CN118624036A - A synchronous phase-shifting interferometer device and method based on Wollaston prism - Google Patents

Abstract

The invention discloses a synchronous phase-shifting interference device and method based on a Wollaston prism. The device comprises: a first beam splitting prism, a first quarter wave plate, a first reflector, a second reflector, a second quarter wave plate, a third quarter wave plate, a second beam splitting prism, a Wollaston prism, an imaging lens, and a camera; the first beam splitting prism is used for uniformly splitting the test light and the reference light incident with orthogonal linear polarization, and the transmission light path is the first light path and the reflected light beam is the second light path, both of which contain the test light and the reference light; the first light path passes through the first quarter wave plate and the first reflector in sequence and then enters the second beam splitting prism; the second light path passes through the second reflector, the second quarter wave plate, and the third quarter wave plate in sequence and then enters the second beam splitting prism; the light beams of the first light path and the second light path enter the second beam splitting prism and are incident on the Wollaston prism to be split into four beams and generate phase-shifting interference; after passing through the imaging lens, four synchronous phase-shifting interference images with a phase shift of 90 degrees are obtained on the camera.

Description

A synchronous phase-shifting interferometer device and method based on Wollaston prism

Technical Field

The invention belongs to the technical field of laser interferometry, and in particular to a synchronous phase-shifting interference device and method based on a Wollaston prism.

Background Art

Optical phase-shifting interferometry is a non-contact, high-precision full-field measurement method that is widely used in the field of optical phase measurement. It introduces a relative phase change between the reference wave and the test wave, collects multiple phase-shifting interference images accordingly, and uses a phase-shifting algorithm to demodulate the wavefront phase to be measured.

Time-domain phase-shifting interferometry collects multiple phase-shifting interferometry images at different times. The measurement results are easily affected by environmental factors such as vibration, and random errors are easily introduced during the phase-shifting process. Therefore, it is only suitable for static or quasi-static measurements. Synchronous phase-shifting interferometry obtains multiple phase-shifting interferometry images at the same time and different spatial positions, which can overcome the shortcomings of time-domain phase-shifting interferometry and realize dynamic measurement.

Robert M. Neal et al. (Polarization phase-shifting point-diffraction interferometer. Applied Optics, 2006, 45(15): 3463-3476) proposed a synchronous phase-shifting interferometer based on prism splitting and polarization phase shifting. In this device, the reference light and the test light are separated from each other. Compared with the common optical path system, this device is easily affected by environmental factors such as air disturbance, and has a relatively large structure and uses more optical components.

The patent (application number: 20100034450.4) uses ordinary beam splitters and polarization beam splitters to split the incident light, and combines polarization phase-shift interference to form multiple phase-shift interference images at different spatial positions, which are received by multiple CCD cameras. This method requires the use of multiple cameras, which is costly and has a large system size.

Chen Lei et al. (Synchronous phase-shifting interferometry based on two-dimensional grating spectrometry, Acta Optica Sinica, 2007, 27(4): 663-667) used two-dimensional grating spectrometry and polarization phase shifting to synchronously collect four frames of phase-shifting interferometry images. The main problems of this technology are: the two-dimensional grating needs to be precisely processed; it is difficult to ensure that the separated diffracted light beams have a consistent light intensity distribution, which affects the accuracy of wavefront restoration; and the light energy utilization rate is low.

There is also a method that uses a micro-polarizer array to achieve synchronous phase shifting, in which the micro-polarizer array mask needs to be strictly matched with the CCD pixel. The mask needs to be precisely processed and has a high production cost, which affects its promotion and application.

Summary of the invention

The purpose of the present invention is to overcome the shortcomings of the existing synchronous phase-shifting interference technology and provide a synchronous phase-shifting interference device and method based on a Wollaston prism. The synchronous phase-shifting interference device can be used in the case where the reference light and the test light share a common path. The structure is compact, the components used are common components, no special production is required, and the debugging is convenient. The synchronous phase-shifting interference method is simple in principle, and the phase distribution to be measured can be restored by obtaining four frames of phase-shifting interference images at the same time.

In order to achieve the above object, the present invention adopts the following technical solutions:

A synchronous phase-shifting interferometer based on a Wollaston prism, comprising: a first beam splitting prism, a first 1/4 wave plate, a first reflector, a second reflector, a second 1/4 wave plate, a third 1/4 wave plate, a second beam splitting prism, a Wollaston prism, an imaging lens, and a camera;

The first beam splitter prism is used to evenly split the orthogonally linearly polarized incident test light and reference light, and the transmission light path is the first light path and the reflected light beam is the second light path, both of which contain the test light and the reference light;

The first optical path passes through the first 1/4 wave plate and the first reflector in sequence and then enters the second beam splitting prism; the second optical path passes through the second reflector, the second 1/4 wave plate, and the third 1/4 wave plate in sequence and then enters the second beam splitting prism; the light beams of the first optical path and the second optical path enter the second beam splitting prism and are incident on the Wollaston prism to be split into four beams and generate phase shift interference, and after passing through the imaging lens, four synchronous phase shift interference images with a phase shift of 90° are obtained on the camera.

More preferably, the angle between the fast axis direction of the first quarter wave plate and the fast (or slow) axis of the incident linear polarized light is 45°.

More preferably, the angle between the fast axis direction of the second quarter wave plate and the fast (or slow) axis of the incident linear polarized light is 0°.

More preferably, the angle between the fast axis direction of the third quarter wave plate and the fast (or) axis of the incident linear polarization light is 45°.

More preferably, the applicable wavelengths of the first 1/4 wave plate, the second 1/4 wave plate and the third 1/4 wave plate are consistent with the wavelength of the laser.

More preferably, when selecting the beam splitting angle of the Wollaston prism, the optical device parameters are combined and the object-image relationship between the Wollaston prism and the imaging lens is calculated, and the vertical axis magnification formula (1), the Gaussian formula (2), and the height D of the beam incident on the imaging lens after the beam splitting are derived and calculated by the formula (3):

D＝2(-l×tanu+y) (3)

Where l is the object distance, l′ is the image distance, y is the beam aperture, i.e. the size of the object, y′ is the size of the image, f′ is the focal length of the imaging lens, u is the beam splitting angle of the Wollaston prism, and D is the height of the beam incident on the imaging lens after splitting;

Combining the above formulas (1) to (3), we can get the relationship between the beam splitting angle of the Wollaston prism:

More preferably, the optimal beam splitting angle of the Wollaston prism is 5°.

A synchronous phase-shifting interference method based on Wollaston prism is implemented based on the device, and the steps are as follows:

(1) In the dual-path interference system, the test beam and the reference beam are incident on the first beam splitting prism in the device along the same optical path, and the test beam and the reference beam are orthogonally linearly polarized lights;

(2) The test beam and the reference beam are simultaneously incident on the first beam splitting prism for beam splitting, the first light path is transmitted through the beam splitting prism, and the second light path is reflected through the beam splitting prism, and both the first light path and the second light path contain the test light and the reference light;

(3) The reference light and the test light in the first optical path pass through the first quarter wave plate and then enter the second beam splitter prism through the first reflector, and the reference light and the test light in the second optical path pass through the second reflector and then enter the second quarter wave plate and the third quarter wave plate and then enter the second beam splitter prism;

(4) The reference light and the test light in the first optical path are converted into left-handed and right-handed circularly polarized light after passing through the first quarter-wave plate; the reference light and the test light in the second optical path are converted into left-handed and right-handed circularly polarized light after passing through the second quarter-wave plate without changing the polarization state, but a 90° phase shift is introduced, and then the reference light and the test light are converted into left-handed and right-handed circularly polarized light after passing through the third quarter-wave plate;

(5) The first light path and the second light path enter the second beam splitting prism, pass through the Wollaston prism, are split into four beams and generate phase-shift interference, and after passing through the imaging lens, four synchronous phase-shift interference images with a phase shift of 90° are obtained on the camera, with intensities of I _0° , I _90° , I _180° , and I _270° ;

(6) The four-step phase shifting algorithm is used to process the four phase shifting interference images and calculate the phase distribution to be measured.

More preferably, the camera can be implemented by using a dual camera. Specifically, the first optical path and the second optical path are imaged separately, and two cameras are used to obtain two phase-shift interference images respectively.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention realizes synchronous phase shifting of the reference light and the measured light in the same optical path, which can overcome the influence of factors such as environmental vibration and air disturbance to the greatest extent and reduce the source of system errors.

(2) The present invention is applicable to a system in which the test light and the reference light share a common optical path, such as a circular path shearing system, and is also applicable to a system in which the test light and the reference light do not share a common optical path, such as a Twyman-Green interferometer system.

(3) The manufacturing process of the key component (Wollaston prism) used in the present invention is mature and the cost is low; the Wollaston prism can evenly split the circularly polarized light into two beams. Compared with two-dimensional grating beam splitting, there is no uneven splitting phenomenon, and the light energy utilization rate is also high.

(4) The relative spatial position relationship of the four phase-shifting interference patterns obtained by the present invention is determined, and the phase shift amount is accurate and stable.

(5) The present invention has a single-phase device and a dual-phase device, which can be selected according to experimental conditions. The device has a compact structure, uses fewer components, is easy to assemble and adjust, and has a simple method principle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the principle of a synchronous phase-shifting interferometer optical path based on a Wollaston prism (single-phase device).

In the figure: 1. first beam splitter prism, 2. first 1/4 wave plate, 3. first reflector, 4. second reflector, 5. second 1/4 wave plate, 6. third 1/4 wave plate, 7. second beam splitter prism, 8. Wollaston prism, 9. imaging lens, 10. camera.

FIG. 2 is a schematic diagram of the principle of a synchronous phase-shifting interferometer optical path based on a Wollaston prism (dual-camera device).

In the figure: 1, first beam splitter prism, 2, first 1/4 wave plate, 5, second 1/4 wave plate, 6, third 1/4 wave plate, 8-1, first Wollaston prism, 8-2, second Wollaston prism, 9-1, first imaging lens, 9-2, second imaging lens, 10-1, first camera, 10-2, second camera.

FIG. 3 is a schematic diagram of the combined optical path in Example 1.

In the figure: 21, laser, 22, beam expander collimator, 23, polarizer, 24, polarization beam splitter prism, 25, reflector, 26, reflector.

FIG. 4 shows four synchronous phase-shifting interference images collected by the experimental system constructed in Example 1.

FIG. 5 is a schematic diagram of the relationship between the Wollaston prism and the object and image of the imaging lens.

FIG. 6 is a schematic diagram of the beam splitting principle of a Wollaston prism.

DETAILED DESCRIPTION

In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described in more detail below in conjunction with the drawings in the preferred embodiments of the present application. In the drawings, the same or similar reference numerals throughout represent the same or similar parts or parts with the same or similar functions. The described embodiments are part of the embodiments of the present application, not all of the embodiments. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limitations on the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

The embodiments of the present application are described in detail below with reference to the accompanying drawings.

In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, or it can be an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are orientations or positional relationships based on the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

In addition, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, for example, a process, method, system, product, or display that includes a series of steps or elements is not necessarily limited to those steps or elements explicitly listed but may include other steps or elements not explicitly listed or inherent to such process, method, product, or display.

The following will describe in detail a synchronous phase-shifting interferometer device and method based on a Wollaston prism according to an embodiment of the present application in conjunction with Figures 1 to 6. It should be noted that the following embodiments are only used to explain the present application and do not constitute a limitation on the present application.

Embodiment 1:

Embodiment 1: In this embodiment, a dual-camera device as shown in FIG2 is selected to build a synchronous phase shifting experimental system, and is combined with a dual-beam Twyman-Green system, and the experimental optical path system is shown in FIG3. The dual-beam Twyman-Green system device includes a laser 21, a beam expander collimator 22, a 1/2 wave plate 23, a polarization beam splitter prism 24, a reflector 25, and a reflector 26. The dual-camera synchronous phase shifting system device includes a first beam splitter prism 1, a first 1/4 wave plate 2, a second 1/4 wave plate 5, a third 1/4 wave plate 6, a first Wollaston prism 8-1, a second Wollaston prism 8-2, a first imaging lens 9-1, a second imaging lens 9-2, a first camera 10-1, and a second camera 10-2.

Among them, the angle between the fast axis direction of the first 1/4 wave plate 2 and the fast (or slow) axis of the incident linear polarization light is 45°; the angle between the fast axis direction of the second 1/4 wave plate 5 and the fast (or slow) axis of the incident linear polarization light is 0°; the angle between the fast axis direction of the third 1/4 wave plate 6 and the fast (or slow) axis of the incident linear polarization light is 45°; rotating the 1/2 wave plate 23 can make the reference light and the test light emitted in the optical path have the same light intensity.

The principle of using this device is as follows: the light beam emitted by the laser 21 becomes a parallel light beam after passing through the beam expander collimator 22, and then passes through the 1/2 wave plate 23 and the polarization beam splitter prism 24, and then part of it is transmitted and part of it is reflected. The phase object to be measured is placed in the middle of the reflected light path, and the transmitted light path is used as the reference light path. After the two light beams pass through the polarization beam splitter prism 24 again, they are incident on the dual-camera synchronous phase shifting system along the same light path. The first beam-splitting prism 1 evenly splits the incident orthogonal linearly polarized test light and reference light, and the transmitted light path is the first light path and the reflected light beam is the second light path, both of which contain the test light and the reference light; the first light path passes through the first 1/4 wave plate 2, the first Wollaston prism 8-1, the first imaging lens 9-1, and the first camera 10-1 in sequence to obtain two synchronous phase-shift interference images a1 and a2, with phase shifts of 0° and 180° respectively; the second light path passes through the second 1/4 wave plate 5, the third 1/4 wave plate 6, the second Wollaston prism 8-2, the second imaging lens 9-2, and the second camera 10-2 in sequence to obtain two synchronous phase-shift interference images b1 and b2, with phase shifts of 90° and 270° respectively.

A synchronous phase-shifting interferometry method based on Wollaston prism, the specific steps are as follows:

(1) A helium-neon laser 21 emits a linearly polarized laser with a wavelength of 633 nm, and a parallel beam with a diameter of 10 mm is obtained through a collimating beam expander 22; after passing through a 1/2 wave plate 23 and a polarization beam splitter prism 24, a portion of the beam is transmitted and a portion of the beam is reflected. A phase object to be measured is placed in the middle of the transmission light path. After the two beams pass through the polarization beam splitter prism 24 again, two orthogonal linearly polarized reference lights and test lights propagating along the same light path are emitted;

(2) The test light and the reference light simultaneously enter the synchronous phase-shifting interferometer dual-camera device based on the Wollaston prism of the present invention, and are first evenly split by the first beam-splitting prism 1. The first light path is transmitted through the first beam-splitting prism, and the second light path is reflected through the first beam-splitting prism. Both the first light path and the second light path contain the test light and the reference light.

(3) The reference light and the test light in the first optical path are converted into left-handed and right-handed circularly polarized light after passing through the first quarter wave plate 2, and then enter the first Wollaston prism 8-1 to be divided into two beams and generate phase shift interference. After passing through the first imaging lens 9-1, two phase shift interference images a1 and a2 are obtained on the first camera 10-1, and the phase shift amounts are 0° and 180°, respectively, as shown in the left figure of FIG. 4 .

(4) The reference light and the test light in the second optical path do not change their polarization state after passing through the second quarter wave plate 5, but a 90° phase shift is introduced. Then, they pass through the third quarter wave plate 6 and become left-handed and right-handed circularly polarized light. After entering the second Wollaston prism 8-2, they are divided into two beams and generate phase shift interference. After passing through the second imaging lens 9-2, two phase shift interference images b1 and b2 are obtained on the second camera 10-2, and the phase shift amounts are 90° and 270°, respectively, as shown in the right figure of Figure 4.

The beam splitting angle of the first and second Wollaston prisms used in this embodiment is 5° (for a wavelength of 633nm); the target size of the CCD camera is 7.2mm×5.4mm, the pixel is 4.4μm, and the spatial resolution is 1628×1236 pixels. According to the object-image relationship between the Wollaston prism and the imaging lens, as shown in FIG5 , the focal length of the imaging lens is determined to be 75mm and the aperture is 50.8mm. When determining the applicable value, it is calculated according to the following formula:

Where D is the height of the beam incident on the imaging lens after beam splitting; y is the beam aperture, i.e. the size of the object; y′ is the size of the image, the maximum of which is determined by the size of the CCD target surface; and u is the beam splitting angle of the Wollaston prism.

(5) The four-step phase shifting algorithm is used to process the four interference images and calculate the phase distribution to be measured.

Among them, I _0° , I _90° , I _180° , and I _270° correspond to the intensities of the four interference images a1, b1, a2, and b2, respectively.

The four phase-shifting interference images obtained in this embodiment are analyzed using the Jones matrix:

The Jones vectors of the reference light and the test light with orthogonal linear polarization are expressed as:

The Jones matrix when the angle between the fast axis of the quarter wave plate and the fast (or) slow axis of the incident linear polarization light is 45° and 0° is expressed as:

The Jones matrix of the Wollaston prism can be expressed as:

The reference light and the test light of orthogonal linear polarization are evenly split by the first beam splitting prism 1 into a transmitted first light path and a reflected second light path, and both the first light path and the second light path contain the test light and the reference light.

The synthetic wave obtained after the first light path enters the first 1/4 wave plate 2 (45°) is expressed as:

E ₁ =M×[QWP _(45°) ×E _r +QWP _(45°) ×E _t ] (8)

After passing through the first Wollaston prism 8-1, it is divided into two beams and generates phase-shift interference. The interference intensity is expressed as:

According to the Wollaston prism beam splitting principle, as shown in FIG6 , a beam of circularly polarized light can be split into two beams of orthogonal linearly polarized light, so the above formula α takes values of 0° and 90°. At this time, two phase-shift interference images a1 and a2 are obtained on the first camera 10 - 1, which are respectively expressed as:

The synthetic wave obtained after the second light path enters the third 1/4 wave plate 5 (0°) and the fourth 1/4 wave plate 6 (45°) is expressed as:

E ₂ =M×[QWO _(45°) ×QWP _(0°) ×E _r +QWP _(45°) ×QWP _(0°) ×E _t ] (11)

After passing through the second Wollaston prism 8-2, it is divided into two beams and generates phase-shift interference. The interference intensity is expressed as:

Similarly, the value of α in the above formula is 0° and 90°. At this time, two phase-shift interference images b1 and b2 are obtained on the second camera 10-2, which are respectively expressed as:

The above derivation confirms that the phase shifts between the four phase-shift interference images a1, b1, a2, and b2 are 0°, 90°, 180°, and 270°, respectively.

The above description is only a preferred embodiment of the present invention and is used to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (9)

1. A synchronous phase-shifting interferometer based on a Wollaston prism, characterized in that it comprises: a first beam splitter prism, a first 1/4 wave plate, a first reflector, a second reflector, a second 1/4 wave plate, a third 1/4 wave plate, a second beam splitter prism, a Wollaston prism, an imaging lens, and a camera; The first beam splitter prism is used to evenly split the orthogonally linearly polarized incident test light and reference light, and the transmission light path is the first light path and the reflected light beam is the second light path, both of which contain the test light and the reference light; The first optical path passes through the first 1/4 wave plate and the first reflector in sequence and then enters the second beam splitting prism; the second optical path passes through the second reflector, the second 1/4 wave plate, and the third 1/4 wave plate in sequence and then enters the second beam splitting prism; the light beams of the first optical path and the second optical path enter the second beam splitting prism and are incident on the Wollaston prism to be split into four beams, and phase shift interference is generated, and four synchronous phase shift interference images with a phase shift of 90° are obtained on the camera after passing through the imaging lens. 2. The synchronous phase-shifting interferometer device based on Wollaston prism according to claim 1 is characterized in that the angle between the fast axis direction of the first quarter wave plate and the fast (or slow) axis of the incident linear polarized light is 45°. 3. The synchronous phase-shifting interferometer device based on Wollaston prism according to claim 1 is characterized in that the angle between the fast axis direction of the second quarter wave plate and the fast (or slow) axis of the incident linear polarization light is 0°. 4. The synchronous phase-shifting interferometer device based on Wollaston prism according to claim 1 is characterized in that the angle between the fast axis direction of the third quarter wave plate and the fast (or slow) axis of the incident linear polarized light is 45°. 5. The synchronous phase-shifting interferometer device based on Wollaston prism according to claim 1 is characterized in that the applicable wavelengths of the first 1/4 wave plate, the second 1/4 wave plate and the third 1/4 wave plate are consistent with the wavelength of the laser. 6. The synchronous phase-shifting interferometer device based on Wollaston prism according to claim 1 is characterized in that: when selecting the beam splitting angle of the Wollaston prism, the optical device parameters are combined and calculated according to the object-image relationship between the Wollaston prism and the imaging lens, and the vertical axis magnification formula (1), the Gaussian formula (2), and the height D formula (3) of the light beam incident on the imaging lens after beam splitting are derived and calculated: D＝2(-l×tanu+y) (3) Where l is the object distance, l' is the image distance, y is the beam aperture, i.e. the size of the object, y' is the size of the image, f' is the focal length of the imaging lens, u is the beam splitting angle of the Wollaston prism, and D is the height of the beam incident on the imaging lens after splitting; Combining the above formulas (1) to (3), we can get the relationship between the beam splitting angle of the Wollaston prism: 7. The synchronous phase-shifting interferometer based on Wollaston prism according to claim 1, characterized in that the optimal beam splitting angle of the Wollaston prism is 5°. 8. A synchronous phase-shifting interferometry method based on Wollaston prism, characterized in that it is implemented based on the device described in claims 1-7, and the steps are as follows: (1) In the dual-path interference system, the test beam and the reference beam are incident on the first beam splitting prism in the device along the same optical path, and the test beam and the reference beam are orthogonally linearly polarized lights; (2) The test beam and the reference beam are simultaneously incident on the first beam splitting prism for beam splitting, the first light path is transmitted through the beam splitting prism, and the second light path is reflected through the beam splitting prism, and both the first light path and the second light path contain the test light and the reference light; (3) The reference light and the test light in the first optical path pass through the first quarter wave plate and then enter the second beam splitter prism through the first reflector, and the reference light and the test light in the second optical path pass through the second reflector and then enter the second quarter wave plate and the third quarter wave plate and then enter the second beam splitter prism; (4) The reference light and the test light in the first optical path become left-handed and right-handed circularly polarized light after passing through the first quarter-wave plate; the reference light and the test light in the second optical path do not change their polarization state after passing through the second quarter-wave plate, but a 90° phase shift is introduced, and then they become left-handed and right-handed circularly polarized light after passing through the third quarter-wave plate; (5) The first light path and the second light path enter the second beam splitting prism, pass through the Wollaston prism, and are split into four beams and generate phase-shift interference. After passing through the imaging lens, four synchronous phase-shift interference images with a phase shift of 90° are obtained on the camera, with intensities of I _0° , I _90° , I _180° , and I _270° ; (6) The four-step phase shifting algorithm is used to process the four phase shifting interference images and calculate the phase distribution to be measured. 9. The synchronous phase-shifting interferometer device based on Wollaston prism according to claim 1 is characterized in that: the camera can be implemented by a dual camera; the specific operation is that the first optical path and the second optical path are imaged separately, and two cameras are used to obtain two phase-shifting interference images respectively.