HYPERSPECTRAL LASERS FOR SPECTROSCOPIC MEASUREMENTS IN THE NEAR-INFRARED

Abstract

This project develops hyperspectral lasers that are built using fiber-optic cavities and broadband semiconductor gain media. These sources are custom designed for high-speed (typically 30 kHz) spectroscopic sensing applications, such as thermometry based on H2O absorption spectroscopy in harsh, combusting environments that are generally not conducive to more conventional thermometry techniques. Novel time- and frequency-division multiplexed lasers are introduced that either scan continuously over chosen wavelength ranges or switch among discrete wavelengths. One example is a laser that scans through a 0.1-4 nm range centered near 1350 nm every 10 ?s; it is an advanced Fourier domain mode locked (FDML) laser that offers ultra low intensity noise and a significantly narrowed spectral linewidth compared to typical FDML performance. Another example is a discrete time-division multiplexed laser that cycles through 19 spectrally narrow wavelengths in a 44-nm-wide spectral band (1333?1377 nm) every 15 ?s, where each wavelength can be aligned to a specific absorption feature. Such engineered lasers are changing the way one looks at solving spectroscopic sensing problems as these sources can be custom designed to address a particular problem instead of making decisions based on the availability of light sources in the marketplace.