RU2154849C2 - Ultraviolet objective - Google Patents

Abstract

FIELD: optics. SUBSTANCE: objective includes primary concave parabolic mirror, secondary spherical mirror and correction element. Correction element is made of three lenses with same refractive index. Extreme lenses are negative and are produced in the form of meniscuses facing space of images with concavity and central lens is biconvex. EFFECT: improved quality of image and expanded spectral range of operation. 5 dwg, 1 tbl

Description

 The invention relates to the field of observing optical devices and can be used to solve problems of detection, recognition and identification of objects of observation in the spectral range of 0.15-0.436 μm.

 A well-known lens for working in the ultraviolet region of the spectrum (Popov G.M. Modern astronomical optics. - M .: Nauka. Gl. Ed. Phys.-Math. Lit., 1988. - S. 163.164), containing the main concave mirror, secondary a convex mirror and a correction element, characterized in that the primary and secondary mirrors are in the form of rotation hyperboloids, and the correction element is made in the form of a quasiconcentric negative meniscus with a convex elliptical surface facing the space of objects.

The main disadvantage of this system is the small field of view, which does not exceed 1.5 ^o .

 The prototype of the invention is a lens for operation in the ultraviolet region of the spectrum (Wolf E. // Progress in Optics. - 1983, V.20), containing the main concave parabolic mirror, a secondary spherical mirror and a correction element of two lenses mounted along the beam behind the secondary mirrors, the first of which is made in the form of a negative meniscus with a concavity facing the space of images, and the second is in the form of a positive meniscus facing with a concavity to the object of observation.

The main disadvantage of the prototype is the low image quality and a narrow spectral range of operation (the dimensions of the scattering spot within the angular field 2ω = 2.5 ^o are of the order of 10 '' arc in the spectrum range of 0.185-0.250 μm with a relative aperture of 1: 2.6).

 The necessary improvement in image quality and the expansion of the spectral range of work in this system cannot be ensured due to the presence of large residual aberrations, of which paramount importance is: chromaticity of magnification and residual spherochromatic aberration.

 The proposed lens system for operation in the ultraviolet region of the spectrum allows to provide higher technical characteristics: improve image quality and expand the spectral range of work.

 Higher technical characteristics of the proposed system are provided by a new set of distinctive features: the corrective element consists of three lenses, the extreme lenses being negative and made in the form of menisci facing concavity to the image space, and the central one is biconvex.

 The implementation of the corrective element of the system of three lenses makes it possible to distribute the optical power of the negative components of the corrector between the two lenses and place the components of the corrector in a symmetrical pattern: negative lenses along the edges, positive in the center. This makes it possible to correct the chromaticity of the increase in a wide spectral region, which inevitably arises during the final layout of the system (entering the actual thickness of the lenses), and which cannot be completely corrected with a dual-lens corrector layout.

 The implementation of negative corrector lenses in the form of menisci facing concavity to the image space, and a central, positive corrector lens in the form of a biconvex makes it possible to reduce the residual spherochromatic aberration in a wide range of the spectrum, since the angles of incidence of rays on the optical surfaces of the corrector are reduced. At the same time, the residual coma also decreases, as a result of which the image quality is increased and the spectral range of the system is expanded.

 The authors are not aware of the optical systems of lenses that have features similar to those that distinguish the proposed system from the prototype, therefore this optical system has significant differences.

The proposed invention is illustrated by the following graphic materials:
FIG. 1 is an optical diagram of a lens.

 FIG. 2 - transverse aberration on the axis.

Transverse aberration off axis:
FIG. 3a - for 2ω = 2.5 ^o and λ = 0.15-0.254 μm.

FIG. 3b - for 2ω = 1.25 ^o and λ = 0.15-0.254 μm.

FIG. 3c - for 2ω = 2.5 ^o and λ = 0.254-0.436 μm.

FIG. 3G - for 2ω = 1.25 ^o and λ = 0.254-0.436 μm.

 FIG. 4 - residual chromatism increase.

Optical Transfer Function:
FIG. 5a - for the spectrum range λ = O, 15-0.254 μm.

 FIG. 5b - for the spectrum range λ = 0.254-0.436 μm.

 In FIG. 1 shows the proposed optical system of the lens. The system contains a main concave parabolic mirror 1, a secondary spherical mirror 2, and a correction element mounted along the beam behind the secondary mirror, consisting of three lenses 3, 4, and 5, of which the extreme lenses 3 and 5 are made in the form of negative menisci facing concavity to image space, and the central lens 4 is biconvex. The corrector lenses are made with the same refractive index (lithium fluoride).

 Rays of light, reflected from the main and secondary mirrors 1 and 2, pass through the lenses of the corrector 3, 4 and 5, forming an image of the object of observation in the focal plane, which is located behind the main mirror 1.

The design parameters of the proposed lens are shown in the table, where:
i is the surface number; r _i are the radii of curvature of the surfaces; d _i - the thickness of the lenses and air gaps; n _i are the refractive indices; O⌀ _i - light diameters of the surfaces. All linear system parameters are given in mm.

To improve image quality, the spectral range of the proposed lens 0.15-0.436 μm is divided into two sub-ranges: 0.15-0.254 μm and 0.254-0.436 μm. The ultraviolet lens has the following characteristics:
Focal length f '= 411 mm.

Back focal length
for 0.15-0.254 μm S ' _F = 51.26 mm;
for 0.254-0.436 μm S '' _F = 51.22 mm.

Angular field 2ω = 2.5 ^o .

 Relative hole D: f '= 1: 3.16.

Main wavelength
for 0.15-0.254 μm λ = 0.203 μm;
for 0.254-0.436 μm λ = 0.334 μm.

 In FIG. 2, 3a, 3b, 3c, 3g, 4 depict graphs of the residual aberrations of the proposed system for wavelengths of 0.15; 0.203; 0.254; 0.334 and 0.436 μm.

 In FIG. Figure 2 shows the course of the transverse axial aberrations, where the ordinate of the entrance pupil m (mm) is plotted along the ordinate axis, and the transverse aberration ΔY ′ (mm) along the abscissa axis.

In FIG. 3a, 3b are graphs of the transverse aberrations of the proposed system in the spectrum ranges from λ = 0.15 μm to λ = 0.254 μm and from λ = 0.254 μm to λ = 0.436 μm (Figs. 3c, 3d) for two tilt angles of the main beam with the axis systems 2ω = 2.5 ^o and 2ω = 1.25 ^o , where the ordinate of the entrance pupil shows the areas of the entrance pupil m (mm) and M (mm) in the meridional and sagittal sections, respectively, and the abscissa shows the values of the transverse aberrations Δy (mm ) in the meridional and ΔY (mm), ΔZ (mm) in the sagittal sections.

значения хроматизма увеличения. Из приведенных графиков видно, что данная хроматическая аберрация достаточно хорошо исправлена в спектральном диапазоне 0,15-0,436 мкм.In FIG. 4 shows graphs of the residual chromatism of increase, where ω ^o is half the angular field, a

chromatism values increase. From the graphs it can be seen that this chromatic aberration is quite well corrected in the spectral range of 0.15-0.436 μm.

 From FIG. 2 - 4 it is seen that the residual aberrations in the proposed system are small, this applies especially to the chromaticity of increase, which does not exceed 0.08% in the spectrum range 0.15-0.254 μm, and residual aberrations on the axis of the system, which, as shown by comparisons, significantly less than in the prototype.

In FIG. 5a, 5b are graphs of the frequency-contrast characteristics of the proposed lens in the spectrum range 0.15-0.254 μm and 0.254-0.436 μm, respectively, where T is the contrast and N (lines / mm) is the resolution. It can be seen that within the field of 2ω = 2.5 ^{o the} proposed lens allows at least 45 lines / mm with a contrast level of 40%. In the center of the field, the resolution rises to 62 lines / mm in the range of 0.15-0.254 microns and 150 lines / mm in the range of 0.254-0.436 microns.

Analysis of the data from [2] shows that in the spectrum range 0.185-0.250 μm the resolution of the prototype (at ⌀ 130 mm, relative aperture 1: 2.6 and field 2ω = 2.5 ^o ) is on average 10 lines / mm less than in the proposed system.

 Thus, the proposed lens for operation in the ultraviolet region of the spectrum has a higher resolution and, as can be seen from the above data, a significantly wider spectral range of operation.

 The proposed lens can be used to solve problems of detection, recognition and identification of observation objects in the atmosphere, as well as in astronomical telescopes operating in the ultraviolet region of the spectrum from 0.15 to 0.436 μm.

LITERATURE
1. Popov G.M. Modern astronomical optics. - M .: Science. Ch. ed. phys.- mat. lit., 1988 .-- 192 p.

 2. Wolf E. // Progress in Optics. - 1983 .-- V. 20.

Claims (1)

 A lens for operating in the ultraviolet region of the spectrum, comprising a main concave parabolic mirror, a secondary spherical mirror and a correction element made of lenses with the same refractive index, characterized in that the correction element consists of three lenses, the extreme lenses being negative and made in the form of menisci, facing concavity to the space of images, and the central one is biconvex.

Images