Mid-Infrared Spectroscopy Platform Based on GaAs/AlGaAs Thin-Film Waveguides and Quantum Cascade Lasers

Abstract

The performance and versatility of GaAs/AlGaAs thin-film waveguide technology in combination with quantum cascade lasers for mid-infrared spectroscopy in comparison to conventional FTIR spectroscopy is presented. Infrared radiation is provided by a quantum cascade laser (QCL) spectrometer comprising four tunable QCLs providing a wavelength range of 5-11 μm (1925-885 cm(-1)) within a single collimated beam. Epitaxially grown GaAs slab waveguides serve as optical transducer for tailored evanescent field absorption analysis. A modular waveguide mounting accessory specifically designed for on-chip thin-film GaAs waveguides is presented serving as a flexible analytical platform in lieu of conventional attenuated total reflection (ATR) crystals uniquely facilitating macroscopic handling and alignment of such microscopic waveguide structures in real-world application scenarios.

Portable Infrared Laser Spectroscopy for On-site Mycotoxin Analysis

“…Recently emerging analytical measurement strategies have demonstrated the utility of quantum cascade lasers (QCLs) in combination with thin-film waveguides as a promising alternative to commonly used Fourier transform infrared (FTIR) spectroscopy techniques222324. Due to their exceedingly compact dimensions, high output power, operational stability, and broad tunability (>400 cm −1 per device), QCLs are unambiguously accepted as the most advanced light source facilitating compact and portable MIR spectroscopy and sensing schemes1325.…”

“…Quantitative evanescent field absorption (A) utilizing thin-film waveguides may accordingly be described via a pseudo-Lambert-Beer relationship A = (εcl)r, where ε is the molar absorptivity, c is the concentration of the analyte, l is the equivalent optical path length, and r is the fraction of radiation power residing outside the waveguide core (i.e., within the evanescent field). Consequently, any intensity enhancement of the evanescent field above the waveguide surface directly increases the obtainable signal-to-noise ratio (SNR), and thus, the overall sensitivity of absorption measurements using such thin-film waveguides2428. Consequently, the high spectral density provided by QCLs in combination with the sensitive thin-film waveguides appear ideal for the spectroscopic investigation of minor components and minute spectral changes in complex matrices29.…”

Progress of infrared guided-wave nanophotonic sensors and devices

“…7h). The light was coupled into and out from the waveguide sensing using MIR objective lenses [158]. To more accurately control the analyze flow, a polydimethylsiloxane (PDMS) chamber was bonded to the nanophotonic biochemical sensor chip (Fig.…”

Advances in Mid-Infrared Spectroscopy for Chemical Analysis

“…Probably the most dramatic (r)evolution in modern IR spectroscopy has to be attributed to IR light source technology, which has seen quantum heterostructure-based laser diodes maturing from a concept proposed in 1971 (20) to the first operating QCL in 1994 (21) and, finally, into commercially available and in part broadly tunable state-of-the-art devices shortly thereafter (22)(23)(24)(25)(26)(27)(28)(29). However, novel detection principles for MIR radiation such as quantum cascade detectors (QCDs) (12,(30)(31)(32) and advanced thin-film (33)(34)(35)(36) and hollow waveguide (HWG) technologies (37)(38)(39) have also contributed to the evolution of conventional MIR spectroscopy into miniaturized chem/bio sensing and assay platforms, as recently reviewed (40,41).…”

“…In addition to NIR methods, the differentiation between corn samples with a fumonisin content below and above 4 mg kg −1 using a PLS-based method and the differentiation between deoxynivalenol contamination levels below or above 60 ppm have also been realized using MIR spectra collected via FTIR-based techniques (135,136). It is anticipated that MIR analyzers based on QCL light sources and thin-film waveguides may provide an advanced platform technology for detecting contaminants such as mycotoxins in a variety of commodities with high sensitivity and at field-usable dimensions (29,137,138).…”