SU682771A1 - Monochromator - Google Patents

Description

(54) MONOCHROL ATOR

The invention relates to the field of spectral instrumentation and can be applied in the design of spectral instruments of medium and high luminosity, operating in a wide spectral range.

Monochromators are known that contain entrance and exit slits, a collimator and chamber lenses, and a dispersing system, which are designed to isolate radiation from a narrow spectral interval 1.

The known monochromators are inherent in the distortion of the image of the direct entrance slit, i.e. the curvature of the spectral line caused by the dispersing system. At the same time, the curvature of the spectral lines varies with wavelength. This leads to the expansion of the spectral bandwidth of the instrument, thereby reducing its resolution, and also leads to errors in spectrometric measurements.

S

Closest to the invention to the technical essence is a monochromator comprising an entrance and exit slit, a collimator and chamber lens, a dispersing system and a compensating element 2.

This device is complicated and, moreover, cannot be used in the case of a prism dispersing system.

The aim of the invention is to simplify the compensation of the curvature of spectral lines over the entire spectral range for any dispersing system.

This goal is achieved due to the fact that the compensating element is made in the form of an optical wedge, the refractive faces of which are second-order surfaces, in particular, straight circular cones, the axes of which lie in the plane of the main section of the wedge at an angle to one another. from 2 ° to 40 °, with the optical wedge mounted in front of the exit slit with the ability to move in the direction perpendicular to the output slit and optical axis, and the plane

0 its main section is perpendicular to the exit slit. Compensation of the curvature of the lines occurs due to the fact that different parts of the beam of rays building the image. the curved line is deviated by different parts of the compensating element by a different amount. Moreover, the deviation is directed in the direction opposite to the deflection of the spectral line, and the magnitude is such that the curved line becomes straight. When moving

of the reversing element B of one or the other side, the amount of beam deflection increases or decreases differently for different parts of the compensating element, which gives, in the following: it is possible: to straighten the line of greater or lesser curvature. With the help of a compensating element, it is possible to compensate for the curvature of the lines, regardless of whether they are dispersed and the system used in the monochromator is diffractive or prismatic. In this case, there is a need to distort the spectral slits.

FIG. Figure 1 shows the optical scheme of one of the possible variants of the proposed monochromator; in fig. 2 - a compensating element in a perspective view; in fig. 3 - COMBTENT Element, side view and ray path through it; in fig. 4 - the same, top view; in fig. 5 is a section along A-A in FIG. 3

The monochromator contains an entrance slit /, a mirror lens 2, a dispersing prism 3, a flat mirror 4, a swiveling mirror 5, a compensating element 6, an exit slit 7, refracting edges 8 and 9 of the wedge.

The monochromator works as follows.

The radiation enters through the entrance slit J (Fig. 1) on the lens 2.

Lens 2 directs the radiation by a parallel beam to a dispersing irisma 3. After passing through the prism, the radiation is expanded into a wavelength spectrum and falls on a flat mirror 4 (Litter's mirror). Reflecting from mirror 4, the radiation passes through the prism 3 again, again, the camera is guided again, and is focused by the lens 2B of its rear focal plane, passing through the compensating element 6, which eliminates the curvature of the spectral lines. Due to this, the All monochromatrix passes through the direct exit slit 7; the radiation of the direct spectral LENIUM is matched. In order to significantly increase the dispersion, the Litter 4 mirror can be replaced with a diffraction grating. To scan the spectrum, the mirror (grid) 4 is rotated around an axis parallel to the working faces of the prism 3 and passing through the middle of its reflecting surface. Prism 3 is fixed motionless.

In the section by the plane A-A (Fig. 5) and the condition of the sections combined with it by the planes BB and B-B, which are shown by a dotted line, the projections of the three main rays emanating from the center (point O) and the edges (points of type) of the entrance slit for the wavelength K. Suppose that the line tOp corresponds to a curved spectral line with a wavelength X, and the curvature

-.TUHML PI

Noah arrows h. In sections A-A, B-B, B-B, it is shown that for certain values of angles a, g, distance I, and also the refractive index n of the material of the compensating element, the projections of the rays that lie before entering the compensating element on the cylindrical surface which, in the absence of the latter, intersects with the plane of the spectrum, forms a curved spectral line, when leaving the compensating element lies already in the same plane, which, having intersected with the plane of the spectrum, forms a straight spectral line. Thus, the beam of rays, which first builds the image of the curved line, now passes through the compensating element, builds the image of the straight line.

During the spectrum scan, the line curvature changes according to the wavelength of the radiation entering the exit slit. To compensate for the curvature of lines of other wavelengths (A and 2) with a smaller or larger curvature (arrows h and hz), the rays enter the compensating element, respectively: at a smaller (point) or larger (point) distance from the wedge top. Thus, the compensating element moves in the direction perpendicular to the exit slit and the optical axis, thereby changing the distance from the top of the wedge to the rays passing through it entering the exit slit. The movement of the compensating element is indicated by arrows in FIG. 1. The exit slit 7 should move a small distance along the optical axis. The dimensions of the compensating element are small: its width is not much larger than the height of the slit.

With the help of a compensating element it is possible to eliminate the aberration - the curvature of the IOL introduced by the optics of the monochromator. Correction of the curvature of the field is achieved by calculating the thickness variation of the figure obtained in the cross section of the compensating element of the meridional plane. The complete compensation of the curvature of the spectral lines eliminates the indicated drawbacks of the known monochromators and makes it possible to replace the laborious curvature gaps by straight slots that are easy to manufacture; increase the dispersion resolution of monochromators; increase the height of the slots, and hence the luminosity of monochromators; expand the spectral range of monochromators; correct the floor, which leads to an increase in the aberration resolution of monochromators.

Claims (2)

1. Paysakhson- I. V. Optics of spectral instruments. L., “L. Ashchinostroenie, 1970, p. 156-159. 2. USSR Author's Certificate No. 263930, G 01 J 3/12, 1970. ut, 1 WIG SrigL P