RU2086945C1 - Method of measurement of divergence angle of collimated bundle of rays - Google Patents

Abstract

FIELD: measuring equipment. SUBSTANCE: optical lens with focal length f′ assembles together the beam in the focal plane in the form of a light spot, its diameter d′ on the preset portion of energy of the maximum is measured, diameter d of the source light area on the same portion of energy of the maximum as d′ is measured, and the angle is calculated from relation

Description

 The invention relates to measuring equipment, namely to the field of light measurements, and can be used to control the angle of divergence.

 Known methods for controlling the angle of divergence. According to the focal spot method, the measurement method consists in collecting a beam of rays with a telephoto lens in the focal plane as a light spot / 1 /. The divergence angle is calculated from the ratio of this diameter to the focal length of the lens. The disadvantages of this method are associated with the inability to control the size of the source, as well as the sign of the angle of divergence, since the focal and prefocal spots are similar to each other.

 In another method, calibrated apertures are introduced into the focal plane of the lens, limiting the size of the focal spot at a given energy level / 2 /. The divergence angle is calculated from the ratio of this diameter to the focal length of the lens. The disadvantages of this method are associated with the inability to control the size of the source and the sign of the angle. The latter is due to the fact that the prefocal and focal spots are similar.

 The closest in technical essence is the method by which an optical lens with a known focal length f 'collects radiation in the focal plane in the form of a light spot, measure its diameter d' at a known fraction of the energy from the maximum and calculate the angle from the relation θ = d ′ / f ′ / 3 /. The disadvantage of this method is the inability to take into account the influence of the size of the source on the size of the focal spot, and also to control the sign of the angle, since the prefocal and focal spots are similar to each other, which reduces the accuracy of measurements and limits the functionality.

 The aim of the invention is to improve the accuracy and expansion of functionality.

после чего непрозрачным экраном перекрывают половину пучка и контролируют форму светового пятна в фокальной плоскости линзы.This goal is achieved by the fact that in the method measure the size of the light platform of the source and calculate the angle from the ratio

then half the beam is blocked with an opaque screen and the shape of the light spot in the focal plane of the lens is controlled.

-диаметр изображения источника I; Δ $\genfrac{}{}{0ex}{}{\text{1}}{\text{1}}$ ,Δ $\genfrac{}{}{0ex}{}{\text{1}}{\text{2}}$ - расфокусировка, соответствующая

Фиг. 2 световой треугольник, d диаметр световой площадки источника, R радиус кривизны волнового фронта, Δ стрелка прогиба волнового фронта, q угол расходимости.In FIG. 2 shows a diagram of the image of the source in positions I and II, d is the diameter of the light platform of the source, R is the radius of curvature of the wavefront, O _b lens, f 'focus,

- image diameter of source I; Δ $\genfrac{}{}{0ex}{}{\text{one}}{\text{one}}$ , Δ $\genfrac{}{}{0ex}{}{\text{one}}{\text{2}}$ - defocus corresponding

FIG. 2 light triangle, d is the diameter of the light platform of the source, R is the radius of curvature of the wavefront, Δ is the arrow deflection of the wavefront, q is the divergence angle.

FIG. 3 angle measurement scheme, d source light area diameter, O _b lens, F 'focal plane, d' focal spot diameter, Δ ¹ defocus corresponding to d ', 2 and 3 photodetector arrays.

FIG. 4 control circuit of the sign of the angle. q _{d is the} diffraction angle of divergence, θ ₁ , θ _{2 are} arbitrary divergence angles of “positive” and “negative” with respect to θ _d F 'the focal plane, C ₁ is the point of intersection of the extreme beam with the optical axis of the beam with divergence θ ₁ C _{2 the} point of intersection beam with the optical axis of the beam with divergence.

FIG. 5 view A half of the lens O _{b is} covered by an opaque screen 4.

могут превзойти размер d' (по фиг. 1).FIG. 6 image of the light spot in the focal plane at θ _d , θ ₁ , θ ₂
Sources of a collimated beam of rays having real finite dimensions are used in collimators, searchlights, and other optical devices (interferometers, microscopes). Therefore, the size of such sources (Fig. 1) affects the image size of the focal spot in accordance with the geometric construction of the source image in positions I and II. Since the divergence angle is estimated from the largest diameter of the focal spot (it is assumed that Δ $\genfrac{}{}{0ex}{}{\text{one}}{\text{one}}$ , Δ $\genfrac{}{}{0ex}{}{\text{one}}{\text{2}}$ are small and close to the focal plane), then the size of the source image

can exceed the size d '(in Fig. 1).

или

Формулу отрезков

из фиг. 1 можно представить в виде

После подстановки находим

Переходя к углу, получаем приближенное

и точное соотношение

Схема измерения угла в соответствии с полученным соотношением приведена на фиг. 3. Измеритель располагается вблизи от источника. В этом случае размер источника мало отличается от размера сечения пучка, в котором располагается линейка фотоприемников 1. Первый параметр размер источника d измеряется на той же доле энергии, на которой контролируется размер фокального пятна. Второй параметр d' измеряется путем контроля размера фокального пятна из анализа доли энергии в фокальной плоскости F' с помощью фотоприемников 2. Доля энергии, на которой производилась оценка пятна, определяет уровень энергии самого угла, рассчитываемого по измеренным d и d'. Возможность измерений на одной и той же доле энергии связана с тем, что оптическая линза в соответствии с

не влияет на распределение энергии.Consider the light triangle (Fig. 2), whence

or

Line formula

from FIG. 1 can be represented as

After substitution we find

Passing to the corner, we get the approximate

and exact ratio

The angle measurement scheme in accordance with the obtained ratio is shown in FIG. 3. The meter is located close to the source. In this case, the size of the source differs little from the size of the beam cross section in which the line of photodetectors is located 1. The first parameter, the size of the source d, is measured on the same fraction of the energy at which the size of the focal spot is controlled. The second parameter d 'is measured by controlling the size of the focal spot from the analysis of the fraction of energy in the focal plane F' using photodetectors 2. The fraction of the energy at which the spot was estimated determines the energy level of the angle itself, calculated from the measured d and d '. The possibility of measurements on the same fraction of energy is due to the fact that the optical lens in accordance with

does not affect energy distribution.

Depending on the change in the source’s operating mode (wear of its parts), the divergence angle can acquire “positive” angles θ ₁ and “negative” angles θ _2. Changing the sign of the angle in each case will increase the size of the focal spot relative to the spot for the diffraction angle θ _d To assess the sign of the angle half of the beam is blocked by an opaque screen (Fig. 6). Then, at the diffraction angle, half of the remaining beam will be collected in the focal plane F 'in the form of a light spot. Changing θ _d to θ ₁ and θ ₂ will lead to the fact that the extreme rays intersect with the optical axis, respectively, at points C ₁ and C ₂ . At the same time, in the focal plane in which the beam is controlled, light will be displayed half-spot either above the axis (at -θ ₂ ) or below the axis (at + θ ₁ ). Consequently, a change in the shape of the spot will indicate the sign of the angle of divergence.

Полученные расчетом близкие значения d' в заявленном способе указывают на то, что при больших R≈10⁵ мм влиянием размера источника можно пренебречь.Let the meter lens have f '= 300 mm, the diameter of the source d 40 mm, the image size of the source (equal to the maximum size x of the photodetector in the line) d' = 0.02 mm. Then according to the invention

The close values of d 'obtained by calculation in the claimed method indicate that at large R≈10 ⁵ mm the influence of the source size can be neglected.

находим

Если взять R 10000 мм, то при тех же параметрах d 1,2 мм. Полученные значения d' значительно превышают значения d', полученные из соотношения d′ = f′θ Следовательно, при переходе от R=10⁶ мм к R= 10⁴ мм и меньше размер фокального пятна, определенный размером источника, может превзойти размер определяемый расходимостью лучей. Способ позволяет учитывать размер источника и, следовательно, устранить погрешность, вызванную источником.When switching to small R, it is necessary to take into account the image size d '. Let R be 1000 mm, f '= 300 mm, d 40 mm. Then from the relation

we find

If we take R 10000 mm, then with the same parameters d 1.2 mm. The obtained values of d 'significantly exceed the values of d' obtained from the relation d ′ = f′θ Therefore, when passing from R = 10 ⁶ mm to R = 10 ⁴ mm or less, the size of the focal spot, determined by the size of the source, can exceed the size determined by the divergence rays. The method allows you to take into account the size of the source and, therefore, eliminate the error caused by the source.

При малых необходимо учитывать размер источника, что позволяет предложенный способ. Поэтому возможность измерений угла описываемым способом как для больших, так и малых, расширяет функциональные возможности по сравнению с прототипом. Кроме того, при измерениях угла расходимости, в особенности, импульсных источников, возникает неопределенность в определении знака угла. Введение непрозрачной шторки позволяет определить знак угла как непрерывных, так и импульсных источников, что расширяет функциональные возможности способа.When measuring the divergence angle for large, the size of the source can be neglected, and in this case, the calculation of the angle is possible both in accordance with the known relation d ′ = f′θ and the proposed

For small, it is necessary to take into account the size of the source, which allows the proposed method. Therefore, the ability to measure the angle in the described manner for both large and small, expands the functionality compared to the prototype. In addition, when measuring the angle of divergence, in particular, of pulsed sources, uncertainty arises in determining the sign of the angle. The introduction of an opaque curtain allows you to determine the sign of the angle of both continuous and pulsed sources, which extends the functionality of the method.

 The development of new methods for controlling the divergence angle is necessary in the manufacture of optical devices with light sources of collimators, microscopes, and interferometers. The creation of angle measuring instruments of increased accuracy is especially necessary in the process of assembly and manufacture of these devices. Providing such control already in the early stages will allow to identify errors in optical circuits and eliminate malfunctions, which will improve the quality of optical devices manufactured by the industry and will give a positive economic effect.

Claims (1)

A method for measuring the divergence angle of a collimated beam of rays, which consists in the fact that an optical lens with a given focal length f ', the beam is collected in the focal plane in the form of a light spot, its diameter d' is measured at a given fraction of the energy from the maximum, and the divergence angle is calculated, characterized in that that measure the diameter d of the light platform of the source at a given fraction of the energy from the maximum, similar to the measurement of d ', and the divergence angle is calculated from the ratio

then half of the beam is blocked by an opaque screen and the sign of the angle is controlled by the shape of the light spot in the focal plane of the lens.

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