Observation of saturation and rapid passage signals in the 10.25 micron spectrum of ethylene using a frequency chirped quantum cascade laser

McCulloch, Michael; Duxbury, G.; Langford, N.

doi:10.1080/00268970600857651

Cited by 37 publications

(37 citation statements)

References 36 publications

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“…This is of particular importance at lower pressures, since under such conditions the effective laser line width of pulsed QCLs exceeds the typical Doppler line broadening. Non-linear effects also appeared more pronounced [26,78].…”

Section: General Spectroscopic Issuesmentioning

confidence: 90%

“…Furthermore, several studies reported observing absorption features with asymmetric line shapes when employing both the short pulse and the long pulse mode (see [3] and references therein). Additionally, the latter method suffers from non-linear absorption effects [78]. The majority of these issues are unknown in using cw QCLs and degrade the performance of pulsed QCL spectrometers.…”

Section: General Spectroscopic Issuesmentioning

confidence: 99%

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Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

et al. 2016

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Abstract:The considerably higher power and wider frequency coverage available from quantum cascade lasers (QCLs) in comparison to lead salt diode lasers has led to substantial advances when QCLs are used in pure and applied infrared spectroscopy. Furthermore, they can be used in both pulsed and continuous wave (cw) operation, opening up new possibilities in quantitative time resolved applications in plasmas both in the laboratory and in industry as shown in this article. However, in order to determine absolute concentrations accurately using pulsed QCLs, careful attention has to be paid to features like power saturation phenomena. Hence, we begin with a discussion of the non-linear effects which must be considered when using short or long pulse mode operation. More recently, cw QCLs have been introduced which have the advantage of higher power, better spectral resolution and lower fluctuations in light intensity compared to pulsed devices. They have proved particularly useful in sensing applications in plasmas when very low concentrations have to be monitored. Finally, the use of cw external cavity QCLs (EC-QCLs) for multi species detection is described, using a diagnostics study of a methane/nitrogen plasma as an example. The wide frequency coverage of this type of QCL laser, which is significantly broader than from a distributed feedback QCL (DFB-QCL), is a substantial advantage for multi species detection. Therefore, cw EC-QCLs are state of the art devices and have enormous potential for future plasma diagnostic studies.

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Section: General Spectroscopic Issuesmentioning

confidence: 90%

Section: General Spectroscopic Issuesmentioning

confidence: 99%

Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

et al. 2016

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“…This is particularly of importance at lower pressures, since under such conditions the laser line width of pulsed QCLs was found to exceed the typical Doppler broadening [27] due to the frequency chirp. Non-linear effects (e.g., fast passage) appeared also more pronounced [26].…”

mentioning

confidence: 97%

“…While a theoretical description for the non-linear absorption phenomena based on optical Bloch equations exists [25,26,28], the origin of distorted line shapes in the short-pulse mode is not yet completely understood [9]. The problem is often empirically minimised by finding a compromise between a reasonable signal-to-noise ratio (SNR) and a narrow spectral width [12].…”

mentioning

confidence: 99%

Non-symmetrical line broadening effects using short-pulse QCL spectrometers as determined with sub-nanosecond time-resolution

Welzel

Röpcke

2010

Appl. Phys. B

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Quantum cascade lasers (QCLs) have attracted considerable interest as an alternative tuneable narrow bandwidth light source in the mid-infrared spectral range for chemical sensing. Pulsed QCL spectrometers are often used with short laser pulses and a bias current ramp similar to diode laser spectroscopy. Artefacts in the recorded spectra such as disturbed line shapes or underestimated absorption coefficients have been reported. A detailed time-resolved high-bandwidth analysis of individual pulses during a laser sweep has been performed. Quantitative results for CH 4 absorption features around 1347 cm −1 (7.42 µm) fell short of the expected values for reasonable operating conditions of the QCL. The origin of the artefacts using short pulses was identified to be partly of the same nature as in the case of long laser pulses. A complex combination with the tuning principle was found, leading to an apparently increased instrumental broadening (effective line width) and underestimated concentrations at low-pressure conditions.

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“…laser pulse which can be used to acquire a full absorption spectrum within the pulse width of typically a few hundred nanoseconds [15]. However, at low pressure conditions the measured absorption features are affected by an obstacle known as the "rapid passage effect" accompanied by potential power saturation effects [16,17]. Nevertheless, if a sensible normalisation [12] or calibration [9,11] is performed quantitative results can be obtained.…”

Section: Introductionmentioning

confidence: 99%

Application of quantum cascade laser absorption spectroscopy to studies of fluorocarbon molecules

Welzel¹,

Степанов²,

Meichsner³

et al. 2009

J. Phys.: Conf. Ser.

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Abstract. The recent advent of quantum cascade lasers (QCLs) enables room-temperature mid-infrared spectrometer operation which is particularly favourable for industrial process monitoring and control, i.e. the detection of transient and stable molecular species. Conversely, fluorocarbon containing radio-frequency discharges are of special interest for plasma etching and deposition as well as for fundamental studies on gas phase and plasma surface reactions. The application of QCL absorption spectroscopy to such low pressure plasmas is typically hampered by non-linear effects connected with the pulsed mode of the lasers. Nevertheless, adequate calibration can eliminate such effects, especially in the case of complex spectra where single line parameters are not available. In order to facilitate measurements in fluorocarbon plasmas, studies on complex spectra of CF 4 and C 3 F 8 at 7.86 µm (1269 -1275 cm -1 ) under low pressure conditions have been performed. The intra-pulse mode, i.e. pulses of up to 300 ns, was applied yielding highly resolved spectral scans of ~ 1 cm -1 coverage. Effective absorption cross sections were determined and their temperature dependence was studied in the relevant range up to 400 K and found to be non-negligible.

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Observation of saturation and rapid passage signals in the 10.25 micron spectrum of ethylene using a frequency chirped quantum cascade laser

Cited by 37 publications

References 36 publications

Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

Non-symmetrical line broadening effects using short-pulse QCL spectrometers as determined with sub-nanosecond time-resolution

Application of quantum cascade laser absorption spectroscopy to studies of fluorocarbon molecules

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