SU1130747A2 - Raster spectrometer having selective modulation - Google Patents

Abstract

RASTER SPECTROMETER WITH SELECTIVE MODULATION by aut. St. No. 968629, characterized in that, in order to increase its sensitivity and measurement accuracy in case of uneven illumination of the output raster floor, located in the direction of dispersion of a row of transparent and opaque rectangular elements of rasters are unequal in height, differ in height from one row to the other is inversely proportional to the mean illuminance along these rows.

Description

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The invention relates to spectral instrumentation, in particular to spectral instruments intended for dp accurate spectrometric measurements, especially for weak light fluxes in the IR region of the spectrum.

According to the main auth. No. 968629 is known a raster spectrometer with selective modulation, used for accurate spectrometric measurements, especially of weak light fluxes in the IR region of the spectrum, and containing an input raster, a collimator installed along the beam path. an objective lens, a dispersing system, a focusing lens, an output raster, a system for eliminating a constant component, and a receiving-recording system. The input and output rasters are some of the same number of transparent and opaque rectangular elements that are located across the field of the rasters in accordance with the positive and negative elements in the rows and columns of the Hadamard matrix, and the transparent raster element corresponds to the negative element of the matrix. The rows of transparent and opaque rectangular elements of rasters located in the direction of dispersion are made equal in height.

Such an implementation of rasters in case of a completely uniform illumination across the field of the output raster provides for obtaining the instrument function of the spectrometers without side maxima, which increases the sensitivity and accuracy of spectrometric measurements of D.

However, in a known instrument, the illumination across the field of the output raster cannot be strictly uniform due to the presence of aberrations of the optical system, vignetting of inclined beams. inaccuracies in the alignment of the lighting system, uneven brightness over the surface of the source under study, etc.

As a result, residual side maxima appear in the contour of the instrument function of the spectrometer, which reduce the sensitivity and accuracy of spectrometric measurements.

The purpose of the invention is to increase the sensitivity and accuracy of measurements of the spectrometer in case of uneven illumination of the output raster floor.

This goal is achieved by the fact that in a raster spectrometer with selective modulation, the rows of transparent and opaque rectangular elements of rasters arranged in the direction of dispersion are not equal in height, and the height of the elements from one row to another is returnable proportional to the average illumination along these rows.

When the height of each row of elements is inversely proportional to the average illumination along the row, side maxima in the contour of the apparatus function are significantly reduced, and in some cases are eliminated almost completely.

Figure 1 shows a schematic diagram of a raster spectrometer with selective modulation {in Figures 2 and 3 rasters with unequal height rows of transparent and opaque elements in FIG. 4 through 7 are examples of uneven distribution of illumination of the output raster field in FIG. 8 and 9 are the corresponding hardware functions of a known spectrometer.

The raster spectrometer (Fig. 1) contains an input raster 1, a collimator lens 2, a dispersing system 3, a focusing lens 4, an output raster 5, a constant component exclusion system consisting of lenses 6 and 7 and a modulator B, and a registration system 9 Dispersing system 3 is a diffraction grating. The modulator 8 has mirror lamellas. Opaque and transparent elements of the raster have a rectangular shape and are located across the field in accordance with 1 and

-1 in the rows and columns of the matrix: Hell Mar QV.

The rows of transparent and opaque elements of the rasters are made different in height in the direction of dispersion (Figures 2 and 3). The height of each row is inversely proportional to the average illuminance along the row.

The device works as follows.

Radiation from the source under study passes through the transparent elements of the input raster 1. hits the collimator lens 2 which forms a parallel beam and passes it onto the dispersing system 3. The radiation spread out into the spectrum falls on the 3 focusing lens 4j which builds a number of displaced one relative to another monochromatic image of the input raster on the output raster 5. Of all the images, only one that corresponds to the wavelength setting J exactly coincides with the output raster. For this wavelength, the magnitude of the light flux F. passing through the output raster is proportional to the total number of transparent elements in the raster, Dn of other wavelengths and the light flux F is much smaller and proportional to the number of mutually coinciding elements of the output raster and the part of the input raster shifted relative to its image . In the light reflected from the mirror elements of the output raster, the light fluxes for the wavelengths and L are, respectively, G. Transmitted and reflected flows FJ. and the Frt mirror lenses 6 and 7 are directed to the rotating modulator 8 with mirrored lamellae. When the modulator 8 rotates, the light fluxes alternately arrive at the program-recording system 9, passing through the raster 5 and reflected from it. The receiving and recording system is configured at the modulation frequency and registers the difference 0. Spectrum scanning is performed with the turn of the diffraction grating. Under actual instrument operation conditions, the illumination in the field of the output raster is uneven. The relative distribution of illumination across the field of the output raster in the study of sources of radiation in one direction is similar to 74 in Fig. 6, and generally in Fig. 7. In the case of the illumination distribution shown in Fig. 6, the illumination along each row is kept constant, and varies from row to row in a ratio of 0.7; 0.8; 0.9; 1.0; 0.9; 0.8; 0.7, so the heights of rows in rasters ratio mc as 1 / 0.7: 1 / 0.8: 1 / 0.9: 1/1: 1 / 0.9: 1 / 0.8: 1/0 , 7. Such a raster is depicted in FIG. , and the corresponding hardware function is shown in FIG. 4, and it is completely free from side maxima, in contrast to the hardware function of the known spectrometer of FIG. 8). In the case of the illumination distribution shown in Fig. 7, the mean values of illumination along the rows vary in accordance with the ratio 0.700: 0.771: 0.814: 829: 0.814, 0.771: 0.700, therefore the height of the rows in the rasters changes in the ratio 1.184: 1.074 : 1.018: 1.000: 1.018: 1.074: 1.184 (FIG. 3). The corresponding hardware function is depicted in Fig. 5 and has a root-mean-square level of side maxima approximately 2.6 times less than the hardware function of the known spectrometer (Fig. 9). In the proposed spectrometer, the side maxima in the circuit of the apparatus function are significantly reduced or eliminated completely due to the fact that the rows of transparent and opaque rectangular elements of the rasters located in the direction of dispersion are not equal in height, and the height of the rows is inversely proportional to the average refreshment along the rows.

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Claims (1)

RASTER SPECTROMETER WITH SELECTIVE MODULATION by ed. St. No. 968629, characterized in that, in order to increase its sensitivity and measurement accuracy in case of uneven illumination, the fields of the output raster, the rows of transparent and opaque rectangular elements of the rasters located in the dispersion direction are made unequal in height, the height of the elements from one row to another is reversed proportional to the average illumination along these rows.