Comparison of cavity enhanced faraday rotation spectroscopy techniques

Patrick, Link

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https://hdl.handle.net/2142/100750 Copy

Description

Title

Comparison of cavity enhanced faraday rotation spectroscopy techniques

Author(s)

Patrick, Link

Contributor(s)

• Wysocki, Gerard
• Westberg, Jonas

Issue Date

2018-06-19

Keyword(s)

Instrument/Technique Demonstration

Abstract

Cavity enhanced absorption techniques derive their sensitivity from an increase in the effective light-matter interaction length provided by a high finesse cavity. However, absorption measurements are often affected by spectrally interfering molecular species, which can hinder selectivity. This issue is addressed by Faraday rotation spectroscopy (FRS), which selectively probes the molecular dispersion of paramagnetic gaseous species (e.g. O2, NO, NO2, OH, etc.) subjected to an external magnetic field. Immunity to interfering diamagnetic compounds is thereby obtained allowing reliable quantitative concentration assessments of paramagnetic species in the presence of spectrally interfering molecules, such as H2O and CO2. Recently, white-noise limited performance over extended averaging times (minutes/hours) was achieved by combining cavity ring-down (CRD) and FRS. While CRD-FRS provides excellent sensitivities down to noise-equivalent rotation angles of 1.3x10−9 rad rtHz−1 , it requires fast detectors, high bandwidth digitization electronics and high throughput data analysis which significantly increases the system complexity and cost. To address these limitations, cavity attenuated phase shift (CAPS) FRS and integrated cavity output spectroscopy (ICOS) FRS has been developed. Here, CAPS-FRS ICOS-FRS, and CRD-FRS systems are compared by detecting oxygen at the P P1(1) transition in the A-electronic band around 762.3 nm. The FRS-based techniques are fully self-referencing and require no additional off-resonance calibration, which provides a powerful, yet simple alternative for cavity-enhanced spectroscopy targeting paramagnetic species. The FRS techniques allow for continuous measurements in a line-locked mode, which further increases the system effective duty-cycle and improves the sensing performance. A comparison of long-term system performance, system modeling, as well as system improvements will be presented in detail. Acknowledgments: The authors acknowledge funding from the National Science Foundation CBET grant #1507358 and from Thorlabs Inc. LP acknowledges the National Science Foundation Graduate Fellowship support.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100750

DOI

10.15278/isms.2018.TI04

Copyright and License Information

Copyright 2018 Link Patrick

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