An Optical Cell for Long Pathlengths at Low Temperatures

McKellar, A. R. W.; Rich, Nathan H.; Soots, V.

doi:10.1364/ao.9.000222

Cited by 17 publications

(7 citation statements)

References 9 publications

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“…A few years later two longpath cooling cells were built with optical lengths of 230 and 165 m, minimum temperatures of 77 and 80 K, and maximum pressures of 3 and 10 bar, respectively. 23,24 The temperature of the latter of the two cells could be adjusted between 80 and 125 K by use of a cryogenerator that worked with a liquid coolant such as nitrogen. Based on this design, another cell was built with 110 m of optical length that could be cooled down to 20 K with a two-stage cryogenerator.…”

Section: Existing Collisional Cooling Cellsmentioning

confidence: 99%

Liquid-helium temperature long-path infrared spectroscopy of molecular clusters and supercooled molecules

Bauerecker

Weitkamp

et al. 2001

Review of Scientific Instruments

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Collisional cooling and supersonic jet expansion both allow us to perform infrared spectroscopy of supercooled molecules and atomic and molecular clusters. Collisional cooling has the advantage of higher sensitivity per molecule and enables working in thermal equilibrium. A new powerful method of collisional cooling is presented in this article. It is based on a cooling cell with integrated temperature-invariant White optics and pulsed or continuous sample-gas inlet. The system can be cooled with liquid nitrogen or liquid helium and operated at gas pressures between <10−5 and 13 bar. Temperatures range from 4.2 to 400 K and can be adjusted to an accuracy of ±0.2 K over most of the useable range. A three-zone heating design allows homogeneous or inhomogeneous temperature distributions. Optical path lengths can be selected up to values of 20 m for Fourier transform infrared (FTIR) and 40 m for laser operation. The cell axis is vertical, so optical windows are at room temperature. Diffusive trapping shields and low-power electric heating keep the mirrors free from perturbing deposits. The cell can be operated in a dynamic buffer-gas flow-cooling mode. A comprehensive review of existing collisional cooling cells is given. The formation of CO clusters from the gas phase was investigated using FTIR spectroscopy. For the isotope mixture consisting of C1613O,13C18O, and C1612O, a conspicuous change in the main spectroscopic structure of the clusters was observed between 20 and 5 K. The cluster bandwidth of the main isotope C1613O triples. This behavior could be interpreted as a change from the crystalline to the amorphous state or as a decrease in size to smaller clusters with relatively larger surfaces. To our knowledge, this is the first IR investigation of molecular clusters obtained by collisional cooling in this temperature range. For CO2 the change from the monomer to crystalline clusters was investigated. The observed spectra vary considerably with temperature. FTIR spectra of CO2 clusters observed previously by other researchers could be reproduced. The system allows us to determine various gases with a FTIR detection limit in the lower ppb range. With these concentrations and at temperatures <10 K the monomers can be supercooled, and small clusters can be obtained.

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Section: Existing Collisional Cooling Cellsmentioning

confidence: 99%

Liquid-helium temperature long-path infrared spectroscopy of molecular clusters and supercooled molecules

Bauerecker

Weitkamp

et al. 2001

Review of Scientific Instruments

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“…For this reason long paths are almost universally used in air pollution spectroscopic analysis. To increase the net absorption the multipass optical cell was developed [9][10][11][12][13][14] , which has, in some cases, increased the effective sample length to several hundred meters.…”

Section: Introductionmentioning

confidence: 99%

Cavity ring-down optical spectrometer for absorption measurements using pulsed laser sources

O’Keefe¹,

Deacon²

1988

Review of Scientific Instruments

1,494

790

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We have developed a technique which allows optical absorption measurements to be made using a pulsed light source and offers a sensitivity significantly greater than that attained using stabilized continuous light sources. The technique is based upon the measurement of the rate of absorption rather than the magnitude of absorption of a light pulse confined within a closed optical cavity. The decay of the light intensity within the cavity is a simple exponential with loss components due to mirror loss, broadband scatter (Rayleigh, Mie), and molecular absorption. Narrowband absorption spectra are recorded by scanning the output of a pulsed laser (which is injected into the optical cavity) through an absorption resonance. We have demonstrated the sensitivity of this technique by measuring several bands in the very weak forbidden b Σg-X Σg transition in gaseous molecular oxygen. Absorptions signals of less than 1 part in 10 6 can be detected.

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“…The sensitivity of CRDS [8,52], phase-shift cavity ring down spectroscopy (PS-CRD) [6] and Fourier transform phase-shift cavity ring down spectroscopy [53] have been demonstrated by using several bands in the very weak forbidden b 1 + g ← X 3 − g transitions on gaseous molecular oxygen. Using the highly sensitive CRDS, the absorption spectra of the A-band of the 16 [54,55]. In addition, calculation of the atmospheric transmission function [38] and the magnetic dipole transition moment for the red atmospheric oxygen bands [56] have been made.…”

Section: Discussionmentioning

confidence: 99%

“…Other investigations that involve low temperature CRD experiments using a static cell have measured the collision induced absorption bands of oxygen [10,11]. Before the introduction of the CRD technique, multiple transversal cell or White cells [12] for gases operating at low temperatures were pioneered by Herzberg [13] cooled with liquid N 2 (78 K) and 80 m path length to give spectroscopic evidence for H 2 in the atmospheres of Uranus and Neptune, Watanabe and Welsh [14], using liquid H 2 (18 K), liquid N 2 (77 K) and 13 m path length studied the collision induced absorption of H 2 and D 2 at low temperatures, Ewing and co-workers [15] using liquid nitrogen (77 K), liquid Ar (87 K) and 230 m path length showed the collision induced absorption spectrum of O 2 , McKellar and co-workers [16] describe a variable temperature (80-125 K) with 165 m path length cell, and Horn and Pimentel [17] describe a variable temperature (120-300 K) and variable path length cell (60 to 2540 m) to study the absorption of constituents of Martian atmosphere. These cells have been very useful to reproduce conditions of planetary atmospheres and obtain spectroscopic constants and molecular structures of van der Waals molecules.…”

Section: Introductionmentioning

confidence: 99%

Low temperature cavity ring down spectroscopy with off-axis alignment: application to the A- and γ-bands of O2 in the visible at 90 K

Perez-Delgado

Manzanares

2011

Appl. Phys. B

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The cavity ring down (CRD) technique presented here involves an optical cavity attached to a cryostat. The static cell and mirrors of the optical cavity are all inside a vacuum chamber at the same temperature of the cryostat. The temperature of the cell can be changed between 77 K and 298 K. An off-axis alignment of the laser beam into the cavity is used to increase the number of resonant modes inside the cavity and improve the signal to noise ratio of the absorption bands. To demonstrate the capabilities of the low temperature CRD cell, the absorption spectra of O 2 are recorded at 90 K for the A (υ = 0 ← υ = 0) and γ (υ = 2 ← υ = 0) bands of the b 1 + g ← X 3 − g transition using cavity ring down spectroscopy. The optical cavity performance was tested using two variations of the CRD technique. The A-band is measured using the phase-shift cavity ring down method and the γ -band using the pulsedlaser exponential-decay method. A comparison between experimental and simulated spectra of the O 2 bands at 90 K confirms the molecular temperature measured by a sensor localized in the cell. Quantitative measurements of the individual rotational line intensities are made for the oxygen γ -band to confirm the temperature of the cell and calculate the vibrational band intensity. The application of this technique for laboratory studies of planetary atmospheres and the spectroscopy of molecular complexes is emphasized.

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An Optical Cell for Long Pathlengths at Low Temperatures

Cited by 17 publications

References 9 publications

Liquid-helium temperature long-path infrared spectroscopy of molecular clusters and supercooled molecules

Liquid-helium temperature long-path infrared spectroscopy of molecular clusters and supercooled molecules

Cavity ring-down optical spectrometer for absorption measurements using pulsed laser sources

Low temperature cavity ring down spectroscopy with off-axis alignment: application to the A- and γ-bands of O2 in the visible at 90 K

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