We demonstrate an all-fiber super-continuum (SC) laser based near infrared (1160nm to 2350nm) spectroscopy system that is capable of measuring protein (gluten) levels in wheat flour, at a stand-off distance. We show that reflectance spectrum between 1160nm and 2350nm can be used to measure protein levels in wheat flour. The measured protein concentration with the partial least square regression shows a good linear correlation (R square >0.95) to the protein level measured by the Dumas method with standard error variance down to 0.5 percent. Our system could be used for non-destructive, real-time determination of the protein level of wheat flour at a stand-off distance in industrial settings such as food factories or flour milling plants.
We demonstrate a prototype sensor capable of measuring specular and diffuse reflectance spectra from samples 3.6 m away. The sensor utilizes mid-wave to long-wave infrared supercontinuum light coupled into a rotational FTIR spectrometer to actively probe remote samples. We measure the diffuse reflectance of acetaminophen at 41.77 μg/cm2 on a glass substrate and find that a modified Bobbert-Vlieger analysis can estimate the effects of particle size distribution on return spectra. We find that the measured return from stand-off particulate measurements depends not only on the chemical identity, but also the size and distribution of particles on the substrate.
All-fiber integrated super-continuum (SC) sources are described based on a platform architecture that can operate in the visible, near-infrared, short-wave infrared, mid-wave infrared and long-wave infrared, with demonstrated SC wavelengths ranging from 0.47 to 12 μm. Modulation instability initiated SC generation leads to a simple SC source with no moving parts and that uses o_-the-shelf components from the mature telecommunications and fiber optics industry. The resulting light sources are basically a cascade of fibers pumped by fiber-pigtailed laser diodes and some drive and control electronics; thus, the SC sources have the potential to be cost-effective, compact, robust and reliable. Starting from fused silica fibers, the SC spectrum can be extended to shorter or longer wavelengths by cascading fibers with appropriate dispersion and/or transparency. As one example, we demonstrate a long-wave infrared SC source that generates a continuous spectrum from approximately 1.57 to 12 μm using a fiber cascade comprising fused silica fiber followed by ZBLAN fluoride fiber followed by sulfide fiber and, finally, a high-numerical-aperture selenide fiber. The time-averaged output power is as high as 417 mW at 33% duty cycle, and we observe a near-diffraction-limit, single spatial-mode beam across the entire spectral range. A prototype is described that is based on a three-layer architecture with a form factor of 16.7 × 10 × 5.7 and that plugs into a standard wall plug. This SC prototype has been used in a number of field tests as the active illuminator for stand-off FTIR system over distances of 5 to 25 m, thus enabling identification of targets or samples based on their chemical signature. Further optimization of the SC source will also be described to increase the output power and to reduce the form factor.