Laser wavefront phase measuring device based on heterodyne shearing interference

Abstract

The utility model discloses a laser wavefront phase measuring device based on heterodyne shearing interference. The device comprises a light source system, an amplification system, a heterodyne shearing interference system and an image acquisition system. Laser beams emitted by the light source system are reflected to a measured plane, and the laser beams carrying phase information of the measured plane pass through the amplification system, then pass through the heterodyne shearing interference system for self-reference heterodyne interference and finally pass through the image acquisition system for acquisition. Compared with a conventional laser wavefront detection scheme, the device provided by the utility model is more compact in structure, lower in implementation cost, and higher in stability and accuracy compared with a conventional interference measurement device.

Description

Technical Field

[0001] The utility model relates to the technical field of laser wavefront detection, in particular to a laser wavefront phase measurement device based on heterodyne shearing interference. Background Art

[0002] Optical interferometry is a technology that uses the principle of light interference for non-contact measurement. Conventional interferometry devices usually use a beam splitter to split a light beam into two beams, one as a reference light and the other as a detection light that is transmitted or reflected through the object being measured. The two beams pass through different paths and are finally superimposed on the detector to form an interference pattern. However, since the reference light and the detection light pass through different paths and optical devices, any one of the light beams is subject to thermal disturbance or mechanical vibration, which will have a huge impact on the final interference superposition pattern. Therefore, this type of interferometry device often has high requirements for the experimental environment.

[0003] Shearing interferometry is a self-referenced interferometry technology that uses a simple optical structure or optical device to divide the laser wavefront to be measured into two beams, one of which moves laterally or radially relative to the other. The two dislocated light waves each maintain complete wavefront information to be measured, and they are superimposed on each other to produce interference. Taking the most common lateral shearing interference as an example, the light wave to be measured is superimposed and interfered with its own dislocated light wave. The optical path difference between the two coherent light beams is very small, close to equal optical path interference, so it can be applied to conventional coherent light sources and partially coherent light source scenes. Since the two beams of light pass through the same optical element, external vibrations or thermal disturbances have the same effect on the two beams of light waves and can cancel each other out, so it has a strong anti-interference ability, and it requires fewer optical elements, and the overall space occupancy rate of the optical path structure is also low.

[0004] Laser heterodyne interferometry technology uses electrical, acoustic, mechanical and other frequency shifting methods to produce a fixed frequency difference between the signal light and the reference light, and obtain dynamic interference fringes that change with time. Laser heterodyne interferometry technology obtains the measured physical quantity by modulating and demodulating the interference signal, and has the advantages of good anti-interference, large measurement range, high measurement accuracy and resolution. Utility Model Content

[0005] Based on the combination of the above-mentioned multiple technologies, the purpose of the utility model is to provide a laser wavefront phase measurement device based on heterodyne shearing interferometry. The measuring device includes a light source system, an amplification system, a heterodyne shearing interferometry system and an image acquisition system. The main body of the light source system adopts a 632.8nm helium-neon laser, the amplification system is composed of a semi-transparent and semi-reflective mirror, a microscope objective, a plane to be measured, and a reflection plane, the heterodyne shearing interferometry system is composed of a convex lens, a grating, a linear translation stage, a stepping motor, and an aperture, the image acquisition system is composed of a CMOS or CCD camera, and the measuring device is as shown in the attached Figure 1shown.

[0006] In order to better realize the present invention, the following configuration is particularly adopted: the light source system (1) mainly adopts a 632.8 nm helium-neon laser.

[0007] In order to better realize the utility model, the following configuration is particularly adopted: the magnification system is composed of a semi-transparent and semi-reflective mirror (2a), a microscope objective lens (2b), a plane to be measured (2c), and a reflection plane (2d).

[0008] In order to further implement the utility model in a better manner, the following configuration is particularly adopted: the semi-transparent and semi-reflective mirror (2a) is placed at an angle of 45° so that the laser emitted by the light source system (1) is reflected into the microscope objective lens (2b).

[0009] In order to better realize the utility model, the following configuration is particularly adopted: the light source system (1) emits a laser beam which is incident on a semi-transparent and semi-reflective mirror (2a), and the reflected beam passes through a microscope objective lens (2b) and is incident on a plane to be measured (2c).

[0010] In order to further better realize the utility model, the following setting structure is particularly adopted: the reflection plane (2d) reflects the light beam carrying the wavefront phase information of the plane to be measured (2c), so that it returns along the original light path, is collimated by the microscope objective lens (2b), and then passes through the semi-transparent and semi-reflective mirror (2a).

[0011] In order to better realize the utility model, the following setting structure is particularly adopted: the heterodyne shearing interference system (3) is located after the amplification system (2), and is composed of a convex lens A (3a), a grating (3b), a linear translation stage (3c), a stepping motor (3d), an aperture (3e), and a convex lens B (3f).

[0012] In order to further better realize the utility model, the following configuration structure is particularly adopted: the A convex lens (3a) converges the light beam, and then passes through the grating (3b) to generate multiple beams of diffracted light.

[0013] In order to further better realize the utility model, the following setting structure is particularly adopted: the aperture (3e) is placed at the focal plane of the A convex lens (3a) to select any two diffracted light beams of different orders.

[0014] In order to better realize the utility model, the following setting structure is particularly adopted: the grating (3b) is placed on a linear translation stage (3c) driven by a stepping motor (3d), and the moving path of the linear translation stage (3c) is perpendicular to the optical axis of the light beam. Due to the Doppler effect of the light beam and the moving grating (3b), any two diffracted light beams of different orders have a frequency difference of 1 Hz to kHz.

[0015] In order to further better realize the utility model, the following configuration structure is particularly adopted: the B convex lens (3f) enables the two diffracted light beams to be imaged to the image acquisition system (4).

[0016] In order to further better implement the present invention, the following configuration is particularly adopted: the image acquisition system (4) is a CMOS or CCD camera (4a).

[0017] In order to better realize the utility model, the following setting structure is particularly adopted: the CMOS or CCD camera (4a) is placed in a position so that any two diffracted light beams of different orders have a lateral position difference of several tens of pixels on the target surface of the CMOS or CCD camera (4a), and the two light beams interfere with each other, and an interference pattern of a series of fringes moving over time as shown in (4b) is obtained on the receiving surface of the CMOS or CCD (4a).

[0018] In summary, the utility model has the following beneficial effects and advantages:

[0019] The utility model combines the advantages of heterodyne and shearing interference, and uses a common commercial motor to drive the grating to achieve heterodyne interference, further reducing the experimental cost. The two light beams pass through the same optical element, making the optical path compact, the space utilization rate high, and the anti-interference ability strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to better illustrate the technical solutions involved in the embodiments and devices of the utility model, the following is a brief description of the drawings required for use in the embodiments and technical descriptions. Obviously, the drawings introduced below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on the drawings without any creative work.

[0021] Figure 1 It is a schematic diagram of the overall structure of the utility model;

[0022] The numbers in the figure are:

[0023] 1—light source system; 1a—laser;

[0024] 2—magnification system; 2a—semi-transparent and semi-reflective mirror; 2b—microscope objective lens; 2c—surface to be measured; 2d—reflection plane;

[0025] 3—heterodyne shearing interferometer system; 3a—A convex lens; 3b—grating; 3c—linear translation stage; 3d—stepping motor; 3e—aperture; 3f—B convex lens;

[0026] 4—Image acquisition system; 4a—CMOS or CCD camera; 4b—Schematic diagram of two-beam interference. DETAILED DESCRIPTION

[0027] In order to more clearly demonstrate the technical solutions and device advantages involved in the utility model, the technical details and specific implementation methods of the utility model are described in detail below:

[0028] The utility model provides a laser wavefront phase measurement device based on heterodyne shearing interferometry, which mainly includes a light source system, an amplification system, a heterodyne shearing interferometry system and an image acquisition system. The main body of the light source system adopts a 632.8nm helium-neon laser. The amplification system is composed of a semi-transparent and semi-reflective mirror, a microscope objective lens, a plane to be measured, and a reflection plane. The heterodyne interferometry system is composed of a convex lens, a grating, a linear translation stage, a stepping motor, and an aperture. The image acquisition system is composed of a CMOS or CCD camera.

[0029] Embodiment 1:

[0030] The light source system (1) is turned on, and the position of the semi-transparent and semi-reflective mirror (2a) is adjusted so that the laser emitted by the light source system (1) is incident on the semi-transparent and semi-reflective mirror (2a) at a 45° angle, and its reflected light beam is vertically incident on the microscope objective lens (2b) and then irradiates the measured plane (2c). The measured wavefront is reflected by the reflection plane (2d) and returns along the original light path, is collimated by the microscope objective lens (2b), and enters the heterodyne shearing interference system (3) through the semi-transparent and semi-reflective mirror (2a). The light beam is converged through the A convex lens (3a), and then passes through the grating (3c) to generate multiple diffracted lights. At this time, the distance between the grating (3b) and the A convex lens (3a) is changed, and the -1 and +1 order diffracted light beams are selected for shearing interference, and the separation degree between the -1 and +1 order diffracted light beams is observed, so that there is a lateral position difference of about several tens of pixels between the two diffracted light beams on the detection surface of the CMOS or CCD camera (4a), as shown in (4b). The position and size of the aperture (3b) are adjusted so that only the -1 and +1 order diffracted beams pass through. The stepper motor (3d) is started, and the belt is used to link with the linear moving platform (3c), and the grating (3b) moves at a constant speed. By adjusting the exposure and integration time of the CMOS or CCD camera (4a), it is possible to observe stably moving stripes with high contrast as shown in (4b).

[0031] The above description is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention.

Claims

1. A laser wavefront phase measurement device based on heterodyne shearing interferometry, comprising a light source system (1), an amplification system (2), a heterodyne shearing interferometry system (3) and an image acquisition system (4), characterized in that: The light source system (1) is composed of a laser, the amplification system (2) is composed of a semi-transparent and semi-reflective mirror (2a), a microscope objective lens (2b), a plane to be measured (2c), and a reflection plane (2d), the heterodyne shearing interferometer system (3) is composed of a convex lens A (3a), a grating (3b), a linear translation stage (3c), a stepping motor (3d), an aperture (3e), and a convex lens B (3f), and the image acquisition system (4) is composed of a CMOS or CCD (4a) camera.

2. The laser wavefront phase measurement device based on heterodyne shearing interferometry according to claim 1, characterized in that: The light source system (1) usually adopts a 632.8nm helium-neon laser.

3. The laser wavefront phase measurement device based on heterodyne shearing interferometry according to claim 1, characterized in that: The laser beam emitted by the light source system (1) first enters the amplification system (2), and is incident on the semi-transparent and semi-reflective mirror (2a) at 45 degrees. The reflected beam passes through the microscope objective lens (2b) and is emitted to the plane to be measured (2c). The beam carrying the wavefront phase information of the plane to be measured (2c) is reflected by the reflection plane (2d) and returns along the original optical path. It is collimated by the microscope objective lens (2b) and then passes through the semi-transparent and semi-reflective mirror (2a).

4. The laser wavefront phase measurement device based on heterodyne shearing interferometry according to claim 1, characterized in that: After passing through the amplification system (2), the light beam enters the heterodyne shearing interferometer system (3), first passes through a convex lens A (3a) to converge the light beam, and then passes through a grating (3b) to generate multiple diffracted lights. An aperture (3e) is placed at the focal plane of the convex lens A (3a) to select any two diffracted light beams of different orders. The grating (3b) is placed on a linear translation stage (3c) driven by a stepper motor (3d), and the moving path of the linear translation stage (3c) is perpendicular to the optical axis of the light beam. Due to the Doppler effect of the light beam and the moving grating (3b), there is a frequency difference of 1 Hz to kHz between the frequencies of any two diffracted light beams of different orders.

5. The laser wavefront phase measurement device based on heterodyne shearing interferometry according to claim 1, characterized in that: In the image acquisition system (4), the CMOS or CCD (4a) camera is placed at the end, and its placement position allows any two selected diffracted light beams of different orders to interfere with each other on the target surface of the CMOS or CCD (4a) as shown in (4b), and an interference pattern of a series of fringes moving over time is obtained on the receiving surface of the CMOS or CCD (4a).

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