Spectral analysis is an important method for noninvasive blood glucose measurement. Presently, Fourier-transform spectroscopy is a well-established technique that provides highly resolved spectral measurements in the infrared, visible and ultraviolet ranges. In this study, we proposed a novel method for obtaining linear spectra based on regular Spatial Heterodyne Spectrometers. In particular, we wanted to use a fluorescent dye-coated screen and a Fourier lens to directly obtain uniform K-space spectra. In the system, the up-conversion luminescent material on the screen is hoped to absorb coherent incident light and emit light of a specific wavelength that maintains the coherence. According to our calculation, the photodetector array receives the Fourier image pattern on the screen and can directly obtain the spectrum of the measured substance, therefore the scientists can directly observe the spectrum of the test sample. Furthermore, we replace the fluorescent dye-coated screen by an infrared laser detector card, which is commonly used in laboratories, to primary verify the feasibility of the method. Up-conversion luminescent materials that are widely used in the fields of analytical chemistry, biomedicine, and life sciences, have very good application prospects in biological imaging, photodynamic therapy, solar cells, flexible fluorescent films and sensing.
In this study, we describe a simple method to produce signals which can reveal the cross-sectional information of samples in an optical coherence tomography (OCT) system. Instead of using the spectrometer and the Fourier transformation calculation in the conventional spectrum domain (SD) OCT system, we use a Mach-Zehnder interferometer structure of the spatial heterodyne spectrometer. In a spatial heterodyne spectrometer, because each position on the photodetector array could be mapped to a specific optical path difference, the spectral density distribution could be retrieved with Fourier transformation. And in an SD-OCT system, cross-section signals are obtained by conducting Fourier transformation to the spectrum signals. Therefore, in our OCT system, the spatial signals captured by the photodetector array is related to the cross-sectional signals obtained in an SD-OCT system. The theoretical study and the numerical simulation demonstrate that by applying our method in an OCT system, the heterodyne spectrometer structure could generate a symmetrical pattern composed of fringes with high spatial frequency. Then the photodetector array captures the pattern to generate a spatial signal. The spatial ordinate of this signal is linearly related to the optical depth in sample, while the amplitude of the signal intensity variation is linearly related to the intensity of coherent backscattered light in the sample. The imaging depth is theoretically unlimited. Also, because of the high spatial frequency of the signal, we further adjust the inclination angle in the heterodyne spectrometer structure to visualize the signal.
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