Investigation of the Possibility of Using Microspectrometers Based on CMOS Photodiode Arrays in Small-Sized Devices for Optical Diagnostics

Abstract

The article considers the potential applicability of C12880MA and C11708MA Hamamatsu microspectrometers, which are characterized by an extremely compact design, occupying a small volume of several cubic centimeters, in portable spectrometric equipment with spatial resolution for monitoring the optical properties of condensed scattering media. The development of methods for determining the reduced scattering and absorption spectral coefficients of radiation from various scattering materials and products allows us to speak about the possibility of real-time control of the volume concentration of optically active components included in them, for example, fat and water in dairy products. For this, it is necessary to provide sufficiently accurate spectra of diffusely reflected broadband light radiation at different distances between the points of radiation entrance and registration. The aim of the manuscript is to assess the possibility of using the considered microspectrometers in compact devices for optical diagnostics and control of the optical properties of condensed scattering media. The features of the connection diagram of these microspectrometers and the necessary methods for correcting the initially obtained spectral dependencies of diffusive reflection, which will be of interest to developers of spectral diagnostic equipment, are considered in detail. The need to eliminate the influence of the inhomogeneity of dark counts of a CMOS photodiode array is shown. The hardware functions of the C12880MA and C11708MA Hamammatsu microspectrometers, as well as the AvaSpec 2048L fiber-optic spectrometer, were experimentally measured and compared. Methods for correcting the nonlinearity of their reading scales and light characteristics, as well as improving their equivalent spectral resolution using digital Wiener filtering, are described. It is shown that the equivalent spectral resolution of C12880MA and C11708MA microspectrometers can be improved by about 40% when recording smooth spectra, subject to the condition that the resulting side oscillations are small. It is pointed out that in order to reduce the level of side oscillations in the corrected spectra with improved resolution, it is necessary to ensure the smoothness of the original spectra and a good signal-to-noise ratio. A conclusion is made about the possibility of using the considered microspectrometers in portable spectrometric equipment with careful consideration of their characteristics, the features of their switching circuit, and the necessary software.

Possibilities of Diffuse Reflectance Spectroscopy in Determining and Operational Control of the Optical Properties of Finely Dispersed Scattering Media

“…In the short-wavelength part of the spectral dependencies for the second and fourth samples, the influence of parasitic radiation is manifested, which is scattered by the concave diffraction grating of the spectrometer into the zero order of diffraction. This effect was revealed by us earlier when calibrating AvaSpec 2048WL and C12880MA Hamamatsu spectrometers according to reference emitters with different temperatures [37,40,41]. The halo maximum of weak radiation scattered by the concave diffraction grating of the AvaSpec 2048WL spectrometer to zero order is located in the area that corresponds to diffracted blue radiation.…”

“…The spectral resolution of modern portable spectrometers based on concave diffraction gratings and linear CCD arrays is sufficient for the problem under consideration [36,40,41], since the absorption spectra of condensed media are smooth, in contrast to the spectra of gases. The presence of instability of the parameters of the equipment used, radiation noise, and intrinsic noise of the spectrometer linear CCD array, as well as the deterioration of the signal-to-noise ratio of the recorded spectra at the edges of the spectral range used, limits the possibilities of the proposed method.…”