Mid-Infrared Multi-Spectrum Sensing and Imaging for Non-Destructive Material Characterization

Abstract

Mid-infrared (mid-IR) spectroscopy has become a powerful technique for chemical analysis. The fingerprint absorption bands in mid-IR can be used to uniquely identify a molecular specie. Such fingerprinting capability along with non-invasive measurement makes mid-IR sensing an ideal technology for applications involving chemical analysis in complex environments, such as pharmaceutical production, clinical health condition monitoring, environment monitoring, and remote sensing. Typically, FTIR is used to obtain the mid-IR spectrum of a specimen. However, such bench-top FTIR instrument is unpractical for field-deployed applications. To address this issue, miniaturized nanophotonic devices are alternatives for mid-IR sensing. The focus of this research is to apply mid-IR sensing technique in non-invasive chemical composition analysis.

First, a mid-IR visualization system was demonstrated to show the capability of mid-IR sensing for ultra-fast chemical identification. The fundamental components for mid-IR sensing were discussed in the experiment. Next, on-chip vortex beam generation from waveguides was studied by FDTD simulation. A spiral phase plate was then fabricated on a glass plate to show the vortex beam generation from 3.0 μm to 3.7 μm experimentally. Third, the second-order nonlinear property of BaTiO3 thin film was studied by second-harmonic generation in the mid-IR region. The nonlinear integrated photonics gives opportunity for on-chip mid-IR light generation. Last, mid-IR integrated photonics for volatile organic compounds (VOC) sensing was studied for enhanced sensitivity. SiN waveguides typically offer 5 times enhancement compared with Si waveguides. Nanoparticles-coated waveguides offer another 10-15 times enhancement. Mid-IR waveguides with nanoparticle coatings is believed to bring the sensitivity towards sub ppm level of VOC gases.