Laser dual-color differential confocal fixed-plane interference aspheric surface parameter measurement device and method

Abstract

The present invention discloses a laser dual-color differential confocal fixed-plane interference non-spherical parameter measurement device and method, which belongs to the field of surface morphology precision measurement, including a laser system, a differential confocal system, an interference precision measurement system, and a signal processing system; the laser system generates a beam of long-wavelength laser and a beam of short-wavelength laser, the short-wavelength laser enters the differential confocal system for positioning the non-spherical surface to be measured, the signal processing system adjusts the position of the laser dual-color differential confocal fixed-plane interference non-spherical parameter measurement device and the non-spherical surface to be measured according to the positioning, the long-wavelength laser enters the interference precision measurement system and outputs an electrical signal of the non-spherical surface to be measured, and the signal processing system obtains the surface shape result of the non-spherical surface to be measured by processing the electrical signal. The present invention can realize the precise positioning of the non-spherical surface to be measured and the rapid and precise measurement of the surface shape with a common optical path, and has the characteristics of high precision, high sensitivity, high resolution and strong versatility.

Description

Technical Field

[0001] The invention relates to the field of surface topography precision measurement, and in particular to a laser two-color differential confocal fixed-plane interference asphericity parameter measurement device and method. Background Art

[0002] Aspheric optical components, with their excellent optical properties, provide optical designers with more design freedom, and their application scenarios are becoming more and more extensive, especially in the development and application of major technical fields such as space telescopic observation, aerospace remote sensing, laser nuclear fusion, and extreme ultraviolet lithography. The demand for aspheric components with various complex surface shapes is showing an explosive growth trend, and high-precision surface shape detection technology is a key link to ensure the quality of aspheric processing and the normal operation of optical systems. At present, there are many methods for measuring aspheric surfaces, including: contact scanning method, confocal scanning measurement method and interferometry measurement method.

[0003] Contact scanning is the most classic surface measurement method. In this method, the mechanical probe is in continuous contact with the measured surface. Changes in the surface structure and morphology will cause the mechanical probe to move in the vertical direction. By sensing this displacement, the contour information of the measured surface can be obtained. The advantages of this method are its reliability and ease of operation. However, since the probe directly contacts the measured surface, this technology has the risk of damaging the surface, so it is not suitable for soft surfaces, biological surfaces, and device surfaces containing sensitive information. Confocal microscopy measurement technology has unique three-dimensional tomography capabilities and can accurately measure tiny structures, but its imaging speed is slow and has high requirements for laser light intensity at the pinhole. Interferometry technology is widely used in the field of surface measurement due to its high accuracy, wide range of measurement range and high detection efficiency. In particular, interferometry can effectively detect isolated defects. However, the core difficulty of interferometry is how to accurately adjust the axial position between the measurement system and the measured surface (i.e., "precise surface positioning") to ensure that the measured surface can be clearly imaged and to maintain the stability of the light source.

[0004] In interferometric measurement, if the object is out of focus, the measured surface morphology will be significantly distorted, which is manifested as a decrease in height and a widening of width. In severe cases, it is even impossible to accurately distinguish the surface structure. In order to solve this problem, the existing technology usually adopts an indirect calculation method to obtain the complex amplitude distribution of the diffraction surface through inverse diffraction calculation. However, although this calculation method can partially solve the defocus problem, its algorithm is complex and its accuracy and efficiency are often not as good as the direct imaging method.

[0005] An effective improvement idea is to combine interferometry technology with confocal microscopy technology. Confocal microscopy technology can achieve accurate morphology measurement of microstructure surfaces by using its zero-point positioning characteristics and the periodic characteristics of the interference signal. However, the current technical solutions still face some challenges. On the one hand, the interferometry system and the confocal microscopy system usually do not share the optical path. When performing precise positioning and measurement, there is a deviation in the optical path between the two, which increases the complexity of the system and reduces the accuracy and stability. In addition, since the two share the same light source, the power of the frequency-stabilized He-Ne laser is low, resulting in a weak light intensity received by the confocal system, which in turn affects the accuracy of zero-point positioning. At the same time, the energy distribution of the confocal part will weaken the interference signal of the interferometry system, thereby affecting the accuracy of the measurement. On the other hand, in order to reduce the error introduced by the change of light intensity in the dual-channel receiving system and avoid the symmetry problem of the three-channel system, laser interferometry technology often uses a four-channel receiving system, in which the phase difference of each signal is 90°. However, the traditional four-channel receiving unit occupies a large space and is not conducive to array integration, and cannot meet the application scenarios with high requirements for space and size. Summary of the invention

[0006] The present invention aims to provide a laser dual-color differential confocal fixed-surface interference aspheric surface parameter measurement device and method.

[0007] To solve the above problems, the technical solution of the present invention is:

[0008] A laser two-color differential confocal fixed-plane interference non-spherical parameter measuring device comprises: a laser system, a differential confocal system, an interference precision measurement system, and a signal processing system; the laser system generates a long-wavelength laser and a short-wavelength laser, the short-wavelength laser enters the differential confocal system for positioning the non-spherical surface to be measured, the signal processing system adjusts the position of the laser two-color differential confocal fixed-plane interference non-spherical parameter measuring device and the non-spherical surface to be measured according to the positioning, the long-wavelength laser enters the interference precision measurement system and outputs an electrical signal of the non-spherical surface to be measured, and the signal processing system obtains the surface shape result of the non-spherical surface to be measured by processing the electrical signal.

[0009] Furthermore, the laser system, the differential confocal system and the interference precision measurement system are in the same optical path, forming a common optical path structure.

[0010] Furthermore, the laser system includes: a long wavelength laser, a short wavelength laser, a wavelength division multiplexer, a collimator, a filter, a first quarter wave plate, a reflector, a polarization beam splitter, a second quarter wave plate, a first lens, and a dichroic mirror; the wavelength division multiplexer, the collimator, and the polarization beam splitter are coaxially arranged in sequence; the filter, the first quarter wave plate, and the reflector are coaxially arranged in sequence in the reflection direction of the polarization beam splitter; the second quarter wave plate and the first lens are coaxially arranged in sequence in the transmission direction of the polarization beam splitter; the reflected light and the transmitted light after passing through the polarization beam splitter pass through the quarter wave plate twice respectively, and the polarization direction is changed, wherein the transmitted light becomes the reflected light, and the reflected light becomes the transmitted light, and returns to the polarization beam splitter to be merged into one beam and then reaches the dichroic mirror; the differential confocal system is arranged in the transmission direction of the dichroic mirror, and the interference precision measurement system is arranged in the reflection direction of the dichroic mirror.

[0011] Furthermore, the long-wavelength laser is a frequency-stabilized He-Ne laser; and the short-wavelength laser is a semiconductor laser.

[0012] Further, the differential confocal system includes: a second lens, a position sensor, a first beam splitter, a third lens, a first pinhole, a first photodetector, a second beam splitter, a second photodetector, a second pinhole, and a fourth lens; the first lens and the position sensor are coaxially placed in sequence in the reflection direction of the first beam splitter; the second beam splitter is arranged in the transmission direction of the first beam splitter; the third lens, the first pinhole, and the first photodetector are placed in sequence in the transmission direction of the second beam splitter; and the second lens, the second pinhole, and the second photodetector are placed in sequence in the reflection direction of the second beam splitter.

[0013] Furthermore, the interference precision measurement system includes: a four-quadrant interference signal detector and a beam splitter; the beam splitter and the four-quadrant interference signal detector are coaxially placed in sequence in the reflection direction of the dichroic mirror.

[0014] Furthermore, the signal processing system comprises a signal processing card; the position sensor, the first photodetector, the four-quadrant interference signal detector and the second photodetector are all connected to the signal processing card.

[0015] A laser dual-color differential confocal fixed-plane interferometry aspheric surface parameter measurement method comprises the following steps:

[0016] Step S1, connecting the short-wavelength laser light emitted by the short-wavelength laser and the long-wavelength laser light emitted by the long-wavelength laser to the wavelength division multiplexer through optical fibers.

[0017] Step S2, the wavelength division multiplexer outputs linearly polarized light, the linearly polarized light is expanded by the collimating lens group and becomes a parallel light beam, and the parallel light beam is divided into two beams when passing through the polarization beam splitter; one beam is reflected and sequentially passes through the filter and the first quarter wave plate to reach the reflector and return, wherein the short wavelength light is filtered out and only the long wavelength light is returned; the other beam sequentially passes through the polarization beam splitter and the second quarter wave plate, and then is converged by the first lens to the aspheric surface to be measured as the measurement light.

[0018] Step S3, the reflected light and the transmitted light after passing through the polarization beam splitter pass through the quarter-wave plate twice respectively, and the polarization direction is changed, wherein the transmitted light becomes the reflected light, and the reflected light becomes the transmitted light, and then passes through the polarization beam splitter again to merge into a mixed light beam, and the mixed light is again divided into short-wavelength laser and long-wavelength laser when passing through the dichroic mirror, wherein the short-wavelength laser enters the differential confocal system, and the long-wavelength laser enters the interference precision measurement system.

[0019] Step S4, the short-wavelength laser is divided into two beams by the second beam splitter, one beam of light is converged by the second lens onto the position sensor, the position information of the converged light spot is converted into a corresponding electrical signal, and the electrical signal of the position sensor is sent to the signal processing system for processing; the signal processing system adjusts the posture of the laser two-color differential confocal fixed-plane interferometry aspheric parameter measurement device according to the electrical signal of the position sensor, so that the measuring light is perpendicular to the aspheric surface to be measured.

[0020] Step S5, when the measuring light is perpendicular to the aspheric surface to be measured, the other beam of light passing through the second beam splitter in step S4 is evenly divided into two parts by the first beam splitter, and is received by the first photodetector and the second photodetector respectively; the first photodetector and the second photodetector output light intensity signals I1 and I2 respectively.

[0021] Step S6, adjusting the distance between the laser dual-color differential confocal fixed-plane interferometry aspheric parameter measuring device and the aspheric surface to be measured until the light intensity signals I1 and I2 are equal;

[0022] Step S7, when the light intensity signals I1 and I2 are equal, the long wavelength laser in step S3 will be divided into four beams through the center of the beam splitter and fall on the four-quadrant interference signal detector, and the four-quadrant interference signal detector converts the optical signal into a corresponding electrical signal.

[0023] Step S8: the signal processing system performs surface measurement by processing the electrical signal of the four-quadrant interference signal detector.

[0024] Furthermore, the position sensor is used to measure the change in the slope of the aspheric surface to be measured, and the signal processing system adjusts the posture of the laser two-color differential confocal fixed-plane interference aspheric parameter measurement device in real time according to the change in the slope, so that the measuring light always remains perpendicular to the aspheric surface to be measured.

[0025] Further, the aspheric surface to be measured is located at the focal position of the first lens, and the first photodetector and the second photodetector receive maximum signals.

[0026] Beneficial effect: the present invention combines the interference measurement optical path and the confocal measurement optical path in the same optical path, improves the accuracy, sensitivity and stability while reducing the system complexity, significantly improves the system integration, and effectively improves the system's ability to resist common-mode interference; through the differential confocal zero point characteristic, accurate surface positioning is achieved to ensure the integrity and accuracy of the interference signal; dual-wavelength lasers are selected to act on the differential confocal system and the interference precision measurement system respectively, and a high-power semiconductor laser is used for the differential confocal system to ensure that the light intensity value after passing through the pinhole can be effectively received by the photodetector to ensure the accuracy of positioning; a frequency-stabilized He-Ne laser is used for the interference precision measurement system to ensure the frequency stability of the interference measurement, thereby using the absolute zero point of the differential confocal curve to achieve accurate positioning of the measured surface in the interference measurement; the entire device is easy to integrate, providing a solution for the miniaturization of the confocal interference measurement device.

[0027] In order to make the above features and advantages of the invention more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a structural diagram of the laser dual-color differential confocal fixed-plane interference aspheric surface parameter measurement device of the present invention.

[0029] Figure 2 The present invention is a flow chart of the laser dual-color differential confocal fixed-plane interference aspheric surface parameter measurement method.

[0030] 1-long wavelength laser; 2-short wavelength laser; 3-wavelength division multiplexer; 4-collimator group; 5-filter; 6-first quarter wave plate; 7-reflector; 8-polarization beam splitter; 9-second quarter wave plate; 10-first lens; 11-dichroic mirror; 12-second lens; 13-position sensor; 14-first beam splitter; 15-third lens; 16-first pinhole; 17-first photodetector; 18-four-quadrant interference signal detector; 19-beam splitter; 20-second beam splitter; 21-second photodetector; 22-second pinhole; 23-fourth lens; 24-signal processing card. DETAILED DESCRIPTION

[0031] In order to make the purpose and technical solution of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Figure 1 The structure diagram of the laser dual-color differential confocal fixed-plane interference non-spherical parameter measurement device of the present invention. The laser dual-color differential confocal fixed-plane interference non-spherical parameter measurement device of the present invention comprises: a laser system, a differential confocal system, an interference precision measurement system, and a signal processing system; the laser system generates a beam of long-wavelength laser and a beam of short-wavelength laser, the short-wavelength laser enters the differential confocal system for positioning the non-spherical surface to be measured, the signal processing system adjusts the position of the laser dual-color differential confocal fixed-plane interference non-spherical parameter measurement device and the non-spherical surface to be measured according to the positioning, the long-wavelength laser enters the interference precision measurement system and outputs the electrical signal of the non-spherical surface to be measured, and the signal processing system obtains the surface shape result of the surface to be measured by processing the signal of the interference precision measurement system.

[0033] The laser system, the differential confocal system and the interference precision measurement system are in the same optical path, forming a common optical path structure.

[0034] Furthermore, the laser system comprises: a long wavelength laser 1, a short wavelength laser 2, a wavelength division multiplexer 3, a collimator lens group 4, a filter 5, a first quarter wave plate 6, a reflector 7, a polarization beam splitter 8, a second quarter wave plate 9, a first lens 10, and a dichroic mirror 11; the wavelength division multiplexer 3, the collimator lens group 4, and the polarization beam splitter 8 are coaxially arranged in sequence; the filter 5, the first quarter wave plate 6, and the reflector 7 are coaxially arranged in sequence in the reflection direction of the polarization beam splitter 8; The second quarter wave plate 9 and the first lens 10 are coaxially placed in the transmission direction of the polarization beam splitter 8; the reflected light and the transmitted light after passing through the polarization beam splitter 8 pass through the quarter wave plate twice respectively, and the polarization direction is changed, wherein the transmitted light becomes the reflected light, and the reflected light becomes the transmitted light, and returns to the polarization beam splitter 8 to be combined into one beam and then reaches the dichroic mirror 11; the differential confocal system is arranged in the transmission direction of the dichroic mirror 11, and the interference precision measurement system is arranged in the reflection direction of the dichroic mirror 11.

[0035] Optionally, the long-wavelength laser is a frequency-stabilized He-Ne laser with a wavelength of 632.8 nm; the short-wavelength laser is a semiconductor laser with a wavelength range of 473 nm-520 nm.

[0036] Further, the differential confocal system includes: a second lens 12, a position sensor 13, a first beam splitter 14, a third lens 15, a first pinhole 16, a first photodetector 17, a second beam splitter 20, a second photodetector 21, a second pinhole 22, and a fourth lens 23; the second lens 12 and the position sensor 13 are coaxially placed in sequence in the reflection direction of the first beam splitter 20; the second beam splitter 14 is set in the transmission direction of the first beam splitter 20; the third lens 15, the first pinhole 16 and the first photodetector 17 are placed in sequence in the transmission direction of the second beam splitter 14; the second lens 23, the second pinhole 22 and the second photodetector 21 are placed in sequence in the reflection direction of the second beam splitter 14.

[0037] Furthermore, the interference precision measurement system includes: a four-quadrant interference signal detector 18 and a beam splitter 19; the beam splitter 19 and the four-quadrant interference signal detector 18 are coaxially placed in sequence in the reflection direction of the dichroic mirror 11.

[0038] Optionally, the signal processing system includes a signal processing card 24 ; the position sensor 13 , the first photodetector 17 , the four-quadrant interference signal detector 18 and the second photodetector 21 are all connected to the signal processing card 24 .

[0039] refer to Figure 2 As shown, a laser dual-color differential confocal fixed-plane interferometry aspheric surface parameter measurement method comprises the following steps:

[0040] Step S1 , connecting the long wavelength laser light emitted by the long wavelength laser 1 and the short wavelength laser light emitted by the short wavelength laser 2 to the wavelength division multiplexer 3 through optical fibers.

[0041] The power of the short-wavelength laser is high enough to ensure that the light intensity reaching the pinhole of the differential confocal system is strong enough; the long-wavelength laser can ensure the stability of the frequency.

[0042] Step S2, the wavelength division multiplexer 3 outputs linearly polarized light, and the linearly polarized light becomes a parallel light beam after being expanded by the collimating lens group 4. The parallel light beam is divided into two beams when passing through the polarization beam splitter 8; one beam is reflected and sequentially passes through the filter 5 and the first quarter wave plate 6 to reach the reflector 7 and return, wherein the short-wavelength light is filtered out and only the long-wavelength light is returned; the other beam sequentially passes through the polarization beam splitter 8 and the second quarter wave plate 9, and then is converged by the first lens to the aspheric surface to be measured as the measurement light.

[0043] Step S3, the reflected light and the transmitted light after passing through the polarization beam splitter 8 pass through the quarter-wave plate twice respectively, and the polarization direction is changed, wherein the transmitted light becomes the reflected light, and the reflected light becomes the transmitted light, and then passes through the polarization beam splitter 8 again to merge into a mixed light, and the mixed light is again divided into short-wavelength laser and long-wavelength laser when passing through the dichroic mirror 11, wherein the short-wavelength laser enters the differential confocal system, and the long-wavelength laser enters the interference precision measurement system.

[0044] Step S4, the short-wavelength laser is divided into two beams by the second beam splitter 20, one beam of light is converged by the second lens 12 onto the position sensor 13, the position information of the converged light spot is converted into a corresponding electrical signal, and the electrical signal of the position sensor 13 is sent to the signal processing system for processing; the signal processing system adjusts the posture of the laser two-color differential confocal fixed-plane interference aspheric parameter measurement device according to the electrical signal of the position sensor 13, so that the measuring light is perpendicular to the aspheric surface to be measured.

[0045] When the measuring light is perpendicular to the measured surface, the convergent light spot is located at the center of the position sensor 13, and the output electrical signal is 0; when the measuring light is not perpendicular to the measured surface, the convergent light spot deviates from the center of the position sensor 13, and the output electrical signal is not 0.

[0046] The position sensor 13 is used to measure the change in the slope of the aspheric surface to be measured. The signal processing system adjusts the posture of the laser two-color differential confocal fixed-plane interference aspheric parameter measurement device in real time according to the change in the slope, so that the measuring light always remains perpendicular to the aspheric surface to be measured.

[0047] Step S5, when the measuring light is perpendicular to the aspheric surface to be measured, the other beam of light passing through the second beam splitter 20 in step S4 is evenly divided into two parts by the first beam splitter 14, and is received by the first photodetector 17 and the second photodetector 21 respectively; the first photodetector 17 and the second photodetector 21 output light intensity signals I1 and I2 respectively.

[0048] More specifically, when the measuring light is perpendicular to the aspheric surface to be measured, the other beam of light passing through the second beam splitter 20 in step S4 is evenly divided into two parts by the first beam splitter 14, one part is received by the first photodetector 17 after passing through the third lens 15 and the first pinhole 16, and the first pinhole 16 is located in front of the focus of the third lens 15; the other part is received by the second photodetector 21 after passing through the fourth lens 23 and the second pinhole 22, and the second pinhole 22 is located behind the focus of the fourth lens 23, and the first pinhole 16 and the second pinhole 22 are symmetrically distributed about the lens focus; the first photodetector 17 and the second photodetector 21 output light intensity signals I1 and I2 respectively.

[0049] Step S6, adjusting the distance between the laser dual-color differential confocal fixed-plane interferometry aspheric parameter measurement device and the aspheric surface to be measured until the light intensity signals I1 and I2 are equal.

[0050] More specifically, when the light intensity signals I1 and I2 are equal, it indicates that the focus of the first lens 10 falls exactly on the aspheric surface to be measured; when the light intensity signals I1 and I2 are not equal, it indicates that the focus of the first lens 10 deviates from the aspheric surface to be measured. At this time, according to the difference between the light intensity signals I1 and I2, the distance between the laser two-color differential confocal fixed-plane interference aspheric parameter measuring device and the aspheric surface to be measured is adjusted until the light intensity signals I1 and I2 are equal.

[0051] The aspheric surface to be measured is located at the focal position of the first lens 10 , and the first photodetector 17 and the second photodetector 21 receive maximum signals.

[0052] Step S7, when the light intensity signals I1 and I2 are equal, the long wavelength laser in step S3 will be divided into four beams through the center of the beam splitter 19 and fall on the four-quadrant interference signal detector 18, and the four-quadrant interference signal detector 18 will convert the optical signal into a corresponding electrical signal.

[0053] Optionally, the four-quadrant interference signal detector 18 is an integrated array wave plate.

[0054] Step S8: the signal processing system performs surface shape measurement by processing the electrical signal of the four-quadrant interference signal detector 18.

[0055] In summary, the laser dual-color differential confocal fixed-surface interference non-spherical parameter measurement device of the present invention includes: a differential confocal system and an interference precision measurement system, and the measurement method flow is: first, the accurate positioning of the measured non-spherical surface is completed, and the position sensor is used to measure the slope change of the measured non-spherical surface and adjust the system posture in real time, so that the system and the measured non-spherical surface are always kept perpendicular, thereby ensuring that the differential confocal positioning part receives enough light signals, and the system position is adjusted to allow visible light to pass through the non-spherical surface, and the moving measurement lens is focused. When the surface of the non-spherical surface is located at the focus position of the light beam, the photodetector receives the maximum signal, and the positioning function is realized at this time; the interference precision measurement part adopts a four-quadrant interference measurement method based on an array wave plate, and the reference light and the measurement light are combined and divided into four beams by a laser divider, and uniformly irradiated onto the four-quadrant interference signal detector of the integrated array wave plate. The differential confocal positioning and interference precision measurement parts share the same optical path to ensure that the positioning and measurement parts work simultaneously, and semiconductor lasers with different wavelengths and a frequency-stabilized He-Ne laser are selected to realize laser dual-color to ensure that the positioning and measurement parts reach the best working state.

[0056] The present invention adopts a common optical path structure, that is, the interference measurement optical path and the confocal measurement optical path are combined in the same optical path, that is, a common optical path structure design is adopted. The common optical path structure design refers to a technology in which multiple optical elements or optical paths share the same optical channel, so that each measuring element is in the same optical path, thereby improving the accuracy, sensitivity and stability of surface shape measurement, reducing the calibration work of the system, reducing the complexity of the system, saving costs, significantly improving the system integration, and effectively improving the system's ability to resist common mode interference; through the differential confocal zero point characteristic, accurate surface positioning is achieved to ensure the integrity and accuracy of the interference signal; dual-wavelength lasers are selected to act on the differential confocal system and the interference precision measurement system respectively, and a semiconductor laser with a large power is used for the differential confocal system to ensure that the light intensity value after passing through the pinhole can be effectively received by the photoelectric detector to ensure the accuracy of positioning; a frequency-stabilized He-Ne laser is used for the interference precision measurement system to ensure the frequency stability of the interference measurement, so as to realize the accurate positioning of the measured surface in the interference measurement by using the absolute zero point of the differential confocal curve; the entire device is easy to integrate, and a solution is provided for the miniaturization of the confocal interference measurement device.

[0057] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Any person having ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the scope of the attached patent application.

Claims

1. A laser dual-color differential confocal fixed-plane interferometry aspheric surface parameter measurement device, characterized in that: include: A laser system, a differential confocal system, an interference precision measurement system, and a signal processing system; the laser system generates a long-wavelength laser and a short-wavelength laser, the short-wavelength laser enters the differential confocal system for positioning the aspheric surface to be measured, the signal processing system adjusts the position of the laser two-color differential confocal fixed-surface interference aspheric parameter measurement device and the aspheric surface to be measured according to the positioning, the long-wavelength laser enters the interference precision measurement system and outputs an electrical signal of the aspheric surface to be measured, and the signal processing system obtains the surface shape result of the aspheric surface to be measured by processing the electrical signal; The laser system comprises: a long-wavelength laser, a short-wavelength laser, a wavelength division multiplexer, a collimator, a filter, a first quarter-wave plate, a reflector, a polarization beam splitter, a second quarter-wave plate, a first lens, and a dichroic mirror; the wavelength division multiplexer, the collimator, and the polarization beam splitter are coaxially arranged in sequence; the filter, the first quarter-wave plate, and the reflector are coaxially arranged in sequence in the reflection direction of the polarization beam splitter; the second quarter-wave plate and the first lens are coaxially arranged in sequence in the transmission direction of the polarization beam splitter; the reflected light and the transmitted light after passing through the polarization beam splitter respectively pass through the quarter-wave plate twice, and the polarization direction is changed, wherein the transmitted light becomes the reflected light, and the reflected light becomes the transmitted light, and returns to the polarization beam splitter to be combined into one beam and then reaches the dichroic mirror; the differential confocal system is arranged in the transmission direction of the dichroic mirror, and the interference precision measurement system is arranged in the reflection direction of the dichroic mirror; The differential confocal system comprises: a second lens, a position sensor, a first beam splitter, a third lens, a first pinhole, a first photodetector, a second beam splitter, a second photodetector, a second pinhole, and a fourth lens; the first lens and the position sensor are coaxially placed in sequence in the reflection direction of the first beam splitter; the second beam splitter is arranged in the transmission direction of the first beam splitter; the third lens, the first pinhole, and the first photodetector are placed in sequence in the transmission direction of the second beam splitter; the second lens, the second pinhole, and the second photodetector are placed in sequence in the reflection direction of the second beam splitter; The interference precision measurement system comprises: a four-quadrant interference signal detector and a beam splitter; the beam splitter and the four-quadrant interference signal detector are coaxially placed in sequence in the reflection direction of the dichroic mirror.

2. A laser dual-color differential confocal fixed-plane interferometry aspheric surface parameter measurement device as claimed in claim 1, characterized in that: The laser system, the differential confocal system and the interference precision measurement system are in the same optical path, forming a common optical path structure.

3. A laser dual-color differential confocal fixed-plane interferometry aspheric surface parameter measurement device as claimed in claim 1, characterized in that: The long-wavelength laser is a frequency-stabilized He-Ne laser; and the short-wavelength laser is a semiconductor laser.

4. A laser dual-color differential confocal fixed-plane interferometry aspheric surface parameter measurement device as claimed in claim 1, characterized in that: The signal processing system comprises a signal processing card; the position sensor, the first photoelectric detector, the four-quadrant interference signal detector and the second photoelectric detector are all connected to the signal processing card.

5. A method for measuring aspheric surface parameters by laser dual-color differential confocal fixed-plane interferometry, applied to the laser dual-color differential confocal fixed-plane interferometry aspheric surface parameter measuring device as claimed in any one of claims 1 to 4, characterized in that: The steps include: Step S1, connecting the short-wavelength laser light emitted by the short-wavelength laser and the long-wavelength laser light emitted by the long-wavelength laser to the wavelength division multiplexer through optical fibers; Step S2, the wavelength division multiplexer outputs linearly polarized light, the linearly polarized light is expanded by the collimator group and becomes a parallel light beam, and the parallel light beam is divided into two beams when passing through the polarization beam splitter; one beam is reflected and sequentially passes through the filter and the first quarter wave plate to reach the reflector and return, wherein the short-wavelength light is filtered out and only the long-wavelength light is returned; the other beam sequentially passes through the polarization beam splitter and the second quarter wave plate, and then is converged by the first lens to the aspheric surface to be measured as the measurement light; Step S3, after passing through the polarization beam splitter, the reflected light and the transmitted light respectively pass through a quarter wave plate twice, and the polarization direction is changed, wherein the transmitted light becomes the reflected light, and the reflected light becomes the transmitted light, and then passes through the polarization beam splitter again to merge into a mixed light, and the mixed light is again divided into a short-wavelength laser and a long-wavelength laser when passing through the dichroic mirror, wherein the short-wavelength laser enters the differential confocal system, and the long-wavelength laser enters the interferometric precision measurement system; Step S4, the short-wavelength laser is divided into two beams by the second beam splitter, one beam of light is converged by the second lens onto the position sensor, the position information of the converged light spot is converted into a corresponding electrical signal, and the electrical signal of the position sensor is sent to the signal processing system for processing; the signal processing system adjusts the posture of the laser two-color differential confocal fixed-plane interferometry aspheric surface parameter measurement device according to the electrical signal of the position sensor so that the measuring light is perpendicular to the aspheric surface to be measured; Step S5, when the measuring light is perpendicular to the aspheric surface to be measured, the other light beam passing through the second beam splitter in step S4 is evenly divided into two parts by the first beam splitter, and received by the first photodetector and the second photodetector respectively; the first photodetector and the second photodetector output light intensity signals I1 and I2 respectively; Step S6, adjusting the distance between the laser dual-color differential confocal fixed-plane interferometry aspheric parameter measuring device and the aspheric surface to be measured until the light intensity signals I1 and I2 are equal; Step S7, when the light intensity signals I1 and I2 are equal, the long wavelength laser in step S3 will be divided into four beams through the center of the beam splitter and fall on the four-quadrant interference signal detector, and the four-quadrant interference signal detector converts the optical signal into a corresponding electrical signal; Step S8: the signal processing system performs surface measurement by processing the electrical signal of the four-quadrant interference signal detector.

6. A method for measuring parameters of aspheric surfaces by laser dual-color differential confocal fixed-plane interferometry as claimed in claim 5, characterized in that: The position sensor is used to measure the change in the slope of the aspheric surface to be measured. The signal processing system adjusts the posture of the laser two-color differential confocal fixed-plane interference aspheric parameter measurement device in real time according to the change in the slope, so that the measuring light always remains perpendicular to the aspheric surface to be measured.

7. A method for measuring aspheric surface parameters by laser dual-color differential confocal fixed-plane interferometry as claimed in claim 6, characterized in that: The aspheric surface to be measured is located at the focal position of the first lens, and the first photodetector and the second photodetector receive maximum signals.

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