CN116379961A - Phase measurement system and method - Google Patents
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- G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
- G01J9/02—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods
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- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
- G01J9/02—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods
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Abstract
The invention relates to the technical field of optical precision measurement and provides a phase measurement system and a phase measurement method, wherein the phase measurement system comprises a tunable laser, a He-Ne laser, a first dichroic mirror, an achromatic half-wave plate, an achromatic beam expander group, a polarization beam splitting cube, a first achromatic quarter-wave plate, a first silver film reflector, a beam splitting cube, a spatial light modulator, a second achromatic quarter-wave plate, a first lens, a half-transparent half-mirror, an off-axis reflector, an indicator light imaging system, a first bandpass filter, a multi-wavelength phase measurement module and a data acquisition processing unit; the invention can realize large-range and high-resolution measurement of the aspheric surface and the free curved surface in particular before the large gradient difference phase by utilizing the tunable wavelength laser measurement technology, the pixel shift measurement technology and introducing the spatial light modulator, and solves the technical problem that the prior interferometry technology can not realize large-range and high-resolution measurement of the large gradient difference phase.
Description
Technical Field
The invention relates to the technical field of optical precision measurement, in particular to a phase measurement system and a phase measurement method.
Background
In modern optical engineering practice, attempts have been made to adopt aspherical surfaces and free-form surfaces with more design flexibility and freedom in design in order to improve the optical performance of optical systems. The high-precision machining of the complex surfaces needs to detect and accurately measure the surface shape errors of the nominal optical surfaces to be measured by means of a precise phase measurement system so as to achieve the purpose that the precise machining is infinitely approximate to the ideal surface shape. Currently, the traditional measurement method commonly used in the optical industry is interferometry. The interferometry is characterized by simple system structure, rapid and direct measurement, and the method is based on the traditional Michelson interference principle, adopts the same monochromatic laser source to generate one path of reference wave front and one path of measurement wave front, and the interference result of the two paths of wave fronts is received by a camera detector and causes the change of image stripes acquired on a camera detector chip. The surface shape data of the surface to be measured can be calculated from the phase difference between the two wave fronts. However, the measurement working condition is often in a non-ideal state, so that the measurement working condition is easily influenced by environmental factors such as inconsistent beam paths, environmental vibration, temperature disturbance, air turbulence and the like, the jitter of a measurement result is caused, and a large system measurement error is introduced.
The interferometry method can be classified into a common-path measurement method and a non-common-path measurement method according to the different forms of the test optical paths. The common-path interferometry system (such as Fizeau interferometry method) can effectively solve the problems of measurement accuracy and stability reduction caused by the fact that a traditional non-common-path measurement method (such as a Tasman-Green interferometry method and the like) does not share a light path with the test light.
However, the influence of the environmental disturbance on the common light path is difficult to eliminate, and only the dynamic interferometry method can reduce the influence of the environmental disturbance on the interferometry accuracy. The dynamic interferometer can further improve the measurement precision and reduce the influence of random errors generated by environmental disturbance on the measurement result by measuring the instantaneous wave front in real time and analyzing the acquired data. For the large-caliber interferometry system, due to the limitations of glass materials and mechanical structures, optical uniformity aberration of the system cannot be completely eliminated, contrast blurring and wavefront measurement errors are caused, and further expansion of the caliber of the large-caliber interferometer is limited.
In modern optical measurement technology, common compensating optical devices comprise a traditional refraction (reflection) compensator, a diffraction compensator based on a calculation hologram (CGH) and a programmable (self-adaptive) compensator based on a Deformable Mirror (DM) or a Spatial Light Modulator (SLM), and in addition, zero position detection can be performed on a conical curved surface by adopting a non-aberration point method, wherein the Computer Generated Hologram (CGH) is the latest technology for measuring an aspheric optical device, and the method has the advantages of high calculation speed and accurate optical interconnection positioning, but different compensating elements are required to be customized according to different measured surfaces. When the measured surface has larger deviation from the reference surface, interference fringes with high fringe density appear, and when the deviation is too large, the vignetting of the test light can also cause the partial area on the measured surface to be undetectable. All of these effects limit the use of conventional fizeau interferometers when testing complex shaped surfaces.
Disclosure of Invention
An object of the present invention is to provide a phase measurement system and method, which can realize large-scale and high-resolution measurement of aspheric surfaces and free curved surfaces before large gradient phases, and solve the technical problem that the existing interferometry technique cannot realize large-scale and high-resolution measurement of large gradient phases.
Another object of the present invention is to provide a phase measurement system and a method thereof, wherein the phase measurement system uses co-optical path interferometry as a system reference, so as to effectively reduce adverse effects of non-co-optical path errors on system measurement accuracy.
The invention further aims to provide a phase measurement system and a phase measurement method, which solve the technical defect that the uncertainty of 2 pi phase cannot be eliminated in the traditional monochromatic light measurement method by selecting a tunable laser as a test light source and utilizing the characteristic that the tunable laser can generate narrow linewidth lasers with different center wavelengths, realize high-precision and large-range wavefront measurement, simultaneously select a He-Ne laser as an indication light source, test light and an indication light beam, realize quick optical alignment of a sample to be tested through an indication light adjustment auxiliary system, save test preparation time and improve test efficiency.
Another object of the present invention is to provide a phase measurement system and method, which perform wavefront regulation and control on a parallel light field by introducing an SLM (spatial light modulator), compensate local gradients by simulating different off-axis point light sources, realize off-axis illumination on a surface to be measured, wavefront interferometry with large gradient difference, and solve the influence of vignetting and high-density interference fringes on a reference wave, and can effectively compensate high-order errors caused by imaging optical devices in the system, thereby realizing high-precision detection of advanced optical manufacturing.
The invention also aims to provide a phase measurement system and a phase measurement method, which can prevent stray light outside a measurement area from influencing measurement accuracy by the system diaphragm, limit fringe density of an interference pattern below a Nyquist standard and solve the problem of interference pattern overlapping in a traditional point source array.
Another object of the present invention is to provide a phase measurement system and method, in which dynamic measurement is realized by a dynamic interferometry based on a polarization phase shift technology, so as to avoid the influence of environmental disturbance on measurement accuracy and stability, and greatly enhance the anti-interference capability of the system.
Another object of the present invention is to provide a phase measurement system and method, which uses a phase amplification technique to achieve improvement of measurement resolution. The phase difference of two polarization modes of the polarization interferometer is amplified by 4 times by using a cascaded second harmonic amplification technology. Four polarization measurements with 45-degree phase difference are realized by using a pixel shift technology, accurate transient measurement is realized, and the influence of measurement errors caused by environmental vibration is avoided. Meanwhile, the phase measurement method of the invention improves the measurement precision of the traditional interferometer by 4 times, is not affected by environmental vibration, and has the advantages of no influence of environmental vibration on transient measurement, high multi-wavelength combined measurement precision, expandable range and no influence of 2 pi phase ambiguity.
To achieve at least one of the above objects, the present invention provides a phase measurement system comprising:
an interference light generating device for generating two beams of polarized light having a wavelength lambda orthogonal to each other 1 The reference linear polarized light of the (2) and the test linear polarized light containing the wavefront information of the surface to be tested of the sample to be tested are interfered to form the wavelength lambda of the wavefront information of the surface to be tested of the sample to be tested 1 Is a light source for emitting light;
The multi-wavelength phase measuring module is arranged on the output light path of the interference light generating device and is used for collecting the wavelength lambda 1 The interference light of (a) is multiplied by frequency and multiplied by frequency in turn to obtain wavelength lambda 1/2 and λ1 Polarization interference pattern corresponding to frequency multiplication light;
the data acquisition processing unit is electrically connected with the interference light generating device and the multi-wavelength phase measurement module, and is used for controlling the interference light generating device and the multi-wavelength phase measurement module to work and carrying out data processing, information extraction and display on the interference light acquired by the multi-wavelength phase measurement module.
Optionally, the interference light generating device comprises a tunable laser used for emitting test light, a He-Ne laser used for emitting indication light, a linearly polarized light generating module, a spatial light modulator and a wavefront information providing module of a sample to be tested, wherein the linearly polarized light generating module, the spatial light modulator and the wavefront information providing module are sequentially arranged on the test light path,
the linear polarized light generating module is used for coupling the test light and the indication light and converting the coupled light into two beams of first linear polarized light and second linear polarized light which have equal energy and mutually orthogonal polarization states so as to output the light with the wavelength lambda 1 Is a reference linearly polarized light of (a);
The spatial light modulator is a reflective spatial light modulator and is used for modulating the wave front phase of part of linearly polarized light output by the linearly polarized light generating module to obtain modulated light, the modulated light is incident to the sample to be tested through the sample wave front information providing module to be tested, and is sequentially reflected back to the sample to be tested wave front information providing module and the linearly polarized light generating module through the sample to be tested, and test linearly polarized light containing wave front information of a surface to be tested of the sample to be tested is output.
Optionally, the linearly polarized light generating module comprises a linearly polarized light generating component arranged on the optical path of the test light, and the linearly polarized light generating component comprises a first dichroic mirror, an achromatic half wave plate, an achromatic beam expander group and a polarization beam splitting cube which are sequentially arranged on the optical path of the test light; wherein,
the first dichroic mirror is used for coupling test light and indicating light; the achromatic half wave plate is used for forming the coupled light into linearly polarized light; the achromatic beam expander group is used for expanding the linearly polarized light; the polarization beam splitting cube is used for splitting the linearly polarized light into the first linearly polarized light and the second linearly polarized light which are equal in energy and orthogonal in polarization state.
Optionally, the linearly polarized light generating module further comprises a first achromatic quarter wave plate and a first silver film reflecting mirror which are sequentially arranged at one side of the polarization beam splitting cube; wherein,
the first achromatic quarter wave plate is used for changing the first linearly polarized light into circularly polarized light; the first silver film mirror is used for adjusting the rotation direction of the circularly polarized light.
Optionally, the phase measurement system further comprises an indicator light imaging system electrically connected to the data acquisition processing unit, the indicator light imaging system being for imaging an indicator light focus spot.
Optionally, the wavefront information providing module of the sample to be tested includes a beam splitting cube, a second achromatic quarter wave plate on a reflection light path of the beam splitting cube, a first lens, a half-transparent half-reflecting mirror and an off-axis reflecting mirror which are sequentially arranged; wherein,
the beam splitting cube is used for normally incidence of the second linearly polarized light of the polarization beam splitting cube to the spatial light modulator, reflecting a part of modulated light modulated by the spatial light modulator to the wavefront information providing module of the sample to be tested, and normally incidence of the other part of modulated light modulated by the spatial light modulator back to the polarization beam splitting cube;
The second achromatic quarter wave plate is used for adjusting the polarization states of the modulated light reflected by the beam splitting cube and the reflected light carrying the wave front information of the sample to be detected, so that the polarization states of the two beams of light are mutually orthogonal;
the focal plane of the first lens coincides with the focal plane of the off-axis reflector;
the half mirror is used for transmitting part of light from the off-axis reflector to the indicator light imaging system for imaging, and reflecting the other part of light from the first lens to the off-axis reflector and reflecting the other part of light from the off-axis reflector back to the first lens;
the reflecting surface of the off-axis reflecting mirror is a curved reflecting surface; the reflecting surface of the off-axis reflector is opposite to the surface to be measured of the sample to be measured, and is used for reflecting the incident modulated light to the surface to be measured of the sample to be measured and reflecting the light beam reflected by the surface to be measured of the sample to be measured back to the half-mirror.
Optionally, the indication light imaging system includes a frosted glass screen, a camera imaging lens and a camera sequentially arranged along a transmission light path of the half mirror, wherein the Mao Boli screen provides a projection screen for an indication light focusing light spot formed by light containing wavefront information of a surface of a sample to be detected; the camera imaging lens is used for imaging the indication light focusing light spots on the ground glass screen on the surface of the detector of the camera; the camera is used for imaging the indication light focusing light spot.
Optionally, the multi-wavelength phase measurement module includes a first pixel shift polarization measurement device, a primary frequency multiplication generator, a second pixel shift polarization measurement device, a secondary frequency multiplication generator, and a third pixel shift polarization measurement device that are sequentially arranged; wherein,
the first pixel shift polarization measuring device is used for measuring the wavelength lambda 1 Carrying out imaging analysis on interference wavefront information of interference light;
the primary frequency multiplication generator is used for multiplying the wavelength lambda 1 Is multiplied by interference light to produce a wavelength lambda 1 Frequency-doubled light of/2;
the second pixel shift polarization measuring device is used for measuring the wavelength lambda 1 Carrying out imaging analysis on interference wavefront information of frequency multiplication light;
the double frequency generator is used for generating the frequency spectrum with the wavelength lambda 1 Frequency multiplication of frequency multiplication light of/2 to generate a frequency with a wavelength lambda 1 Frequency-doubled light of/4;
the third pixel shift polarization measuring device is used for measuring the wavelength lambda 1 Interference wave front of frequency multiplication light of/4And (5) performing imaging analysis.
Optionally, the first pixel shift polarization measurement device, the second pixel shift polarization measurement device and the third pixel shift polarization measurement device have the same structure, and all three include a beam splitter and a pixel shift polarization measurement device, where the beam splitter is used to split a part of interference light into the pixel shift polarization measurement device, and the pixel shift polarization measurement device is used to perform imaging analysis on interference wavefront information of the interference light split by the beam splitter.
Optionally, the pixel shift polarization measurement device comprises a second semi-transparent semi-reflecting mirror, an imaging lens and a polarization imaging assembly which are sequentially arranged, wherein the polarization imaging assembly comprises a micro lens array, a micro polarizer array and a photoelectric detector array which are sequentially arranged.
Optionally, the first pixel shift polarization measurement device, the second pixel shift polarization measurement device and the third pixel shift polarization measurement device use light intensity signals recorded by four wire grid polaroid classification pixels collected by the photoelectric detector array, and transmit the light intensity signals to the data collection processing unit, the data collection processing unit obtains four phase shift interferograms according to light intensity signal processing, and high-precision wavefront or surface shape data of the surface of the sample to be detected is obtained by performing phase unwrapping data processing on the four phase shift interferograms.
Optionally, the multi-wavelength phase measurement module further includes a second silver film mirror and a second dichroic mirror sequentially disposed between the first pixel shift polarization measurement device and the frequency multiplication generator, where the second silver film mirror is configured to output the first pixel shift polarization measurement device with a wavelength λ 1 Is deflected to be incident on the second dichroic mirror; the second dichroic mirror is used for transmitting the wavelength lambda 1 And is used for generating the primary frequency multiplication generator with the wavelength lambda 1 And/2, reflecting the frequency-doubled light to the second pixel shift polarization measurement device.
Optionally, the primary frequency multiplication generator comprises a dichroic polarization beam splitting cube, a dichroic half wave plate, a first parabolic silver mirror, a first crystal and a second parabolic silver mirror which are sequentially arranged; wherein,
the dichroic polarization beam splitting cube is used for transmitting the wavelength lambda 1 Reflecting the interference light of wavelength lambda generated by frequency multiplication of the first crystal 1 Frequency-doubled light of/2;
the dichroic half wave plate is used for adjusting the wavelength to lambda 1 To the polarization direction of the interference light of the wavelength lambda 1 The polarization direction of the interference light of the first crystal is matched with the phase of the first crystal;
the first parabolic silver mirror is used for reflecting the wavelength lambda 1 Focusing the interference light of the first crystal at the center of the crystal length of the first crystal;
the first crystal is used for transmitting the wavelength lambda 1 Is lambda in wavelength generated by frequency multiplication of interference light 1 Frequency-doubled light of/2;
the second parabolic silver mirror is used for generating the first crystal with the wavelength lambda 1 Frequency doubling light collimation of/2.
Optionally, the second frequency doubling generator comprises a second lens, a second crystal, a third lens and a second band-pass filter which are sequentially arranged; wherein,
the second lens is used for transmitting the wavelength lambda 1 Is focused in the second crystal;
the second crystal is used for making wavelength lambda 1 Frequency doubling light frequency doubling generating wavelength lambda of/2 1 Frequency-doubled light of/4;
the third lens is used for transmitting the wavelength lambda 1 Frequency multiplication light collimation of/4;
the second band-pass filter is used for filtering the wavelength lambda 1 Stray light in the frequency multiplied light of/4.
Optionally, the first crystal is a periodically poled lithium niobate crystal, and the second crystal is a beta-barium borate crystal.
The invention also provides a phase measurement method, which adopts a phase measurement system to measure the surface wavefront or surface shape data of a sample to be measured, wherein the phase measurement system comprises a tunable laser, a He-Ne laser, a first dichroic mirror, an achromatic half wave plate, an achromatic beam expander group, a polarization beam splitting cube, a first achromatic quarter wave plate, a first silver film reflecting mirror, a beam splitting cube, a spatial light modulator, a second achromatic quarter wave plate, a first lens, a half-transparent half-reflecting mirror, an off-axis reflecting mirror, an indicator light imaging system, a multi-wavelength phase measurement module and a data acquisition processing unit; the phase measurement method comprises the following steps:
S1, coupling test light emitted by the tunable laser and indication light emitted by the He-Ne laser on the first dichroic mirror, wherein the coupled light is changed into linear polarized light through the achromatic half wave plate, and the linear polarized light is expanded by the achromatic beam expander group;
s2, the linearly polarized light after beam expansion is incident on the polarization beam splitting cube and then split into a first linearly polarized light and a second linearly polarized light which have equal energy and mutually orthogonal polarization states;
s3, the first linearly polarized light is incident into the first achromatic quarter wave plate to be changed into circularly polarized light, then reflected on the first silver film reflecting mirror and rotated reversely, and returns to the polarization beam splitting cube through the first achromatic quarter wave plate to form a wavelength lambda 1 Is a reference linearly polarized light of (a);
s4, modulating the second linearly polarized light which is normally incident to the spatial light modulator through the beam splitting cube to obtain modulated light, and normally incident to the polarized beam splitting cube through the beam splitting cube and then reflecting the modulated light to the first band-pass filter; another portion is reflected to the second achromatic quarter waveplate; a part of modulated light emitted from the second achromatic quarter wave plate is reflected to the off-axis reflector through the semi-transparent semi-reflective mirror, collimated by the off-axis reflector, incident to the surface of the sample to be detected and returned to the spatial light modulator along the original path, and the wavelength lambda of wave front information of the surface to be detected containing the sample to be detected is obtained 1 Another part of the linearly polarized light enters an indicator light imaging system;
s5, wavelength lambda 1 Reference linearly polarized light of (2) and sample containing the sample to be measuredThe wavelength of the wave front information of the surface to be measured is lambda 1 Interference between linearly polarized light of (2) to form a wavelength lambda 1 Is a light source for emitting light;
s6, wavelength lambda 1 The interference light of (2) is incident into the multi-wavelength phase measurement module after passing through the first band-pass filter, and the wavelength lambda is obtained by the multi-wavelength phase measurement module 1 Is lambda in wavelength 1 /2、λ 1 Frequency-doubled light of/4;
s7, the data acquisition processing unit collects the wavelength lambda 1 Is lambda in wavelength 1 /2、λ 1 And 4, processing, analyzing and displaying the surface shape pattern and the data information of the surface of the sample to be detected.
Optionally, the multi-wavelength phase measurement module includes: the device comprises a first pixel shift polarization measuring device, a second silver film reflecting mirror, a second dichroic mirror, a dichroic polarization beam splitting cube, a dichroic half wave plate, a first parabolic silver mirror, a first crystal, a second parabolic silver mirror, a second pixel shift polarization measuring device, a second lens, a second crystal, a third lens, a second band-pass filter and a third pixel shift polarization measuring device;
The step S6 specifically comprises the steps of:
s61, wavelength lambda 1 The interference light of the first pass filter is transmitted to the first pixel shift polarization measuring device and then enters the first pixel shift polarization measuring device, and interference fringe information is obtained through the data acquisition processing unit;
s62, the wavelength transmitted through the first pixel shift polarization measurement device is lambda 1 The interference light of (a) passes through the second silver film reflector and the second dichroic mirror and enters a primary frequency multiplication generator consisting of the dichroic polarization beam splitting cube, the dichroic half wave plate, the first parabolic silver mirror, the first crystal and the second parabolic silver mirror, and the output wavelength is lambda 1 Frequency-doubled light of/2;
s63 wavelength is lambda 1 The frequency multiplication light of/2 is incident to the second pixel shift polarization measurement device, and the data acquisition processing unit is used for acquiring the light with the wavelength lambda 1 Carrying out imaging analysis on the frequency multiplication light of/2;
s64, transmitting the second pixel shift polarization measurement device with wavelength lambda 1 The frequency multiplication light of/2 passes through a secondary frequency multiplication generator composed of the second lens, the second crystal, the third lens and the second band-pass filter, and the output wavelength is lambda 1 Frequency-doubled light of/4;
s65, wavelength lambda 1 The frequency multiplication light of/4 is incident to the third pixel shift polarization measuring device, and the data acquisition processing unit 21 performs the data acquisition processing on the light with the wavelength lambda 1 And/4, carrying out imaging analysis on the interference wavefront information of the frequency-doubled light.
Optionally, the indicator light imaging system comprises a ground glass screen, a camera imaging lens and a camera; step S4 includes the steps of:
s41, a part of modulated light incident to the second achromatic quarter wave plate is transmitted to the ground glass screen through the half mirror to form an indication light focusing light spot, and the indication light focusing light spot is imaged through the camera imaging lens and the camera.
The invention has the following beneficial effects:
(1) The invention realizes common-path measurement based on the Fizeau interferometry principle, avoids non-common-path errors caused by inconsistent optical paths and mediums in a sample optical path and a reference light indication optical path in the non-common-path measurement of the traditional measurement method, and greatly improves the detection precision and the anti-interference capability of the system.
(2) Compared with the interference measurement technology of monochromatic light, the invention can realize multi-wavelength measurement by utilizing the tunable laser, effectively solves the technical defect of unavoidable 2 pi phase uncertainty in the monochromatic light measurement technology, and can realize interference measurement in a wider range.
(3) The invention uses He-Ne laser as indication light to assist the optical system to adjust and sample to adjust and align rapidly, thus greatly improving the installation and debugging efficiency of the whole machine, shortening the test preparation time and enhancing the operability of the equipment.
(4) Compared with the traditional fixed-direction illumination interferometry method, the invention utilizes the SLM (spatial light modulator) to carry out wave front regulation and control on a parallel light field, converts an incident plane wave into a spherical wave sent by a point light source, and generates different sub-interferograms on a camera chip by different illumination sources and common reference wave fronts. The influence of the gradient difference of the wavefront to be detected is partially compensated by the preset inclination angle of the inclined wavefront, the adverse influence of vignetting and high fringe density of an interference pattern on phase unwrapping is overcome, the measurement precision and the measurement range are improved, the tolerance of an imaging optical device used in an interferometer is greatly widened, and the contribution of the high-order error of the optical device is compensated; and the problem of reference wave is overcome by introducing aperture to shield unnecessary light information, thereby solving the actual requirement of urgent high-precision detection in advanced optical manufacturing.
(5) Compared with the traditional interferometry method, the method utilizes the frequency multiplication technology to collect 12 phase-shifting interferometry spectrums of interference light, frequency doubling light and frequency doubling light, wherein the two-stage frequency multiplication technology amplifies the phase to be measured by 4 times, the measurement precision of the common-path coherent measurement is improved by 4 times, and the precision and the signal-to-noise ratio of the interferometry are greatly improved.
(6) The invention utilizes polarized light measurement and pixel shift technology, utilizes a polarized imaging component, can simultaneously obtain four phase shift interferograms, can obtain instantaneous sample surface shape data to be measured by calculation of a data acquisition processing computer data acquisition processing unit, realizes dynamic instantaneous measurement, and can effectively inhibit measurement errors caused by environmental disturbance.
(7) Compared with the technical strategy of using lens collimation in the traditional interferometry method, the invention avoids the influence of optical medium chromatic aberration on measurement precision, and simultaneously is influenced by the reflector manufacturing process, the manufacturing difficulty and cost of the large-size reflector with the same caliber are relatively lower, and the design, production, manufacture and adjustment of the interferometry equipment with the larger caliber can be realized by using relatively lower cost and relatively lower technical and engineering risks.
(8) The technical scheme of the invention solves the problem of 2 pi uncertainty by utilizing multiple wavelengths, and compensates the wave-front gradient influence of the wave-front with large gradient difference (such as an aspheric surface and a free curved surface) by utilizing variable off-axis illumination, so that the measuring range is larger compared with the traditional interferometry method under the condition of not losing the measuring precision, and the high-precision interferometry can be carried out on the wave-front with large gradient difference.
(9) The key components used in the invention are easy to process, easy to obtain, good in interchangeability and easy to replace and maintain.
Further objects and advantages of the present invention will become fully apparent from the following description and the accompanying drawings.
Drawings
Fig. 1 is a schematic diagram of the phase measurement system according to the present invention.
Fig. 2 is a schematic structural diagram of a multi-wavelength phase measurement module of the phase measurement system according to the present invention.
Fig. 3A is a schematic structural diagram of a pixel shift polarization measurement device.
Fig. 3B is a schematic side view of a pixel shift polarization measurement device.
Fig. 3C is a schematic top view of a micro polarizer array of a pixel shift polarization measurement device.
Fig. 3D is a schematic diagram of the structure of a polarizer unit of a micro-polarizer array.
Reference numerals illustrate: a tunable laser 1; he—ne laser 2; a first dichroic mirror 3; an achromatic half wave plate 4; achromatic beam expander group 5; a polarization beam splitting cube 6; a first achromatic quarter waveplate 7; a first silver film mirror 8; a beam splitting cube 9; a spatial light modulator 10; a second achromatic quarter waveplate 11; a first lens 12; a half mirror 13; an off-axis mirror 14; a sample 15 to be measured; mao Boli screen 16; a camera imaging lens 17; a camera 18; a first bandpass filter 19; a multi-wavelength phase measurement module 20; a data acquisition processing unit 21;
A first pixel shift polarization measurement device 2001; a second silver film mirror 2002; a second dichroic mirror 2003; dichroic polarizing beam splitting cube 2004; dichroic half wave plate 2005; a first parabolic silver mirror 2006; a first crystal 2007; a second parabolic silver mirror 2008; a second pixel shift polarization measurement device 2009; a second lens 2010; a second crystal 2011; a third lens 2012; a second band-pass filter 2013; a third pixel shift polarization measurement device 2014; a second half mirror 22; an imaging lens 23; a polarization imaging assembly 24; a microlens array 241; a micro polarizer array 242; photodetector array 243.
Detailed Description
The following description is presented to enable one of ordinary skill in the art to make and use the invention. The preferred embodiments in the following description are by way of example only and other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description may be applied to other embodiments, variations, modifications, equivalents, and other technical solutions without departing from the spirit and scope of the invention.
It will be appreciated by those skilled in the art that in the present disclosure, the terms "vertical," "transverse," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," etc. refer to an orientation or positional relationship based on that shown in the drawings, which is merely for convenience of description and to simplify the description, and do not indicate or imply that the apparatus or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore the above terms should not be construed as limiting the present invention.
It will be understood that the terms "a" and "an" should be interpreted as referring to "at least one" or "one or more," i.e., in one embodiment, the number of elements may be one, while in another embodiment, the number of elements may be plural, and the term "a" should not be interpreted as limiting the number.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically connected, electrically connected or can be communicated with each other; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.
Aiming at the technical problem that the prior interferometry technique cannot realize large-range and high-resolution measurement of large-gradient-difference phases, the invention provides a high-resolution phase measurement system and a high-resolution phase measurement method, which can realize large-range and high-resolution measurement of large-gradient-difference phases, especially aspherical surfaces and free curved surfaces.
As shown in fig. 1 to 3D, a phase measurement system and method according to the present invention is specifically illustrated.
As shown in fig. 1, the phase measurement system includes an interference light generating device, a multi-wavelength phase measurement module 20 disposed on an output optical path of the interference light generating device, and a data acquisition processing unit 21.
Specifically, the interference light generating device is used for generating two beams of polarized light with mutually orthogonal wavelengths lambda 1 And test linear polarized light containing the wavefront information of the surface to be measured of the sample 15 to be measured, and the wavelength of the wavefront information of the surface to be measured of the sample 15 to be measured formed by interference of the reference linear polarized light and the test linear polarized light is lambda 1 Is a light source for emitting light;
specifically, the multi-wavelength phase measurement module 20 is configured to collect a signal having a wavelength λ 1 Is lambda in wavelength 1/2 and λ1 Frequency multiplied light of/4.
Specifically, the data acquisition processing unit 21 is configured to control the interference light generating device and the multi-wavelength phase measurement module 20, and is configured to perform data processing, information extraction and display on the polarized interference pattern acquired by the multi-wavelength phase measurement module 20.
More specifically, the interference light generating device includes a tunable laser 1 for emitting test light, a he—ne laser 2 for emitting indication light, a linearly polarized light generating module, a spatial light modulator, and a wavefront information providing module of a sample 15 to be measured, which are sequentially disposed on the optical path of the test light.
It should be noted that the tunable laser 1 is a test light source, generates narrow linewidth lasers with different wavelengths, is used for solving the problem of uncertainty of a medium 2 pi phase caused by taking a traditional monochromatic light laser as a system light source, and realizes high-precision large-range wavefront measurement. The He-Ne laser 2 is used for coupling visible red laser into a system optical path, and optimizing and simplifying the adjustment of the system.
The linear polarized light generating module is used for coupling the test light and the indication light and converting the test light into a first linear polarized light and a second linear polarized light which have equal energy and mutually orthogonal polarization states so as to output the wavelength lambda 1 Is a reference to linearly polarized light.
The spatial light modulator 10 is configured to perform wavefront phase modulation on a portion of the linearly polarized light output by the linearly polarized light generating module, so as to obtain modulated light, where the modulated light is reflected by the wavefront information providing module of the sample 15 to be tested, enters the sample 15 to be tested, and is sequentially reflected by the sample 15 to be tested back to the wavefront information providing module of the sample 15 to be tested and the linearly polarized light generating module, so as to output test linearly polarized light containing wavefront information of a surface to be tested of the sample 15 to be tested.
It can be understood that the invention constructs a common light path system of the test light and the reference light through the linearly polarized light generating module, the spatial light modulator 10 and the wavefront information providing module of the sample 15 to be tested, and the invention realizes the common light path measurement based on the Fizeau interferometry principle, thereby avoiding the non-common light path error caused by inconsistent optical path and medium in the sample light path and the reference light indicating light path in the traditional measurement method and greatly improving the detection precision and the anti-interference capability of the system.
More specifically, the linearly polarized light generating module includes a linearly polarized light generating assembly disposed on the optical path of the test light, the linearly polarized light generating assembly including a first dichroic mirror 3, an achromatic half wave plate 4, an achromatic beam expander group 5, and a polarization beam splitting cube 6 sequentially disposed on the optical path of the test light.
The first dichroic mirror 3 is used for coupling the test light and the indicator light, that is, the first dichroic mirror 3 functions to couple the light beams emitted by the tunable laser 1 and the He-Ne laser 2, which in this particular embodiment are coaxial with the original test light.
The achromatic half wave plate 4 is used to form the coupled light into linearly polarized light. Specifically, the achromatic half wave plate 4 functions to adjust the polarization state of the light beam of the tunable laser 1 to 45 ° so that the linearly polarized light incident to the polarization beam splitting cube 6 is split into horizontally polarized light and vertically polarized light.
The achromatic beam expander group 5 is used for expanding the linearly polarized light. Specifically, the achromatic beam expander group 5 expands the incident light, and the beam diameter after expansion is slightly smaller than the diameter of the inscribed circle in the working area of the spatial light modulator 10.
The polarization beam splitting cube 6 is configured to split the linearly polarized light passing through the achromatic beam expander group 5 into the first linearly polarized light and the second linearly polarized light having equal energy and mutually orthogonal polarization states.
The first linearly polarized light and the second linearly polarized light are generated by coupling the test light emitted by the tunable laser 1 and the indication light emitted by the He-Ne laser 2 on the first dichroic mirror 3, converting the coupled light into linearly polarized light through the achromatic half wave plate 4, expanding the linearly polarized light by the achromatic beam expander group 5, and then, dividing the linearly polarized light into the first linearly polarized light and the second linearly polarized light which have equal energy and mutually orthogonal polarization states, wherein the linearly polarized light is incident on the polarization beam splitter cube 6.
Further, the linearly polarized light generating module further includes a first achromatic quarter wave plate 7 and a first silver film mirror 8 sequentially disposed at one side of the polarization beam splitting cube 6.
The first achromatic quarter wave plate 7 is used to change the first linearly polarized light into circularly polarized light. Specifically, the first achromatic quarter waveplate 7 functions such that the linearly polarized light incident to the first achromatic quarter waveplate 7 from the polarization beam splitting cube 6 is orthogonal to each other in the polarization state of both the linearly polarized light reflected from the first silver mirror 8 and transmitted through the first achromatic quarter waveplate 7.
The first silver mirror 8 is used to adjust the rotation direction of the circularly polarized light. Specifically, the first silver film mirror 8 functions to reverse the rotation direction of circularly polarized light passing through the first achromatic quarter wave plate 7.
The phase measurement system further comprises a polarization beam splitting cube 6, a spatial light modulator 10 and a beam splitting cube 9, wherein the beam splitting cube 9 is used for normally inputting second linear polarized light of the polarization beam splitting cube 6 to the spatial light modulator 10, reflecting part of modulated light modulated by the spatial light modulator 10 to the wavefront information providing module of the sample 15 to be measured, and normally inputting the other part of modulated light modulated by the spatial light modulator 10 back to the polarization beam splitting cube 6.
It can be understood that the polarization beam splitting cube 6 outputs the first linearly polarized light, the first linearly polarized light enters the first achromatic quarter wave plate 7 and then is changed into circularly polarized light, the circularly polarized light is incident on the first silver film reflecting mirror 8 and then passes through the first achromatic quarter wave plate 7 again, the polarization state of the light beam is changed into original orthogonal linearly polarized light, and the light beam passes through the polarization beam splitting cube 6 and reaches the multi-wavelength phase measuring module 20. While the second linearly polarized light output by the polarization beam splitting cube 6 is normally incident into the spatial light modulator 10 via the beam splitting cube 9 for modulation, a part of the modulated light of the spatial light modulator 10 is normally incident back into the polarization beam splitting cube 6 via the beam splitting cube 9, and another part of the modulated light is reflected to the second achromatic quarter waveplate 11 via the beam splitting cube 9.
Specifically, the wavefront information providing module of the sample 15 to be measured includes a beam splitting cube 9, a second achromatic quarter wave plate 11, a first lens 12, a half mirror 13, and an off-axis mirror 14.
The second achromatic quarter wave plate 11 is used for adjusting the polarization states of the modulated light reflected by the beam splitting cube 9 and the reflected light carrying the wavefront information of the sample 15 to be measured, so that the polarization states of the two light beams are orthogonal to each other.
The focal plane of the first lens 12 coincides with the focal plane of the off-axis mirror 14.
The half mirror 13 is used for imaging a part of the light transmitted through the off-axis mirror 14 to the index light imaging system, and for reflecting a part of the light transmitted through the first lens 12 to the off-axis mirror 14 and a part of the light transmitted through the off-axis mirror 14 back to the first lens 12, respectively.
The reflecting surface of the off-axis reflecting mirror 14 is opposite to the surface to be measured of the sample 15 to be measured, and is used for reflecting the incident modulated light to the surface to be measured of the sample 15 to be measured, and reflecting the light reflected by the surface to be measured of the sample 15 to be measured back into the half-mirror 13 and focusing on the Mao Boli screen 16.
That is, the off-axis reflecting mirror 14 is used to collimate the light beam incident through the focal point of the off-axis reflecting mirror 14, thereby realizing the parallel light output of the plane wavefront, and simultaneously, enlarging the aperture of the measuring light measuring beam, thereby realizing the large aperture interferometry. In particular, the off-axis mirror 14 has a curved reflective surface.
Further, the phase measurement system further comprises an indicator light imaging system electrically connected to the data acquisition processing unit 21, the indicator light imaging system being configured to image an indicator light focus spot. The indication light imaging system comprises a ground glass screen 16, a camera imaging lens 17 and a camera 18 which are sequentially arranged along a transmission light path of the half mirror 13, wherein the Mao Boli screen 16 is used for providing a projection screen for an indication light focusing light spot containing wavefront information on the surface of a sample 15 to be detected; the camera imaging lens 17 is used for imaging a complete planar image of the indication light focusing light spot on the Mao Boli screen 16 on the detector surface of the camera 18; the camera 18 is used to image the indicated light focus spot on the Mao Boli screen 16.
More specifically, the Mao Boli screen 16 is centered with an observation reticle that functions to assist in the debugging of the light path. The light containing the wave front information on the surface of the sample 15 to be measured is focused on the Mao Boli screen 16 to form a visual indication light focusing light spot, the indication light focusing light spot is imaged by an imaging system consisting of the camera imaging lens 17 and the camera 18, the deviation degree of the indication light focusing light spot represents the deviation condition of the surface of the sample 15 to be measured, and the space pose of the measured surface of the sample 15 to be measured needs to be adjusted until the center of the focusing light spot coincides with the focus of the observation cross line during assembly and adjustment, so that accurate alignment is realized.
In particular, the spatial light modulator 10 of the present invention is a reflective spatial light modulator, which is used for performing high-precision phase modulation on an incident wavefront according to the wavefront characteristics of a surface to be measured, simulating standard spherical waves incident in different directions, and performing tilt interferometry. Compared with the traditional fixed-direction illumination interferometry method, the invention utilizes the SLM (spatial light modulator) to carry out wave front regulation and control on a parallel light field, converts an incident plane wave into a spherical wave sent by a point light source, and generates different sub-interferograms on a camera chip by different illumination sources and common reference wave fronts. The influence of the gradient difference of the wavefront to be detected is partially compensated by the preset inclination angle of the inclined wavefront, the adverse influence of vignetting and high fringe density of an interference pattern on phase unwrapping is overcome, the measurement precision and the measurement range are improved, the tolerance of an imaging optical device used in an interferometer is greatly widened, and the contribution of the high-order error of the optical device is compensated; and the problem of reference wave is overcome by introducing aperture to shield unnecessary light information, thereby solving the actual requirement of urgent high-precision detection in advanced optical manufacturing.
Further, the phase measurement system further comprises a first bandpass filter 19 disposed between the interference light generating device and the multi-wavelength phase measurement module 20, wherein the first bandpass filter 19 is used for filtering out the wavelength lambda 1 Stray light in the interference light.
Further, as shown in fig. 2, the multi-wavelength phase measurement module 20 includes a first pixel shift polarization measurement device 2001, a frequency doubling generator, a second pixel shift polarization measurement device 2009, a frequency doubling generator, and a third pixel shift polarization measurement device 2014, which are sequentially disposed.
Specifically, the first pixel shift polarization measurement device 2001 is used for measuring the polarization of light transmitted through the first bandpass filter 19Wavelength lambda 1 The interference wavefront information of the interference light of (a) is subjected to imaging analysis.
In particular, the frequency doubling generator is used for generating the frequency of lambda 1 Is multiplied by interference light to produce a wavelength lambda 1 Frequency multiplied light of/2.
Specifically, the second pixel shift polarization measurement device 2009 is configured to measure a wavelength λ 1 And (2) carrying out imaging analysis on the interference wavefront information of the frequency-doubled light.
In particular, the double frequency generator is used for generating the frequency spectrum with the wavelength lambda 1 Frequency multiplication of frequency multiplication light of/2 to generate a frequency with a wavelength lambda 1 Frequency multiplied light of/4.
Specifically, the third pixel shift polarization measurement device 2014 is configured to measure a wavelength λ 1 And/4, carrying out imaging analysis on the interference wavefront information of the frequency-doubled light.
Further, the multi-wavelength phase measurement module 20 further includes a second silver mirror 2002 and a second dichroic mirror 2003 disposed in this order between the first pixel shift polarization measurement device 2001 and the once-doubled generator, the second silver mirror 2002 reflecting interference light transmitted through the first pixel shift polarization measurement device 2001 to the second dichroic mirror 2003; the second dichroic mirror 2003 transmits light having a wavelength lambda 1 And generating the primary frequency multiplication generator to generate the interference light with the wavelength lambda 1 The frequency-doubled light of/2 is reflected to the second pixel shift polarization measurement device 2009.
Further, the frequency once generator includes a dichroic polarization beam splitting cube 2004, a dichroic half wave plate 2005, a first parabolic silver mirror 2006, a first crystal 2007, a second parabolic silver mirror 2008, which are arranged in this order.
In particular, the dichroic polarizing beam splitting cube 2004 is for transmitting wavelengths λ 1 Is reflected by the first crystal 2007 to generate frequency multiplication with a wavelength lambda 1 Frequency multiplied light of/2.
Specifically, the dichroic half wave plate 2005 is used to adjust the wavelength to λ 1 The polarization direction of the interference light is made to be equal toThe phases of the first crystals 2007 are matched.
In particular, the first parabolic silver mirror 2006 is used to convert a wavelength λ 1 Is focused in the first crystal 2007 to achieve frequency conversion.
Specifically, the first crystal 2007 is used to convert a wavelength λ 1 Is lambda in wavelength generated by frequency multiplication of interference light 1 Frequency multiplied light of/2.
Specifically, the second parabolic silver mirror 2008 is configured to convert a wavelength λ to a wavelength 1 Frequency doubling light collimation of/2.
Further, the frequency doubling generator includes a second lens 2010, a second crystal 2011, a third lens 2012, and a second band-pass filter 2013, which are sequentially arranged.
Specifically, the second lens 2010 is used to convert a wavelength λ 1 Focusing the interference light of the second crystal 2011 to achieve frequency doubling.
Specifically, the second crystal 2011 is configured to convert a wavelength λ to 1 Frequency doubling light frequency doubling generating wavelength lambda of/2 1 Frequency multiplied light of/4.
Specifically, the third lens 2012 is configured to convert a wavelength λ 1 Frequency doubling light collimation of/4.
Specifically, the second band-pass filter 2013 is configured to filter out the wavelength λ 1 Stray light in the frequency multiplied light of/4.
In particular, in this particular embodiment of the invention, the first crystal 2007 is a periodically poled lithium niobate crystal and the second crystal 2011 is a β -barium borate crystal.
Further, the first pixel shift polarization measurement device 2001 includes a beam splitter and a pixel shift polarization measurement device, wherein the pixel shift polarization measurement device is composed of a focusing and collimating system and a camera. The focal collimation system is responsible for collimating the incident parallel light at the camera focal plane. And a part of the interference light which is split by the beam splitter enters a pixel shift polarization measuring device, and the pixel shift polarization measuring device is used for carrying out imaging analysis on interference wavefront information of the interference light split by the beam splitter.
In particular, the first pixel shift polarization measurement device 2001, the second pixel shift polarization measurement device 2009 and the third pixel shift polarization measurement device 2014 have the same structure, that is, all three include a beam splitter for splitting a part of interference light into the pixel shift polarization measurement device and a pixel shift polarization measurement device for performing imaging analysis on interference wavefront information of the interference light split by the beam splitter
Specifically, as shown in fig. 3A to 3D, the pixel shift polarization measurement device includes a second half mirror 22, an imaging lens 23, and a polarization imaging component 24 sequentially disposed, where the polarization imaging component 24 is a polarization imaging component, and includes a microlens array 241, a micro polarizer array 242, and a photodetector array 243 sequentially disposed. In practice, the polarization imaging assembly 24 may employ an IMX250MZR sensor, as the invention is not limited in this regard.
In the present invention, the first pixel shift polarization measuring device 2001 and the second pixel shift polarization measuring device 2009 are disposed on an optical path, and partially optically sample the second half mirror 22, and the third pixel shift polarization measuring device 2014 is disposed at the end of the optical path, and is an incident all-optical sample.
In particular, the light intensity signals recorded by the first pixel shift polarization measurement device 2001, the second pixel shift polarization measurement device 2009 and the third pixel shift polarization measurement device 2014 are transmitted to the data acquisition processing unit 21, the data acquisition processing unit 21 obtains four phase shift interferograms according to the light intensity signal processing, and the high-precision wavefront or surface shape data of the surface of the sample 15 to be measured is obtained by performing phase unwrapping data processing on the four phase shift interferograms.
It should be noted that the data acquisition processing unit 21 is used for controlling the tunable laser 1, the he—ne laser 2, the spatial light modulator 10, the camera 18, the first pixel shift polarization measuring device 2001, the second pixel shift polarization measuring device 2009, the third pixel shift polarization measuring device 2014, and collecting image data acquired by the camera 18, the first pixel shift polarization measuring device 2001, the second pixel shift polarization measuring device 2009, and the third pixel shift polarization measuring device 2014 in real time, and processing, extracting information, and displaying the image data.
Example 1
The phase measurement system includes: the tunable laser 1, the He-Ne laser 2, the first dichroic mirror 3, the achromatic half wave plate 4, the achromatic beam expander group 5, the polarization beam splitting cube 6, the first achromatic quarter wave plate 7, the first silver film mirror 8, the beam splitting cube 9, the spatial light modulator 10, the second achromatic quarter wave plate 11, the first lens 12, the half mirror 13, the off-axis mirror 14, the index light imaging system, the first bandpass filter 19, the multi-wavelength phase measurement module 20, the data acquisition processing unit 21.
The indicator light imaging system includes: the Mao Boli screen 16, the camera imaging lens 17, the camera 18.
The multi-wavelength phase measurement module 20 includes: the first pixel shift polarization measurement device 2001, the second silver mirror 2002, the second dichroic mirror 2003, the dichroic polarization beam splitting cube 2004, the dichroic half wave plate 2005, the first parabolic silver mirror 2006, the first crystal 2007, the second parabolic silver mirror 2008, the second pixel shift polarization measurement device 2009, the second lens 2010, the second crystal 2011, the third lens 2012, the second bandpass filter 2013, the third pixel shift polarization measurement device 2014.
The data acquisition processing unit 21 is electrically connected to the tunable laser 1, the he—ne laser 2, the camera 18, the spatial light modulator 10, and the multi-wavelength phase measurement module 20, respectively.
The phase measurement system of the invention mainly comprises two light paths: one path is a test light path, and the other path is an indication light path. The test light path is that the test light emitted by the tunable laser 1 is incident on the sample 15 to be tested and returns to be incident on the multi-wavelength phase measurement module 20, and the indication light path is that the indication light emitted by the He-Ne laser 2 is incident on the sample 15 to be tested and returns to be incident on the camera 18.
The linear polarization test light emitted by the tunable laser 1 and the indication light emitted by the He-Ne laser 2 are combined through the first dichroic mirror 3 and then pass through the achromatic half wave plate 4, wherein the linear polarization test light emitted by the tunable laser 1 becomes 45 ° linear polarization light. The linearly polarized light is expanded by the achromatic beam expander group 5, and the beam diameter is expanded to be close to but slightly smaller than the effective liquid crystal pixel area of the spatial light modulator 10.
The linear polarization test light emitted by the tunable laser 1 is expanded and then is incident on the polarization beam splitting cube 6, so as to generate linear polarized light with mutually orthogonal polarization states. After the linearly polarized light reflected by the polarization beam splitting cube 6 sequentially passes through the first achromatic quarter wave plate 7 and is reflected by the first silver film reflecting mirror 8 and passes through the first achromatic quarter wave plate 7 again, the light beam becomes an orthogonal polarization state of an incident polarization state, and enters the first band-pass filter 19 through the polarization beam splitting cube 6 as a wavelength lambda 1 Is a reference to linearly polarized light.
Wherein the linear polarization test light transmitted through the polarization beam splitting cube 6 passes through the beam splitting cube 9 to be incident on the spatial light modulator 10. It should be noted that the polarization state of the test light incident on the spatial light modulator 10 is aligned by adjusting the achromatic half wave plate 4 to match in advance with the polarization sensitive direction of the liquid crystal of the spatial light modulator 10.
The spatial light modulator 10 converts an incident plane wave into a spherical wave emitted by a point light source, and generates different focal positions of virtual point light sources according to the calculation hologram, so as to realize off-axis illumination, expand an interferometry area and compensate adverse effects of a gradient of a surface to be measured on the density of measurement interference fringes.
The light phase modulated by the spatial light modulator 10 is reflected by the beam splitting cube 9 in sequence and then is changed into circularly polarized light by the second achromatic quarter wave plate 11, the circularly polarized light is focused by the first lens 12 in sequence and then is reflected by the half mirror 13 and the off-axis reflector 14, and then is incident to the sample 15 to be tested and returns in a primary path carrying phase information of the surface to be tested of the sample 15 to be tested.
The first lens 12 is conjugate to the focal point of the off-axis mirror 14, and directs the test light through the focal point of the off-axis mirror 14 onto the off-axis mirror 14 and is collimated. The collimated test light is incident on the optical surface to be measured of the sample 15 to be measured and reflected, the reflected light sequentially passes through the off-axis reflector 14, the half-mirror 13, the first lens 12, the first achromatic quarter-wave plate 11, and then the polarization state of the light beam becomes the orthogonal direction of the polarization state of the light beam from the first incident light to the first achromatic quarter-wave plate 11, is orthogonal to the polarization sensitive direction of the spatial light modulator 10, is not affected by the phase modulation of the spatial light modulator 10, and sequentially passes through the spatial light modulator 10, the beam splitting cube 9, the polarization beam splitting cube 6, the first bandpass filter 19 and the wavelength lambda 1 Is a reference to a linearly polarized light beam.
The first bandpass filter 19 converts the wavelength lambda of the interference light 1 Is used to filter out light components of other wavelengths. Wavelength lambda 1 Is passed through the beam splitter of the first pixel shift polarization measuring device 2001, and a part of the interference light is incident on the pixel shift polarization measuring device. The first pixel shift polarization measuring device 2001 has a wavelength lambda of the beam split by the beam splitter 1 The interference wavefront information of the interference light of (a) is subjected to imaging analysis.
A part of the interference light transmitted through the first pixel shift polarization measurement device 2001 sequentially passes through the second silver film mirror 2002, the second dichroic mirror 2003, the dichroic polarization beam splitting cube 2004, the dichroic half wave plate 2005, the first parabolic silver mirror 2006, the first crystal 2007, and an incident wavelength is λ by the first crystal 2007 1 Is a wavelength lambda 1 Frequency multiplied light of/2. After being collimated by the second parabolic silver mirror 2008, the wavelength is lambda 1 The frequency-doubled light of/2 is reflected to the second pixel shift polarization measurement device 2009 after passing through the dichroic polarization beam splitting cube 2004 and the second dichroic mirror 2003 in order.
The second pixel shift polarization measurement device 2009 beam splitting part lambda 1 2 and analyzing the polarization interference pattern thereof.
Another part of the wavelengths is lambda 1 The frequency-doubled light of/2 sequentially passes through the second lens 2010 and the second crystal 2011, and the wavelength is lambda through the frequency doubling function of the second crystal 2011 1 Frequency doubling light of/2 to a wavelength lambda 1 Frequency multiplied light of/4. The wavelength is lambda 1 After being collimated by the third lens 2012, the frequency-doubled light of/4 is kept to have the wavelength lambda by the second band-pass filter 2013 1 Light of/4, and then the third pixel shift polarization measurement device 2014 is directed to a wavelength λ 1 And/4, carrying out imaging analysis on the interference wavefront information of the frequency-doubled light.
The data acquisition processing unit 21 is electrically connected to each component, and is used for controlling the phase output of the spatial light modulator 10, collecting the image information acquired by the camera 18, and processing, analyzing and displaying the phase pattern and the data information on the interference image information acquired by the three pixel shift polarization measuring devices.
The mixed light carrying the surface shape information of the sample 15 to be tested is reflected by the off-axis reflector 14, and is focused on the Mao Boli screen 16 through the half mirror 13. The camera imaging lens 17 images the position information of the focal point on the camera 18, and the camera 18 uploads the image information to the data collection processing unit 21. The indicating light focus spot position information is collected, processed, analyzed and displayed by the data acquisition processing unit 21.
In the test preparation stage, the space pose of the surface of the sample 15 to be tested is adjusted according to the center of the indication light focusing light spot on the Mao Boli screen 16 and the center of the cross line on the Mao Boli screen 16, so that the quick alignment of the sample pose to be tested is realized, and the test preparation time is greatly reduced.
And in the system adjustment stage, the polarization direction of the polaroid is adjusted so that the polarization directions of the test light and the indication light are consistent with the polarization direction required by the incidence of the spatial light modulator, and the maximum efficiency of phase modulation is ensured. The spatial light modulator 10 used in the present invention is a reflective spatial light modulator, and does not function when the polarization direction of the reflective spatial light modulator is orthogonal to the polarization direction of the incident light, but changes the optical path by changing the voltage on the liquid crystal molecules when the polarization direction of the reflective spatial light modulator is not orthogonal to the polarization direction of the incident light, so as to achieve the purpose of phase modulation. As shown in fig. 3A, the pixel shift polarization measuring means among the first pixel shift polarization measuring means 2001, the second pixel shift polarization measuring means 2009, and the third pixel shift polarization measuring means 2014 each include: the second half mirror 22, the imaging lens 23 and the polarization imaging component 24 are polarization imaging components. Wherein the polarized imaging assembly 24 includes a microlens array 241, a micropolarizer array 242, and a photodetector array 243, which are disposed in sequence.
Further, fig. 3B is a side view of the pixel shift polarization measurement device, where the microlens array 241, the micro polarizer array 242, and the photodetector array 243 are sequentially arranged from top to bottom; fig. 3C is a top view of the micro polarizer array 242, and fig. 3D is a schematic diagram of a polarizer unit.
Thus, the polarized light of the combined beam passes through the microlens array 241 and the micropolarizer array 242 and then enters the photodetector array 243, and the two-dimensional lattice holes of the photodetector array 243 correspond to the detector pixel points. The pixel shift polarization measurement device collects light intensity signals (i.e. interference fringes) recorded by classifying pixels of the four wire grid polarizers by using the photodetector array 243, and sends the light intensity signals to the data collection processing unit 21, then the data collection processing unit 21 obtains four phase shift interferograms through processing, and optical wavefront information on the surface of the sample 15 to be measured can be obtained through performing phase unwrapping processing on the four phase shift interferograms. The data acquisition processing unit 21 is electrically connected with and controls the tunable laser 1 to emit narrow linewidth lasers with different center wavelengths, so that free switching of multiple wavelengths is realized, measurement of the surface of a wavefront sample 15 to be measured of multiple colors is realized, the influence of 2 pi fuzzy effect commonly existing in the existing single-wavelength optical interference detection can be effectively avoided, and the measurement range of the wavefront with large gradient difference is greatly improved.
Optionally, first lens 12, second lens 2010, and third lens 2012 are achromatic collimating lenses.
Optionally, the photodetector arrays 243 of the pixel shift polarization measurement devices of the first, second, and third pixel shift polarization measurement devices 2001, 2009, 2014 are CMOS sensors.
Optionally, the pixel shift polarization measurement devices of the first pixel shift polarization measurement device 2001, the second pixel shift polarization measurement device 2009, and the third pixel shift polarization measurement device 2014 are IMX250MZR sensors.
Alternatively, the off-axis reflector 14 is an off-axis parabolic reflector.
Optionally, the photodetector array 243 of the camera is a CCD sensor or a CMOS sensor.
The invention also provides a phase measurement method in another aspect, which comprises the following steps:
s1, coupling test light emitted by the tunable laser 1 and indication light emitted by the He-Ne laser 2 on the first dichroic mirror 3, wherein the coupling light is changed into linear polarized light through the achromatic half wave plate 4, and the linear polarized light is expanded by the achromatic beam expander group 5.
S2, the linearly polarized light after beam expansion is incident on the polarization beam splitting cube 6 and then split into a first linearly polarized light and a second linearly polarized light which have equal energy and mutually orthogonal polarization states.
S3, the first linearly polarized light is incident into the first achromatic quarter wave plate 7 to be changed into circularly polarized light, then reflected on the first silver film reflecting mirror 8, the rotation direction is turned, and the circularly polarized light returns to the polarization beam splitting cube 6 through the first achromatic quarter wave plate 7 to form a wavelength lambda 1 To the first bandpass filter 19.
It will be appreciated that the polarizing beamsplitter cube 6, the first achromatic quarter waveplate 7, and the first silver mirror 8 herein function to provide an equivalent reference plane wavefront.
S4, the second linearly polarized light is normally incident to the spatial light modulator 10 through the beam splitting cube 9 to obtain modulated light, at this time, the spatial light modulator 10 adjusts each polarizer array according to the target wave surface, and a part of the modulated light (i.e. the modulated linearly polarized light) is normally incident to the polarized beam splitting cube 6 through the beam splitting cube 9 and then reflected to the first bandpass filter 19; another part is reflected to the second achromatic quarter wave plate 11, reflected to the off-axis reflector 14 via the half-mirror 13, collimated by the off-axis reflector 14, incident to the surface of the sample 15 to be measured and returned to the spatial light modulator along the original path to obtain the wave length lambda containing the wavefront information of the surface to be measured of the sample 15 to be measured 1 Linearly polarized light.
It can be understood that, since the focal plane of the first lens 12 coincides with the focal plane of the off-axis reflector 14 through the half mirror 13, the modulated light energy incident on the second achromatic quarter wave plate 11 is reflected to the off-axis reflector 14 through the half mirror 13, collimated by the off-axis reflector 14, incident on the surface of the sample 15 to be measured, returns to the spatial light modulator 10 along the original path, and part of the light is reflected to the spatial light modulator 10 through the polarization beam splitting cube 6 and then reflected to the first bandpass filter 19.
It will be further appreciated that some polarized light is reflected from the surface of the sample 15 to be measured and then focused onto the Mao Boli screen 16, and then imaged by the camera imaging lens 17 and the camera 18. The visible part of the coupled light is used as the indicating light for system debugging to assist the system debugging.
That is, step S4 includes the steps of:
and S41, a part of the modulated light incident on the second achromatic quarter wave plate 11 is transmitted to the Mao Boli screen 16 through the half mirror 13 to form an indication light focusing light spot, and the indication light focusing light spot is imaged through the camera imaging lens 17 and the camera 18.
S5, wavelength lambda 1 The wavelength of the reference linear polarized light of (2) and the wavefront information of the surface to be measured containing the sample to be measured 15 is lambda 1 Interference between linearly polarized light of (2) to form a wavelength lambda 1 Is a light source, and interference light of the same.
It will be appreciated that, in step S5, the light beam on the first band-pass filter 19 mainly comprises the following parts: the wavelength of lambda reflected by the first achromatic quarter wave plate 7 and the first silver mirror 8 1 Is a reference linearly polarized light of (a); the wave length of the wave front information of the surface to be measured containing the sample to be measured 15 obtained by the reflection of the sample to be measured 15 is lambda 1 Is a linear polarized light, and the two interfere with each other. The first bandpass filter 19 functions to filter out stray light.
S6, wavelength lambda 1 Is incident into the multi-wavelength phase measurement module 20 after passing through the first bandpass filter 19, and has a wavelength lambda obtained by the multi-wavelength phase measurement module 20 1 Is lambda in wavelength 1 /2、λ 1 Frequency multiplied light of/4.
Specifically, step S6 specifically includes the steps of:
s61, wavelength lambda 1 After passing through the first bandpass filter 19, the interference light is incident on the first pixel shift polarization measuring device 2001, and interference fringe information is acquired by the data acquisition processing unit 21.
S62, the wavelength transmitted through the first pixel shift polarization measurement device 2001 is lambda 1 Through the second silver mirror 2002 and the second dichroic mirror 2003, and is incident on a frequency multiplication generator composed of the dichroic polarization beam splitting cube 2004, the dichroic half wave plate 2005, the first parabolic silver mirror 2006, the first crystal 2007, and the second parabolic silver mirror 2008, and has an output wavelength λ 1 Frequency multiplied light of/2.
It will be appreciated that in step S62, the dichroic half wave plate 2005 is to adjust the polarization direction of the input linearly polarized light so that the polarization direction is phase-matched with the first crystal 2007 to achieve frequency multiplication. The first parabolic silver mirror 2006 serves to focus pump light at the center of the crystal length of the first crystal 2007 to achieve a Boyd-Kleinman focused state. The first crystal 2007 has the function of bringing the wavelength to lambda 1 Is multiplied by a frequency to produce interference light having a wavelength lambda 1 Frequency multiplied light of/2. The second parabolic silver mirror 2008 is used to collimate the light beam passing through the first crystal 2007.
S63 wavelength is lambda 1 The frequency-doubled light of/2 is incident to the second pixel shift polarization measurement device 2009, and the data acquisition processing unit 21 performs the data acquisition processing on the light with the wavelength lambda 1 And (2) carrying out imaging analysis on the frequency multiplication light.
It will be appreciated that in step S63, the wavelength is λ 1 The frequency-doubled light of/2 is incident at the second pixel shift polarization measurement device 2009 via the second parabolic silver mirror 2008, the dichroic polarization beam splitting cube 2004, the second dichroic mirror 2003, and the second dichroic mirror 2003.
S64, transmitting the second pixel shift polarization measurement device 2009 with wavelength lambda 1 The frequency-doubled light of/2 passes through a secondary frequency-doubled generator composed of the second lens 2010, the second crystal 2011, the third lens 2012 and the second band-pass filter 2013, and the output wavelength is lambda 1 Frequency multiplied light of/4.
It will be appreciated that in step S64, the second lens 2010 functions to convert the wavelength λ 1 The frequency-doubled light of/2 is focused in the second crystal 2011 to achieve frequency doubling. The second crystal 2011 has the function of inputting a wavelength lambda through the second lens 2010 1 Frequency multiplication of frequency multiplication light of/2 to generate a frequency with a wavelength lambda 1 Frequency multiplied light of/4. The third lens 2012 functions to collimate the incident light beam. The second band-pass filter has the function of passing the wavelength lambda 1 And/4, filtering out light with other wavelengths.
S65, wavelength lambda 1 Frequency multiplication light of/4 is incident onA third pixel shift polarization measurement device 2014, wherein the data acquisition processing unit 21 performs a polarization measurement on the light with a wavelength lambda 1 And/4, carrying out imaging analysis on the interference wavefront information of the frequency-doubled light.
S7, the data acquisition processing unit 21 commonly collects the data with the wavelength lambda 1 Is lambda in wavelength 1 /2、λ 1 And 4, processing, analyzing and displaying the surface shape pattern and the data information by the frequency multiplication light.
It can be understood that the phase measurement system and the method provided by the invention utilize the principle of polarized light interferometry, utilize the second harmonic amplification technology of the frequency doubling crystal to realize 4 times of amplification of the phase to be measured, utilize the pixel shift polarization measurement device to simultaneously generate four interferograms with phase differences of pi/4 in sequence, realize high-precision transient wave front measurement, avoid the influence of environmental disturbance, and utilize the four polarized light interferograms with phase differences of pi/4 in sequence to calculate the wave front of the optical surface to be measured, and have the precision far higher than that of the non-common-path interferometry technology.
In summary, the invention solves the technical problems of 2 pi uncertainty in the prior monochromatic light measurement technology by utilizing a tunable wavelength laser measurement technology, reduces the system measurement precision by utilizing a pixel shift measurement technology, solves the technical problems of difficult environmental disturbance reduction system measurement precision by utilizing a pixel shift measurement technology, realizes multi-view interferometry by utilizing a spatial light modulator, solves the technical problems of high-precision interferometry of large gradient wavefront (such as an aspheric surface and a free curved surface) which cannot be realized by the traditional interferometry, and solves the technical problems of measurement precision improvement by utilizing a multi-wavelength phase amplification technology.
The invention is applicable to interferometry of planar, spherical, aspherical, freeform and discontinuous optical surfaces, and is not limited to the specific application of the phase measurement system and method.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The foregoing examples only represent preferred embodiments of the present invention, which are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.
Claims (9)
1. A phase measurement system, comprising:
an interference light generating device for generating two beams of polarized light having a wavelength lambda orthogonal to each other 1 The reference linear polarized light of the (2) and the test linear polarized light containing the wavefront information of the surface to be tested of the sample to be tested are interfered to form the wavelength lambda of the wavefront information of the surface to be tested of the sample to be tested 1 Is a light source for emitting light;
the multi-wavelength phase measuring module is arranged on the output light path of the interference light generating device and is used for collecting the wavelength lambda 1 The interference light of (a) is multiplied by frequency and multiplied by frequency in turn to obtain wavelength lambda 1/2 and λ1 Polarization interference pattern corresponding to frequency multiplication light;
the data acquisition processing unit is electrically connected with the interference light generating device and the multi-wavelength phase measurement module, and is used for controlling the interference light generating device and the multi-wavelength phase measurement module to work and carrying out data processing, information extraction and display on the polarized interference pattern acquired by the multi-wavelength phase measurement module.
2. The phase measurement system according to claim 1, wherein the interference light generating device comprises a tunable laser for emitting test light, a He-Ne laser for emitting indication light, a linearly polarized light generating module, a spatial light modulator and a sample wavefront information providing module to be measured, which are sequentially arranged on the test light path; the phase measurement system further comprises an indication light imaging system electrically connected with the data acquisition processing unit, and the indication light imaging system is used for imaging an indication light focusing light spot;
The linearly polarized light generation module comprises a linearly polarized light generation assembly arranged on the optical path of the test light, and the linearly polarized light generation assembly comprises a first dichroic mirror, an achromatic half-wave plate, an achromatic beam expander group and a polarization beam splitting cube which are sequentially arranged on the optical path of the test light; wherein the first dichroic mirror is for coupling test light and indicator light; the achromatic half wave plate is used for forming linear polarized light by the coupled light output by the first dichroic mirror; the achromatic beam expander group is used for expanding the linearly polarized light; the polarization beam splitting cube is used for splitting the linearly polarized light into a first linearly polarized light and a second linearly polarized light which are equal in energy and orthogonal in polarization state; the linearly polarized light generating module further comprises a first achromatic quarter wave plate and a first silver film reflecting mirror at one side of the polarization beam splitting cube; wherein the first achromatic quarter wave plate is used for changing the first linearly polarized light into circularly polarized light; the first silver film reflecting mirror is used for reversing the rotation direction of the circularly polarized light;
the space light modulator is a reflective space light modulator and is used for modulating the wave front phase of part of linearly polarized light output by the linearly polarized light generating module to obtain modulated light, the modulated light is reflected by the wave front information providing module of the sample to be tested and enters the sample to be tested, and the modulated light is sequentially reflected by the sample to be tested back to the wave front information providing module of the sample to be tested and the linearly polarized light generating module to output test linearly polarized light containing wave front information of a surface to be tested of the sample to be tested;
The wave front information providing module of the sample to be tested comprises a beam splitting cube, a second achromatic quarter wave plate, a first lens, a half-transparent half-reflecting mirror and an off-axis reflecting mirror, wherein the second achromatic quarter wave plate, the first lens, the half-transparent half-reflecting mirror and the off-axis reflecting mirror are arranged on a reflecting light path of the beam splitting cube; the beam splitting cube is used for normally inputting second linearly polarized light of the polarization beam splitting cube to the spatial light modulator, reflecting part of modulated light modulated by the spatial light modulator to the wavefront information providing module of the sample to be detected, and normally inputting the other part of modulated light back to the polarization beam splitting cube; the second achromatic quarter wave plate is used for adjusting the polarization states of the modulated light reflected by the beam splitting cube and the reflected light carrying the wave front information of the sample to be detected, so that the polarization states of the two beams of light are mutually orthogonal; the first lens is used for enabling the modulated light reflected by the beam splitting cube to be conjugate with the focus of the off-axis reflector; the half mirror is used for transmitting part of light from the first lens and the off-axis reflector to the indication light imaging system for imaging, and is used for reflecting the other part of light from the first lens to the off-axis reflector and reflecting the other part of light from the off-axis reflector back to the first lens respectively; the off-axis reflector is opposite to the surface to be measured of the sample to be measured, and is used for reflecting the incident modulated light to the surface to be measured of the sample to be measured and reflecting the light beam reflected by the surface to be measured of the sample to be measured back to the half-mirror, wherein the reflecting surface of the off-axis reflector is a curved reflecting surface.
3. The phase measurement system according to claim 2, wherein the indicator light imaging system comprises a frosted glass screen, a camera imaging lens and a camera which are sequentially arranged along a transmission light path of the half mirror, wherein the Mao Boli screen is used for focusing the light which is transmitted by the half mirror and contains the wavefront information of the surface of the sample to be measured to form an indicator light focusing light spot; the camera imaging lens is used for imaging a complete plane image of the indication light focusing light spot on the ground glass screen on the surface of the detector of the camera; the camera is used for imaging the indication light focusing light spot on the ground glass screen.
4. The phase measurement system of claim 1, wherein the phase measurement systemThe device also comprises a first band-pass filter arranged between the interference light generating device and the multi-wavelength phase measurement module, wherein the first band-pass filter is used for filtering out the wavelength lambda 1 Stray light in the interference light; the multi-wavelength phase measurement module comprises a first pixel shift polarization measurement device, a primary frequency multiplication generator, a second pixel shift polarization measurement device, a secondary frequency multiplication generator and a third pixel shift polarization measurement device which are sequentially arranged; wherein,
The first pixel shift polarization measurement device is used for measuring the wavelength lambda transmitted through the first band-pass filter 1 Carrying out imaging analysis on interference wavefront information of interference light;
the primary frequency multiplication generator is used for multiplying the wavelength lambda 1 Is multiplied by the interference light of (a) to produce a wavelength lambda 1 Frequency-doubled light of/2;
the second pixel shift polarization measuring device is used for measuring the wavelength lambda 1 Carrying out imaging analysis on interference wavefront information of frequency multiplication light;
the double frequency generator is used for generating the frequency spectrum with the wavelength lambda 1 Frequency multiplication is carried out on frequency multiplication light of/2 to generate a wave length lambda 1 Frequency-doubled light of/4;
the third pixel shift polarization measuring device is used for measuring the wavelength lambda 1 And/4, carrying out imaging analysis on the interference wavefront information of the frequency-doubled light.
5. The phase measurement system according to claim 4, wherein the first pixel shift polarization measurement device, the second pixel shift polarization measurement device and the third pixel shift polarization measurement device have the same structure, and all three include a beam splitter and a pixel shift polarization measurement device, wherein a polarization imaging component, the beam splitter is used for splitting part of interference light into the pixel shift polarization measurement device, the pixel shift polarization measurement device is used for performing imaging analysis on interference wavefront information of the interference light split by the beam splitter, the pixel shift polarization measurement device includes a second half-mirror, an imaging lens and a polarization imaging component which are sequentially arranged, the polarization imaging component includes a micro lens array, a micro polarizer array and a photoelectric detector array which are sequentially arranged, the micro polarizer array is composed of a plurality of polarizer units, each polarizer unit corresponds to one pixel unit of the photoelectric detector array and one micro lens in the micro lens array, and the polarizer unit is composed of wire grid polarizers with pi/4 equi-differential number of four polarization angles;
The first pixel shift polarization measuring device, the second pixel shift polarization measuring device and the third pixel shift polarization measuring device utilize light intensity signals recorded by four wire grid polaroid classification pixels collected by the polarization imaging component and transmit the light intensity signals to the data acquisition processing unit, the data acquisition processing unit obtains four phase shift interferograms according to the light intensity signal processing, and high-precision wavefront or surface shape data of the surface of the sample to be detected is obtained by carrying out phase unwrapping data processing on the four phase shift interferograms;
the multi-wavelength phase measurement module further comprises a second silver film reflecting mirror and a second dichroic mirror which are sequentially arranged between the first pixel shift polarization measurement device and the primary frequency multiplication generator, wherein the second silver film reflecting mirror is used for outputting the wavelength lambda output by the first pixel shift polarization measurement device 1 Is deflected to be incident on the second dichroic mirror; the second dichroic mirror is used for transmitting the wavelength lambda 1 And is used for generating the primary frequency multiplication generator with the wavelength lambda 1 And/2, reflecting the frequency-doubled light to the second pixel shift polarization measurement device.
6. The phase measurement system of claim 5, wherein the frequency doubling generator comprises a dichroic polarization beam splitting cube, a dichroic half wave plate, a first parabolic silver mirror, a first crystal, a second parabolic silver mirror, arranged in that order; wherein,
the dichroic polarization beam splitting cube is used for transmitting the wavelength lambda 1 And a wavelength lambda generated by reflection through frequency multiplication of the first crystal 1 Frequency-doubled light of/2;
the two directionsThe color half wave plate is used for adjusting the wavelength to lambda 1 To the polarization direction of the interference light of the wavelength lambda 1 The polarization direction of the interference light of the first crystal is matched with the phase of the first crystal;
the first parabolic silver mirror is used for reflecting the wavelength lambda 1 Focusing the interference light of the first crystal at the center of the crystal length of the first crystal;
the first crystal is a periodically polarized lithium niobate crystal for converting wavelength lambda 1 Is lambda in wavelength generated by frequency multiplication of interference light 1 Frequency-doubled light of/2;
the second parabolic silver mirror is used for generating the first crystal with the wavelength lambda 1 2, frequency multiplication light collimation;
the secondary frequency multiplication generator comprises a second lens, a second crystal, a third lens and a second band-pass filter which are sequentially arranged; wherein,
The second lens is used for transmitting the wavelength lambda 1 Is focused in the second crystal;
the second crystal is beta-barium borate crystal for converting wavelength to lambda 1 Frequency doubling light frequency doubling generating wavelength lambda of/2 1 Frequency-doubled light of/4;
the third lens is used for transmitting the wavelength lambda 1 Frequency multiplication light collimation of/4;
the second band-pass filter is used for filtering the wavelength lambda 1 Stray light in the frequency multiplied light of/4.
7. The phase measurement method is characterized in that a phase measurement system is adopted to measure surface wavefront or surface shape data of a sample to be measured, and comprises a tunable laser, a He-Ne laser, a first dichroic mirror, an achromatic half-wave plate, an achromatic beam expander group, a polarization beam splitting cube, a first achromatic quarter-wave plate, a first silver film reflecting mirror, a beam splitting cube, a spatial light modulator, a second achromatic quarter-wave plate, a first lens, a half-mirror, an off-axis reflecting mirror, an indicator light imaging system, a first bandpass filter, a multi-wavelength phase measurement module and a data acquisition processing unit; the phase measurement method comprises the following steps:
s1, coupling test light emitted by the tunable laser and indication light emitted by the He-Ne laser on the first dichroic mirror, wherein the coupled light is changed into linear polarized light through the achromatic half wave plate, and the linear polarized light is expanded by the achromatic beam expander group;
S2, the linearly polarized light after beam expansion is incident on the polarization beam splitting cube and then split into a first linearly polarized light and a second linearly polarized light which have equal energy and mutually orthogonal polarization states;
s3, the first linearly polarized light is incident into the first achromatic quarter wave plate to be changed into circularly polarized light, then reflected on the first silver film reflecting mirror, the rotation direction is turned, and the circularly polarized light returns to the polarization beam splitting cube through the first achromatic quarter wave plate to form a wavelength lambda 1 Is a reference linearly polarized light of (a);
s4, modulating the second linearly polarized light which is normally incident to the spatial light modulator through the beam splitting cube to obtain modulated light, and normally incident to the polarized beam splitting cube through the beam splitting cube and then reflecting the modulated light to the first band-pass filter; another portion is reflected to the second achromatic quarter waveplate; a part of modulated light emitted from the second achromatic quarter wave plate is reflected to the off-axis reflector through the semi-transparent semi-reflective mirror, collimated by the off-axis reflector, incident to the surface of the sample to be detected and returned to the spatial light modulator along the original path, and the wavelength lambda of wave front information of the surface to be detected containing the sample to be detected is obtained 1 Another part of the linearly polarized light enters an indicator light imaging system;
s5, wavelength lambda 1 The wavelength of the reference linear polarized light and the wave front information of the surface to be measured containing the sample to be measured is lambda 1 Interference between linearly polarized light of (2) to form a wavelength lambda 1 Is a light source for emitting light;
s6, wavelength lambda 1 The interference light of (2) is incident into the multi-wavelength phase measurement module after passing through the first band-pass filter, and the wavelength lambda is obtained by the multi-wavelength phase measurement module 1 Is lambda in wavelength 1 /2、λ 1 Frequency-doubled light of/4;
s7, the data acquisition processing unit collects the wavelength lambda sent by the multi-wavelength phase measurement module 1 Is lambda in wavelength 1 Frequency doubling light of/2 with wavelength lambda 1 And 4, the interference wavefront information of the frequency multiplication light is processed, analyzed and displayed, and the surface shape pattern and the data information of the sample to be detected are displayed.
8. The phase measurement method according to claim 7, wherein the multi-wavelength phase measurement module includes: the device comprises a first pixel shift polarization measuring device, a second silver film reflecting mirror, a second dichroic mirror, a dichroic polarization beam splitting cube, a dichroic half wave plate, a first parabolic silver mirror, a first crystal, a second parabolic silver mirror, a second pixel shift polarization measuring device, a second lens, a second crystal, a third lens, a second band-pass filter and a third pixel shift polarization measuring device;
The step S6 specifically comprises the steps of:
s61, wavelength lambda 1 The interference light of the first pass filter is transmitted to the first pixel shift polarization measuring device and then enters the first pixel shift polarization measuring device, and interference fringe information is obtained through the data acquisition processing unit;
s62, the wavelength transmitted through the first pixel shift polarization measurement device is lambda 1 The interference light of (a) passes through the second silver film reflector and the second dichroic mirror and enters a primary frequency multiplication generator consisting of the dichroic polarization beam splitting cube, the dichroic half wave plate, the first parabolic silver mirror, the first crystal and the second parabolic silver mirror, and the output wavelength is lambda 1 Frequency-doubled light of/2;
s63 wavelength is lambda 1 The frequency multiplication light of/2 is incident to the second pixel shift polarization measurement device, and the data acquisition processing unit is used for acquiring the light with the wavelength lambda 1 Carrying out imaging analysis on the frequency multiplication light of/2;
s64, transmitting the second pixel shift polarization measurement device with wavelength lambda 1 The frequency multiplication light of/2 passes through a secondary frequency multiplication generator composed of the second lens, the second crystal, the third lens and the second band-pass filter, and the output wavelength is lambda 1 Frequency-doubled light of/4;
s65, wavelength lambda 1 The frequency multiplication light of/4 is incident to a third pixel shift polarization measurement device, and the data acquisition processing unit is used for measuring the wavelength lambda 1 And/4, carrying out imaging analysis on the interference wavefront information of the frequency-doubled light.
9. The phase measurement method according to claim 7, wherein the indicator light imaging system comprises a frosted glass screen, a camera imaging lens, a camera; step S4 includes the steps of:
s41, a part of modulated light incident to the second achromatic quarter wave plate is transmitted to the ground glass screen through the half mirror to form an indication light focusing light spot, and the indication light focusing light spot is imaged through the camera imaging lens and the camera.
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