CN107462149B - A phase shift interferometry system and its wave plate phase shift method - Google Patents

Abstract

The invention relates to the technical field of optical interferometry and digital holographic measurement, and provides a phase-shift interferometry system and a wave plate phase-shift method thereof, wherein the phase-shift interferometry system is built and comprises a light source, a light filter, a first half wave plate, a polarization beam splitting element, a first beam splitter, a quarter wave plate, a second half wave plate, a first polaroid and a first monochromatic black-and-white image sensor, the phase-shift interferometry system realizes any phase shift by fixing the angle of the quarter wave plate to be unchanged and adjusting the rotation angle of the second half wave plate, is not limited to be combined with a phase-shift algorithm with a specific step length, and can be combined with the phase-shift algorithm with any phase-shift quantity at present to realize rapid and high-precision phase-shift interferometry; a driving device capable of accurately moving or rotating is not needed, the system is simple, and the operation is simple and convenient; the second half wave plate is equivalent to a phase shifter and does not need to be placed in an interference light path, so that the system is not influenced by mechanical motion, and the stability of the system is better.

Description

A phase shift interferometry system and its wave plate phase shift method

technical field

The invention relates to the technical field of optical interferometry and digital holographic measurement, in particular to a phase shift interferometry system and a wave plate phase shift method thereof.

Background technique

Phase-shift interferometry is an optical phase measurement technology with the characteristics of non-contact, full-field, non-destructive, fast measurement, high measurement accuracy, and the ability to measure irregular objects. It has been widely used in optical surface inspection, Three-dimensional topography measurement, biological cell imaging and digital holography and other fields. In recent years, with the continuous development of computer technology and digital image processing technology, the technology of interferometry, which uses light waves as the measurement scale and measurement benchmark, has been widely used.

In the actual phase shift interferometry, the phase shift error and mechanical vibration of the phase shifter will directly affect the phase measurement accuracy. Therefore, the accuracy and stability of the phase shift amount play a crucial role in phase shift interferometry. The traditional time-domain phase shift methods mainly include: piezoelectric ceramic (PZT) method, moving grating method, stretched fiber method, liquid crystal phase shift method, polarization phase shift method, air phase shift method, etc. However, these methods all have the following disadvantages: (1) the system is complicated due to the need for a driving device that can move or rotate accurately; (2) the phase shifters all need to be placed in the interference optical path, so the system is susceptible to mechanical motion (3) Although the traditional wave plate phase shift method can achieve simple phase shift, it can only obtain some special phase shift values, and there is no way to achieve arbitrary phase shift, so it can only be combined with some specific phase shift values. Algorithms are used in combination with limited accuracy and application range.

SUMMARY OF THE INVENTION

Aiming at the problems existing in the prior art, the present invention provides a phase shift interferometric measurement system and a wave plate phase shift method thereof, which are simple in combination, simple and stable in operation, and effectively solve the problem of phase shift interferometry in single-channel and multi-channel phase-shift interferometry systems. To solve the problem of shifting, realize simple, fast, high-precision and stable phase shifting.

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

A phase shift interferometric measurement system, comprising a light source, an optical filter, a first half-wave plate, a polarization splitting element, a first beam splitter, a quarter-wave plate, a second half-wave plate, The first polarizer and the first monochrome black and white image sensor, the light emitted by the light source enters the polarization beam splitter element after passing through the filter and the first half-wave plate, and is divided into a first beam of light and a second beam of light, a first plane mirror and a first microscope objective lens are arranged on the optical path direction of the first beam of light, and a second plane mirror and a second plane mirror are arranged on the optical path direction of the second beam of light. Microscopic objective lens, the object to be measured is placed between the second flat mirror and the second microscopic objective, and the light reflected by the first flat mirror and the second flat mirror passes through the The first microscope objective lens and the second microscope objective lens enter the first beam splitter, and enter the first beam splitter after passing through the quarter wave plate and the second half wave plate The polarizer is collected by the first monochrome black and white image sensor.

Further, the first polarizer and the first monochrome black and white image sensor are arranged in the optical path direction of the first beam of light, and the first monochrome black and white image sensor is used to collect the light emitted from the first polarizer. The optical signal of the first beam of light, a second polarizer and a second monochrome black and white image sensor are also provided in the direction of the optical path of the second beam of light, and the second monochrome black and white image sensor is used to collect data from all sources. The optical signal of the second beam of light emitted from the second polarizer.

Further, the polarization directions of the first polarizer and the second polarizer are set at 45°.

A wave plate phase shift method of a phase shift interferometry system, comprising:

Step 1: Build the above-mentioned phase-shift interferometric measurement system;

Step 2: Adjust the filter and the first half-wave plate in Step 1 to adjust the contrast;

Step 3: Fix the angle of the quarter wave plate unchanged, and adjust the rotation angle of the second half wave plate to achieve any phase shift.

Further, taking the direction of the light emitted by the light source as the z-axis direction, then the x-axis direction or the y-axis direction is perpendicular to the z-axis direction, and the fast axis of the quarter-wave plate described in step 1 is 45° from the x-axis or the y-axis. °.

Further, in step 3, the specific method for adjusting the rotation angle of the second half-wave plate to realize any phase shift is:

它们的琼斯矢量E₁和E₂分别为The reference light and the object light of the interferometer are a pair of orthogonally polarized lights whose polarization directions are in the horizontal and vertical directions, respectively, and the phase difference is

Their Jones vectors _E1 and _E2 are respectively

The Jones matrix of the first polarizer or the second polarizer whose transmission direction is at 45°, the Jones matrix of a quarter-wave plate whose fast axis is 45° to the x-axis, and the fast axis that is bisected by θ with the x-axis The Jones matrices of one waveplate are:

Then the Jones vector of the outgoing light after the reference light and the object light pass through the quarter wave plate, the second half wave plate and the first polarizer or the second polarizer is expressed as:

The light intensity I of the interferogram finally formed on the imaging device is:

有关，还与所述第二二分之一波片的放置角度θ有关，因此，当转动所述第二二分之一波片改变放置角度时，干涉条纹明暗发生变化。The symbol * represents conjugation, e is a natural constant, i is an imaginary unit, A ₁ , A ₂ are the amplitudes of the reference light and the object light, respectively. From the above formula (4), it can be seen that the light intensity of a certain point in the interference field , not only with the phase difference

It is also related to the placement angle θ of the second half-wave plate. Therefore, when the second half-wave plate is rotated to change the placement angle, the light and dark of the interference fringes will change.

Further, the phase shift amount is 4 times the rotation angle of the second half-wave plate.

Beneficial effects of the present invention:

The phase shift method of the phase shift interferometric measurement system of the present invention can realize any phase shift, and is not limited to being combined with the phase shift algorithm of a specific step size, and can be combined with the current phase shift algorithm of any phase shift amount to realize fast and high-precision measurement. Phase-shift interferometry; and does not require a drive device that can move or rotate accurately, the system is simple and easy to operate; the second half-wave plate is equivalent to a phase shifter and does not need to be placed in the interference optical path, so the system will not Affected by mechanical movement, the system stability is better.

Description of drawings

1 is a schematic structural diagram of a dual-channel simultaneous phase-shift interference system provided by a first embodiment of the present invention;

2 is a schematic structural diagram of a single-channel phase-shift interference system provided by a second embodiment of the present invention;

Fig. 3 is a phase shift interferogram collected during the experimental measurement of the second embodiment of the present invention;

Fig. 4 is the phase shift amount distribution curve corresponding to 37 phase shift interferograms collected during the experimental measurement according to the second embodiment of the present invention;

In the figure, 1-light source, 2-filter, 3-first half-wave plate, 4-polarization beam splitter, 5-first plane mirror, 6-second plane mirror, 7-to be measured Object, 8—second microscope objective, 9—first microscope objective, 10—first beam splitter, 11—quarter wave plate, 12—second half wave plate, 13—second Beam splitter, 14—first polarizer, 15—second polarizer, 16—first monochrome monochrome image sensor, 17—second monochrome monochrome image sensor, 101—light source, 102—filter, 103— The first half-wave plate, 104—polarizing beam splitting element, 105—first plane mirror, 106—second plane mirror, 107—object to be measured, 108—second microscope objective, 109—first display Micro-objective lens, 110—first beam splitter, 111—quarter wave plate, 112—second half wave plate, 113—first polarizer, 114—first monochrome black and white image sensor.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

As shown in FIG. 1, the first embodiment of the present invention provides a dual-channel simultaneous phase-shift interferometric measurement system, including a light source 1, a filter 2, a first half-wave plate 3, a polarization beam splitting element 4, and a first beam splitter 10 , the quarter wave plate 11, the second half wave plate 12 and the second beam splitter 13, the light emitted by the light source 1 enters the polarization beam splitter after passing through the filter 2 and the first half wave plate 3 Element 4, the incident light is decomposed into P-polarized light and S-polarized light by the polarization beam splitting element 4, and a first plane mirror 5 and a first microscopic objective lens 9 are provided in the optical path direction of the P-polarized light. A second plane mirror 6 and a second microscopic objective lens 8 are arranged in the direction, the object to be measured 7 is placed between the second plane mirror 6 and the second microscopic objective lens 8, and the P-polarized light passes through the first plane mirror 5. It is reflected and enters the first beam splitter 10 after passing through the first microscope objective 9, and the S-polarized light is reflected by the second plane mirror 6 and enters the first beam splitter 10 after passing through the object to be measured 7 and the second microscope objective 8 , then the P-polarized light and the S-polarized light enter the second beam splitter 13 after passing through the quarter-wave plate 11 and the second half-wave plate 12, and a first polarizer is provided on the optical path direction of the P-polarized light 14 and the first monochrome black and white image sensor 16, a second polarizer 15 and a second monochrome black and white image sensor 17 are provided in the optical path direction of the S-polarized light, and the first monochrome black and white image sensor 16 is used to collect data from the first For the optical signal of the P-polarized light emitted from the polarizer 14 , the second monochrome black and white image sensor 17 is used to collect the optical signal of the S-polarized light emitted from the second polarizer 15 .

In this embodiment, the light source 1 is a He-Ne laser with a wavelength of 632.8 nm, and the filter 2 is a neutral density filter.

The dual-channel simultaneous phase-shift interferometric measurement system of the present invention can realize any phase shift by rotating the second half-wave plate 12 .

In this embodiment, the direction of the light emitted by the light source 1 is the z-axis direction, and the x-axis direction or the y-axis direction is perpendicular to the z-axis direction, then the fast axis of the quarter-wave plate 11 should be 45° from x or y. °.

The parameters of the first polarizer 14 and the second polarizer 15 are the same. In this embodiment, the polarization directions of the first polarizer 14 and the second polarizer 15 are set at 45°.

The first monochrome monochrome image sensor 16 and the second monochrome monochrome image sensor 17 have the same specifications.

As shown in FIG. 2, the second embodiment of the present invention provides a single-channel phase-shift interferometry system, including a light source 101, a filter 102, a first half-wave plate 103, a polarization beam splitting element 104, a first beam splitter 110, A quarter wave plate 111 , a second half wave plate 112 , a first polarizer 113 and a first monochrome black and white image sensor 114 . The light emitted by the light source 101 enters the polarization beam splitting element 104 after passing through the filter 102 and the first half-wave plate 103, and the incident light is decomposed into P-polarized light and S-polarized light by the polarization beam splitting element 104. A first plane mirror 105 and a first microscope objective 109 are arranged in the direction, a second plane mirror 106 and a second microscope objective 108 are arranged in the optical path direction of the S-polarized light, and the object to be measured 107 is placed on the second Between the plane mirror 106 and the second microscope objective 108, the P-polarized light is reflected by the first plane mirror 105 and then enters the first beam splitter 110 after passing through the first microscope objective 109, and the S-polarized light is reflected by the second plane The mirror 106 reflects and enters the first beam splitter 110 after passing through the object to be measured 107 and the second microscope objective lens 108, and then the P-polarized light and the S-polarized light pass through the quarter-wave plate 111 and the second half-wave plate After 112 , it enters the first polarizer 113 and is collected by the first monochrome black and white image sensor 114 , which is used to collect the optical signal of the P-polarized light emitted from the first polarizer 113 .

In this embodiment, the light source 101 is a He-Ne laser with a wavelength of 632.8 nm, and the filter 2 is a neutral density filter.

The single-channel phase-shift interferometric measurement system of the present invention can realize any phase shift by rotating the second half-wave plate 112 .

In this embodiment, the direction of the light emitted by the light source 101 is the z-axis direction, and the x-axis direction or the y-axis direction is perpendicular to the z-axis direction, then the fast axis of the quarter-wave plate 111 should be 45° from x or y. °.

The present invention also provides a wave plate phase shift method of the phase shift interferometric measurement system, comprising:

Step 1: Build a phase-shift interferometric measurement system as shown in Figure 1 or Figure 2;

Step 2: Adjust the contrast by adjusting the filters 2, 102 and the first half-wave plates 3, 103 in step 1;

Step 3: Fix the angles of the quarter wave plates 11 and 111 unchanged, and adjust the rotation angles of the second half wave plates 12 and 112 to achieve any phase shift.

Specifically, in step 1, the fast axis of the quarter-wave plates 11 and 111 should be 45° from the x-axis or the y-axis in the figure.

Specifically, in step 1 of the first embodiment, the polarization directions of the first polarizer 14 and the second polarizer 15 should be set at 45°.

In the present invention, the specific method for realizing any phase shift by adjusting the rotation angles of the second half-wave plates 12 and 112 in step 3 is:

它们的琼斯矢量E₁和E₂分别为The reference light and the object light of the interferometer are a pair of orthogonally polarized lights whose polarization directions are in the horizontal and vertical directions, respectively, and the phase difference is

Their Jones vectors _E1 and _E2 are respectively

The Jones matrix of the first polarizer 14 or the second polarizer 15 with the vibration transmission direction at 45°, the Jones matrix of the quarter-wave plate 11 with the fast axis forming 45° with the x-axis, and the fast axis forming θ with the x-axis The Jones matrices of the second half-wave plate 12 are:

Then the reference light and the object light pass through the quarter wave plate 11, the second half wave plate 12 and the first polarizer 14 or the second polarizer 15. The Jones vector of the emitted light is expressed as:

The light intensity I of the interferogram finally formed on the imaging device is:

有关，还与第二二分之一波片12的放置角度θ有关，因此，当转动第二二分之一波片12改变放置角度时，干涉条纹明暗发生变化。这里第二二分之一波片12相当于时域相移器，相移量为第二二分之一波片旋转角度的4倍。The symbol * represents conjugation, e is a natural constant, i is an imaginary unit, A ₁ , A ₂ are the amplitudes of the reference light and the object light, respectively. From the above formula (4), it can be seen that the light intensity of a certain point in the interference field , not only with the phase difference

It is also related to the placement angle θ of the second half-wave plate 12 . Therefore, when the second half-wave plate 12 is rotated to change the placement angle, the intensity of the interference fringes changes. Here, the second half wave plate 12 is equivalent to a time domain phase shifter, and the phase shift amount is 4 times the rotation angle of the second half wave plate.

In order to further demonstrate the practicability of the method of the present invention, the present invention adopts the second embodiment, such as the measurement optical path system shown in FIG. 2 , to perform experimental measurements. Keep the fast axis of the quarter-wave plate 111 at 45° to the x direction, and rotate the second half-wave plate 112 at intervals of 10° until it rotates 360°. The improved least squares iterative method (AIA) calculates the phase shift of these 37 interferograms. One of the collected phase shift interferograms is shown in Figure 3, and the 37 corresponding phase shift distribution curves are shown in Figure 4. Show. It can be seen from the results in FIG. 4 that any phase shift of the system can be achieved by rotating the second half wave plate 112 , and the phase shift amount is 4 times the rotation angle of the second half wave plate 112 .

The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without Deviating from the spirit and scope of the technical solution, all of them should be covered within the scope of the claims of the present invention.

Claims (3)

1. a wave plate phase shift method of a phase shift interferometry system, is characterized in that, comprising: Step 1: Build a phase-shift interferometry system; the phase-shift interferometry system includes: a light source, a filter, a first half-wave plate, a polarization splitting element, a first beam splitter, and a quarter-wave plate , the second half-wave plate, the first polarizer and the first monochrome black and white image sensor, the light emitted by the light source enters the The polarization beam splitting element is divided into a first beam of light and a second beam of light, a first plane mirror and a first microscope objective are arranged in the direction of the optical path of the first beam of light, and the direction of the optical path of the second beam of light is provided A second plane mirror and a second microscope objective lens are provided, and the object to be measured is placed between the second plane mirror and the second microscope objective lens, and is The light reflected by the plane mirror enters the first beam splitter after passing through the first microscope objective lens and the second microscope objective lens respectively, and passes through the quarter-wave plate and the second half-wave plate One wave plate enters the first polarizer, and is collected by the first monochrome black and white image sensor; The first polarizer and the first monochrome black and white image sensor are arranged in the optical path direction of the first beam of light, and the first monochrome black and white image sensor is used to collect the light emitted from the first polarizer. The optical signal of the first beam of light, a second polarizer and a second monochrome black-and-white image sensor are also provided in the optical path direction of the second beam of light, and the second monochrome black-and-white image sensor is used to collect data from the second beam. The optical signal of the second beam of light emitted by the two polarizers; The polarization directions of the first polarizer and the second polarizer are set at 45°; Step 2: Adjust the filter and the first half-wave plate in Step 1 to adjust the contrast; Step 3: fix the angle of the quarter wave plate unchanged, and adjust the rotation angle of the second half wave plate to achieve any phase shift; In step 3, the specific method for adjusting the rotation angle of the second half-wave plate to realize any phase shift is as follows: The reference light and the object light of the interferometer are a pair of orthogonally polarized lights whose polarization directions are in the horizontal and vertical directions, respectively, and the phase difference is

Their Jones vectors _E1 and _E2 are respectively

The Jones matrix of the first polarizer or the second polarizer whose transmission direction is at 45°, the Jones matrix of a quarter-wave plate whose fast axis is 45° to the x-axis, and the fast axis that is bisected by θ with the x-axis The Jones matrices of one waveplate are:

Then the Jones vector of the outgoing light after the reference light and the object light pass through the quarter wave plate, the second half wave plate and the first polarizer or the second polarizer is expressed as:

The light intensity I of the interferogram finally formed on the imaging device is:

The symbol * represents conjugation, e is a natural constant, i is an imaginary unit, A ₁ , A ₂ are the amplitudes of the reference light and the object light, respectively. From the above formula (4), it can be seen that the light intensity of a certain point in the interference field , not only with the phase difference

It is also related to the placement angle θ of the second half-wave plate. Therefore, when the second half-wave plate is rotated to change the placement angle, the light and dark of the interference fringes will change. 2. The wave plate phase-shift method of the phase-shift interferometry system according to claim 1, wherein the direction of the light emitted by the light source is the z-axis direction, then the x-axis direction or the y-axis direction is perpendicular to the z-axis direction , the fast axis of the quarter-wave plate in step 1 is 45° to the x-axis or the y-axis. 3 . The wave plate phase shift method of the phase shift interferometry system according to claim 1 , wherein the phase shift amount is 4 times the rotation angle of the second half wave plate. 4 .

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