Rapid passage effects in nitrous oxide induced by a chirped external cavity quantum cascade laser

Helden, J. H. van; Peverall, R.; Ritchie, Grant A. D.; Walker, Richard

doi:10.1063/1.3079420

Cited by 15 publications

(15 citation statements)

References 18 publications

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“…The continuous frequency drifts of zones III and V and at the end on the pulse are identified as the so-called frequency downchirp, of thermal origin, which has been used to map frequency versus time in QCL spectrometers [4]. The values found here are close to those reported in [5] for a similar EC-QCL.…”

Section: Resultssupporting

confidence: 72%

Time-resolved spectral characterization of a pulsed external-cavity quantum cascade laser

et al. 2012

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Spectrally tunable narrow-linewidth mid-infrared sources are used in a variety of spectrometric optical systems for detection, identification, and/or quantification of chemical species. However, in the pulsed regime they often display a varying spectrum in time, either from shot-to-shot or during the pulse itself, with consequences on the measurement accuracy, resolution, and repeatability. This is, for instance, the case of pulsed quantum cascade lasers (QCL), mainly because of strong transient thermal effects in the optical waveguide. Unfortunately, little information has been published on this subject because mid-infrared time-resolved spectrometers are extremely scarce. In this paper, we explain how this can be circumvented by using time-gated frequency upconversion in a nonlinear crystal. We apply this principle to characterize a pulsed external cavity QCL (EC-QCL) at 7.8 µm, using AgGaS 2 as the nonlinear crystal and a Q-switched Nd:YAG laser as the pump source. The upconverted near infrared spectrum is conveniently analyzed with a high resolution lambdameter and an optical spectrum analyzer. We evidence frequency chirp at an average rate of -50 MHz/ns and mode hops spanning 15 GHz for the EC-QCL. These results are compared to published data.

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Section: Resultssupporting

confidence: 72%

Time-resolved spectral characterization of a pulsed external-cavity quantum cascade laser

et al. 2012

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“…This is due to the rapid passage (RP) effect, where the laser frequency is chirped through the molecular resonance on a timescale that is short compared to the time between collisions; as such, the sample is polarized and it is the interference between this induced polarization and the chirped laser radiation field that results in the observed signal. 3,[14][15][16] The RP effect, however, can be removed by increasing the overall pressure by the introduction of an inert buffer gas, typically of the order of 100 Torr, such that the collision rate is increased and the sample polarization and/or coherence is destroyed on a timescale shorter than that of the signal acquisition system. 12 An example of such behavior is shown in Fig.…”

Section: Qcls Operated In the Pulsed Mode 21 Rapid Passage Effectmentioning

confidence: 99%

Applications of midinfrared quantum cascade lasers to spectroscopy

et al. 2010

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We review the use of both pulsed and continuous wave quantum cascade lasers in high-resolution spectroscopic studies of gas phase species. In particular, the application of pulsed systems for probing kinetic processes and the inherent rapid passage structure that accompanies observations of low-pressure samples using these rapidly chirped devices are highlighted. Broadband absorber spectroscopy and time-resolved concentration measurements of short-lived species, respectively exploiting the wide intrapulse tuning range and the pulse temporal resolution, are also mentioned. For comparison, we also present recent sub-Doppler Lamb-dip measurements on a low-pressure sample of NO, using a continuous wave external cavity quantum cascade laser system. Using this methodology the stability and resolution of this source is quantified. We find that the laser linewidth as measured via the Lambdip is ca. 2.7 MHz as the laser is tuned at comparably slow rates, but decreases to 1.3 MHz as the laser scan rate is increased such that the transition is observed at 30 kHz. Using this source, wavelength modulation spectroscopy of NO is presented.

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“…1 The frequency chirping also limits the resolution of direct absorption spectroscopy studies with pulsed external cavity ͑EC͒-QCLs, but an advantage is that their application with long path cells such as Herriott cells is not hampered by fringing effects. [2][3][4][5][6] True cw sources are generally limited however, in terms of both the wavelengths commercially available ͑ϳ4-10 m͒, and their tuning range ͑of the order of a few cm −1 ͒. There is therefore great interest in the development of cw EC-QCLs with wide tunability that will allow detection of either multiple species within a reasonable spectral range, or continuous spectra of large gaseous and condensed phase species.…”

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confidence: 99%

Direct and wavelength modulation spectroscopy using a cw external cavity quantum cascade laser

Hancock

Helden

Peverall

et al. 2009

Applied Physics Letters

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A continuous wave external cavity quantum cascade laser ͑EC-QCL͒ operating between 1872 and 1958 cm −1 has been used to make rotationally resolved measurements in the fundamental band of nitric oxide at 140 mTorr, and the 2 band of water at atmospheric pressure. These measurements demonstrate the advantages of wide tunability and high resolution of the EC-QCL system. From direct absorption spectroscopy on nitric oxide a laser bandwidth of 20 MHz has been deduced and a sensitivity of 8.4ϫ 10 −4 cm −1 Hz −1/2 was achieved. Wavelength modulation spectroscopy using current modulation enhances the sensitivity by a factor of 23 to 3.7ϫ 10 −5 cm −1 Hz −1/2 .

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Rapid passage effects in nitrous oxide induced by a chirped external cavity quantum cascade laser

Cited by 15 publications

References 18 publications

Time-resolved spectral characterization of a pulsed external-cavity quantum cascade laser

Time-resolved spectral characterization of a pulsed external-cavity quantum cascade laser

Applications of midinfrared quantum cascade lasers to spectroscopy

Direct and wavelength modulation spectroscopy using a cw external cavity quantum cascade laser

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