brian, E-mail: b.leen@lgrinc.com, & O’Keefe, Anthony. Optical re-injection in cavity-enhanced absorption spectroscopy. United States. https://doi.org/10.1063/1.4893972
Leen, J. Brian, E-mail: b.leen@lgrinc.com, and O’Keefe, Anthony. 2014. "Optical re-injection in cavity-enhanced absorption spectroscopy". United States. https://doi.org/10.1063/1.4893972.
@article{osti_22314439,
title = {Optical re-injection in cavity-enhanced absorption spectroscopy},
author = {Leen, J. Brian, E-mail: b.leen@lgrinc.com and O’Keefe, Anthony},
abstractNote = {Non-mode-matched cavity-enhanced absorption spectrometry (e.g., cavity ringdown spectroscopy and integrated cavity output spectroscopy) is commonly used for the ultrasensitive detection of trace gases. These techniques are attractive for their simplicity and robustness, but their performance may be limited by the reflection of light from the front mirror and the resulting low optical transmission. Although this low transmitted power can sometimes be overcome with higher power lasers and lower noise detectors (e.g., in the near-infrared), many regimes exist where the available light intensity or photodetector sensitivity limits instrument performance (e.g., in the mid-infrared). In this article, we describe a method of repeatedly re-injecting light reflected off the front mirror of the optical cavity to boost the cavity's circulating power and deliver more light to the photodetector and thus increase the signal-to-noise ratio of the absorption measurement. We model and experimentally demonstrate the method's performance using off-axis cavity ringdown spectroscopy (OA-CRDS) with a broadly tunable external cavity quantum cascade laser. The power coupled through the cavity to the detector is increased by a factor of 22.5. The cavity loss is measured with a precision of 2 × 10{sup −10} cm{sup −1}/√(Hz;) an increase of 12 times over the standard off-axis configuration without reinjection and comparable to the best reported sensitivities in the mid-infrared. Finally, the re-injected CRDS system is used to measure the spectrum of several volatile organic compounds, demonstrating the improved ability to resolve weakly absorbing spectroscopic features.},
doi = {10.1063/1.4893972},
url = {https://www.osti.gov/biblio/22314439}, journal = {Review of Scientific Instruments},
issn = {0034-6748},
number = 9,
volume = 85,
place = {United States},
year = {Mon Sep 15 00:00:00 EDT 2014},
month = {Mon Sep 15 00:00:00 EDT 2014}
}