TRIPLE Q: A three channel quantum cascade laser absorption spectrometer for fast multiple species concentration measurements

Abstract

A compact and transportable three channel quantum cascade laser system (TRIPLE Q) based on mid-infrared absorption spectroscopy has been developed for time-resolved plasma diagnostics. The TRIPLE Q spectrometer encompasses three independently controlled quantum cascade lasers (QCLs), which can be used for chemical sensing, particularly for gas phase analysis of plasmas. All three QCLs are operated in the intra-pulse mode with typical pulse lengths of the order of 150 ns. Using a multiplexed detection, a time resolution shorter than 1 μs can be achieved. Hence, the spectrometer is well suited to study kinetic processes of multiple infrared active compounds in reactive plasmas. A special data processing and analysis technique has been established to account for time jitter effects of the infrared emission of the QCLs. The performance of the TRIPLE Q system has been validated in pulsed direct current plasmas containing N(2)O/air and NO(2)/air.

Dual-Section DFB-QCLs for Multi-Species Trace Gas Analysis

“…With such an approach combinations of three [9] or even four [10] QCLs were realized at the expense of increased optical complexity, complicated and sensitive alignment, bulky instrumental setups and higher overall costs.…”

Highly sensitive and fast detection of propane–butane using a 3 μm quantum cascade laser

“…However, in this case, the choice of the broadband laser source is justified by the fact that the broad and quasi-structureless propane absorption spectrum does not require high spectral resolution, and at the same time, for leak-detection, a precise and fast "on-off" decision without a detailed spectral analysis is fully sufficient. Yet, the low spectral resolution brings several advantages over interpulse or intrapulse tunable diode laser absorption spectroscopy techniques typically employed for high sensitivity trace gas measurements [16][17][18][19][20]. First, the broadband laser signal, which is spectrally matched to the propane absorption features, gives us the possibility to perform the measurement in one shot without wavelength scanning, thus gaining at speed.…”

Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

“…Using time resolved quantum cascade laser absorption spectroscopy, the densities of NO, NO2 and N2O have been measured in synthetic air as well as in air with 0.8% of NO2 or N2O. Figure 12 shows a schematic sketch of the experimental set-up consisting of a closed tube reactor made of Pyrex and a 3 channel QCLAS spectrometer, TRIPLE Q [15]. This study showed that IR titration coupled with QCLAS is a reliable technique for the determination of the quenching probability of vibrationally excited nitrogen molecules on a wide range of materials relevant to plasma technology.…”

“…Using time resolved quantum cascade laser absorption spectroscopy, the densities of NO, NO 2 and N 2 O have been measured in synthetic air as well as in air with 0.8% of NO 2 or N 2 O. Figure 12 shows a schematic sketch of the experimental set-up consisting of a closed tube reactor made of Pyrex and a 3 channel QCLAS spectrometer, TRIPLE Q [15].…”

“…The total emission range of a single DFB-QCL is typically less than 7 cm´1 (see [2] and references therein). Therefore, multi-component detection to study infrared active compounds in reactive plasmas and gases requires, as in the case of TDLAS, the combination of several QCLs in a spectrometer [15,16]. Nevertheless, the variety of QCLs and ICLs operating at room temperature provide alternatives to cryogenically cooled lead salt lasers.…”