Abstract: An interference fringe projection apparatus includes light source units that selectively emit light from a coherent light source from one of a plurality of optical emitters, a polarization-maintaining waveguide unit with a plurality of PANDA fibers (polarization-maintaining waveguides) that each guide light emitted from one of the plurality of optical emitters, polarization splitters that split an optical path of light emitted from each of the PANDA fibers by polarization direction, and a polarizing film that transmits only a linear polarization component in a particular direction of light split by the polarization splitter. The light source unit only emits linearly polarized light in one polarization-maintaining direction for at least one of the PANDA fibers, and the polarization-maintaining waveguide unit causes retardation of light emitted from the PANDA fibers to vary.

Abstract: Technologies for detecting absorption of electromagnetic radiation traveling through a measurement volume of interest are described herein. In a general embodiment, a laser is used to emit electromagnetic radiation through the measurement volume where absorption is desirably detected. An optical collector receives a portion of the radiation and directs a first fraction of the portion back to a gain medium of the laser, where the radiation is amplified and emitted again, and directs a second fraction to an optical sensor that can detect absorption in the measurement volume based upon attenuation of energy of the radiation. As the radiation feeds back to the gain medium and is emitted again, energy at attenuated wavelengths is amplified less than at other wavelengths. Thus, attenuation of energy of the radiation due to absorption in the measurement volume is cumulative, and relatively small absorptions are amplified, allowing smaller absorptions to be detected more easily.

Abstract: A method of detecting a tracer compound dissolved in a liquid composition via surface-enhanced spectroscopy includes the steps of: a. optionally, diluting the liquid composition or the separated liquid by mixing with a diluent liquid; b. bringing a sample of the separated liquid into contact with, a spectroscopy-enhancing surface including gold, silver or copper; c. obtaining a Raman spectrum from the sample; and d. calculating, from the spectrum, the concentration of the tracer in the sample relative to the concentration of a second component of the composition.