CN100587443C - Large aperture stray light coefficient test method and system based on computer holographic optical element - Google Patents

Abstract

The invention relates to a stray light coefficient testing method and a system thereof, in particular to a large-caliber stray light coefficient testing method and a system thereof based on a computer-generated holographic element. The technical solution is as follows: the method comprises the following steps: 1) expanding the emergent laser beam into large-caliber parallel light; 2) irradiating the large-caliber parallel light onto a computer holographic optical element to obtain a hollow light beam; 3) after the hollow light beam is emitted into the optical system to be detected, a black spot area surrounded by a bright light area is formed on the back focal plane of the optical system to be detected; 4) respectively measuring the illuminance E of black spot areas_bAnd illuminance E of the bright area_w(ii) a 5) According to the formula E ═ E (E)_b/E_w) X 100% gives the veiling glare coefficient e. The technical problems that the test is inconvenient and the realization difficulty is difficult in the common technology are solved.

Description

Large aperture stray light coefficient test method and system based on computer holographic optical element

technical field

The invention relates to a stray light coefficient testing method and system thereof, in particular to a large-aperture stray light coefficient testing method and system based on a computer holographic optical element.

Background technique

The development of large-aperture imaging optical systems has greatly promoted the development of various related technologies. As an important indicator of the optical system, its stray light level can have an important impact on the imaging contrast and resolution of the imaging optical system, especially in some In the field of detection applications, the level of stray light directly affects the improvement of detection capabilities, so the design and detection of stray light in the optical system is imperative. From the research in related fields at home and abroad, the evaluation and inspection of the level of stray light is mainly solved by testing the two parameters of point source transmittance (PST) and stray light coefficient (V).

In China, the inspection of PST parameters of large-aperture optical systems is mainly completed by using a laser-illuminated collimator and a turntable. Since the PST parameters are mainly estimated for the stray light caused by point light sources, they cannot be used to evaluate the level of stray light in the application of space optics to Earth observation with the Earth as the background.

Theoretically, the measurement of the stray light coefficient can be realized by using a large-aperture integrating sphere as a uniform surface light source with a black target. In this method, the opening diameter of the large-aperture integrating sphere must exceed the caliber of the optical system to be tested, and a collimating optical lens of the same caliber must be installed at the exit, and the exit diameter of the large-aperture integrating sphere should be less than 1/3 of its diameter. When the optical aperture of the optical system under test exceeds 500mm, the aperture of the integrating sphere and collimating optical lens becomes unrealizable, so there has never been a method to solve the stray light test of the large aperture optical system.

Contents of the invention

The invention solves the above-mentioned technical problems existing in the background technology, and provides a large-aperture stray light coefficient testing method and system thereof which are convenient for testing and less difficult to implement.

The technical solution of the present invention is: the present invention is a large-aperture stray light coefficient testing method based on computer holographic optical elements, and its special feature is that the method includes the following steps:

1) Expand the outgoing laser beam into a large-aperture parallel light;

2) irradiating the large-aperture parallel light onto the computer holographic optical element to obtain a hollow beam;

3) After injecting the hollow beam into the optical system to be tested, a black spot area surrounded by bright light areas is formed on the back focal plane of the optical system to be tested;

4) Measure the illuminance E _b of the dark spot area and the illuminance E _w of the bright light area respectively;

5) According to the formula $e=\frac{{\mathrm{E.}}_b}{{\mathrm{E.}}_w}\×100\%$ Get the stray light coefficient e.

In the above step 5), the radiometer can be used to calibrate the radiance at each exit angle to obtain the correction curve C (ω, ψ), and the formula of the stray light coefficient e is corrected as $e=\frac{{\mathrm{E.}}_b}{{\mathrm{E.}}_w}\×C(\mathrm{\ω},\mathrm{\ψ})\×100\%.$

A test system for realizing the above-mentioned large-aperture stray light coefficient test method based on computer holographic optical elements. , the laser, the large-aperture collimator, and the computer holographic optical element are sequentially arranged on the same optical path.

A folded axis reflector is arranged between the laser and the large-diameter collimator.

The above test system also includes a radiometer capable of radiance calibration.

The present invention has the following advantages:

1. The present invention uses a large-diameter collimator for laser illumination and a large-diameter computer holographic optical element (CGH) placed at the pupil to simulate the black target under the bright background that produces infinity, and the computer holographic optical element (CGH) As a key component, its aperture can be equivalent to the optical system to be tested. It does not need to use a large-aperture integrating sphere and collimating optical system to realize the test of the stray light coefficient of the large-aperture optical system. At the same time, the CGH used has no According to the requirements of the center, it is less difficult to prepare, and large-diameter CGH can be spliced by film pressing, so it can be made on plastic film under the condition that the definition of the edge of the black target is not affected by the flatness of the CGH element. Therefore, the method of the utility model can be used to measure the stray light coefficient no matter how large the aperture optical system is, so as to fundamentally solve the measurement problem of the stray light coefficient of the large aperture optical system.

2. Light weight and small size. The entire system for realizing the method of the invention is light in weight and small in size, and can conveniently realize the measurement of the optical system with large aperture.

Description of drawings

Fig. 1 is a schematic structural diagram of the testing system of the present invention.

Detailed ways

Concrete method steps of the present invention are as follows:

1) Expand the outgoing laser beam into a large-aperture parallel light;

2) irradiating the large-aperture parallel light onto the computer holographic optical element to obtain a hollow beam;

3) After injecting the hollow beam into the optical system to be tested, a black spot area surrounded by bright light areas is formed on the back focal plane of the optical system to be tested;

4) Measure the illuminance E _b of the dark spot area and the illuminance E _w of the bright light area respectively;

5) According to the formula $e=\frac{{\mathrm{E.}}_b}{{\mathrm{E.}}_w}\×100\%$ Get the stray light coefficient e. Since the _Ew caused by the design and manufacturing error of the computer holographic optical element (CGH) will change with the change of the illumination angle and the exit angle, the radiometer can be used to calibrate the radiance at each exit angle, and the correction curve C( ω, ψ), modify the formula of stray light coefficient e as $e=\frac{{\mathrm{E.}}_b}{{\mathrm{E.}}_w}\×C(\mathrm{\ω},\mathrm{\ψ})\×100\%,$ In order to eliminate the error caused by the computer holographic optical element, the measured stray light coefficient is more accurate.

Referring to Fig. 1, the test system of the present invention includes a laser 1, a large-aperture collimator 5 and a computer holographic optical element 6 arranged in sequence on the same optical path, and an illuminance meter 4 capable of measuring illuminance, a laser 1 and a large-aperture parallel light Refractive mirrors 2 can also be arranged between the tubes 5, which can refract the laser light emitted by the laser 1, making the test system of the present invention compact; degree meter.

When the testing system of the present invention works, the laser 1 emits laser light of a certain power, which is collimated into a parallel beam through the large-aperture collimator 5, and irradiated on the large-aperture computer holographic optical element (CGH) 6 to obtain a so-called hollow beam. That is, by the beam decomposition ability of the computer holographic optical element, the parallel beam is transformed into a zero-order angle, and the light energy is evenly decomposed into other angle ranges, thus forming a uniform surface light source with a black target corresponding to infinity . At this time, if the optical axis of the optical system under test 3 is aligned with the zero-order position of the computer holographic optical element 6 , an optical background image purely caused by stray light can be obtained on the focal plane of the optical system under test 3 . By staggering the optical axes of the two, the response of the optical system under a uniformly bright object can be obtained. The illuminance of the stray light background image and the focal plane image illuminance of a uniformly bright target are measured by the illuminance meter 4 , and the ratio of the illuminance of the two images is corresponding to the stray light coefficient.

Glossary:

Hollow beam: It means that a certain beam has no light radiation in a specific solid angle area (generally conical), but has uniform light radiation in other solid angle areas in the half space.

Claims (5)

1. A large aperture stray light coefficient testing method based on computer holographic optical elements, characterized in that: the method comprises the following steps: 1) Expand the outgoing laser beam into a large-aperture parallel light; 2) irradiating the large-aperture parallel light onto the computer holographic optical element to obtain a hollow beam; 3) After injecting the hollow beam into the optical system to be tested, a black spot area surrounded by bright light areas is formed on the back focal plane of the optical system to be tested; 4) Measure the illuminance E _b of the dark spot area and the illuminance E _w of the bright light area respectively; 5) According to the formula $e=\frac{{\mathrm{E.}}_b}{{\mathrm{E.}}_w}\×100\%$ Get the stray light coefficient e. 2. The large-aperture stray light coefficient test method based on computer holographic optical elements according to claim 1, characterized in that: in the step 5), the radiometer can be used to calibrate the radiance at each exit angle, and the correction is obtained. Curve C(ω, ψ), correct the formula of stray light coefficient e as $e=\frac{{\mathrm{E.}}_b}{{\mathrm{E.}}_w}\×C(\mathrm{\ω},\mathrm{\ψ})\×100\%.$ 3. A test system for realizing the large-aperture stray light coefficient test method based on computer holographic optical elements according to claim 1, characterized in that: the system includes a laser, a large-aperture collimator, a computer holographic optical element, and a measurable An illuminance meter for illuminance, the laser, the large-diameter collimator, and the computer holographic optical element are sequentially arranged on the same optical path. 4. The test system according to claim 3, characterized in that: a folding axis reflector is arranged between the laser and the large-aperture collimator. 5. The test system according to claim 3 or 4, characterized in that the test system further comprises a radiometer capable of radiance calibration.

Images