CN211740138U - A combined interferometric measuring device of plane, sphere and paraboloid - Google Patents

Abstract

The utility model discloses a plane, spherical and paraboloid combined interferometric measurement device, belonging to the technical field of optical interference measurement instruments. The device comprises: a laser beam-folding beam expanding system, a main interferometer system and an imaging system; the main interference system is composed of a polarization modulation component , a surface measurement component and a phase modulation component; the polarization component realizes the contrast adjustment of the interferogram by adjusting the angle of the polarizer and the analyzer, the surface measurement component adjusts the optical path structure according to the different surface shapes to be measured, and the phase modulation component according to different The demodulation algorithm modulates the interferogram phase. The utility model has the advantages of accurate and high efficiency, compact structure, simple operation, uniform beam expansion spot, adjustable contrast, and can measure various optical mirror surfaces of plane, spherical and parabolic surfaces, and can use phase shifting, Fourier carrier wave, normalized phase following method ( RPT) the advantages of multiple demodulation algorithms.

Description

A combined interferometric measuring device of plane, sphere and paraboloid

technical field

The utility model belongs to the technical field of optical interference measuring instruments, in particular to a combined interference measuring device of a plane, a spherical surface and a parabolic surface.

Background technique

In the field of industrial production, mechanical or electrical methods are usually used to measure the surface topography of the device. This type of contact measurement often causes certain damage to the test piece, and can only measure a specific trajectory profile or the surface shape distribution of a limited measurement area. Interferometry is a surface topography measurement method based on the principle of optical interference. It has the advantages of fast measurement speed, high precision and non-contact, and is widely used in various surface profile measurements. Common interference structures include Fizeau structure, Taiman Green structure and Mach-Zehnder structure, which have high measurement sensitivity and can measure nanometer-scale optical surfaces, but are not universal for the measurement of different surface shapes.

For example, the Chinese patent document with publication number CN101672632A discloses an optical fiber point diffraction phase-shifting interferometric measurement method. First, the spherical wave diffracted by the optical fiber is reflected to the auxiliary positive lens through the beam splitting prism, and is converted into a convergent spherical wave and Reflected on the surface of the sphere to be measured, the reflected wavefront carrying the information of the sphere to be measured passes through the auxiliary positive lens and the beam splitter prism and converges to the end face of the reference fiber to form a measurement wavefront; remove the sphere to be measured, and other optical components remain unchanged. A flat mirror is placed at the focal point of the auxiliary positive lens, and the aberration brought by the roughness of the end face of the auxiliary positive lens, beam splitter prism and reference fiber can be measured by the same method.

The commonly used demodulation algorithms include phase-shifting algorithm, Fourier carrier algorithm and regularized phase-following method (RPT). The phase-shifting algorithm collects multiple phase-shifted interferograms by phase-shifting. The demodulation speed is fast and the accuracy is high, but the environmental disturbance is required to be small, and multiple interferograms are required. The Fourier carrier algorithm has a fast demodulation speed and only needs a single interferogram to demodulate, but it needs to introduce a carrier, and the accuracy is slightly lower than that of the phase-shift algorithm. The RPT demodulation algorithm only needs a single interferogram to demodulate, but the demodulation time is relatively long. Various demodulation algorithms have their own advantages and disadvantages, and are suitable for different measurement environments.

Utility model content

In order to solve the shortcomings of the prior art, the utility model provides a plane, spherical, and parabolic combined interferometric measurement device, which has the advantages of being accurate and efficient, compact in structure, simple in operation, uniform in the expanded beam spot, and adjustable in contrast, and can measure the plane. , spherical, parabolic optical mirror, can use phase shift, Fourier carrier, regularized phase tracking method (RPT) a variety of demodulation algorithms.

A plane, spherical, and parabolic combined interferometric measurement device, comprising a laser foldback beam expansion system, a main interferometer system and an imaging system, and the laser foldback beam expansion system is used to realize the collimation of the expanded beam;

The main interferometer system includes a polarization modulation component, a surface shape measurement component and a phase modulation component; wherein, the polarization modulation component includes a polarizer, a polarization beam splitter prism, a quarter-wave plate and an analyzer;

After the collimated beam emitted from the laser beam-folding and expanding system enters the main interference system, it is first converted into linearly polarized light by a polarizer, and then divided into two paths of measurement path and reference path by the polarization beam splitter. Among them, the parallel polarization of the measurement path The light is incident on the surface measurement component through the quarter-wave plate, reflected by the surface to be measured in the component, and returns to the original path as the measurement light; the vertically polarized light of the reference path is reflected by the phase modulation component through the quarter-wave plate. The measurement light and the reference light pass through the quarter-wave plate twice, and the polarization states are rotated by 90 degrees respectively, and then pass through the polarization beam splitter prism and the analyzer in turn to form an interference pattern in the imaging system;

The surface shape measurement component is a plane measurement component, a spherical surface measurement component or a parabolic surface measurement component, and the corresponding optical path structure is adjusted according to different surface shapes to be measured.

The utility model extends the distance from the laser to the beam expander through the folded optical path of the right-angle prism, and improves the uniformity of the beam expansion spot; the light intensity ratio of the reference light and the measuring light is adjusted by polarization, so that the contrast of the interferogram can be adjusted; Spherical and parabolic interferometry methods and phase-shifting, Fourier carrier, and RPT demodulation algorithms can handle plane, spherical, and parabolic measurements in different scenarios.

The laser foldback beam expanding system includes a He-Ne laser, a first plane mirror, a first right angle prism, a second right angle prism, a second plane mirror and a laser beam expander arranged in sequence; the He-Ne laser exits The Gaussian beam is folded many times in the laser beam expansion system and reaches the laser beam expander to realize the collimation of the expanded beam.

In the present invention, the laser beam-returning beam expanding system returns the optical path through a right-angle prism. Preferably, the two waist surfaces of the first right-angle prism are coated with an anti-reflection film, which prolongs the Gaussian beam emitted by the He-Ne laser to reach the laser beam expander. distance, which improves the uniformity of the expanded beam spot.

The imaging system includes an imaging mirror and a detector arranged in sequence; the interference field generated by the main interferometer system is imaged onto the detector target surface through the imaging mirror to form a clear interferogram, which can be recovered by a demodulation algorithm. face distribution.

The phase modulation component includes a reference mirror and a piezoelectric ceramic, and the reference mirror is used to reflect the vertically polarized light in the reference path through a quarter-wave plate and return it to the original path as the reference light; the piezoelectric The ceramic is located behind the reference mirror and is used to move the reference mirror position for phase modulation and demodulate the phase of the interferogram.

The polarization modulation component is used for adjusting the contrast of the interferogram; adjusting the angle relationship between the polarizer and the analyzer, changing the light intensity ratio of the reference light and the measuring light, and realizing the adjustable contrast of the interferogram.

The structure of the surface measurement assembly can be installed according to the object to be measured in a plane measurement assembly, a spherical measurement assembly or a parabolic measurement assembly; wherein, the plane measurement assembly is the plane to be measured; the spherical measurement assembly includes: A first aspherical lens and a spherical surface to be measured, wherein the focus of the first aspherical lens is coincident with the spherical center of the spherical surface to be measured; the parabolic surface measurement component includes a second aspherical lens, a middle hole mirror and a spherical surface to be measured A paraboloid, wherein the focal point of the second aspheric lens coincides with the focal point of the paraboloid to be measured, and the mesoporous mirror is placed at the focal point.

In plane measurement, the surface measurement component is the plane to be measured, which realizes the self-collimation reflection of the measurement beam; in spherical measurement, the surface measurement component includes the aspheric lens and the spherical surface to be measured, the focus of the aspheric lens and the spherical center of the spherical surface to be measured. Coincidence, the divergent wavefront of the measurement light is consistent with the spherical surface shape, and the self-collimation reflection of the measurement beam is realized; when the parabolic surface is measured, the surface shape measurement component includes an aspheric lens, a meso-hole mirror and a paraboloid to be measured, and the measurement light is aspherical aberration The lens converges, the focus of the aspheric lens coincides with the focus of the paraboloid to be measured, and the measurement light is reflected by the paraboloid to be measured into parallel light, which is then reflected by the middle hole reflector to realize the self-collimated reflection of the measurement beam;

The phase modulation component introduces different phase modulations corresponding to different demodulation algorithms; when the phase-shifting algorithm is used, the optical path difference between the reference light and the measurement light is changed through piezoelectric ceramics, and different phase-shifting quantities are introduced into the interferogram to collect more data. Interferogram modulation can obtain extremely high interferogram phase demodulation accuracy in a stable environment; when using the Fourier carrier algorithm, by adjusting the angle of the reference mirror, a tilted carrier is introduced into the interferogram, and a single interferogram is collected. The modulation and demodulation speed is fast, which can be used in environments with large vibrations; when using the RPT demodulation algorithm, no phase modulation is required, and single-amplitude interferometric modulation is directly collected, but the demodulation speed is slow, suitable for vibration environments and difficult to detect. Adjustment with reference to mirror.

Compared with the prior art, the utility model has the following beneficial effects:

The utility model combines plane, spherical and parabolic interference measurement devices, utilizes the right-angle prism in the laser beam expansion system to return the optical path, prolongs the distance between the He-Ne laser and the Gaussian beam of the laser beam expander, and improves the uniformity of the beam expansion spot. ;Using the polarization modulation component to change the light intensity ratio of the reference light and the measuring light to realize the adjustment of the contrast of the interferogram; using the structural transformation of the surface measurement component to realize the self-collimation interference of the beam, which effectively solves the problem of the existing interference structure for different surface measurements. Non-universal; it can be combined with phase shift, Fourier, and RPT demodulation algorithms, and the phase modulation component can be used to modulate the phase to meet the phase recovery requirements in different environments and achieve high-precision measurement of the surface to be measured.

Description of drawings

1 is a schematic view of the optical path structure of the plane, spherical, and parabolic combined interferometric measuring device of the present utility model;

Fig. 2 is the optical path schematic diagram of the different surface shape measuring components of the present invention;

3 is an example of a measurement result of a plane mirror using Fourier demodulation algorithm in an embodiment of the present invention;

Fig. 4 is the measurement result example of adopting RPT demodulation algorithm to spherical mirror in the embodiment of the present utility model;

FIG. 5 is an example of a measurement result of a paraboloid using a phase-shift demodulation algorithm in an embodiment of the present invention.

In the figure: S1, laser foldback beam expander system; S2, main interferometer system; S3, imaging system; P1, polarization modulation component, P2-a, plane measurement component; P2-b, spherical measurement component; P2-c, paraboloid Measurement component; P3, phase modulation component; 1, HeNe laser; 2, first plane mirror; 3, first right angle prism; 4, second right angle prism; 5, second plane mirror; 6, laser beam expander ;7, polarizer; 8, polarizing beam splitter prism; 9, quarter wave plate; 10, analyzer; 11, reference mirror; 12, piezoelectric ceramics; 13, imaging mirror; 14, detector; 15 , the plane to be measured; 16, the first aspheric lens; 17, the spherical surface to be measured; 18, the aperture mirror; 19, the paraboloid to be measured; 20, the second aspheric lens.

Detailed ways

The present utility model will be described in further detail below with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present utility model, but do not have any limiting effect on it.

As shown in FIG. 1 , a combined interferometric measuring device of plane, spherical and parabolic surface includes three parts: a laser beam return beam expanding system S1, a main interferometer system S2 and an imaging system S3.

Wherein, the laser foldback beam expanding system S1 includes a He-Ne laser 1, a first plane mirror 2, a first right angle prism 3, a second right angle prism 4, a second plane mirror 5 and a laser beam expander 6 arranged in sequence . The two waist surfaces of the first right-angle prism 3 are coated with anti-reflection coating, and the Gaussian beam emitted from the He-Ne laser 1 is folded several times in the laser fold-back beam expander system, and reaches the laser beam expander 6. The Gaussian beam is folded back through the right-angle prism to prolong the propagation. The uniformity of the expanded beam spot is improved, and the defocus distance of the laser beam expander 6 is adjusted to realize the collimation of the expanded beam.

The main interferometer system S2 includes a polarization modulation component P1, a surface shape measurement component and a phase modulation component P3. The polarization modulation component P1 includes a polarizer 7 , a polarization beam splitter prism 8 , a quarter-wave plate 9 and an analyzer 10 ; the phase modulation component P3 includes a reference mirror 11 and a piezoelectric ceramic 12 .

The collimated beam enters the main interferometer system S2, first passes through the polarizer 7, and then is converted into linearly polarized light, which is divided into measurement light and reference light by the polarization beam splitter 8, wherein the parallel polarized measurement light passes through the quarter-wave plate 9 Incident to the surface measurement component, reflected by the surface to be measured in the component, and returned to the original path; the vertically polarized reference light is reflected by the reference mirror 11 through the quarter-wave plate 9 and returned to the original path; the measurement light and the reference light pass through twice respectively The quarter-wave plate 9, whose polarization states are rotated by 90 degrees, passes through the polarization beam splitter prism 8 and the analyzer 10 in turn to obtain an interference pattern.

The piezoelectric ceramic 12 is located behind the reference mirror, and is used to adjust the position of the reference mirror 11 to perform phase modulation and demodulate the phase of the interferogram. Adjust the angle relationship between the polarizer 7 and the analyzer 9 in the interferometric system, change the light intensity ratio of the reference light and the measurement light, and realize the adjustment of the contrast of the interferogram; adjust the structure of the surface measurement component to cope with different surface measurements.

As shown in FIG. 2 , the plane measuring component P2-a is the plane 15 to be measured; the spherical measuring component P2-b includes a first aspheric lens 16 and a spherical surface 17 to be measured, wherein the focus of the first aspheric lens 16 is the same as the one to be measured. The spherical center of the spherical surface 17 is coincident; the parabolic surface measuring component P2-c includes a second aspherical lens 20, a meso-aspherical mirror 18 and a paraboloid to be measured 19, wherein the focal point of the second aspherical lens 20 is coincident with the focal point of the paraboloid to be measured 19, and the center Aperture mirror 18 is placed at the focal point.

For the phase modulation component P3, when the phase shift algorithm is used, the optical path difference between the reference light and the measurement light is changed by the piezoelectric ceramic 12, and different phase shift amounts are introduced into the interferogram; when the Fourier carrier algorithm is used, the reference light is adjusted by adjusting the reference light. The angle of the mirror is 11, and the inclined carrier is introduced into the interferogram; when the RPT demodulation algorithm is used, the single-frame interferogram modulation is directly collected, and different phase modulations are introduced corresponding to different demodulation algorithms to realize phase shift, Fourier carrier, and RPT. The demodulation algorithm demodulates.

The imaging system S3 includes an imaging mirror 13 and a detector 14 arranged in sequence; the interference field is imaged onto the target surface of the detector 14 through the imaging mirror 13 to form a clear interferogram, and the surface distribution of the surface to be measured is restored by a demodulation algorithm.

The steps of using the above-mentioned plane, sphere, and paraboloid combined interferometric measuring device are:

Step 1: The laser beam-folding and expanding system S1 generates collimated light that coincides with the optical axis. In the main interferometer system S2, a measurement component is set according to the surface to be measured, its spatial position and tilt state are adjusted, and a clear image is collected on the detector 14. the interferogram;

Step 2, adjust the polarizer 7 and the analyzer 10 in the polarization modulation component P1 to obtain a higher contrast of the interferogram, and adjust the phase modulation component P3 according to the demodulation algorithm to realize the phase modulation of the interferogram;

Step 3: After the phase modulation interferogram is collected, the surface shape distribution of the DUT is restored through a demodulation algorithm.

In order to verify the effectiveness of the device of the present invention, the following interferometric measurements are performed on the plane, spherical and parabolic surfaces.

3 is an example of the measurement results of the present utility model using the Fourier demodulation algorithm to the plane in the vibration environment. When the Fourier demodulation algorithm is selected to carry out the plane measurement, the plane measurement component P2-a is used; Spatial position and tilt state, until a clear imaging interferogram with tilted straight fringes is obtained on the detector 14, adjust the angles of the polarizer 7 and the analyzer 10 in the polarization modulation component P1 to enhance the contrast of the interferogram, as shown in Figure 3 (a). Zernike polynomial coefficients are obtained after Fourier demodulation algorithm and wavefront fitting, the coefficients of the first three terms (representing the constant term, the x-direction tilt term and the y-direction tilt term, respectively) are removed and corresponding calculations are performed to obtain the measured value of the plane mirror. As a result, as shown in (b) in Fig. 3, the peak-to-valley (PV) value was 0.3809λ, and the root mean square (RMS) value was 0.0644λ.

4 is an example of the measurement result of the present utility model using the RPT demodulation algorithm to measure the spherical surface in a vibration environment. When selecting the RPT demodulation algorithm to measure the spherical surface, the spherical surface measurement component P2-b is used; wherein the focal length of the aspheric lens is 75mm, and the The spherical surface is a concave spherical surface, and the radius of curvature of the vertex ball is -90mm; first, place a plane mirror at the position to be measured, and adjust the plane mirror to the detector 14 to generate as sparse stripes as possible; place the first aspheric lens 16 in front of the plane mirror, and move the plane mirror to the first At the focal point of the aspheric lens 16, adjust the spatial position and inclination state of the first aspheric lens 16 to generate as sparse stripes as possible on the detector 14; remove the plane mirror and install the spherical surface 17 to be measured, so that the The center of the sphere coincides with the focal point of the first aspheric lens 16, adjust the spatial position and tilt state of the spherical surface 18 to be measured, obtain a clear image of the interferogram on the detector 14, and adjust the polarizer 7 and the detector in the polarization modulation component P1. The angle of the polarizer is 10 to enhance the contrast of the interferogram, as shown in (a) in Figure 4; Zernike polynomial coefficients are obtained after RPT algorithm and wavefront fitting, and the first four terms (representing constant term, x-direction tilt term, y The coefficients of the direction inclination term and the defocus term) are calculated accordingly, and the measurement result of the spherical mirror is obtained, as shown in Fig. 4(b), the PV value is 0.5483λ, and the RMS value is 0.1057λ.

5 is an example of the measurement result of the paraboloid using the phase-shift demodulation algorithm of the present invention in a stable environment. When the phase-shift demodulation algorithm is selected to measure the paraboloid, the paraboloid measurement component P2-c is used; wherein the focal length of the aspheric lens is 75mm, The curvature radius of the apex ball of the paraboloid to be tested is -90mm; first, place a plane mirror at the position to be measured, and adjust the plane mirror to the detector 14 to generate as sparse stripes as possible; place a second aspheric lens 20 in front of the plane mirror, and move the plane mirror to the second aspheric lens At the focal point of the aberration lens 20, adjust the spatial position and inclination state of the second aspheric aberration lens 20 to generate as sparse fringes as possible on the detector 14; Pass through the middle hole mirror 18; install the paraboloid 19 to be measured, make the focus of the paraboloid 19 to be measured coincide with the focus of the second aspheric lens 20, and adjust the spatial position and inclination state of the paraboloid 19 to be measured and the middle hole mirror 18 in the tilted state, obtain a clearly imaged interferogram on the detector 14, adjust the angles of the polarizer 7 and the analyzer 10 in the polarization modulation component P1, and enhance the contrast of the interferogram, as shown in Figure 5(a). The optical path difference between the reference light and the measurement light is changed by the piezoelectric ceramics 12 to obtain multiple phase-shifted interferograms; Zernike polynomial coefficients are obtained through the phase-shift algorithm and wavefront fitting, and the first four terms (representing the constant terms respectively) are removed. , x-direction inclination term, y-direction inclination term and defocus term) and perform corresponding calculations to obtain the measurement result of the parabolic mirror, as shown in (b) in Figure 5, the PV value is 1.1569λ, and the RMS value is 0.2141λ .

To sum up, the combined interferometric measuring device for plane, sphere and paraboloid of the present utility model has a compact structure, is accurate and efficient, and is simple to operate. The uniformity of the light spot is improved by the reentrant optical path, the contrast is adjustable, and it can measure various surface shapes of plane, sphere and paraboloid. , can use phase shift, Fourier carrier, RPT multiple demodulation algorithms, applicable to different measurement environments.

The above-mentioned embodiments describe in detail the technical solutions and beneficial effects of the present utility model. It should be understood that the above-mentioned embodiments are only specific embodiments of the present utility model, and are not intended to limit the present utility model. Any modifications, additions and equivalent replacements made within the scope of the principles of the present invention shall be included within the protection scope of the present invention.

Claims (6)

1. A plane, spherical surface and paraboloid combined interference measuring device is characterized by comprising a laser turn-back beam expanding system, a main interferometer system and an imaging system, wherein the laser turn-back beam expanding system is used for realizing collimation of a beam expanding beam;

the main interferometer system comprises a polarization modulation component, a surface shape measurement component and a phase modulation component; the polarization modulation component comprises a polarizer, a polarization splitting prism, a quarter wave plate and an analyzer;

after collimated light beams emitted by the laser retrace beam expanding system enter the main interference system, the collimated light beams are converted into linearly polarized light through the polarizer, and then are divided into two paths of light rays of a measuring path and a reference path through the polarization beam splitter prism, wherein the parallel polarized light of the measuring path penetrates through the quarter-wave plate to be incident to the surface shape measuring assembly, is reflected by a surface to be measured in the assembly, and returns to the original path to be used as measuring light; the vertical polarized light of the reference path is reflected by the phase modulation component through the quarter-wave plate and returns to the original path to be used as reference light; the measuring light and the reference light respectively pass through the quarter-wave plate twice, the polarization states respectively rotate by 90 degrees, and an interference pattern is formed in an imaging system after the measuring light and the reference light sequentially pass through the polarization beam splitter prism and the analyzer;

the surface shape measuring component is a plane measuring component, a spherical surface measuring component or a paraboloid measuring component, and the corresponding optical path structure is adjusted according to different surface shapes to be measured.

2. The combined planar, spherical and parabolic interferometry device according to claim 1, wherein said laser fold-back beam-expanding system comprises a He-Ne laser, a first planar mirror, a first right-angle prism, a second planar mirror and a laser beam expander, which are arranged in sequence; and the Gaussian beam emitted by the He-Ne laser is folded back for multiple times in the laser folding-back beam expanding system and reaches the laser beam expander, so that the collimation of the expanded beam is realized.

3. The combined planar, spherical and parabolic interferometry device according to claim 2, wherein both waist surfaces of said first right-angle prism are coated with a reflection increasing film.

4. The combined planar, spherical and parabolic interferometry device according to claim 1, wherein said imaging system comprises an imaging mirror and a detector arranged in sequence; the interference field generated by the main interferometer system is imaged on the target surface of the detector through the imaging mirror to form a clear interference pattern.

5. The combined planar, spherical and parabolic interferometer of claim 1, wherein the phase modulation module comprises a reference mirror and piezoelectric ceramics, the reference mirror is configured to reflect the vertically polarized light in the reference path back to the reference path as the reference light after passing through the quarter-wave plate; the piezoelectric ceramic is positioned behind the reference mirror and used for moving the position of the reference mirror to perform phase modulation and demodulating the phase of the interference pattern.

6. The planar, spherical and parabolic combined interferometry device of claim 1, wherein the planar measurement component is a plane to be measured; the spherical surface measuring component comprises a first spherical aberration eliminating lens and a spherical surface to be measured, wherein the focus of the first spherical aberration eliminating lens is superposed with the spherical center of the spherical surface to be measured; the paraboloid measuring component comprises a second aplanatic lens, a middle hole reflector and a paraboloid to be measured, wherein the focus of the second aplanatic lens is coincided with the focus of the paraboloid to be measured, and the middle hole reflector is arranged at the focus.

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