Mid-infrared surface transmitting and detecting quantum cascade device for gas-sensing

Abstract

We present a bi-functional surface emitting and surface detecting mid-infrared device applicable for gas-sensing. A distributed feedback ring quantum cascade laser is monolithically integrated with a detector structured from a bi-functional material for same frequency lasing and detection. The emitted single mode radiation is collimated, back reflected by a flat mirror and detected by the detector element of the sensor. The surface operation mode combined with the low divergence emission of the ring quantum cascade laser enables for long analyte interaction regions spatially separated from the sample surface. The device enables for sensing of gaseous analytes which requires a relatively long interaction region. Our design is suitable for 2D array integration with multiple emission and detection frequencies. Proof of principle measurements with isobutane (2-methylpropane) and propane as gaseous analytes were conducted. Detectable concentration values of 0–70% for propane and 0–90% for isobutane were reached at a laser operation wavelength of 6.5 μm utilizing a 10 cm gas cell in double pass configuration.

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

“…Thus, other ro-vibrationally accessible analytes of particular interest can be measured as well. In addition, integration of laser source and detectors in one device is possibly opening the path for highly miniaturized, sensitive gas sensors for detecting multiple gas species [55, 56]. …”

An Overview on Quantum Cascade Lasers: Origins and Development

“…About gas detection, Harrer et al [68] combined the operation mode and low-divergence emission from QCLs with two-dimensional array integration with multiple emission and detection frequencies leading to detecting propane concentrations of 0-70 and 0-90% for isobutane at a laser operation wavelength of 6.5 μm using a 10 cm gas cell in double-pass configuration.…”

Surface emitting ring quantum cascade lasers for chemical sensing

“…34,35 The latter is a molecular dispersion technique that probes a sample's refractive index spectrum, rather than its absorption, via the phase of radio frequency-modulated laser light. 36 Its sensitivity to the signal's phase makes 27 (b) Two concentric DFB ring quantum cascade laser/detector (QCLD) devices. 28 Each ring can be used for light emission and detection.…”

“…27,28 Furthermore, the small footprint of such sensors enables the realization of compact sensing systems. Figure 1(a) shows a scanning electron microscope (SEM) image of a surface emitting ring QCL with a surface detecting disk QCD in its center.…”

“…Figure 1(a) shows a scanning electron microscope (SEM) image of a surface emitting ring QCL with a surface detecting disk QCD in its center. 27 Vertical light emission and detection are provided by the second-order DFB grating (QCL) and the metal hole grating (QCD), respectively. A sketch of the corresponding sensing setup is shown in Fig.…”