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CN-121829999-B - Single absolute measurement system and method for reflection surface shape

CN121829999BCN 121829999 BCN121829999 BCN 121829999BCN-121829999-B

Abstract

The invention relates to the technical field of optical detection, and discloses a single absolute measurement system and a method of a reflection surface shape, wherein the system comprises a frequency spectrum separation unit, a wavefront measurement acquisition unit and a surface shape recovery unit; the method comprises the steps of dividing a light beam emitted by a light source into a reference light beam and a test light beam by a frequency spectrum separation unit, superposing a linear phase carrier frequency by using a beam splitting optical wedge as the test light beam and projecting the test light beam to a tested reflector, receiving the reference light beam and the reflected test light beam by a wavefront measurement acquisition unit, performing two-dimensional shearing by using a chessboard grating, recording a transverse shearing interference pattern of single exposure by a photoelectric detector, performing frequency domain demodulation on the interference pattern by a surface shape recovery unit, intercepting a first-order frequency spectrum component to obtain a demodulation complex amplitude, eliminating a system common-path error by conjugate multiplication operation, extracting an absolute phase gradient field, and constructing a Poisson equation to calculate absolute surface shape height distribution of the tested reflector. The invention does not need multi-step phase shifting, reduces environmental sensitivity, simplifies optical structure and reduces system measurement error.

Inventors

  • ZENG ZHICHAO
  • ZHANG LAN

Assignees

  • 上海芬创信息科技有限公司

Dates

Publication Date
20260508
Application Date
20260311

Claims (10)

  1. 1. A single absolute measurement system of a reflective surface shape, comprising: A spectrum separating unit (10) for emitting a monochromatic collimated light beam, dividing the monochromatic collimated light beam into a reference light beam and a test light beam, superimposing a linear phase carrier frequency for the test light beam by beam splitting processing, and projecting the test light beam carrying the linear phase carrier frequency to a mirror (4) to be tested; A wavefront measurement acquisition unit (20) for receiving the reference beam and the test beam reflected back via the mirror under test (4), performing two-dimensional shearing on the reference beam and the test beam by spatial diffraction to form a multi-wave transverse shearing interference field, and recording a transverse shearing interference pattern in a single exposure state; the surface shape recovery unit (30) is used for acquiring the transverse shearing interference image output by the wave front measurement acquisition unit (20), respectively extracting phase information of the reference beam and the test beam through a frequency domain demodulation algorithm, eliminating a system common path error through phase subtraction, acquiring two phase gradient fields of the tested reflector (4) in mutually orthogonal directions, constructing a Poisson equation and calculating absolute surface shape height distribution of the tested reflector (4).
  2. 2. The single absolute measurement system of a reflection surface shape according to claim 1, wherein the spectrum separating unit (10) comprises a light source (1), a beam splitting prism (2) and a beam splitting wedge (3), the light source (1) is arranged at a light path starting end for emitting the monochromatic collimated light beam, the beam splitting prism (2) is arranged on an outgoing light path of the light source for dividing the reference light beam and the test light beam, and the beam splitting wedge (3) is arranged on a propagation path of the test light beam for superposing the linear phase carrier frequency by utilizing a material refraction characteristic.
  3. 3. The reflection profile single absolute measurement system according to claim 1, characterized in that the wavefront measurement acquisition unit (20) comprises a checkerboard grating (5) and a photodetector (6), the checkerboard grating (5) being arranged on a common optical path of the reference beam and the test beam, the photodetector (6) being arranged behind the checkerboard grating (5) for recording the transverse shearing interferograms formed by the diffracted waves of the multiple orders.
  4. 4. The single absolute measurement system of the reflection profile according to claim 2, characterized in that the beam splitting optical wedge (3) generates a center frequency shift of the test beam relative to the reference beam in a frequency domain distribution by setting a wedge angle, a refractive index and an installation rotation angle, and the center frequency shift value is larger than the highest spatial frequency bandwidth of the wavefront to be measured, so as to complete orthogonal separation of the reference beam and the test beam in a frequency spectrum space.
  5. 5. A single absolute measurement system of a reflection profile according to claim 3, characterized in that the checkerboard grating (5) has a two-dimensional periodic structure, and by setting a spatial period and a propagation distance, the transverse shearing amount between different diffraction orders is adjusted, so that the partial derivative information of the profile deviation of the measured mirror (4) in the vertical direction and the horizontal direction is hidden in the intensity information recorded by the photodetector (6).
  6. 6. The single absolute measurement system of a reflection profile according to claim 1, wherein when the profile restoration unit (30) performs a frequency domain demodulation algorithm, first a two-dimensional fourier transform is performed on the transverse shearing interferogram to obtain a composite spectrum distribution, and first-order spectrum components of the reference beam and the test beam are respectively intercepted in the composite spectrum distribution by using a preset band-pass filter.
  7. 7. The single absolute measurement system of a reflection profile according to claim 6, wherein the profile restoration unit (30) translates each spectral component to an origin position in a frequency domain after extracting the first-order spectral component, performs inverse fourier transform to obtain a demodulated complex amplitude distribution in a spatial domain, and extracts an absolute phase gradient field free from a systematic common-path error by a conjugate multiplication operation between the demodulated complex amplitude distribution of the test beam and the demodulated complex amplitude distribution of the reference beam.
  8. 8. The single absolute measurement system of a reflection surface shape according to claim 1, wherein the surface shape recovery unit (30) is a computer (7), the computer (7) adopts a frequency domain integral solving mode realized by discrete cosine transform to convert gradient field divergence distribution of a space domain into algebraic operation of a frequency domain after the poisson equation is constructed by the surface shape recovery unit (30), and original height data of the measured reflector (4) in a full aperture range is obtained through calculation.
  9. 9. The single absolute measurement system of the reflection surface shape according to claim 8, wherein the surface shape restoring unit (30) maps the pixel index to a physical space coordinate by coordinate transformation after acquiring the original height data, performs reference alignment by removing a direct current component, and outputs a peak-to-valley value and a square root value reflecting the processing quality of the measured mirror (4).
  10. 10. A single absolute measurement method of a reflection profile, characterized by being applied to a single absolute measurement system of a reflection profile as claimed in any one of claims 1 to 9, comprising the steps of: the spectrum separation unit (10) is utilized to emit monochromatic collimated light beams and divide the monochromatic collimated light beams into reference light beams and test light beams, linear phase carrier frequencies are superimposed on the test light beams, and the test light beams are guided to the tested reflector (4); the wavefront measurement acquisition unit (20) is used for receiving the reference beam and the reflected test beam, and the reference beam and the test beam are subjected to two-dimensional shearing through space diffraction to form a transverse shearing interference pattern and perform single exposure recording; Performing a frequency domain demodulation algorithm on the transverse shearing interference pattern by using a surface shape recovery unit (30), extracting shearing phases of the reference beam and the test beam in the orthogonal direction, and eliminating a system common path error by complex conjugate subtraction to obtain an absolute phase gradient field; and constructing a poisson equation based on the absolute phase gradient field by using the surface shape recovery unit (30) and carrying out numerical solution, and converting the calculated mathematical potential function field into the absolute surface shape height distribution with physical indexes.

Description

Single absolute measurement system and method for reflection surface shape Technical Field The invention relates to the technical field of optical detection, in particular to a single absolute measurement system and method of a reflection surface shape. Background Reflecting elements such as plane mirrors, concave mirrors, and reflecting axicon mirrors are widely used in high-power laser devices, large-caliber astronomical optical systems, and precision imaging systems. The accuracy of the surface shape of the reflective element directly determines the overall imaging quality and energy transfer efficiency of the optical system. Therefore, obtaining high resolution and high accuracy surface shape data of the reflective element is a fundamental link for ensuring the performance of the relevant system. The existing reflection surface shape detection mainly adopts an interferometry technology. When the traditional interferometry method extracts the surface shape phase distribution, the traditional interferometry method relies on multi-step phase shifting operations such as piezoelectric ceramics and the like or performs double exposure comparison. The multi-frame data acquisition mode has high requirement on the environmental stability of a measurement period, and under the field working condition or dynamic measurement environment, the interference fringe state can be destroyed by the tiny vibration of a mechanical platform and the disturbance of air flow, so that uncontrollable relative deviation is generated among the multi-frame data, and the quick and stable measurement is difficult to realize. The conventional interference detection system mostly adopts a non-common-path structure on a hardware architecture, and the structure needs to additionally configure a high-precision standard reference plane mirror to construct an independent reference arm, and the complicated reference arm and test arm light paths increase the hardware cost and the overall adjustment difficulty of the system. Meanwhile, the optical path difference between the reference arm and the test arm and the asymmetric environmental state change in the two optical paths can introduce dynamic system errors, so that the measurement accuracy is reduced. In addition, in the wavefront reconstruction and the surface shape data recovery processes, common path geometrical aberration carried by a light splitting element and a transmission element in an optical system can interfere with interference patterns, the conventional surface shape calculation technology needs to execute a complicated system error calibration program in advance, and under the condition of lacking high-precision front calibration, the background error interference in an optical path is difficult to directly peel off in the conventional calculation process, so that absolute numerical reconstruction of surface shape height distribution of a reflecting mirror to be detected cannot be directly realized from interference data. Disclosure of Invention Aiming at the defects of the prior art, the invention provides a single absolute measurement system and a method of a reflection surface shape, which solve the problems that the prior interferometry technology is sensitive to environmental vibration and airflow disturbance due to dependence on multi-frame data acquisition, and a non-common-path measurement architecture needs to be additionally provided with a high-precision reference plane mirror, so that the system structure is complex and dynamic system errors are easy to introduce. In order to achieve the above purpose, the invention is realized by the following technical scheme: The first aspect of the present invention provides a single absolute measurement system of a reflection surface shape, comprising: The spectrum separation unit is used for emitting monochromatic collimated light beams and dividing the monochromatic collimated light beams into reference light beams and test light beams, superposing space linear phase carrier frequencies for the test light beams by utilizing beam splitting treatment, and then projecting the test light beams carrying the carrier frequencies to a reflector to be tested; The wavefront measurement acquisition unit is used for receiving the reference beam and the test beam reflected by the reflecting mirror to be measured, generating two-dimensional transverse shearing of the reference beam and the test beam through a space diffraction effect, generating a multi-wave transverse shearing interference field, and recording a transverse shearing interference pattern under a single exposure condition; The surface shape recovery unit is used for receiving the transverse shearing interference pattern output by the wave front measurement acquisition unit, extracting phase distribution information of the reference beam and the test beam respectively by using a frequency domain demodulation algorithm, performing phase subtraction operation to eliminate aber