A surface property measuring device and method for an ultra-smooth surface optical element

Abstract

The application relates to a surface characteristic measuring device and method, in particular to a surface characteristic measuring device and method for super-smooth surface optical elements, which are used to solve the problems that, when a super-smooth surface optical element is detected by a scanning probe profiler, the surface of the to-be-detected optical element needs to be contacted, the to-be-detected optical element is easily damaged, the application range is limited by the material of the to-be-detected optical element, the detection process is complex, professional technical personnel are needed to operate, and the detection and maintenance costs are high. The surface characteristic measuring device for the super-smooth surface optical element realizes double-light-path measurement through a polarization beam splitter prism, a first measuring assembly and a second measuring assembly, a reference signal of a synchronous acquisition system is calculated with a detection signal, the error of the measuring device is effectively reduced, and the measurement precision is improved. The application can realize sub-nanometer level measurement precision and is suitable for high-precision surface characteristic measurement.

Description

Technical Field

[0001] This invention relates to a surface property measurement device and method, specifically to a surface property measurement device and method for an ultra-smooth surface optical element. Background Technology

[0002] The use of ultra-smooth surface optical components is becoming increasingly common in many fields such as aerospace, photolithography, and scientific research. With the rapid advancement of related technologies in microelectronics, short-wavelength optics, and thin-film optics, and the emergence of large scientific facilities and high-end instruments, the requirements for the surface quality of optical components are becoming increasingly stringent.

[0003] Ultrasmooth surface optical elements refer to optical elements with a root mean square (RMS) surface roughness of less than 1 nanometer. They possess a complete physical structure with a perfect crystal lattice; surface damage is strictly controlled, resulting in high surface precision and extremely low residual stress. Ultrasmooth surfaces are a key technology in modern science and technology, widely used in optics, semiconductors, aerospace, electronics, and other fields. The preparation of ultrasmooth surfaces is crucial for improving equipment performance and enhancing product quality.

[0004] Generally, limitations in manufacturing environment and processing technology lead to defects such as bubbles, scratches, and burrs in optical components during processing, causing a significant decline in their quality. If such optical components are used without being detected, they can have unpredictable and uncontrollable effects on the optical system. Even a tiny burr or scratch can have a fatal impact on the optical system, rendering it unable to function properly. Therefore, in addition to processing technology, the detection technology for ultra-smooth surfaces is also a crucial factor restricting the development of this field. In particular, the surface characteristics of optical components can reflect a wealth of information and are a key indicator in the field of optics.

[0005] Measuring the surface shape of ultra-smooth surfaces presents several unique challenges. First, due to their extremely high smoothness, traditional touch-based measurement methods often fall short. Second, ultra-smooth surfaces frequently possess complex geometries, such as aspherical or freeform surfaces, further complicating the measurement process. Furthermore, the sensitivity of ultra-smooth surfaces to environmental factors, such as variations in temperature and humidity, can also affect the measurement results.

[0006] For surface inspection of ultra-smooth surfaces, traditional methods involve scanning probe profilometers. This method obtains information about the surface by directly contacting the surface to be measured with the inspection device. However, firstly, this method requires contact with the surface of the object being measured, which can easily cause secondary damage to the component. Secondly, its applicability is limited by the material of the object being measured; for example, soft or easily deformable objects cannot be accurately measured. Moreover, this method is complex, requires specialized technicians to operate, and is costly. Furthermore, it requires regular maintenance and calibration to ensure accuracy and stability, further increasing the maintenance costs and time of the measurement system. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of using a scanning probe profilometer to detect the surface characteristics of ultra-smooth surface optical elements. This method requires contact with the surface of the optical element under test, which can easily cause secondary damage. The applicability is limited by the material of the optical element under test. Furthermore, the detection process is complex, requires professional technicians to operate, and has high detection and maintenance costs. Therefore, this invention provides a device and method for measuring the surface characteristics of ultra-smooth surface optical elements.

[0008] To address the shortcomings of the existing technology, the present invention provides the following technical solution:

[0009] A surface characteristic measurement device for an ultra-smooth surface optical element, characterized in that it includes a light source assembly, a polarizing beam splitter, a first measurement assembly, a second measurement assembly, a signal processing unit, and a computer;

[0010] The light source assembly is used to generate incident light and divide the incident light into a first ray and a second ray with different frequencies and mutually perpendicular polarization directions;

[0011] The polarizing beam splitter is positioned in the optical paths of the first and second rays to generate reflected light, transmitted light, reflected light, and transmitted light of the second ray; the optical element under test is positioned in the transmitted light path of the first ray.

[0012] The first measurement component includes a reflecting mirror b and a reflecting mirror d, sequentially arranged in the transmitted light path of the second light ray, as well as a prism a, an analyzer a, a lens group a, and a photodetector a. The reflecting mirror b and reflecting mirror d are used to input the transmitted light of the second light ray into the prism a. The prism a is arranged in the reflected light path of the first light ray and is used to refract the transmitted light of the second light ray and the reflected light of the first light ray into the analyzer a. The analyzer a is used to cause interference between the reflected light of the first light ray and the transmitted light of the second light ray, and output a first interference light. The lens group a and the photodetector a are sequentially arranged in the light path of the first interference light and are used to collect a first signal after focusing.

[0013] The second measurement component includes a reflector c disposed in the optical path of the reflected second light, as well as a reflector e, a prism b, an analyzer b, a lens group b, and a photodetector b. The reflector c is used to refract the reflected second light into the prism b. The reflector e is used to input the scattered light generated after the transmitted light of the first light is focused on the surface of the optical element under test into the prism b. The prism b is used to refract the reflected and scattered light of the second light into the analyzer b. The analyzer b is used to cause the reflected and scattered light of the second light to interfere, outputting a second interference light. The lens group b and the photodetector b are sequentially disposed in the optical path of the second interference light to collect the second signal after focusing.

[0014] The input terminal of the signal processing unit is connected to the output terminals of photodetector a and photodetector b, respectively, and the output terminal is connected to the input terminal of the computer. It is used to calculate the surface information of the optical element under test by the first signal and the second signal and input it into the computer.

[0015] Furthermore, the light source assembly includes a light source for generating incident light, and a beam-shaping and expanding lens group, a Bragg modulator, a reflecting mirror a, an aperture, and a λ / 2 waveplate sequentially arranged in the incident light path; the beam-shaping and expanding lens group is used to shape and expand the incident light and output the shaped and expanded light; the Bragg modulator is used to generate a first light and a second light with different frequencies and mutually perpendicular polarization directions by modulation; the aperture is used to filter out stray light interference; the λ / 2 waveplate is used to adjust the polarization state of the first light and the second light and input them into the polarization beam splitter.

[0016] A Bragg modulator is used to generate two beams of light with different frequencies and perpendicular polarization directions, effectively avoiding interference from stray light and feedback light.

[0017] Furthermore, an acousto-optic frequency shifter is provided between the shaping and beam-expanding lens group and the Bragg modulator. The acousto-optic frequency shifter is used to perform frequency modulation processing on the light after shaping and beam expansion.

[0018] By using an acoustic-optical frequency shifter to perform frequency shifting on the signal, low-frequency noise in the environment can be effectively avoided.

[0019] Furthermore, the second measuring component also includes an aberration-free condenser lens disposed in the transmitted light path of the first light ray, used to focus the transmitted light of the first light ray onto the surface of the optical element under test, and to converge the scattered light generated on the surface of the optical element under test to the reflector e.

[0020] Aberration-free condenser lenses can correct spherical and chromatic aberrations, reduce reflection and absorption, and increase light transmittance. This allows more light to pass through the lens, improving the brightness and efficiency of the optical system.

[0021] Furthermore, it also includes a high-precision translation stage, on which the optical element under test is placed, and the output of the computer is connected to the high-precision translation stage for moving the optical element under test by controlling the high-precision translation stage.

[0022] Meanwhile, this invention also discloses a method for measuring the surface characteristics of an ultra-smooth surface optical element, which is characterized by including the following steps:

[0023] Step 1: Set up a surface characteristic measurement device for the above-mentioned ultra-smooth surface optical element;

[0024] Step 2: Generate incident light through the light source assembly, and split the incident light into a first ray and a second ray with different frequencies and perpendicular polarization directions, and input them into a polarizing beam splitter; generate reflected light of the first ray, transmitted light of the first ray, reflected light of the second ray, and transmitted light of the second ray through the polarizing beam splitter;

[0025] Step 3: The reflected light of the first ray enters prism a, while the transmitted light of the second ray enters prism a after passing through mirrors b and d. The second ray and the reflected light of the first ray are transmitted and reflected in prism a respectively, and then enter analyzer a. Interference occurs in analyzer a, and the first interference light is output. The first interference light is focused by lens group a onto photodetector a to obtain the first signal, which is then output to the signal processing unit.

[0026] Simultaneously, the transmitted light of the first ray is focused onto the surface of the optical element under test, generating scattered light, which is then incident on prism b through mirror e; the reflected light of the second ray passes through mirror c and then incident on prism b, where it is reflected and transmitted with the scattered light in prism b before entering analyzer b. Interference occurs in analyzer b, and a second interference light is output; the second interference light is focused onto photodetector b through lens group b to obtain a second signal, which is then output to the signal processing unit.

[0027] Step 4: The signal processing unit calculates the first signal and the second signal to obtain the surface information of the optical element under test, and outputs it to the computer to complete the surface characteristic measurement of the ultra-smooth surface optical element.

[0028] Furthermore, in step 4, before completing the surface characteristic measurement of the ultra-smooth surface optical element, the following steps are also included: determining whether the measurement of each subdivided region of the optical element under test has been completed. If so, the process ends and the surface characteristic measurement of the ultra-smooth surface optical element is completed. Otherwise, the optical element under test is moved into the next subdivided region by controlling the high-precision translation stage, and then the process returns to step 2.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] (1) This invention provides a surface characteristic measurement device for ultra-smooth surface optical elements. It achieves dual-optical-path measurement through a polarizing beam splitter, a first measurement component, and a second measurement component. The device synchronously acquires the system's reference signal and performs calculations with the detection signal, effectively reducing the measurement device's error and improving measurement accuracy. This invention can achieve sub-nanometer level measurement accuracy and is suitable for high-precision surface characteristic measurement.

[0031] This invention not only obtains the surface characteristics of the optical element under test, but also simultaneously measures other parameters, such as refractive index and film thickness, enabling a more comprehensive and accurate understanding of the optical properties of the element. Compared to using light intensity characteristics as the primary feature for optical detection, identification, and characteristic research of optical elements, this invention is less susceptible to interference from external measurement environments and is more comprehensive and accurate, providing more information for scientific research and engineering applications.

[0032] (2) The present invention provides a surface characteristic measurement method for an ultra-smooth surface optical element. It is a non-contact measurement method that is applicable to surfaces of various shapes, including planes, spheres, and optical elements with complex surface shapes, such as aspherical or freeform surfaces. It will not cause any damage to the target object and can therefore be applied to elements of various materials and shapes.

[0033] (3) The present invention provides a method for measuring the surface characteristics of an ultra-smooth surface optical element. It is simple to operate, fast to measure, and can acquire a large amount of data in a short time to achieve real-time measurement. It is suitable for rapid detection and real-time monitoring of surface shape and is very beneficial for scenarios that require large-scale surface shape measurement.

[0034] (4) The present invention provides a method for measuring the surface characteristics of an ultra-smooth surface optical element. This method uses multi-beam polarized light for measurement, achieving high resolution and high sensitivity, and enabling high-precision measurement of the surface morphology of the optical element under test. Compared to traditional measurement methods, the present invention provides more accurate data and more detailed surface morphology information.

[0035] (5) The present invention provides a method for measuring the surface characteristics of an ultra-smooth surface optical element. It uses a Bragg modulator to generate two beams of light with different frequencies and perpendicular polarization directions, effectively avoiding interference from stray light and feedback light.

[0036] (6) The present invention provides a method for measuring the surface characteristics of an ultra-smooth surface optical element. In the process of optical signal interference, no glass plate is used to change the polarization state of the light, thus eliminating the linear error introduced by the glass plate from the source, while reducing costs and lowering the difficulty of operation.

[0037] (7) The present invention provides a method for measuring the surface characteristics of an ultra-smooth surface optical element, which uses an acousto-optic frequency shifter to perform frequency shifting processing on the signal, effectively avoiding low-frequency noise in the environment.

[0038] (8) The present invention provides a method for measuring the surface characteristics of an ultra-smooth surface optical element. An aberration-free condenser lens is used in front of the optical element under test to correct spherical aberration and chromatic aberration, reduce reflection and absorption, and improve light transmittance. This allows more light to pass through the aberration-free condenser lens, improving the brightness and efficiency of the measuring device. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of an embodiment of the surface characteristic measurement device for an ultra-smooth surface optical element according to the present invention.

[0040] The reference numerals in the attached figures are explained as follows: 1-Light source; 2-Shaping beam expander group; 3-Acousto-optic frequency shifter; 4-Bracket modulator; 5-Reflector a; 6-Aperture stop; 7-λ / 2 waveplate; 8-Polarizing beam splitter prism; 9-Reflector b; 10-Reflector c; 11-Reflector d; 12-Prism a; 13-Analyzer a; 14-Lens group a; 15-Photodetector a; 16-Aberration-free condenser lens; 17-Optical element under test; 18-High-precision translation stage; 19-Reflector e; 20-Prism b; 21-Analyzer b; 22-Lens group b; 23-Photodetector b; 24-Signal processing unit; 25-Computer. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and exemplary embodiments.

[0042] Reference Figure 1 A surface characteristic measurement device for an ultra-smooth surface optical element includes a light source assembly, a polarizing beam splitter 8, a first measurement assembly, a second measurement assembly, a signal processing unit 24, a high-precision translation stage 18, and a computer 25.

[0043] The light source assembly includes a light source 1 for emitting incident light rays, and a beam-shaping and expanding lens group 2, an acousto-optic frequency shifter 3, a Bragg modulator 4, a reflector a5, an aperture 6, and a λ / 2 waveplate 7, which are sequentially arranged in the optical path of the incident light rays.

[0044] If light source 1 can be a He-Ne laser, then the incident light is a laser beam.

[0045] The beam-shaping and beam-expanding lens group 2 is used to shape and expand the incident light beam and output the shaped and expanded light beam; the acousto-optic frequency shifter 3 is used to perform frequency modulation processing on the shaped and expanded light beam and output the frequency-modulated light beam; the Bragg modulator 4 is used to modulate the frequency-modulated light beam and generate a first light beam and a second light beam with different frequencies and mutually perpendicular polarization directions; the aperture 6 is used to filter out other stray light interference; the λ / 2 waveplate 7 is used to adjust the polarization state of the first light beam and the second light beam and input them into the polarization beam splitter prism 8.

[0046] The polarizing beam splitter 8 is used to generate the reflected light of the first ray, the transmitted light of the first ray, the reflected light of the second ray, and the transmitted light of the second ray.

[0047] The optical element under test 17 is positioned on the transmitted light path of the first light ray and on the high-precision translation stage 18. The output of the computer 25 is connected to the high-precision translation stage 18 and is used to move the optical element under test 17 by controlling the high-precision translation stage 18 to ensure that the transmitted light of the first light ray sweeps through every subdivided region of the optical element under test 17.

[0048] The first measuring component includes a reflector b9 and a reflector d11, sequentially arranged in the transmitted light path of the second light ray, as well as a prism a12, an analyzer a13, a lens group a14, and a photodetector a15. Reflectors b9 and d11 input the transmitted light of the second light ray into the prism a12. The prism a12 is arranged in the reflected light path of the first light ray and refracts the transmitted light of the second light ray and the reflected light of the first light ray into the analyzer a13. The analyzer a13 causes interference between the reflected light of the first light ray and the transmitted light of the second light ray, outputting a first interference light. The lens group a14 and the photodetector a15 are sequentially arranged in the optical path of the first interference light and are used to collect a first signal after focusing.

[0049] The second measurement assembly includes a reflector c10 positioned on the reflected light path of the second light beam, an aberration-free condenser lens 16 positioned on the transmitted light path of the first light beam, a reflector e19, a prism b20, an analyzer b21, a lens group b22, and a photodetector b23. The reflector c10 refracts the reflected light of the second light beam into the prism b20. The aberration-free condenser lens 16 focuses the transmitted light of the first light beam onto the surface of the optical element 17 under test. The reflector e19 refracts the scattered light generated after the transmitted light of the first light beam is focused onto the surface of the optical element 17 under test into the prism b20. The prism b20 inputs the reflected and scattered light of the second light beam into the analyzer b21. The analyzer b21 causes the reflected and scattered light of the second light beam to interfere, outputting a second interference light. The lens group b22 and the photodetector b23 are sequentially positioned on the optical path of the second interference light to collect the second signal after focusing.

[0050] The input terminals of the signal processing unit 24 are connected to the output terminals of photodetector a15 and photodetector b23, respectively, and the output terminals are connected to the input terminals of computer 25. The unit is used to calculate the surface information of the optical element 17 under test by the first signal and the second signal and input the information into computer 25.

[0051] A method for measuring the surface properties of an ultra-smooth surface optical element includes the following steps:

[0052] Step 1: Set up a surface characteristic measurement device for the above-mentioned ultra-smooth surface optical element;

[0053] Step 2: An incident light beam is emitted from light source 1 to beam-shaping and beam-expanding lens group 2; the incident light beam is shaped and expanded by beam-shaping and beam-expanding lens group 2 and then output to acousto-optic frequency shifter 3; the acousto-optic frequency shifter 3 performs frequency modulation processing on the shaped and expanded light beam and outputs the frequency-modulated light beam to Bragg modulator 4; the Bragg modulator 4 modulates the frequency-modulated light beam to generate a first light beam and a second light beam with different frequencies and perpendicular polarization directions, and outputs them to aperture 6; after filtering out other stray light interference by aperture 6, the light beam is output to λ / 2 waveplate 7; after adjusting the polarization state of the first light beam and the second light beam by λ / 2 waveplate 7, the light beam is output to polarizing beam splitter prism 8.

[0054] The polarizing beam splitter 8 generates the reflected light of the first ray, the transmitted light of the first ray, the reflected light of the second ray, and the transmitted light of the second ray.

[0055] Step 3: The reflected light of the first ray enters prism a12, while the transmitted light of the second ray enters prism a12 after passing through mirror b9 and mirror d11. The second ray and the reflected light of the first ray are transmitted and reflected in prism a12 respectively, and then enter analyzer a13. Interference occurs in analyzer a13, and the first interference light is output. The first interference light is focused by lens group a14 onto photodetector a15 to obtain the first signal, which is then output to signal processing unit 24.

[0056] Simultaneously, the transmitted light of the first ray is focused onto the surface of the optical element 17 under test, generating scattered light, which then passes through the reflector e19 and enters the prism b20; the reflected light of the second ray passes through the reflector c10 and enters the prism b20, where it is reflected and transmitted with the scattered light, and then enters the analyzer b21. Interference occurs in the analyzer b21, and the second interference light is output; the second interference light is focused by the lens group b22 onto the photodetector b23 to obtain the second signal, which is then output to the signal processing unit 24.

[0057] Step 4: The signal processing unit 24 calculates the first signal and the second signal to obtain the surface information of the optical element 17 under test, and outputs it to the computer 25.

[0058] Step 5: Determine whether the measurement of each subdivided region of the optical element under test 17 has been completed. If yes, end the process and complete the surface characteristic measurement of the ultra-smooth surface optical element. Otherwise, after moving the optical element under test 17 into the next subdivided region by controlling the high-precision translation stage 18, return to step 2.

Claims

1. A surface characteristic measurement device for an ultra-smooth surface optical element, characterized in that: It includes a light source assembly, a polarizing beam splitter (8), a first measurement assembly, a second measurement assembly, a signal processing unit (24), and a computer (25); The light source assembly is used to generate incident light and divide the incident light into a first ray and a second ray with different frequencies and mutually perpendicular polarization directions; The polarizing beam splitter (8) is disposed in the optical path of the first ray and the second ray, and is used to generate the reflected light of the first ray, the transmitted light of the first ray, the reflected light of the second ray, and the transmitted light of the second ray; the optical element to be tested (17) is disposed in the optical path of the transmitted light of the first ray; The first measuring component includes a reflector b (9) and a reflector d (11) arranged sequentially on the transmitted light path of the second light ray, as well as a prism a (12), an analyzer a (13), a lens group a (14), and a photodetector a (15). The reflector b (9) and reflector d (11) are used to refract the transmitted light of the second light ray into the prism a (12). The prism a (12) is arranged on the reflected light path of the first light ray and is used to input the transmitted light of the second light ray and the reflected light of the first light ray into the analyzer a (13). The analyzer a (13) is used to cause the reflected light of the first light ray and the transmitted light of the second light ray to interfere and output the first interference light. The lens group a (14) and the photodetector a (15) are arranged sequentially on the light path of the first interference light and are used to collect the first signal after focusing. The second measurement component includes a reflector c (10) disposed on the optical path of the reflected light of the second light, as well as a reflector e (19), a prism b (20), an analyzer b (21), a lens group b (22), and a photodetector b (23). The reflector c (10) is used to refract the reflected light of the second light into the prism b (20). The reflector e (19) is used to refract the scattered light generated after the transmitted light of the first light is focused on the surface of the optical element (17) under test into the prism b (20). The prism b (20) is used to input the reflected light and scattered light of the second light into the analyzer b (21). The analyzer b (21) is used to cause the reflected light and scattered light of the second light to interfere and output the second interference light. The lens group b (22) and the photodetector b (23) are disposed sequentially on the optical path of the second interference light and are used to collect the second signal after focusing. The input terminal of the signal processing unit (24) is connected to the output terminals of photodetector a (15) and photodetector b (23), respectively, and the output terminal is connected to the input terminal of computer (25). It is used to calculate the surface information of the optical element (17) under test by the first signal and the second signal and input it into computer (25).

2. The surface characteristic measuring device for an ultra-smooth surface optical element according to claim 1, characterized in that: The light source assembly includes a light source (1) for generating incident light, and a beam-shaping and expanding lens group (2), a Bragg modulator (4), a reflecting mirror a (5), an aperture (6), and a λ / 2 waveplate (7) arranged sequentially on the incident light path; the beam-shaping and expanding lens group (2) is used to shape and expand the incident light and output the shaped and expanded light; the Bragg modulator (4) is used to generate a first light and a second light with different frequencies and perpendicular polarization directions by modulation; the aperture (6) is used to filter out stray light interference; the λ / 2 waveplate (7) is used to adjust the polarization state of the first light and the second light and input them into the polarization beam splitter (8).

3. The surface characteristic measuring device for an ultra-smooth surface optical element according to claim 2, characterized in that: An acousto-optic frequency shifter (3) is provided between the shaping and beam-expanding lens group (2) and the Bragg modulator (4). The acousto-optic frequency shifter (3) is used to perform frequency modulation processing on the light after shaping and beam expansion.

4. The surface characteristic measuring device for an ultra-smooth surface optical element according to claim 3, characterized in that: The second measuring component also includes an aberration-free condenser lens (16) disposed in the transmitted light path of the first light ray, for focusing the transmitted light of the first light ray onto the surface of the optical element under test (17), and converging the scattered light generated on the surface of the optical element under test (17) to the reflector e (19).

5. A surface characteristic measuring device for an ultra-smooth surface optical element according to any one of claims 1 to 4, characterized in that: It also includes a high-precision translation stage (18), on which the optical element to be tested (17) is placed. The output of the computer (25) is connected to the high-precision translation stage (18) for moving the optical element to be tested (17) by controlling the high-precision translation stage (18).

6. A method for measuring the surface characteristics of an ultra-smooth surface optical element, characterized in that, Includes the following steps: Step 1: Set up the surface characteristic measurement device for the ultra-smooth surface optical element as described in claim 1; Step 2: The incident light is generated by the light source assembly and divided into a first light and a second light with different frequencies and perpendicular polarization directions, and input into the polarization beam splitter (8); the polarization beam splitter (8) generates the reflected light of the first light, the transmitted light of the first light, the reflected light of the second light, and the transmitted light of the second light. Step 3: The reflected light of the first ray enters prism a (12), and the transmitted light of the second ray enters prism a (12) after passing through mirror b (9) and mirror d (11). The first ray and the reflected light of the second ray are transmitted and reflected in prism a (12) respectively and then enter analyzer a (13). Interference occurs in analyzer a (13), and the first interference light is output. The first interference light is focused by lens group a (14) onto photodetector a (15) to obtain the first signal, and then output to signal processing unit (24). At the same time, the transmitted light of the first ray is focused on the surface of the optical element (17) under test, generating scattered light, and the scattered light is incident into the prism (20) through the reflector e (19); The reflected light of the second light is reflected by mirror c(10) and then incident on prism b(20). The reflected light and the scattered light are reflected and transmitted in prism b(20) respectively and then enter analyzer b(21). The second interference light is output after interference by analyzer b(21). The second interference light is focused by lens group b (22) onto photodetector b (23) to obtain the second signal, which is then output to signal processing unit (24). Step 4: The first signal and the second signal are calculated by the signal processing unit (24) to obtain the surface information of the optical element (17) under test and output to the computer (25) to complete the surface characteristic measurement of the ultra-smooth surface optical element.

7. The method for measuring the surface characteristics of an ultra-smooth surface optical element according to claim 6, characterized in that: In step 4, before completing the surface characteristic measurement of the ultra-smooth surface optical element, the following steps are also included: determining whether the measurement of each subdivided region of the optical element under test (17) has been completed. If so, the process ends and the surface characteristic measurement of the ultra-smooth surface optical element is completed. Otherwise, the optical element under test (17) is moved into the next subdivided region by controlling the high-precision translation stage (18), and then the process returns to step 2.

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