Ultra-sensitive optical measurements of high-J transitions in the O2 A-band

Havey, Daniel K.; Long, David A.; Okumura, Mitchio; Miller, Charles E.; Hodges, Joseph T.

doi:10.1016/j.cplett.2009.10.067

Cited by 27 publications

(20 citation statements)

References 47 publications

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“…All measurements were made over the temperature range 297.7-299.4 K. The combined standard uncertainty in the cell temperature has recently been shown to be ∼30 mK. 40 Measured air-broadening parameters were temperature corrected to T ref = 296 K using the temperature dependences found in the HITRAN 2008 database. 51 As these measurements were made near the reference temperature, temperature corrections to the air-broadening parameters were small.…”

Section: Methodsmentioning

confidence: 99%

“…In addition, FS-CRDS is a single-mode technique that enables the accurate measurement of sample absorption coefficient in terms of observed ring-down cavity decay time constants. FS-CRDS has been employed to measure ultra-weak transitions, 39,40 hyperfine structure 37 and rare isotopes, 42,43,49 and to produce reference standard spectroscopic data. 36,38,42,43,50 For the measurements described herein the probe laser was an external cavity diode laser with an output power of ∼15 mW and the reference laser was a frequency-stabilized HeNe laser with a long-term stability of 1 MHz (8 h).…”

Section: Methodsmentioning

confidence: 99%

“…As previously demonstrated, the sensitivity and spectral fidelity of FS-CRDS make it an ideal technique for detailed study of subtle line shape effects. [36][37][38][39][40][41][42][43] Furthermore, the use of multi-spectrum fitting, [44][45][46] which simultaneously fits spectra across a wide pressure range, can enable the collisional narrowing and speed-dependent effects to be separated and quantified. Below, we present FS-CRDS line shape measurements of an air-broadened near-infrared CO 2 transition near 6360 cm −1 , and we compare our measured Lorentzian broadening parameters to literature values.…”

Section: Introductionmentioning

confidence: 99%

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The air-broadened, near-infrared CO2 line shape in the spectrally isolated regime: Evidence of simultaneous Dicke narrowing and speed dependence

Long

Bielska²,

Lisak³

et al. 2011

The Journal of Chemical Physics

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Frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) was employed to measure airbroadened CO 2 line shape parameters for transitions near 1.6 μm over a pressure range of 6.7-33 kPa. The high sensitivity of FS-CRDS allowed for the first measurements in this wavelength range of air-broadened line shape parameters on samples with CO 2 mixing ratios near those of the atmosphere. The measured air-broadening parameters show several percent deviations (0.9%-2.7%) from values found in the HITRAN 2008 database. Spectra were fit with a variety of models including the Voigt, Galatry, Nelkin-Ghatak, and speed-dependent Nelkin-Ghatak line profiles. Clear evidence of line narrowing was observed, which if unaccounted for can lead to several percent biases. Furthermore, it was observed that only the speed-dependent Nelkin-Ghatak line profile was able to model the spectra to within the instrumental noise level because of the concurrent effects of collisional narrowing and speed dependence of collisional broadening and shifting.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The air-broadened, near-infrared CO2 line shape in the spectrally isolated regime: Evidence of simultaneous Dicke narrowing and speed dependence

Long

Bielska²,

Lisak³

et al. 2011

The Journal of Chemical Physics

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“…A The combined uncertainty (random and systematic) of this temperature measurement is ∼28 mK [14]. Spectra were fit using Voigt line-shape profiles, which account for pressure (Lorentzian) and Doppler (Gaussian) broadening.…”

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confidence: 99%

“…A continuous spectrum was measured over the R branch of the b 1 + g ← X 3 − g (0,0) band (13126-13165 cm −1 ) with a step size of 100 MHz (∼0.003 cm −1 ). Sub-FSR frequency steps were enabled by frequency shifting the HeNe reference laser through the use of an acousto-optic modulator in a double-pass configuration [10].A The combined uncertainty (random and systematic) of this temperature measurement is ∼28 mK [14]. Spectra were fit using Voigt line-shape profiles, which account for pressure (Lorentzian) and Doppler (Gaussian) broadening.…”

mentioning

confidence: 99%

Cavity ring-down spectroscopy measurements of sub-Doppler hyperfine structure

et al. 2010

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Frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) was used to measure magnetic dipole transitions in the b 1 + g ← X 3 − g (0,0) band of O 2 . The 17 O-containing isotopologues show unresolved hyperfine structure due to magnetic hyperfine splitting in the ground state. The sensitivity and stability of FS-CRDS allow for quantitative sub-Doppler measurements of the hyperfine constants, even when the hyperfine splittings are much smaller than the Doppler width. Unlike saturation spectroscopy, this linear absorption technique can be applied to weak transitions and employed to quantitatively measure intensities and line shapes. This method may be an attractive approach for measuring unresolved hyperfine structure in excited electronic states. Recent advances in near-infrared spectroscopy have enabled measurements with frequency precision previously only possible in the microwave regime [1][2][3]. Unfortunately, large near-infrared Doppler widths often obscure any hyperfine structure. While saturation spectroscopy can resolve individual hyperfine components [2,4], it is by its very nature a nonlinear technique. As a result, saturation spectroscopy leads to distortion of the spectral line shape and cannot be employed to quantitatively measure line-shape parameters [5][6][7]. In addition, saturation spectroscopy is less general than traditional absorption spectroscopy and cannot easily be applied to the study of weak transitions, such as those described herein.Here we describe an alternate approach to the measurement of hyperfine structure in the near-infrared region: the use of a linear and highly sensitive cavity ring-down spectrometer. In particular, the hyperfine splitting of the 17 O-containing isotopologues of O 2 were measured for magnetic dipole transitions in the b 1 + g ← X 3 − g (0,0) band. While individual hyperfine transitions are unresolved, the spectra exhibit a sufficiently large signal-to-noise ratio to enable quantitative measurements of hyperfine coupling constants. We note that despite the large number of recent studies which have measured spectroscopic parameters of the b 1 + g ← X 3 − g (0,0) band for 16 O 2 and the rare isotopologues [9], observation of hyperfine splitting has not previously been reported.Measurements were made using the frequency-stabilized cavity ring-down spectrometer (FS-CRDS) located at the National Institute of Standards and Technology (NIST) in Gaithersburg, MD. The FS-CRDS system has been described in detail previously [10,11], and therefore only the most important details are given. FS-CRDS differs from other single-mode cw-CRDS spectroscopies by actively stabilizing the intracavity length to an external frequency reference. This length stabilization in turn stabilizes the cavity's free spectral range (FSR). The probe laser frequency is then stepped between successive TEM 00 cavity modes, resulting in an accurate, stable, and linear frequency axis. FS-CRDS has been utilized to measure transition frequencies to better than 0.5 MHz [1] and line intensities to bet...

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