Large-aperture wavefront scanning measurement device and method based on wavefront modulation

Abstract

A large-aperture wavefront scanning measurement device and method based on wavefront modulation is disclosed. The device includes: a structural aperture for partially transmitting light through a large-aperture beam; an encoding plate disposed in the output beam direction of the structural aperture for wavefront modulation of the beam; a spot detector disposed in the output beam direction of the encoding plate for recording the diffraction spot of the beam; a displacement stage for placing the structural aperture, encoding plate, and spot detector; and a control and calculation module connected to the spot detector and displacement stage, respectively, for controlling the movement of the displacement stage and acquiring and processing the diffraction spot recorded by the spot detector. This invention has significant application prospects for the transmission complex amplitude measurement of large-aperture devices, offering advantages such as high accuracy, high speed, simple device, and wide applicability.

Description

Technical Field

[0001] This invention relates to the measurement of complex amplitude of wavefronts of large-aperture objects or light beams, and in particular to a large-aperture wavefront scanning measurement device and method based on wavefront modulation. Background Technology

[0002] Traditional methods for measuring the amplitude and phase of large-aperture devices include interferometry and holographic measurement. However, these methods require a uniform and stable reference beam with an aperture larger than that of the beam under test, which limits their applicability. Furthermore, traditional phase retrieval methods using a single pinhole scanning technique suffer from poor convergence and high noise, making it difficult to detect minute defects in large-aperture devices. Summary of the Invention

[0003] To address the limitations of the prior art, this invention proposes a large-aperture wavefront scanning measurement device and method based on wavefront modulation. An encoding plate is added behind the aperture, and the aperture structure can be selected in different combinations. This facilitates interference formation on the detector surface, thereby increasing redundancy. This can effectively improve convergence performance and signal-to-noise ratio.

[0004] The technical solution of the present invention is as follows:

[0005] This invention provides a large-aperture wavefront scanning measurement device based on wavefront modulation, characterized in that it includes:

[0006] A small structural aperture is used to partially allow light to pass through a large-aperture beam of light to be tested.

[0007] An encoder board is positioned in the direction of the output beam from the small aperture of the structure and is used to perform wavefront modulation on the beam under test.

[0008] A spot detector is positioned in the direction of the output beam of the encoder plate to record the diffraction spot of the beam under test.

[0009] A displacement stage is used to place the structural apertures, the encoding plate, and the light spot detector.

[0010] The control and calculation module is connected to the spot detector and the displacement stage respectively, and is used to control the movement of the displacement stage, acquire the diffraction spot recorded by the spot detector, and process it.

[0011] Furthermore, the structured apertures can be selected according to the size of the wavefront to be measured, including a single circular aperture or multiple apertures arranged in an array, wherein the multiple apertures are circular apertures, elliptical apertures or polygonal apertures.

[0012] Furthermore, the encoding board can be configured with an appropriate density based on the size of the wavefront to be measured, including binary step phase wavefront modulators, ternary step phase wavefront modulators, deca-step phase wavefront modulators, continuous phase modulators, continuous amplitude phase modulators, and pure amplitude wavefront modulators.

[0013] On the other hand, the present invention also provides a large-aperture wavefront scanning measurement method based on wavefront modulation, characterized by comprising the following steps:

[0014] Step 1) Determine the common transmittance function T of the structural aperture and the encoding plate;

[0015] Step 2): The control and calculation module acquires the diffraction spot detected by the spot detector and records I. jk , j = 1...J, k = 1...K, where j and k represent the coordinate positions of the structural aperture, the encoder plate, and the spot detector in two orthogonal directions within the plane perpendicular to the optical axis, respectively, as determined by the displacement stage;

[0016] Step 3): Initial guess of the control and calculation module: wavefront Ehole in front of the structural aperture jk The wavefront Ehole in front of the small hole in this structure jk Wavefront Em after passing through structural holes and encoding plate jk Em jk =Ehole jk •T; Wavefront Ed reaching the spot detector jk That is, wavefront Em jk Propagation distance L h The wavefront Ed jk L h This is the distance from the encoder board to the spot detector;

[0017] Step 4): The control and calculation module calculates the wavefront Ehole to be measured. jk The steps are as follows:

[0018] Step 4.1) Update the new wavefront Ed′ that arrives before the spot detector. jk And calculate the wavefront error ERR. jk The formula is as follows:

[0019] Ed′ jk =I jk ·exp(i·angle(Em jk ));

[0020]

[0021] Step 4.2) The new wavefront Ed′ jk Backpropagation L hThe updated wavefront Em′ after obtaining the structural aperture and the coding plate jk And update the wavefront Ehole′ in front of the structural aperture. jk The formula is as follows:

[0022]

[0023] Step 4.3) Return to step 3) and set the wavefront Ehole in front of the structural aperture. jk Replace with updated wavefront Ehole′ jk Until the wavefront error ERR jk If the value is less than a preset threshold, at this moment, the wavefront Ehole jk This is the final wavefront to be measured, at which point the cycle terminates.

[0024] Furthermore, when the wavefront exceeds the scanning range, it is necessary to first divide it into regions, then calculate the wavefront to be measured in each region, and finally stitch them together to obtain the entire wavefront to be measured.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1) It enables rapid retrieval of large-aperture instruments and allows for high-precision measurement over a small area. It can simultaneously measure amplitude and phase distribution. This invention has the advantages of large measurement aperture, high precision, and system stability.

[0027] 2) Due to the combined modulation effect of the structural aperture and the encoder plate, the convergence performance and signal-to-noise ratio can be effectively improved. By translating the structural aperture, the encoder plate, and the spot detector to scan the large-aperture wavefront under test, it is possible to measure sizes much larger than the detector target surface. Furthermore, by using a stitching method, the measurable aperture size can be further expanded.

[0028] 3) It can accurately screen out bad spots in large-diameter uniform wavefronts; it has high convergence performance and low noise; it has a simple structure, is easy to operate, and has high redundancy.

[0029] 4) This invention has important application prospects for the transmission amplitude measurement of large-diameter devices, and has the advantages of high accuracy, fast speed, simple device and wide applicability. Attached Figure Description

[0030] Figure 1 A schematic diagram of the large-aperture wavefront scanning measurement device based on wavefront modulation of the present invention.

[0031] Figure 2 Schematic diagram of the beam expander system in Embodiment 1 of the present invention.

[0032] Figure 3 Schematic diagram of the beam-shrinking system in Embodiment 2 of the present invention.

[0033] Figure 4 Example diagram of the structural small hole in this invention. Detailed Implementation

[0034] The present invention will be further described in conjunction with embodiments and accompanying drawings to address different types of measurement requirements, but the scope of protection of the present invention should not be limited by these embodiments.

[0035] Please refer to 1 first. Figure 1 The schematic diagram of the large-aperture wavefront scanning measurement device based on wavefront modulation of the present invention is shown in the figure. It includes a structural aperture 1, an encoding plate 2 and a spot detector 3 placed on a displacement stage 4, and a control and calculation module 5 connected to the displacement stage 4 and the spot detector 3 respectively. The structural aperture 1, the encoding plate 2 and the spot detector 3 are coaxial.

[0036] Example 1: Used in beam expansion systems

[0037] like Figure 2 As shown, the sample to be tested 6, the amplification and beam expansion module 7, the structural aperture 1, the encoding plate 2 and the light spot detector 3 are placed sequentially along the optical path.

[0038] The aforementioned small hole 1 is used to partially transmit light through a large-aperture illumination beam, and multiple circular holes 11 are selected.

[0039] The encoder board 2 is used for wavefront modulation of the beam under test, and a random phase 0-π step board with a unit size of 50um is selected.

[0040] The light spot detector 3 is used to record the diffraction spot of the beam under test after passing through the structural aperture 1 and the encoding plate 2, and a 16-bit CMOS detector is selected.

[0041] The displacement stage 4 is used to control the position movement of the structural hole 1, the encoder plate 2, and the light spot detector 3.

[0042] The control and calculation module 5 is used to control the displacement parameter settings of the displacement stage 4, and to control the spot detector 3 to record the diffraction spot, and then calculate and store the data.

[0043] The sample to be tested, 6, is a large-diameter transmission sample, and is selected as quartz glass with tiny damage points.

[0044] The aforementioned beam amplification and expansion module 7 is used to amplify the beam under test and improve the spatial resolution of the system.

[0045] Example 2

[0046] like Figure 3 As shown Figure 2As shown, the sample to be tested 6, lens A8, lens B9, sample to be tested 6, magnification and beam expansion module 7, structural aperture 1, encoding plate 2 and spot detector 3 are placed sequentially along the optical path.

[0047] The aforementioned small hole 1 is used to partially transmit light through a large-diameter illumination beam, and multiple polygonal holes 12 are selected.

[0048] The encoding board 2 is used for wavefront modulation of the beam under test, and a random amplitude 0-1 modulation board with a unit size of 50um is selected.

[0049] The light spot detector 3 is used to record the diffraction spot of the beam under test after passing through the structural aperture 1 and the encoding plate 2, and an 8-bit CCD detector is selected.

[0050] The displacement stage 4 is used to control the position movement of the structural hole 1, the encoder plate 2, and the light spot detector 3.

[0051] The control and calculation module 5 is used to control the displacement parameter settings of the displacement stage 4, and to control the spot detector 3 to record the diffraction spot, and then calculate and store the data.

[0052] The sample to be tested, 6, is a large-diameter transmission sample, and is selected as quartz glass with tiny damage points.

[0053] The lenses A8 and B9 are used to reduce the beam of light to be measured, enabling measurements over a wide range.

[0054] The method based on the large-aperture wavefront scanning measurement device of Embodiments 1 and 2 comprises the following steps:

[0055] The transmitted light after parallel light illuminates the large-diameter sample 6 is the wavefront to be measured.

[0056] Step 1): Determine the transmittance function T of the combined effect of the structural aperture and the encoding plate;

[0057] Step 2): The control and calculation module stores the diffraction spot recorded by the spot detector into variable I. jk , where the subscripts j = 1...J and j = 1...K are the coordinate positions of the small hole in the displacement stage control structure, the encoder plate, and the spot detector in two orthogonal directions in the plane perpendicular to the optical axis, respectively.

[0058] Step 3): The control and calculation module initially guesses the wavefront in front of the small hole in the structure as Ehole. jk Ehole jk After passing through structural holes and an encoder plate, the wavefront becomes Em. jk =Ehole jk ·T, Em jk Propagation distance L hThe wavefront becomes Ed jk L h This represents the distance from the encoder board to the detector.

[0059] Step 4): The control and calculation module uses the following formula to calculate Ed. jk The process is becoming more apparent, leading to a new wavefront:

[0060] Ed′ jk =I jk ·exp(i·angle(Em jk )),

[0061] Simultaneously calculate the error: Then Ed' jk Backpropagation L h Obtain the wavefront Em′ jk The following formula is used to calculate Em′. jk The wavefront was obtained before updating to the structural aperture (1):

[0062]

[0063] Then Ehole in step 3) jk Replace with Ehole′ jk .

[0064] For j = 1...J, k = 1...K, repeat steps 3) and 4) to complete one full iteration, then proceed to the next iteration until ERR is reached. jk The calculation stops when the value is less than the set value, thus obtaining the final wavefront Ehole. jk .

[0065] The method of large-aperture wavefront scanning measurement based on wavefront modulation requires calculation of the wavefront in different regions when the wavefront exceeds the scanning range, and finally the regions are stitched together to obtain the entire wavefront to be measured.

Claims

1. A large-aperture wavefront scanning measurement method based on wavefront modulation, characterized in that, Includes the following steps: Step 1) Determine the common transmittance function T of the structural aperture and the encoding plate; Step 2): The control and calculation module acquires the diffraction spot detected by the spot detector and records it. , , where j and k represent the coordinate positions of the structural aperture, the encoder plate, and the spot detector in two orthogonal directions within the plane perpendicular to the optical axis, respectively, as determined by the displacement stage; Step 3): Initial guess of the control and calculation module: wavefront in front of the structural aperture The wavefront in front of the small aperture of this structure Wavefront after passing through structural holes and coding plate , ; wavefront before reaching the spot detector , i.e., wavefront Transmission distance The wavefront after ,in This is the distance from the encoder board to the spot detector; Step 4): The control and calculation module calculates the wavefront to be measured. The steps are as follows: Step 4.1) Update the new wavefront before it reaches the spot detector. And calculate the wavefront error The formula is as follows: ； Step 4.2) The new wavefront Backpropagation The updated wavefront after obtaining the structural aperture and the coding plate And update the wavefront in front of the structural aperture. The formula is as follows: Step 4.3) Return to step 3), and then... (The sentence is incomplete and ends abruptly.) Replace with update wavefront until wavefront error If the wavefront is less than the preset threshold, at this moment... This is the final wavefront to be measured, at which point the cycle terminates.

2. The large-aperture wavefront scanning measurement method based on wavefront modulation according to claim 1, characterized in that, When the wavefront exceeds the scanning range, it is necessary to divide it into regions first, then calculate the wavefront to be measured in each region, and finally stitch them together to obtain the entire wavefront to be measured.

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