Abstract
The use of the wide-field-stop and beam-expansion method for sensitivity enhancement of one-shot Fourier spectroscopy is proposed to realize health care sensors installed in smartphones for daily monitoring. When measuring the spectral components of human bodies noninvasively, diffuse reflected light from biological membranes is too weak for detection using conventional hyperspectral cameras. One-shot Fourier spectroscopy is a spatial phase-shift-type interferometer that can determine the one-dimensional spectral characteristics from a single frame. However, this method has low sensitivity, so that only the spectral characteristics of light sources with direct illumination can be obtained, because a single slit is used as a field stop. The sensitivity of the proposed spectroscopic method is improved by using the wide-field-stop and beam-expansion method. The use of a wider field stop slit width increases the detected light intensity; however, this simultaneously narrows the diffraction angle. The narrower collimated objective beam diameter degrades the visibility of interferograms. Therefore, a plane-concave cylindrical lens between the objective plane and the single slit is introduced to expand the beam diameter. The resulting sensitivity improvement achieved when using the wide-field-stop and beam-expansion method allows the spectral characteristics of hemoglobin to be obtained noninvasively from a human palm using a midget lamp.
Highlights
The “internet of things” has become a hot topic for researchers worldwide
Our proposed one-shot Fourier spectroscopic imager[1] is configured with a near-common-path wavefront-division interferometer,[2,3] is strongly robust against mechanical vibration, and will be realized as a low-cost and smallsized spectroscopic unit because the imager consists of only three lenses
We introduced a planoconcave cylindrical lens into the optical system to act as a Galilean beam expander
Summary
The “internet of things” has become a hot topic for researchers worldwide. One result of this development is. Demand for compact-size spectrometers already exists and they have been researched,[8,9,10] but it will be necessary for spectroscopic imagers to use the weak reflected light from biological tissues for blood glucose measurements. Acousto-optic tunable filter-based and dispersive spectrometers cannot improve the sensitivity, at least in principle,[11,12,13,14] because these spectroscopies receive narrowband light. It is impossible for conventional methods to achieve the required wavelength resolution and sensitivity because smartphones cannot accommodate expensive and large-scale cameras with high sensitivity and we cannot use strong light sources that are unsafe for use on human skin. We explain the principle and availability of the method and demonstrate the feasibility
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