Spectroscopy in the gas phase with GaAs/AlGaAs quantum-cascade lasers

Abstract

We demonstrate what we believe is the first application of the recently developed electrically pumped GaAs/AlGaAs quantum-cascade lasers in a spectroscopic gas-sensing system by use of hollow waveguides. Laser light with an emission maximum at 10.009 microm is used to investigate the mid-infrared absorption of ethene at atmospheric pressure. We used a 434-mm-long silver-coated silica hollow waveguide as a sensing element, which served as a gas absorption cell. Different mixtures of helium and ethene with known concentrations are flushed through the waveguide while the laser radiation that passes through the waveguide is analyzed with a Fourier-transform infrared spectrometer. The experimentally obtained discrete ethene spectrum agrees well with the calculated spectrum. A detection threshold of 250 parts per million is achieved with the current setup.

Peer Reviewed: Mid-IR Fiber-Optic Sensors

“…Hollow waveguides acting as a capillary flow cell enable gas-sensing applications for numerous relevant compounds. This miniaturized gas-sensing approach, in combination with quantum cascade lasers, has recently been demonstrated for the first time (22).…”

“…Analytical applications of QCLs are still rare, in part because the commercial availability of lasers with relevant emission frequencies is still limited. Other than a few demonstrations of using QCLs in liquidphase transmission spectroscopy for flow-injection analysis (51), most sensing applications currently focus on gas-phase measurements (22,52). Evanescent field-based liquid-phase sensing using QCLs has not been demonstrated yet.…”

Sensor Systems Based on Mid‐Infrared Transparent Fibers

“…Fluoride fibers consist of materials like ZrF 4 or AlF 3 with a refractive index in the range of 1.4 to 1.5. As they currently offer the lowest attenuation losses of all reported IR fiberoptic materials, they are of particular interest for remote sensing applications.…”

Fast infrared spectrometer for flowing gases by the use of a hollow fiber and a PtSi sensor array

“…Fast spectrometry is achievable with tunable diode lasers, but the tuning range is limited to a narrow spectral band, e.g., 9.96-10.06 [7] or 1.532-1.534 lm [8]. Spectral measurements in a wider wavelength range (>1 lm) are difficult to conduct with a single diode laser.…”