RU2427814C1 - Method of measuring lens transmission coefficient - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: three controlled lenses are taken, the optical axes of which are parallel and foci of which are superimposed by two plane switching mirrors. Photometered pairs of lenses which are formed by the switching mirrors are successively placed in a collimated radiation flux. The first lenses in the pair are successively illuminated. Collimated radiation flux from second lenses is directed by the plane mirror into a photodetector system and picked up. The plane mirror directs the illuminating collimated radiation flux onto the photodetector system and the radiation flux is picked up at the input of the lenses. Without the controlled lenses, radiation flux reflected by the switching mirrors is picked up and the transmission coefficient of the lenses is determined using formulae given in the claim.

EFFECT: high measurement accuracy due to elimination of the effect of external factors owing to rapid formation of photometered pairs of lenses and virtually simultaneous photometering thereof.

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Description

The invention relates to photometry and spectrophotometry and can be used to determine the transmittance of lenses and lenses by the relative method mainly in the infrared region of the spectrum.

A known method of measuring the transmittance of a lens using a beam splitter (Problems of energy photometry. Collection of articles - M., Atomizdat. - 1979 - S. 63-69). The method consists in the fact that the measured lens, in the focus of which an autocollimation flat mirror is placed, is illuminated through a beam splitter with a collimated radiation beam. The photodetector signal U _{1 is} recorded, due to the radiation flux that passes through the lens, is reflected from the autocollimation mirror, again passes through the lens, and is reflected from the surface of the beam splitter. The lens is removed from the illuminating beam and the signal U ₂ corresponding to the level of 100% transmittance is recorded. The transmittance of the lens is determined by the formula:

The disadvantage of this method is the low accuracy of the measurements, due to the large loss of the radiation flux when passing through the beam splitter and the subsequent reflection of the photometric radiation flux from it, which limits the application of the method, especially when measuring in the infrared region of the spectrum.

Closest to the invention in technical essence is a method for measuring the transmittance of lenses (copyright certificate No. 1435980, MKI G01M 11/02, published 1988, Bull. No. 41), which consists in the fact that at least three lenses are taken as controlled, introduced into the radiation flux, in turn, their combinations of two sequentially mounted lenses, register the radiation fluxes at the output and input of the controlled lenses, the transmittance of the lenses is determined by the formulas.

In the method under consideration, the transmittance of the lenses is determined over a period of time, a significant part of which, in addition to the time spent on registering the radiation fluxes, is occupied by the lengthy tuning procedures associated with the formation of photometric pairs of lenses, with the movements of the photodetector and installing it in working provisions. In this regard, the duration of measurements, especially spectral, carried out, as a rule, in a wide working spectral transmission range of the lenses, can be several hours. During this time, the result of registration of radiation fluxes is influenced by external factors that change the parameters of the photodetector system, for example, a change in the sensitivity of the photodetector depending on the background situation, which causes a drift in the values of the detected fluxes. In addition, the fact of the movement of the photodetector can lead to significant registration errors. In view of the foregoing, the considered method for measuring the transmittance of lenses has low accuracy.

The technical result consists in increasing the accuracy of measuring the transmittance of the lens by eliminating the influence of external factors on the measurement result, which is achieved due to the rapid formation of photometric pairs of lenses and almost simultaneous (within a short period of time) photometry of them.

The technical result is achieved by the fact that in the method of measuring the transmittance of the lenses, which consists in taking at least three lenses as controlled, they are introduced into the radiation flux by combinations of two lenses in series, registering the radiation fluxes at the input and output of the controlled lenses and the transmittance of the lenses is determined by the formulas, the controlled lenses are set so that their optical axes are parallel to each other, while the foci of the lens They are combined with two flat commuting mirrors, photometric pairs of lenses are formed by commuting mirrors, sequentially illuminate the first pair of lenses with a collimated radiation flux, direct the collimated radiation fluxes coming out of the second lenses in the pair of lenses to the photodetector system and register them, direct the illuminated collimated lens with a flat mirror the radiation flux to the photodetector system and register the radiation flux at the entrance to the lenses, then without controlled lenses register the radiation flux reflected by the switching mirrors, and determine the transmittance of the lenses according to the formulas:

where τ ₁ , τ ₂ and τ ₃ are the transmittance of the lenses;

a - readings of the recording device for the radiation flux at the entrance to the lenses;

b - readings of the recording device for the radiation flux at the output of the first and third lenses;

c - readings of the recording device for the radiation flux at the output of the first and second lenses;

d - readings of the recording device for the radiation flux at the output of the second and third lenses;

, где e - показания регистрирующего прибора для потока излучения, отраженного от коммутирующих зеркал без контролируемых объективов.ρ is the reflection coefficient of the switching mirrors:

where e is the reading of the recording device for the radiation flux reflected from the switching mirrors without controlled lenses.

The drawing shows an optical diagram of a device that implements the proposed method for measuring the transmittance of the lenses.

The device contains controlled lenses 1, 2, 3, two flat commuting mirrors 4 and 5, each of which is equipped with a linear displacement mechanism along an axis perpendicular to the optical axes of the controlled lenses, a radiation source 6, in the form of a monochromator output slit, a lens 7 forming a collimated stream radiation, and an aperture diaphragm 8 and a flat mirror 9 with a linear displacement mechanism along the optical axis of the radiation flux perpendicular to the optical the number of monitored lenses, a flat mirror 10 with a linear movement mechanism along the optical axis of the photometric fluxes perpendicular to the optical axes of the monitored lenses and a 90 ° rotation mechanism, the lens 11 and a photodetector system containing a photodetector 12 located in the focal plane of the lens 11, the recording device 13 .

The measurement method is as follows.

Install flat switching mirrors in positions 4 and 5 and form a photometric pair of the first and third lenses. The controlled lens 1 is illuminated with a collimated radiation flux reflected from a flat mirror 9 set to position I. The collimated flux coming out of the controlled lens 3 is directed with a flat mirror 10 in position II onto the lens 11 and the reading device 13 is taken for the output radiation flux 1 and 3 lenses b = L · τ ₇ · ρ ₉ · τ ₁ · ρ ₄ · ρ ₅ · τ ₃ · ρ ₁₀ · τ ₁₁ , the value of which is proportional to the brightness of the radiation source L, the transmittance τ _{7 of the} lens 7, the reflection coefficient ρ ₉ flat mirror positions la 9, transmittance τ ₁ and τ ₃ controlled lenses 1 and 3, reflection coefficients ρ ρ ₄ and _5, switching mirrors 4 and 5, the reflectance ρ ₁₀ of the flat mirror 10 and a transmittance τ ₁₁ of the lens 11.

Set the switching mirror 5 in position 5 '(the point of intersection of the optical axes of the lenses 1 and 2) and form a photometric pair of the first and second controlled lenses. Set the flat mirror of the photodetector system 10 to position I and take a reading of the recording device for the radiation flux at the output of 1 and 2 lenses c = L · τ ₇ · ρ ₉ · τ ₁ · ρ ₄ · ρ ₅ · τ ₂ · ρ ₁₀ · τ ₁₁ .

The switching mirrors are installed in positions 5 and 4 '(the point of intersection of the optical axes of the lenses 2 and 3) and form a photometric pair of the second and third controlled lenses. Set flat mirrors 9 and 10 in position II. Take the reading of the recording device for the radiation flux at the output of 2 and 3 lenses d = L · τ ₇ · ρ ₉ · τ ₂ · ρ ₄ · ρ ₅ · τ ₃ · ρ ₁₀ · τ ₁₁ .

Set the flat mirror 10 to position III and take the reading of the recording device for the radiation flux at the entrance to the controlled lenses a = L · τ ₇ · ρ ₉ · ρ ₁₀ · τ ₁₁ .

The readings of the recording device a, b, c and d are taken at each wavelength within the working spectral range of the controlled lenses.

Without controlled lenses, the reflection coefficient of switching mirrors is measured. To do this, set the flat mirror 10 to position II, direct the collimated radiation flux to the first switching mirror installed in position 4. Reflected by the switching mirrors 4 and 5, the radiation flux by the flat mirror 10 is directed to the lens 11 and take the reading of the recording device e = L Τ ₇ · ρ ₉ · ρ ₄ · ρ ₅ · ρ ₁₀ · τ ₁₁ . From the ratio of the readings of the recording device e / a, the reflection coefficient of the switching mirrors ρ is determined. The coefficient ρ is measured at wavelengths within the working spectral range of the monitored lenses.

;

;

.Using the readings of the recording device, the transmittance of the lenses is determined:

;

;

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The method of measuring the transmittance of the lenses allows you to perform the sequential registration of signals a, b, c and d for a time not exceeding 3-4 minutes, taking into account the time required to install the flat moving mirrors in the working position.

Claims (1)

The method of measuring the transmittance of the lenses, which consists in the fact that three lenses are taken as controlled, their combinations are inserted into the radiation flux, two sequentially mounted lenses in succession, the radiation fluxes at the input and output of the controlled lenses are recorded and the transmittance of the lenses is determined by the formulas, characterized in that controlled lenses are set so that their optical axes are parallel to each other, while the foci of the lenses combine two flat commutations They can be used to create photometric pairs of lenses with commuting mirrors, sequentially illuminate the first pair of lenses with a collimated radiation flux, direct the collimated radiation flux emerging from the second lenses in the pair of lenses to the photodetector system and register them, direct the illuminated collimated radiation flux to the photodetector with a flat mirror system and register the radiation flux at the entrance to the lenses, then without controlled lenses register the radiation flux, reflecting nny switching mirrors and lenses define the transmission ratio by the formulas

where τ ₁ , τ ₂ and τ ₃ are the transmittance of the lenses;
a - readings of the recording device for the radiation flux at the entrance to the lenses;
b - readings of the recording device for the radiation flux at the output of the first and third lenses;
c - readings of the recording device for the radiation flux at the output of the first and second lenses;
d - readings of the recording device for the radiation flux at the output of the second and third lenses;
ρ is the reflection coefficient of commuting mirrors, equal to

where e is the reading of the recording device for the radiation flux reflected from the switching mirrors without controlled lenses.