Large-stroke deformable mirror surface shape measuring device and method

Abstract

The invention provides a large-stroke deformable mirror surface shape measuring device and method, the device comprises a reference reflector, a large-stroke deformable mirror and a deformable mirror surface shape measuring system, and the reference reflector reflects a light path folded by the deformable mirror surface shape measuring system; the reference reflector performs in-situ replacement on the large-stroke deformable mirror, and the calibrated optical path aberration deformable mirror surface shape measurement system measures the surface shape of the large-stroke deformable mirror; the wave aberration on the large-stroke deformable mirror surface shape is changed by moving the position of a movable light source module in the deformable mirror surface shape measurement system; the method comprises the following steps: a light path emitted by the movable light source is reflected by the reflex reflector and then enters the large-stroke deformable mirror; and a light beam reflected by the large-stroke deformable mirror penetrates through the beam splitter and then enters the Hartmann sensor through the relay lens. According to the invention, high-precision measurement of the large-stroke deformable mirror surface shape can be realized by adopting a simple optical system and a common Hartmann sensor, and the device is simple and low in cost.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measurement, and in particular relates to a device and method for measuring the shape of a large-stroke deformable mirror. Background Art

[0002] As a core component of adaptive optics systems, the Adaptive Deformable Mirror (ADM) actively adjusts the curvature of its reflective surface to compensate for wavefront distortion. It is widely used in fields such as astronomical observation, laser communications and processing, biomedical imaging, and military and defense. As an active optical element, the ADM can produce different defocus wave aberrations by varying the curvature radius of its reflective surface. This not only improves the beam quality of solid-state lasers, but also enables zoom imaging without moving parts.

[0003] The surface accuracy of a deformable mirror (ADM) with adjustable curvature can affect the imaging quality of an optical system. In adaptive optics systems, ADM surface errors are propagated into the correction results, resulting in residual aberrations. In laser processing systems, insufficient ADM surface accuracy can affect machining accuracy. Because timely curvature adjustment in ADM applications can accommodate defocus wave aberrations, accurately measuring the ADM surface shape is crucial for evaluating deformable mirror performance.

[0004] Interferometer measurement is an optical interference technique for measuring the shape of deformable mirrors. It uses reference light and test light to form interference fringes, and then analyzes these fringes to measure the shape of smooth surfaces. Among many measurement methods, it has become an important solution for detecting deformation of smooth surfaces. However, while interferometers combined with length measurement systems can accurately measure the surface shape of deformable mirrors, measuring the shape of deformable mirrors with different curvature radii requires a series of standard lenses or even the design of special optical systems. This makes interferometer-based length measurement systems complex and expensive. This is because the reference light may not be well matched to the varying curvature radius of the measured surface, different curvature radii require different wavefront compensation, and the curvature of the measured surface may introduce aberrations that affect the contrast and accuracy of the interference fringes.

[0005] Compared to interferometer-coupled length measurement systems, Hartmann sensors have been widely used for wavefront aberration measurement of optical components, despite their advantages such as environmental insusceptibility, small size, simple structure, and low cost. However, measurement methods based on Hartmann sensors typically require high-precision relay lenses. This is especially true when large-stroke deformable mirrors generate significant defocus wavefront aberrations, as the wavefront aberrations introduced by conventional relay lenses can no longer be ignored. Summary of the Invention

[0006] The present invention aims to address the shortcomings of existing technologies, which require the development of extremely complex relay lenses. By providing a device and method for measuring the surface shape of a long-stroke deformable mirror, the present invention adaptively adjusts the position of the defocused light source based on the deformable mirror's wavefront aberration to limit the wavefront aberration of the light beam emitted from the long-stroke deformable mirror to a relatively small range. This allows the relay lens between the long-stroke deformable mirror and the Hartmann sensor to ignore the influence of wavefront aberration. Using a simple optical system and a standard Hartmann sensor, high-precision surface shape measurement of a long-stroke deformable mirror can be achieved, resulting in a simple and low-cost device.

[0007] To achieve the above objectives, the technical solutions provided by the present invention are:

[0008] In one aspect, the present invention discloses a long-stroke deformable mirror surface shape measurement device, comprising: a reference reflector, a long-stroke deformable mirror, and a deformable mirror surface shape measurement system, wherein the reference reflector reflects the optical path folded by the deformable mirror surface shape measurement system for calibrating the optical path aberration of the deformable mirror surface shape measurement system; the reference reflector replaces the long-stroke deformable mirror in situ, and the deformable mirror surface shape measurement system measures the long-stroke deformable mirror surface shape based on the calibrated optical path aberration; wherein:

[0009] The deformable mirror surface shape measurement system includes a movable light source module, a folding reflector, an optical lens assembly and a Hartmann sensor. Moving the position of the movable light source module changes the wave aberration on the large-stroke deformable mirror surface shape; the light path emitted by the movable light source is folded by the folding reflector and then incident on the large-stroke deformable mirror; the optical lens assembly includes a beam splitter and a relay lens. The light beam reflected by the large-stroke deformable mirror passes through the beam splitter and then passes through the relay lens to be incident on the Hartmann sensor.

[0010] Based on one aspect, in a specific implementation of the present invention, the movable light source module includes a light source, a high-precision guide rail and a collimating lens. The light source is placed on the high-precision guide rail, and the position of the light source is moved axially by the guide rail. The collimating lens performs a collimating operation on the light emitted by the light source. The collimated light path is reflected by the folding reflector and the beam splitter and then incident on the large-stroke surface mirror.

[0011] Based on one aspect, in a specific implementation of the present invention, the folding reflector is an ordinary plane reflector, and the collimating lens and the relay lens are both composed of ordinary doublet lenses.

[0012] Based on one aspect, in a specific implementation of the present invention, the Hartmann sensor is an ordinary Hartmann sensor that measures wave aberration of the optical path; the Hartmann sensor and the large-stroke deformable mirror achieve aperture conjugation through the relay lens.

[0013] In another aspect, the present invention discloses a method for measuring the shape of a large-stroke deformable mirror, based on the device for measuring the shape of a large-stroke deformable mirror disclosed in the above aspect, comprising the following steps:

[0014] Step 1: Use the reference reflector to replace the long-stroke deformable mirror in situ to obtain the Hartmann sensor measurement wave aberration;

[0015] Step 2: Replace the reference reflector with a long-stroke deformable mirror, move the light source from the initial position to different positions, obtain the corresponding Hartmann sensor measurement wave aberration, and the difference in the wave aberration incident on the long-stroke deformable mirror;

[0016] Step 3: Based on the Hartmann sensor measuring the wave aberration, a closed-loop adjustment is performed on the long-stroke deformable mirror to stabilize the wave aberration of the deformable mirror. The light source is defocused to different positions to obtain different Hartmann sensor measuring wave aberrations and the corresponding differences in the wave aberrations incident on the long-stroke deformable mirror.

[0017] Step 4: Set the large-stroke deformable mirror to the position of the surface to be measured, adjust the light source position to minimize the defocus wave aberration on the Hartmann sensor, record the light source position and the Hartmann sensor wave aberration, and obtain the deformable mirror wave aberration estimate.

[0018] Based on another aspect, in a specific implementation of the present invention, the step 1 specifically includes:

[0019] Step S11: Place the reference reflector at the position of the deformable mirror and replace the deformable mirror in situ; place the light source near the front focal plane of the collimator lens, and the wave aberration incident on the reference reflector is defined as W I,0 , Hartmann sensor measures wave aberration W S,0 Expressed as:

[0020] W S,0 =W I,0 +W R,0 Formula (1)

[0021] In formula (1), W R,0 Indicates the wave aberration of the relay lens corresponding to this working condition.

[0022] Based on another aspect, in a specific implementation of the present invention, the step 2 specifically includes:

[0023] Step S21: Replace the reference reflector with a large-stroke deformable mirror. The large-stroke deformable mirror operates near its flattened state. At this time, the Hartmann sensor measures the wave aberration W S,1 Expressed as:

[0024] W S,1 =W I,0 +W M,1 +WR，1 Formula (2)

[0025] In formula (2), W M,1 It represents the deformable mirror wave aberration corresponding to this working condition, W R，1 Indicates the wave aberration of the relay lens corresponding to this working condition;

[0026] Step S22: Defocus the light source to the first position through the guide rail. Under this working condition, the Hartmann sensor measures the wave aberration W. S,2 Expressed as:

[0027] W S,2 =W I,1 +W M,1 +W R，2 Formula (3)

[0028] In formula (3), W I,1 It represents the wave aberration incident on the deformable mirror under this working condition, W M,1 It represents the deformable mirror wave aberration corresponding to this working condition, W R，2 It represents the wave aberration of the relay lens under this working condition;

[0029] When the light source is at the first position and the second position, the difference in wave aberration incident on the large-stroke deformable mirror is expressed as:

[0030] W I,1 -W I,0 =(W S,2 -W S,1 )-(W R,2 -W R,1 ) Formula (4)

[0031] In formula (4), W I,1 It represents the wave aberration incident on the deformable mirror under this working condition, W I,0 represents the defined wave aberration incident on the deformable mirror, W S,2 It represents the wave aberration measured by the Hartmann sensor under the corresponding working condition when the light source is at the first position, W S,1 It represents the wave aberration measured by the Hartmann sensor under the corresponding working condition when the light source is at the initial position, W R,2 It represents the wave aberration of the relay lens when the light source is defocused to the first position, W R,1 It represents the wavefront aberration of the relay lens corresponding to the working condition when the light source is at the initial position.

[0032] Based on another aspect, in a specific implementation of the present invention, the step three specifically includes:

[0033] Step S31: The Hartmann sensor and the long-stroke deformable mirror form a closed loop, and the defocus wave aberration of the long-stroke deformable mirror is adjusted based on the wave aberration measured by the Hartmann sensor to reduce the wave aberration measured by the Hartmann sensor and stabilize the wave aberration of the deformable mirror to W. M,2 At this time, the Hartmann sensor measures the wave aberration W S,3 Expressed as:

[0034] W S,3 =W I,1 +W M,2 +W R，3 Formula (5)

[0035] In formula (5), W I,1 It represents the wave aberration incident on the deformable mirror under this working condition, W R，3 Indicates the wave aberration of the relay lens corresponding to this working condition;

[0036] Step S32: Defocus the light source to the second position, and measure the wavefront aberration W using the Hartmann sensor. S,4 Expressed as:

[0037] W S,4 =W I,2 +W M,2 +W R，4 Formula (6)

[0038] In formula (6), W I,2 It represents the wave aberration incident on the large-stroke deformable mirror under this working condition, W R，4 It represents the wave aberration of the relay lens under this working condition;

[0039] The wave aberration W incident on the large-stroke deformable mirror when the light source is at the first and second positions I,1 and W I,2 The difference is expressed as:

[0040] W I,2 -W I,1 =(W S,4 -W S,3 )-(W R,4 -W R,3 ) Formula (7)

[0041] In formula (7), W I,2 It represents the wave aberration incident on the large-stroke deformable mirror when the light source is defocused to the second position, W I,1 It represents the wave aberration incident on the large-stroke deformable mirror when the light source is defocused to the first position, W S,4 Indicates the wave aberration measured by the Hartmann sensor when the light source is defocused to the second position, W S,3 Indicates the stable deformable mirror wave aberration to W M,2 When the Hartmann sensor measures the wave aberration, WR,4 Indicates that the light source is defocused to the second position. The wave aberration of the relay lens under this working condition, W R,3 Indicates the stable deformable mirror wave aberration to W M,2 Wave aberration of the relay lens corresponding to the working conditions;

[0042] Step S33: Repeat steps S31 and S32 to obtain the wave aberration W incident on the large-stroke deformable mirror when the light source is at positions (n-1) and n. I,n-1 and W I,n The difference is expressed as:

[0043] W I,n -W I,n-1 =(W S,2n -W S,2n-1 )-(W R,2n -W R,2n-1 ) Formula (8)

[0044] In formula (8), W I,n It represents the wave aberration when the light source is at position n and incident on the large-stroke deformable mirror, W I,n-1 It represents the wave aberration when the light source is at position (n-1) incident on the large-stroke deformable mirror, W S,2n It represents the wave aberration measured by the Hartmann sensor when the light source is defocused to position n, W S,2n-1 It represents the wave aberration measured by the Hartmann sensor when the light source is defocused to position (n-1), W R,2n W represents the wave aberration of the relay lens when the light source is defocused to position n. R,2n-1 It represents the wavefront aberration of the relay lens when the light source is defocused to position (n-1);

[0045] When the light source is at position n, the wave aberration incident on the large-stroke deformable mirror is expressed as:

[0046]

[0047] After calibrating a series of light source positions and their corresponding wave aberrations incident on the deformable mirror, the long-stroke deformable mirror surface shape measurement is performed.

[0048] Based on another aspect, in a specific implementation of the present invention, the step 4 specifically includes:

[0049] Set the deformable mirror to the position of the surface to be measured, discretely adjust the light source position based on the Hartmann sensor wave aberration measurement to minimize the defocus wave aberration on the Hartmann sensor, and record the light source position n′ and the Hartmann sensor wave aberration W S ;include:

[0050] Step S41, the deformable mirror wave aberration is expressed as:

[0051]

[0052] In formula (10), W M represents the deformable mirror's own wave aberration, W S W is the wave aberration measured by the Hartmann sensor. R represents the wave aberration of the relay lens, W I,n′ It represents the wave aberration incident on the large-stroke deformable mirror when the light source is at position n,

[0053] Step S42: Due to the relay lens wave aberration W R The change of can be ignored, so the deformable mirror wave aberration estimate is Expressed as:

[0054]

[0055] In formula (11), W S It indicates that the Hartmann sensor measures wave aberration;

[0056] Step S43: Define the wave aberration incident on the deformable mirror Expressed as:

[0057]

[0058] Deformable mirror wave aberration estimation Expressed as:

[0059]

[0060] In formula (13), W S represents the wave aberration measured by the Hartmann sensor, represents the wave aberration incident on the deformable mirror.

[0061] The advantages of the present invention are:

[0062] This invention adapts the position of the defocused light source to the deformable mirror's wavefront aberration, limiting the wavefront aberration of the light beam emitted from the long-stroke deformable mirror to a relatively small range. This allows the relay lens between the long-stroke deformable mirror and the Hartmann sensor to ignore the influence of wavefront aberration. This invention utilizes a simple optical system and a conventional Hartmann sensor to achieve high-precision measurement of the long-stroke deformable mirror's surface shape, resulting in a simple and low-cost device.

[0063] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0065] Figure 1 : Schematic diagram of a large-stroke deformable mirror shape measuring device provided by the present invention;

[0066] Figure 2 : Schematic diagram of the long-stroke deformable mirror surface shape measurement device provided by the present invention, wherein: (a) indicates that the light source is not defocused and the deformable mirror has a defocus wave aberration of 0; (b) indicates that the light source is not defocused and the deformable mirror has a defocus wave aberration of -160λ; (c) indicates that the light source is defocused by -200mm and the deformable mirror has a defocus wave aberration of -160λ;

[0067] Figure 3 : The estimated value of the wave aberration incident on the deformable mirror provided by the present invention;

[0068] Figure 4 : Error diagram of the deformable mirror wave aberration estimation provided by the present invention;

[0069] Figure 5 : Diagram of the deformable mirror wave aberration estimation process provided by the present invention, wherein: (a) estimation of the wave aberration incident on the deformable mirror, (b) measurement of the wave aberration by the Hartmann sensor, (c) estimation of the deformable mirror wave aberration, and (d) estimation error of the deformable mirror wave aberration;

[0070] Figure 6 : Data table of the wave aberration measurement process incident on the deformable mirror provided by the present invention;

[0071] Figure 7 : Data table of the deformable mirror wave aberration measurement process provided by the present invention;

[0072] Figure 8 : The estimated value of the deformable mirror wave aberration provided by the present invention;

[0073] Figure 9 : A flow chart of a large-stroke deformable mirror shape measurement method provided by the present invention. DETAILED DESCRIPTION

[0074] The following describes in detail embodiments of the present invention. The embodiments are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0075] See Figure 1 and Figure 2The embodiment of the present invention discloses a long-stroke deformable mirror surface shape measurement device, comprising: a reference reflector, a long-stroke deformable mirror and a deformable mirror surface shape measurement system, wherein the reference reflector reflects the optical path folded by the deformable mirror surface shape measurement system for calibrating the optical path aberration; the reference reflector replaces the long-stroke deformable mirror in situ, and the deformable mirror surface shape measurement system measures the long-stroke deformable mirror surface shape based on the calibrated optical path aberration; wherein: the deformable mirror surface shape measurement system comprises a movable light source module, a folding reflector, an optical lens assembly and a Hartmann sensor, and moving the position of the movable light source module changes the wave aberration on the long-stroke deformable mirror surface shape; the light path emitted by the movable light source is folded by the folding reflector and then incident on the long-stroke deformable mirror; the optical lens assembly comprises a beam splitter and a relay lens, and the light beam reflected by the long-stroke deformable mirror passes through the beam splitter and then incident on the Hartmann sensor through the relay lens. Specifically:

[0076] Continue reading Figure 2 The movable light source module in the embodiment of the present invention includes a light source, a high-precision guide rail (with a grating scale) and a collimating lens. The light source is placed on the high-precision guide rail, and the position of the light source is moved axially by the guide rail. The collimating lens collimates the light emitted by the light source. The collimated light path is reflected by the folding reflector and the beam splitter and then incident on the large-stroke surface mirror.

[0077] Preferably, the folding reflector in the embodiment of the present invention is a common plane reflector for folding the optical path. The collimating lens and relay lens in the embodiment of the present invention are both composed of common doublet lenses. The Hartmann sensor in the embodiment of the present invention is preferably a common Hartmann sensor for wavefront aberration measurement. The Hartmann sensor and the long-stroke deformable mirror are aperture-conjugated via the relay lens.

[0078] Continue reading Figure 2 The present invention discloses a device for measuring the surface shape of a large-stroke deformable mirror. Light emitted from a light source is collimated by a collimating lens, then reflected by a folding reflector and a beam splitter before being incident on the deformable mirror. The light is then reflected by the large-stroke deformable mirror, passes through the beam splitter, and then passes through a relay lens before being incident on a Hartmann sensor. Because the light source is placed on a high-precision guide rail, its position can be moved axially by the rail to change the wavefront aberration incident on the deformable mirror.

[0079] The reference mirror in embodiments of the present invention is preferably a high-precision flat mirror, used for in-situ replacement of the deformable mirror and calibration of optical path aberrations. The surface accuracy of the reference mirror is much higher than that of the deformable mirror, and its surface error is negligible, allowing it to be considered an absolutely flat surface. The positional relationship between the reference mirror and the long-stroke deformable mirror is such that their reflective surfaces overlap.

[0080] See Figure 9The embodiment of the present invention further discloses a method for measuring the shape of a large-stroke deformable mirror, based on the above-mentioned large-stroke deformable mirror shape measuring device, comprising the following steps S1-S8:

[0081] Step S1: Place the reference reflector at the position of the deformable mirror and replace the deformable mirror in situ; place the light source near the front focal plane of the collimator lens (recorded as position 0). The wave aberration incident on the reference reflector is defined as W I,0 , based on the Hartmann sensor, it is possible to measure the wave aberration. The Hartmann sensor measures the wave aberration W S,0 Expressed as:

[0082] W S,0 =W I,0 +W R,0 Formula (1)

[0083] In formula (1), W R,0 Indicates the wave aberration of the relay lens corresponding to this working condition.

[0084] In the large-stroke deformable mirror shape measurement method disclosed in the embodiment of the present invention, only the Hartmann sensor can measure the wavefront aberration, and the others are unknown or inferred.

[0085] Step S2: Replace the reference reflector with a large-stroke deformable mirror. The large-stroke deformable mirror operates near its flattened state. At this time, the Hartmann sensor measures the wave aberration W S,1 Expressed as:

[0086] W S,1 =W I,0 +W M,1 +W R，1 Formula (2)

[0087] In formula (2), W M,1 It represents the deformable mirror wave aberration corresponding to this working condition, W R，1 Indicates the wave aberration of the relay lens corresponding to this working condition; the wave aberration of the relay lens is related to the wave aberration of the light beam incident on it. Steps S1 and S2 use a reference reflector and a deformable mirror respectively. Although the large-stroke deformable mirror is near the flattened state, the wave aberration of the relay lens can only be approximately equal, not completely consistent. For rigorous derivation, step S2 measures the wave aberration W of the Hartmann sensor. S,1 Indicates that different symbols are used. The long-stroke deformable mirror is twice the deformable mirror surface shape.

[0088] Step S3: Defocus the light source to the first position through the guide rail. Under this working condition, the Hartmann sensor measures the wave aberration W. S,2 Expressed as:

[0089] W S,2 =W I,1 +WM,1 +W R，2 Formula (3)

[0090] In formula (3), W I,1 It represents the wave aberration incident on the deformable mirror under this working condition, W M,1 It represents the deformable mirror wave aberration corresponding to this working condition, W R，2 It represents the wave aberration of the relay lens under this working condition;

[0091] When the light source is at the first position and the second position, the difference in wave aberration incident on the large-stroke deformable mirror is expressed as:

[0092] W I,1 -W I,0 =(W S,2 -W S,1 )-(W R,2 -W R,1 ) Formula (4)

[0093] In formula (4), W I,1 It represents the wave aberration incident on the deformable mirror under this working condition, W I,0 represents the defined wave aberration incident on the deformable mirror, W S,2 It represents the wave aberration measured by the Hartmann sensor under the corresponding working condition when the light source is at the first position, W S,1 It represents the wave aberration measured by the Hartmann sensor under the corresponding working condition when the light source is at the initial position, W R,2 It represents the wave aberration of the relay lens when the light source is defocused to the first position, W R,1 Indicates the wave aberration of the relay lens corresponding to the working condition when the light source is at the initial position. In the embodiment of the present invention, S represents the Hartmann sensor measurement sensor, I represents the incident incident, M represents the measurement, and R represents the relay. During the light source position adjustment process, it is necessary to control the defocus step of the light source to ensure that the wave aberration measured by the Hartmann sensor is in a smaller range, such as ≤30λ, so that the influence of the relay lens wave aberration can be ignored. The defocus step of the light source is controlled in a smaller range. Since the relay lens aberration is related to the wave aberration of the light beam incident thereon, and the small focusing range makes the wave aberration incident on the relay lens change less, the relay lens wave aberration changes less during the movement of the guide rail and can be ignored.

[0094] Step S4: The Hartmann sensor and the long-stroke deformable mirror form a closed loop, and the defocus wave aberration of the long-stroke deformable mirror is adjusted based on the wave aberration measured by the Hartmann sensor to reduce the wave aberration measured by the Hartmann sensor and stabilize the wave aberration of the deformable mirror to W. M,2 At this time, the Hartmann sensor measures the wave aberration W S,3 Expressed as:

[0095] W S,3 =W I,1 +W M,2 +W R，3 Formula (5)

[0096] In formula (5), W I,1 It represents the wave aberration incident on the deformable mirror under this working condition, W R，3 Indicates the wavefront aberration of the relay lens corresponding to this working condition; in the closed-loop circuit described above in the embodiment of the present invention, a light beam is incident on the deformable mirror, and after reflection enters the Hartmann, the deformable mirror shape changes, and the Hartmann measurement wavefront also changes. Therefore, the deformable mirror shape can be adjusted according to the Hartmann measurement wavefront until the Hartmann measurement wavefront reaches a certain state.

[0097] Step S5: Defocus the light source to the second position, and measure the wavefront aberration W using the Hartmann sensor. S,4 Expressed as:

[0098] W S,4 =W I,2 +W M,2 +W R，4 Formula (6)

[0099] In formula (6), W I,2 It represents the wave aberration incident on the large-stroke deformable mirror under this working condition, W R，4 Indicates the wave aberration of the relay lens under this working condition; W M,2 Since the deformed mirror shape changes, there is a new symbol.

[0100] The wave aberration W incident on the large-stroke deformable mirror when the light source is at the first and second positions I,1 and W I,2 The difference is expressed as:

[0101] W I,2 -W I,1 =(W S,4 -W S,3 )-(W R,4 -W R,3 ) Formula (7)

[0102] In formula (7), W I,2 It represents the wave aberration incident on the large-stroke deformable mirror when the light source is defocused to the second position, W I,1 It represents the wave aberration incident on the large-stroke deformable mirror when the light source is defocused to the first position, W S,4 Indicates the wave aberration measured by the Hartmann sensor when the light source is defocused to the second position, W S,3 Indicates the stable deformable mirror wave aberration to W M,2 When the Hartmann sensor measures the wave aberration, W R,4Indicates that the light source is defocused to the second position. The wave aberration of the relay lens under this working condition, W R,3 Indicates the stable deformable mirror wave aberration to W M,2 Wave aberration of the relay lens corresponding to the working conditions;

[0103] Step S6: Repeat steps S4 and S5 to obtain the wave aberration W incident on the large-stroke deformable mirror when the light source is at positions (n-1) and n. I,n-1 and W I,n The difference is expressed as:

[0104] W I,n -W I,n-1 =(W S,2n -W S,2n-1 )-(W R,2n -W R,2n-1 ) Formula (8)

[0105] In formula (8), W I,n It represents the wave aberration when the light source is at position n and incident on the large-stroke deformable mirror, W I,n-1 It represents the wave aberration when the light source is at position (n-1) incident on the large-stroke deformable mirror, W S,2n It represents the wave aberration measured by the Hartmann sensor when the light source is defocused to position n, W S,2n-1 It represents the wave aberration measured by the Hartmann sensor when the light source is defocused to position (n-1), W R,2n W represents the wave aberration of the relay lens when the light source is defocused to position n. R,2n-1 It represents the wavefront aberration of the relay lens when the light source is defocused to position (n-1);

[0106] Step S7: When the light source is at position n, the wave aberration incident on the large-stroke deformable mirror is expressed as:

[0107]

[0108] After calibrating a series of light source positions and their corresponding wavefront aberrations incident on the deformable mirror, the deformable mirror surface shape measurement with a large stroke is performed; Through the above process, a series of light source positions and their corresponding wavefront aberrations incident on the deformable mirror are calibrated, and then the deformable mirror surface shape measurement can be performed;

[0109] Step S8: Set the deformable mirror to the position of the surface to be measured, discretely adjust the light source position based on the Hartmann sensor wave aberration measurement to minimize the defocus wave aberration on the Hartmann sensor, and record the light source position n′ and the Hartmann sensor wave aberration W S ;include:

[0110] The deformable mirror wave aberration is expressed as:

[0111]

[0112] In formula (10), W M represents the deformable mirror's own wave aberration, W S W is the wave aberration measured by the Hartmann sensor. R represents the wave aberration of the relay lens, W I,n′ It represents the wave aberration incident on the large-stroke deformable mirror when the light source is at position n,

[0113] Substituting formula (9) into formula (10), we get:

[0114]

[0115] Due to the relay lens wave aberration W R The change can be ignored, so the estimated value of the deformable mirror wave aberration is expressed as:

[0116]

[0117] Define the wave aberration incident on the deformable mirror, the wave aberration W due to the relay lens R The change of can be ignored, so the deformable mirror wave aberration estimate is Expressed as:

[0118]

[0119] In formula (11), W S It indicates that the Hartmann sensor measures wave aberration;

[0120] Define the aberration of the wave incident on the deformable mirror Expressed as:

[0121]

[0122] Then, the deformable mirror wave aberration estimate is Expressed as:

[0123]

[0124] In formula (13), W S represents the wave aberration measured by the Hartmann sensor, represents the wave aberration incident on the deformable mirror.

[0125] Based on the above-disclosed method for measuring the shape of a large-stroke deformable mirror, the measurement of the shape of a large-stroke deformable mirror in the embodiment of the present invention only requires a simple optical system and an ordinary Hartmann sensor to achieve high-precision measurement of the shape of a large-stroke deformable mirror. The structure and algorithm of the measuring device are simple and the cost is low.

[0126] In addition, the embodiment of the present invention is simulated based on Zemax optical design software, and a large-stroke deformable mirror shape measurement device is established based on Zemax optical design software. Figure 2 Light emitted from the light source is collimated by the collimating lens (lens 1), then reflected by the deflecting mirror and beam splitter before being incident on the deformable mirror. After reflection from the deformable mirror, the beam passes through the beam splitter, passes through the relay lenses (lenses 2 and 3), and then enters the Hartmann sensor. The focal lengths of lenses 1 and 3 are approximately 500mm, and the focal length of lens 2 is approximately 100mm. The effective aperture of all lenses is 50mm. The reference wavelength is 632.8nm. Figure 2 (a) The light source is not defocused, and the deformable mirror defocus wave aberration is 0. At this time, the incident and outgoing beams of the relay lens have very small wave aberrations and are almost parallel. Figure 2 (b) The light source is not defocused, and the deformable mirror has a defocus wave aberration of -160λ. At this time, the incident and outgoing beam wave aberrations of the relay lens are very large. Figure 2 (a), the incident and outgoing light heights and angles vary greatly, so the wave aberration introduced by the relay lens also varies greatly. Figure 2 (c) The light source is defocused -200mm, and the deformable mirror defocus wave aberration is -160λ. The wave aberration caused by the light source defocus and the deformable mirror defocus wave aberration compensate each other. At this time, the incident and outgoing beam wave aberrations of the relay lens are very small, and the wave aberration introduced by the relay lens is Figure 2 (a) Similar.

[0127] First, the wave aberration incident on the deformable mirror is estimated, and the measurement process data is as follows: Figure 3 、 Figure 4 、 Figure 5 and Figure 6 shown. Figure 4 The corresponding deformable mirror wave aberration estimation error histogram shows that the measurement error is only about 0.1λ. Figure 5 The wave aberration estimation process data of the deformable mirror is shown when the wave aberration is -160λ. Figure 5 (a) is the estimated wave aberration incident on the deformable mirror, Figure 5 (b) is the wave aberration measured by the Hartmann sensor, Figure 5 (c) is the estimated deformable mirror wave aberration, Figure 5 (d) is the error in estimating the wave aberration of the deformable mirror. Figure 4 and Figure 5It can be seen that the estimated wave aberration incident on the deformable mirror is almost equal to the wave aberration of the deformable mirror, but with opposite signs. After the two compensate each other, the wave aberration measured by the Hartmann sensor can be very small. It should be pointed out that in the embodiment of the present invention, the wave aberration incident on the deformable mirror is unknown and can only be estimated. The deformable mirror wave aberration is -160. During simulation, the theoretical value of the deformable mirror wave aberration is set to this value, and then the deformable mirror wave aberration is estimated using the method disclosed in this embodiment. The estimated value is Figure 5 Where (c) is estimated based on formula (12) or formula (14). The former is the simulation data of zemax under specific circumstances, and the latter is the formula method.

[0128] To illustrate the robustness of the method of the embodiment of the present invention, the wavefront aberration on the Hartmann sensor is not reduced to a very small level after the closed-loop correction of the deformable mirror. The wavefront aberration in the embodiment of the present invention uses the Zernike coefficients of the fringe with normalized radius, with Z4, Z9, Z16, and Z25 representing the 4th, 9th, 16th, and 25th Zernike coefficients, respectively. The wavefront aberration of the deformable mirror is twice its surface shape. This shows that during the defocusing of the light source and the deformable mirror, the wavefront aberration measured by the wavefront sensor is mainly defocus, with very little spherical aberration. To more clearly demonstrate the 9th, 16th, and 25th Zernike coefficients, they are magnified by 102, 104, and 106 times, respectively.

[0129] Based on formula (12) and Figure 6 The data in can be used to calculate the wave aberration incident on the deformable mirror corresponding to different light source defocus. The results are as follows: Figure 7 shown. Figure 7 A series of deformable mirror wave aberration measurement process data are given, including light source defocus, deformable mirror wave aberration, and Hartmann sensor wave aberration data. n represents the light source position, dn represents the defocus amount corresponding to different positions, that is, the axial movement of the light source from the focal plane position; WM represents the deformable mirror wave aberration theoretical value, and Represents an estimated value. The deformable mirror wavefront aberration measurement process data is obtained through Zemax simulation, so they are all known values, not calculated. They are used as theoretical values ​​to facilitate comparison with subsequent estimated values.

[0130] The embodiments of the present invention disclosed Figure 8 The corresponding deformable mirror wave aberration estimate is given by Figure 8 It can be seen that the estimated value of the deformable mirror wave aberration is very close to the true value.

[0131] The disclosed device and method for measuring the shape of a deformable mirror over a long range, as described above, require only a simple optical system and a standard Hartmann sensor to achieve high-precision measurement of the shape of a deformable mirror over a long range. The core of this method is to adaptively adjust the position of the defocused light source based on the wavefront aberration of the deformable mirror, thereby limiting the wavefront aberration of the light beam emitted from the deformable mirror to a relatively small range. This negligible effect of the wavefront aberration of the relay lens between the deformable mirror and the Hartmann sensor can be achieved. This demonstrates that the device and method for measuring the shape of a deformable mirror over a long range, as described above, are simple in structure and algorithm, and relatively low in cost.

[0132] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present invention, and these modifications or replacements should all be included in the scope of protection of the present invention.

Claims

1. A large-stroke deformable mirror shape measuring device, characterized in that: include: A reference reflector, a long-stroke deformable mirror, and a deformable mirror surface shape measurement system, wherein the reference reflector reflects the optical path folded by the deformable mirror surface shape measurement system for calibrating the optical path aberration of the deformable mirror surface shape measurement system; the reference reflector replaces the long-stroke deformable mirror in situ, and the deformable mirror surface shape measurement system measures the long-stroke deformable mirror surface shape based on the calibrated optical path aberration; wherein: The deformable mirror surface shape measurement system includes a movable light source module, a folding reflector, an optical lens assembly and a Hartmann sensor. Moving the position of the movable light source module changes the wave aberration on the large-stroke deformable mirror surface shape; the light path emitted by the movable light source is folded by the folding reflector and then incident on the large-stroke deformable mirror; the optical lens assembly includes a beam splitter and a relay lens. The light beam reflected by the large-stroke deformable mirror passes through the beam splitter and then passes through the relay lens to be incident on the Hartmann sensor.

2. The long-stroke deformable mirror shape measuring device according to claim 1, characterized in that: The movable light source module includes a light source, a high-precision guide rail and a collimating lens. The light source is placed on the high-precision guide rail, and the position of the light source is moved axially by the guide rail. The collimating lens collimates the light emitted by the light source. The collimated light path is reflected by the folding reflector and the beam splitter and then incident on the large-stroke surface mirror.

3. The long-stroke deformable mirror shape measuring device according to claim 2, characterized in that: The folding reflector is an ordinary plane reflector, and the collimating lens and the relay lens are both composed of ordinary doublet lenses.

4. The long-stroke deformable mirror shape measuring device according to claim 1, characterized in that: The Hartmann sensor is an ordinary Hartmann sensor that performs wave aberration measurement on the optical path; the Hartmann sensor and the large-stroke deformable mirror achieve aperture conjugation through the relay lens.

5. A method for measuring the shape of a large-stroke deformable mirror, based on the device for measuring the shape of a large-stroke deformable mirror according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Use the reference reflector to replace the long-stroke deformable mirror in situ to obtain the Hartmann sensor measurement wave aberration; Step 2: Replace the reference reflector with a long-stroke deformable mirror, move the light source from the initial position to different positions, obtain the corresponding Hartmann sensor measurement wave aberration, and the difference in the wave aberration incident on the long-stroke deformable mirror; Step 3: Based on the Hartmann sensor measuring the wave aberration, a closed-loop adjustment is performed on the long-stroke deformable mirror to stabilize the wave aberration of the deformable mirror. The light source is defocused to different positions to obtain different Hartmann sensor measuring wave aberrations and the corresponding differences in the wave aberrations incident on the long-stroke deformable mirror. Step 4: Set the large-stroke deformable mirror to the position of the surface to be measured, adjust the light source position to minimize the defocus wave aberration on the Hartmann sensor, record the light source position and the Hartmann sensor wave aberration, and obtain the deformable mirror wave aberration estimate.

6. The method for measuring the shape of a large-stroke deformable mirror according to claim 5, characterized in that: The step 1 specifically includes: Step S11: Place the reference reflector at the position of the deformable mirror and replace the deformable mirror in situ; place the light source near the front focal plane of the collimator lens, and the wave aberration incident on the reference reflector is defined as W I,0 , Hartmann sensor measures wave aberration W S,0 Expressed as: W S,0 =W I,0 +W R,0 Formula (1) In formula (1), W R,0 Indicates the wave aberration of the relay lens corresponding to this working condition.

7. The method for measuring the shape of a large-stroke deformable mirror according to claim 5, characterized in that: The second step specifically includes: Step S21: Replace the reference reflector with a large-stroke deformable mirror. The large-stroke deformable mirror operates near its flattened state. At this time, the Hartmann sensor measures the wave aberration W S,1 Expressed as: W S,1 =W I,0 +W M,1 +W R，1 Formula (2) In formula (2), W M,1 It represents the deformable mirror wave aberration corresponding to this working condition, W R，1 Indicates the wave aberration of the relay lens corresponding to this working condition; Step S22: Defocus the light source to the first position through the guide rail. Under this working condition, the Hartmann sensor measures the wave aberration W. S,2 Expressed as: W S,2 =W I,1 +W M,1 +W R，2 Formula (3) In formula (3), W I,1 It represents the wave aberration incident on the deformable mirror under this working condition, W M,1 It represents the deformable mirror wave aberration corresponding to this working condition, W R，2 It represents the wave aberration of the relay lens under this working condition; When the light source is at the first position and the second position, the difference in wave aberration incident on the large-stroke deformable mirror is expressed as: W I,1 -W I,0 =(W S,2 -W S,1 )-(W R,2 -W R,1 ) Equation (4) In formula (4), W I,1 It represents the wave aberration incident on the deformable mirror under this working condition, W I,0 represents the defined wave aberration incident on the deformable mirror, W S,2 It represents the wave aberration measured by the Hartmann sensor under the corresponding working condition when the light source is at the first position, W S,1 It represents the wave aberration measured by the Hartmann sensor under the corresponding working condition when the light source is at the initial position, W R,2 It represents the wave aberration of the relay lens when the light source is defocused to the first position, W R,1 It represents the wavefront aberration of the relay lens corresponding to the working condition when the light source is at the initial position.

8. The method for measuring the shape of a large-stroke deformable mirror according to claim 5, characterized in that: The step three specifically includes: Step S31: The Hartmann sensor and the long-stroke deformable mirror form a closed loop, and the defocus wave aberration of the long-stroke deformable mirror is adjusted based on the wave aberration measured by the Hartmann sensor to reduce the wave aberration measured by the Hartmann sensor and stabilize the wave aberration of the deformable mirror to W. M,2 At this time, the Hartmann sensor measures the wave aberration W S,3 Expressed as: W S,3 =W I,1 +W M,2 +W R，3 Formula (5) In formula (5), W I,1 It represents the wave aberration incident on the deformable mirror under this working condition, W R，3 Indicates the wave aberration of the relay lens corresponding to this working condition; Step S32: Defocus the light source to the second position, and measure the wavefront aberration W using the Hartmann sensor. S,4 Expressed as: W S,4 =W I,2 +W M,2 +W R，4 Formula (6) In formula (6), W I,2 It represents the wave aberration incident on the large-stroke deformable mirror under this working condition, W R，4 It represents the wave aberration of the relay lens under this working condition; The wave aberration W incident on the large-stroke deformable mirror when the light source is at the first and second positions I,1 and W I,2 The difference is expressed as: W I,2 -W I,1 = (W S,4 -W S,3 ) - (W R,4 -W R,3 ) Equation (7) In formula (7), W I,2 It represents the wave aberration incident on the large-stroke deformable mirror when the light source is defocused to the second position, W I,1 It represents the wave aberration incident on the large-stroke deformable mirror when the light source is defocused to the first position, W S,4 Indicates the wave aberration measured by the Hartmann sensor when the light source is defocused to the second position, W S,3 Indicates the stable deformable mirror wave aberration to W M,2 When the Hartmann sensor measures the wave aberration, W R,4 Indicates that the light source is defocused to the second position. The wave aberration of the relay lens under this working condition, W R,3 Indicates the stable deformable mirror wave aberration to W M,2 Wave aberration of the relay lens corresponding to the working conditions; Step S33: Repeat steps S31 and S32 to obtain the wave aberration W incident on the large-stroke deformable mirror when the light source is at positions (n-1) and n. I,n-1 and W I,n The difference is expressed as: W I,n -W I,n-1 =(W S,2n -W S,2n-1 )-(W R,2n -W R,2n-1 ) Equation (8) In formula (8), W I,n It represents the wave aberration when the light source is at position n and incident on the large-stroke deformable mirror, W I,n-1 It represents the wave aberration when the light source is at position (n-1) incident on the large-stroke deformable mirror, W S,2n It represents the wave aberration measured by the Hartmann sensor when the light source is defocused to position n, W S,2n-1 It represents the wave aberration measured by the Hartmann sensor when the light source is defocused to position (n-1), W R,2n W represents the wave aberration of the relay lens when the light source is defocused to position n. R,2n-1 It represents the wavefront aberration of the relay lens when the light source is defocused to position (n-1); When the light source is at position n, the wave aberration incident on the large-stroke deformable mirror is expressed as: In formula (9), after a series of light source positions and their corresponding wave aberrations incident on the deformable mirror are calibrated, the long-stroke deformable mirror surface shape measurement is performed.

9. The method for measuring the shape of a large-stroke deformable mirror according to claim 5, characterized in that: The step 4 specifically includes: Set the deformable mirror to the position of the surface to be measured, discretely adjust the light source position based on the Hartmann sensor wave aberration measurement to minimize the defocus wave aberration on the Hartmann sensor, and record the light source position n′ and the Hartmann sensor wave aberration W S ;include: Step S41, the deformable mirror wave aberration is expressed as: In formula (10), W M represents the deformable mirror's own wave aberration, W S W is the wave aberration measured by the Hartmann sensor. R represents the wave aberration of the relay lens, W I,n′ It represents the wave aberration incident on the large-stroke deformable mirror when the light source is at position n, Step S42: Due to the wave aberration W of the relay lens R The change of can be ignored, so the deformable mirror wave aberration estimate is Expressed as: In formula (11), W S It indicates that the Hartmann sensor measures wave aberration; Step S43: Define the wave aberration incident on the deformable mirror Expressed as: Deformable mirror wave aberration estimation Expressed as: In formula (13), W S represents the wave aberration measured by the Hartmann sensor, represents the wave aberration incident on the deformable mirror.

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