Applications of midinfrared quantum cascade lasers to spectroscopy

Abstract

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.

Implementation of a quantum cascade laser-based gas sensor prototype for sub-ppmv H2S measurements in a petrochemical process gas stream

“…Since its first operational demonstration in 1994 [6], the quantum cascade laser (QCL) advanced to a powerful and reliable spectroscopic source of coherent light covering the mid-infrared (MIR) and terahertz spectral region for sensitive detection of molecular species on their fundamental vibrational bands and rendered laser-based absorption spectroscopy a powerful tool for industrial gas sensing [6–9]. The high-quality implications encompassing stringent single-mode emission and superior wavelength stability as required for industrial trace gas sensing are met by distributed feedback (DFB)-type QCLs [10].…”

Off-beam quartz-enhanced photoacoustic spectroscopy-based sensor for hydrogen sulfide trace gas detection using a mode-hop-free external cavity quantum cascade laser

“…In practice, concentrations ranging from sub-ppmv levels at low pressures to several per cents at atmospheric conditions need to be monitored. Despite a variety of online monitoring options for gaseous H 2 S, its reliable quantitative and selective determination still remains challenging in the field of chemical sensors [3][4][5].In the field of laser spectroscopy, the constant improvement of quantum cascade lasers (QCLs) has led to their application as reliable sources of coherent light ranging from the mid-infrared (MIR) to the terahertz spectral region for sensitive detection of molecular species on their fundamental vibrational, respectively, rotational bands [6][7][8][9]. Due to their tailorable emission wavelength, high output power, compactness, narrow spectral linewidth, and wavelength tuneability, QCLs are optimal choices for spectroscopic applications.…”

“…In the field of laser spectroscopy, the constant improvement of quantum cascade lasers (QCLs) has led to their application as reliable sources of coherent light ranging from the mid-infrared (MIR) to the terahertz spectral region for sensitive detection of molecular species on their fundamental vibrational, respectively, rotational bands [6][7][8][9]. Due to their tailorable emission wavelength, high output power, compactness, narrow spectral linewidth, and wavelength tuneability, QCLs are optimal choices for spectroscopic applications.…”

Polarization spectroscopy of a velocity-selected molecular sample

“…In this case a commercial cw external cavity QCL (Daylight Solutions) covering the range 1776-1958 cm −1 , that emits up to 140 mW of optical power and exhibits a linewidth of ∼2 MHz [5,6]), is used as the pump field, and a distributed-feedback cw QCL (Maxion Technologies M575AH-NS) covering 1897-1904 cm −1 , with up to 250 mW of optical power and a linewidth of ∼800 kHz, [7,8], was the probe. The pump laser was circularly polarized using a λ∕4 waveplate (Alphalas) and its frequency tuned to a fixed frequency within the R14.5 1∕2 v 1 0 transition.…”