A quantum cascade laser cw cavity ringdown spectrometer coupled to a supersonic expansion source

Brian E. Brumfield; Jacob T. Stewart; Susanna L. Widicus Weaver; Matthew D. Escarra; Scott S. Howard; Claire F. Gmachl; Benjamin J. McCall

doi:10.1063/1.3427357

A quantum cascade laser cw cavity ringdown spectrometer coupled to a supersonic expansion source

Brian E. Brumfield, Jacob T. Stewart, Susanna L. Widicus Weaver, Matthew D. Escarra, Scott S. Howard, Claire F. Gmachl, Benjamin J. McCall

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28 Scopus citations

Abstract

A new instrument has been constructed that couples a supersonic expansion source to a continuous wave cavity ringdown spectrometer using a Fabry-Perot quantum cascade laser (QCL). The purpose of the instrument is to enable the acquisition of a cold, rotationally resolved gas phase spectrum of buckminsterfullerene (C₆₀). As a first test of the system, high resolution spectra of the ν₈ vibrational band of CH₂ Br₂ have been acquired at ∼1197 cm^-1. To our knowledge, this is the first time that a vibrational band not previously recorded with rotational resolution has been acquired with a QCL-based ringdown spectrometer. 62 transitions of the three isotopologues of CH₂ Br₂ were assigned and fit to effective Hamiltonians with a standard deviation of 14 MHz, which is smaller than the laser frequency step size. The spectra have a noise equivalent absorption coefficient of 1.4× 10-8 cm^-1. Spectral simulations of the band indicate that the supersonic source produces rotationally cold (∼7 K) molecules.

Original language	English (US)
Article number	063102
Journal	Review of Scientific Instruments
Volume	81
Issue number	6
DOIs	https://doi.org/10.1063/1.3427357
State	Published - Jun 2010

All Science Journal Classification (ASJC) codes

Instrumentation

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10.1063/1.3427357

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title = "A quantum cascade laser cw cavity ringdown spectrometer coupled to a supersonic expansion source",

abstract = "A new instrument has been constructed that couples a supersonic expansion source to a continuous wave cavity ringdown spectrometer using a Fabry-Perot quantum cascade laser (QCL). The purpose of the instrument is to enable the acquisition of a cold, rotationally resolved gas phase spectrum of buckminsterfullerene (C60). As a first test of the system, high resolution spectra of the ν8 vibrational band of CH2 Br2 have been acquired at ∼1197 cm-1. To our knowledge, this is the first time that a vibrational band not previously recorded with rotational resolution has been acquired with a QCL-based ringdown spectrometer. 62 transitions of the three isotopologues of CH2 Br2 were assigned and fit to effective Hamiltonians with a standard deviation of 14 MHz, which is smaller than the laser frequency step size. The spectra have a noise equivalent absorption coefficient of 1.4× 10-8 cm-1. Spectral simulations of the band indicate that the supersonic source produces rotationally cold (∼7 K) molecules.",

author = "Brumfield, {Brian E.} and Stewart, {Jacob T.} and {Widicus Weaver}, {Susanna L.} and Escarra, {Matthew D.} and Howard, {Scott S.} and Gmachl, {Claire F.} and McCall, {Benjamin J.}",

note = "Funding Information: The authors wish to thank Richard Saykally for the loan of the cryostat and the cavity ringdown mirrors used in this work, and Frank Tittel for helpful conversations regarding the frequency stability of QCLs. We also wish to acknowledge experimental assistance from Brian Siller, Brian Pohrte, and Brett McGuire. The Illinois team acknowledges financial support from NASA Laboratory Astrophysics Grant No. NNG05GE59G, the Camille and Henry Dreyfus Foundation, the David and Lucile Packard Foundation, and the University of Illinois. The Princeton team has been supported by funding from the Mid-Infrared Technologies for Health and the Environment NSF Engineering Research Center.",

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AU - Gmachl, Claire F.

AU - McCall, Benjamin J.

N1 - Funding Information: The authors wish to thank Richard Saykally for the loan of the cryostat and the cavity ringdown mirrors used in this work, and Frank Tittel for helpful conversations regarding the frequency stability of QCLs. We also wish to acknowledge experimental assistance from Brian Siller, Brian Pohrte, and Brett McGuire. The Illinois team acknowledges financial support from NASA Laboratory Astrophysics Grant No. NNG05GE59G, the Camille and Henry Dreyfus Foundation, the David and Lucile Packard Foundation, and the University of Illinois. The Princeton team has been supported by funding from the Mid-Infrared Technologies for Health and the Environment NSF Engineering Research Center.

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N2 - A new instrument has been constructed that couples a supersonic expansion source to a continuous wave cavity ringdown spectrometer using a Fabry-Perot quantum cascade laser (QCL). The purpose of the instrument is to enable the acquisition of a cold, rotationally resolved gas phase spectrum of buckminsterfullerene (C60). As a first test of the system, high resolution spectra of the ν8 vibrational band of CH2 Br2 have been acquired at ∼1197 cm-1. To our knowledge, this is the first time that a vibrational band not previously recorded with rotational resolution has been acquired with a QCL-based ringdown spectrometer. 62 transitions of the three isotopologues of CH2 Br2 were assigned and fit to effective Hamiltonians with a standard deviation of 14 MHz, which is smaller than the laser frequency step size. The spectra have a noise equivalent absorption coefficient of 1.4× 10-8 cm-1. Spectral simulations of the band indicate that the supersonic source produces rotationally cold (∼7 K) molecules.

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A quantum cascade laser cw cavity ringdown spectrometer coupled to a supersonic expansion source

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