CN118372174B - Optical performance measurement and compensating polishing method for multi-reflective optical system - Google Patents

Abstract

The invention discloses an optical performance measuring and compensating polishing method of a multi-reflecting optical system, which comprises the following steps: 1) Determining a surface to be repaired; 2) Wavefront aberration measurement; 3) Calculating the surface shape of the surface to be repaired; 4) Compensating the polishing path planning; 5) Compensating polishing. The method of the invention attributes the surface shape deviation and the pose deviation of each mirror surface in the multi-reflecting optical system to one mirror surface for evaluation and compensation, compensates the pose deviation introduced by the adjustment, and greatly improves the compensation polishing efficiency on the basis of ensuring the overall performance of the multi-reflecting optical system.

Description

Optical performance measurement and compensating polishing method for multi-reflective optical system

Technical Field

The invention relates to the field of optical technology, and in particular to an optical performance measurement and compensating polishing method for a multi-reflection optical system.

Background Art

Generally speaking, the precision requirements of multi-reflection optical systems cannot be met by manufacturing accuracy alone, so measurements are required after manufacturing to avoid unqualified products from being put into use. However, there are usually two ways to measure multi-reflection optical systems. The first way is to cut each reflector separately, measure the surface shape and perform compensatory polishing, and finally install and adjust the reflector to form a multi-reflection optical system; the other way is to use instruments such as laser interferometers for offline measurement after cutting and adjustment, and then perform compensation processing. Both methods have certain shortcomings. The first method only guarantees the surface shape of a single reflector, but the posture error introduced by optical adjustment will completely affect the final optical performance; although the second method evaluates the overall optical performance and improves it through processing, offline measurement reduces the efficiency of this process, and the measurement results cannot accurately guide the compensation processing.

Summary of the invention

In view of the above-mentioned defects or deficiencies in the prior art, it is desired to provide a method for measuring the optical performance and compensatory polishing of a multi-reflective optical system, which can attribute the surface shape deviation and posture deviation of each mirror in the multi-reflective optical system to one mirror for evaluation and compensation, and compensate for the posture deviation introduced by the installation, thereby greatly improving the compensatory polishing efficiency while ensuring the overall performance of the multi-reflective optical system.

The present invention provides a method for measuring the optical performance of a multi-reflection optical system and for compensating for polishing, comprising the following steps:

1) determining a surface to be repaired, first designing a corresponding ray tracing model according to the parameters of the multi-reflection optical system, calculating the outgoing wavefront aberration _Wi of the ray tracing model, then adding the same size of surface shape deviation or posture deviation to each reflective surface of the ray tracing model, obtaining a reflective surface that makes the outgoing wavefront aberration _Wi change the most, defining it as the surface to be repaired, and obtaining the ideal surface shape parameter _Mi of the surface to be repaired;

2) wavefront aberration measurement, measuring the outgoing wavefront of the multi-reflection optical system and calculating the current outgoing wavefront aberration W _r ;

3) Calculating the surface shape of the surface to be trimmed, substituting the W _r into the ray tracing model to obtain the optimized surface shape parameter _Mr of the surface to be trimmed, and then obtaining the removal function H;

H = λ(M _r -M _i );

M _r = arcmin(||f(W _r ,M _r )-W _i ||);

Wherein, λ is the scaling factor; f is the shaping function of the multi-reflection optical system for the input wavefront under the action of _Mr ;

4) Compensation polishing path planning, arranging the dwell points according to the process parameters of the polishing device and fitting to obtain the dwell function R, combining the removal function H with an iterative optimization process to calculate the dwell time T at each dwell point, and generating a series of compensation polishing paths containing the dwell point coordinates and the dwell time;

5) Compensation polishing: polish the reflective surface of the multi-reflection optical system corresponding to the surface to be repaired according to the compensation polishing path, and then repeat steps 2)-5) until the output wavefront aberration W _r in step 2) meets the application requirements, and the compensation polishing of the multi-reflection optical system is completed.

Furthermore, in step 1), the direction vector of the incident light from the object side intersects with each reflection surface of the ray tracing model in turn, and then the outgoing light is calculated according to the law of reflection, and then the outgoing wavefront aberration W _i of the ray tracing model is calculated.

Furthermore, in the step 2), the multi-reflection optical system to be polished and the in-situ measuring device are installed in a polishing device, and the in-situ measuring device is aligned with the multi-reflection optical system; after the polishing device polishes each reflective surface of the multi-reflection optical system, each reflective surface of the multi-reflection optical system is wiped clean, and the multi-reflection optical system is measured for an outgoing wavefront by the in-situ measuring device, and the current outgoing wavefront aberration W _r is calculated.

Furthermore, in the step 3), the parallel incident light without aberration in the ray tracing model is set as the parallel light with the current outgoing wavefront aberration W _r , and the optimized surface parameter _Mr of the surface to be repaired is solved by a multi-starting point global optimal algorithm, and the optimized surface parameter _Mr is the surface parameter that makes the outgoing wavefront aberration closest to 0;

Furthermore, the iterative optimization process is:

A series of dwell points with appropriate intervals are generated according to the surface to be trimmed, and the initial dwell time T ₀ is calculated in combination with the dwell function R:

T ₀ =H/R;

The initial residual error _E0 is:

E ₀ = HT ₀ * R;

To further approximate the residual error, the residual time _ti of the i-th iteration is:

t _i =E _i-1 /R;

The new dwell time _Ti and residual error _Ei after this iteration are:

_Ti = Ti _-1 + λt _i ;

E _i =H-(T _i +λt _i )*R;

The value of T is accurately solved step by step through the iterative optimization process until the RMS of the residual error is less than the preset threshold, thereby obtaining the residence time T of each residence point.

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

(1) The present invention is guided by the actual application requirements of the optical system and directly evaluates the wave aberration of the multi-reflector optical system instead of the surface deviation. The surface deviation and posture deviation of each mirror surface in the multi-reflector optical system are attributed to one mirror surface for evaluation and compensation by ray tracing, which has higher efficiency and can also compensate for the posture deviation introduced by the adjustment, effectively improving the optical performance of the multi-reflector optical system.

(2) The wavefront aberration measurement of the multi-reflection optical system adopts an in-situ measurement method and is measured directly in the polishing device, avoiding the tedious operation of the offline measurement-processing cycle and improving efficiency.

It should be understood that the contents described in the summary of the invention are not intended to limit the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

FIG1 is a flow chart of the compensation polishing path planning of a multi-reflection optical system;

FIG2 is a flow chart of an iterative optimization process;

FIG3 is a schematic diagram of the ray tracing principle of a three-mirror optical system;

FIG4 is a schematic diagram of the structure of wavefront aberration measurement of a three-mirror optical system;

FIG5 is a comparison diagram of the three-mirror optical system before and after compensatory polishing.

DETAILED DESCRIPTION

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It should also be noted that, for ease of description, only the parts related to the invention are shown in the accompanying drawings.

It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

Referring to FIG. 1 and FIG. 2 , an embodiment of the present invention provides an optical performance measurement and compensatory polishing method for a multi-reflection optical system, comprising the following steps:

1) Determine the surface to be repaired. First, design a corresponding ray tracing model according to the parameters of the multi-reflection optical system. The direction vector of the incident light from the object side intersects with each reflection surface of the ray tracing model in turn. Then, calculate the outgoing light according to the law of reflection, and then calculate the outgoing wavefront aberration W _i of the ray tracing model.

Then, the same size of surface shape deviation or position deviation is added to each reflective surface of the ray tracing model to obtain the reflective surface that causes the maximum change in the outgoing wavefront aberration _Wi , which is defined as the surface to be repaired, and the ideal surface shape parameter _Mi of the surface to be repaired is obtained;

2) Wavefront aberration measurement: the multi-reflection optical system to be polished and the in-situ measurement device are installed in the polishing device, and the in-situ measurement device is aligned with the multi-reflection optical system; after the polishing device polishes each reflection surface of the multi-reflection optical system, each reflection surface of the multi-reflection optical system is wiped clean, and the in-situ measurement device is used to measure the outgoing wavefront of the multi-reflection optical system, and the current outgoing wavefront aberration W _r is calculated;

3) Calculate the surface shape of the surface to be repaired. Substitute W _r into the ray tracing model, that is, set the parallel incident light without aberration in the ray tracing model to be the parallel light with W _r , and use the multi-starting point global optimal algorithm to solve the optimized surface shape parameter _Mr of the surface to be repaired. The optimized surface shape parameter _Mr is the surface shape parameter that makes the outgoing wavefront aberration closest to 0, and then obtain the removal function H;

H = λ(M _r -M _i );

M _r = arcmin(||f(W _r ,M _r )-W _i ||);

Wherein, λ is the scaling factor; f is the shaping function of the multi-reflection optical system for the input wavefront under the action of _Mr ;

4) Compensation polishing path planning: the dwell points are arranged according to the process parameters of the polishing device and the dwell function R is obtained by fitting. The dwell time T at each dwell point is calculated by an iterative optimization process in combination with the removal function H, and a series of compensation polishing paths containing the coordinates of the dwell points and the dwell time are generated;

The iterative optimization process is:

Generate a series of dwell points with appropriate intervals according to the surface to be repaired, and calculate the initial dwell time T ₀ in combination with the dwell function R:

T ₀ =H/R;

The initial residual error _E0 is:

E ₀ = HT ₀ * R;

To further approximate the residual error, the residual time _ti of the i-th iteration is:

t _i =E _i-1 /R;

The new dwell time _Ti and residual error _Ei after this iteration are:

_Ti = Ti _-1 + λt _i ;

E _i =H-(T _i +λt _i )*R;

The value of T is accurately solved step by step through the iterative optimization process until the RMS of the residual error is less than the preset threshold, thereby obtaining the dwell time T of each dwell point;

5) Compensation polishing: polish the corresponding reflective surface to be repaired of the multi-reflection optical system according to the compensation polishing path, and then repeat steps 2)-5) until the current output wavefront aberration W _r in step 2) meets the application requirements, and the compensation polishing of the multi-reflection optical system is completed.

Example 1

Please refer to Figures 3 to 5, taking a three-mirror optical system as an example. Substitute the surface shape parameters and posture parameters of the three off-axis free-form surfaces of the three-mirror optical system into the ray tracing program to construct a ray tracing model.

As shown in FIG3 , since the three-mirror optical system is an afocal optical path on the object side and converging optical path on the image side, parallel incident light along the optical axis is added to the ray tracing model and the outgoing wavefront aberration W _i is calculated at this time. This wavefront aberration is the ideal outgoing wavefront aberration of the three-mirror optical system.

Sinusoidal surface shape error and posture error are applied to the first, second and third mirrors respectively. The surface shape error is set as follows: the amplitude is not greater than 0.1% of the surface shape vector height, and the spatial frequency is not greater than 1/5 of the mirror aperture; the posture error is set as follows: the posture deviation is the rotation angle around the X-axis, Y-axis and Z-axis, which is not greater than 1°, and the position deviation is the offset along the X-axis, Y-axis and Z-axis, which is not greater than 0.01mm.

For the above situation, the outgoing wavefront aberration of the image plane is simulated and calculated. The surface error and posture error of the second mirror have more influence on the aberration than the first and third mirrors. Therefore, for this three-mirror optical system, the second mirror is the surface to be corrected.

The three-mirror optical system and the in-situ measurement device are installed in the polishing device and the wavefront is measured to evaluate the outgoing wavefront aberration W _r . The schematic diagram of the system structure is shown in FIG4 . The entire system is built in a set of mechanical arm polishing devices. The mechanical arm is equipped with an airbag polishing head to perform compensation polishing on the three-mirror optical system in the lateral direction. The three-mirror optical system is placed in the polishing pool. The in-situ measurement device is aligned with the exit window of the three-mirror optical system, and the plane mirror or screen is aligned with the entrance window of the three-mirror optical system. When the in-situ measurement device is a sensor based on the Shack-Hartmann principle, a plane mirror reflection is used. When the in-situ measurement device is a sensor based on the inverse Hartmann principle, a screen display pattern is used.

Substitute the measured outgoing wavefront aberration W _r into the ray tracing model to obtain the surface shape parameter Mr of the surface to be repaired. That is, the parallel incident light without aberration in the ray tracing model is set as the parallel light with the outgoing wavefront aberration W _r , and the multi-starting point global optimal algorithm is used to solve the surface shape parameter _Mr of _the surface to be repaired that makes the outgoing aberration of the ray tracing model closest to 0. The constructed optimization function is:

M _r = arcmin(||f(W _r ,M _r )-W _i ||);

Where f represents the shaping function of the input wavefront of the three-mirror optical system under the action of _Mr.

The generated removal function H is as follows:

H = λ(M _r -M _i );

The dwell time distribution is iteratively calculated according to the required removal function H. In order to prevent over-compensation, only a certain proportion of the residual error is often compensated during compensation processing, rather than all compensation. The optimal solution is approached through repeated compensation iterations, and the scaling factor λ is set to 0.5.

Generate a series of dwell points with appropriate intervals according to the surface to be repaired, and calculate the initial dwell time T0 in combination with the dwell function R:

T ₀ =H/R;

The initial residual error _E0 is:

E ₀ = HT ₀ * R;

To further approximate the residual error, the residual time _ti of the i-th iteration is:

t _i =E _i-1 /R;

After this iteration, the new dwell time _Ti and residual error _Ei are:

_Ti = Ti _-1 + λt _i ;

E _i =H-(T _i +λt _i )*R;

Through the above iterative process, the value of T is accurately solved step by step until the RMS of the residual error is less than the required threshold. At this time, the dwell time distribution at each dwell point is known, and the compensation polishing path is formed accordingly.

Compensation polishing is performed according to the compensation polishing path, and the process parameters correspond to the dwell function used. After polishing is completed, the wavefront measurement of the three-mirror optical system is repeatedly cycled until compensation polishing is performed according to the compensation polishing path until the wavefront aberration meets the requirements when measuring the three-mirror optical system.

The effect of the final output wavefront aberration-guided compensatory polishing is shown in Figure 5. Before compensatory polishing, the image is blurred and the wavefront aberration is large, showing an obvious annular error. However, after compensatory polishing, the image quality and wavefront aberration are significantly improved.

In the description of this specification, the description of the terms "one embodiment", "some embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (5)

1. The optical performance measuring and compensating polishing method for the multi-reflecting optical system is characterized by comprising the following steps:

1) Determining a surface to be repaired, firstly designing a corresponding ray tracing model according to parameters of a multi-reflection optical system, calculating emergent wavefront aberration W _i of the ray tracing model, then respectively adding surface shape deviation or pose deviation with the same size to each reflecting surface of the ray tracing model to obtain a reflecting surface with the maximum change of the emergent wavefront aberration W _i, defining the reflecting surface as the surface to be repaired, and obtaining ideal surface shape parameters M _i of the surface to be repaired;

2) Wave-front aberration measurement, namely performing emergent wave-front measurement on the multi-reflection optical system, and calculating current emergent wave-front aberration W _r;

3) Calculating the surface shape of the surface to be repaired, substituting the W _r into the ray tracing model to obtain an optimized surface shape parameter M _r of the surface to be repaired, and further obtaining a removal function H;

H＝λ(M_r-M_i)；

M_r＝arcmin(||f(W_r,M_r)-W_i||)；

wherein λ is the scaling factor; f is a shaping function of the multi-reflectometry system on the input wavefront under the action of M _r;

4) Performing compensation polishing path planning, carrying out resident point arrangement according to technological parameters of a polishing device, fitting to obtain a resident function R, calculating resident time T at each resident point by adopting an iterative optimization process in combination with the removal function H, and generating a series of compensation polishing paths containing resident point coordinates and resident time;

5) And (3) compensating and polishing, namely polishing the reflecting surface of the multi-reflecting optical system corresponding to the surface to be repaired according to the compensating and polishing path, and repeating the steps 2) -5) until the emergent wavefront aberration W _r in the step 2) meets the application requirement, thereby finishing the compensating and polishing of the multi-reflecting optical system.

2. The method according to claim 1, wherein in the step 1), the direction vector of the incident light beam from the object side sequentially intersects with each reflecting surface of the ray tracing model, and then the outgoing light beam is calculated according to the reflection law, and then the outgoing wavefront aberration W _i of the ray tracing model is calculated.

3. The method for measuring and compensating for optical performance of a multi-reflecting optical system according to claim 1, wherein in the step 2), the multi-reflecting optical system to be polished and an in-situ measuring device are installed in a polishing device, and the in-situ measuring device is aligned with the multi-reflecting optical system; after polishing the reflecting surfaces of the multi-reflection optical system, the polishing device wipes the reflecting surfaces of the multi-reflection optical system clean, and the in-situ measuring device measures the emergent wavefront of the multi-reflection optical system to calculate the current emergent wavefront aberration W _r.

4. The method according to claim 1, wherein in the step 3), the parallel incident light without aberration in the ray tracing model is set as the parallel light with the current outgoing wavefront aberration W _r, and the optimized surface type parameter M _r of the surface to be repaired is solved by using a multi-start global optimization algorithm, and the optimized surface type parameter M _r is a surface type parameter for making the outgoing wavefront aberration closest to 0.

5. The method for measuring and compensating for polishing optical performance of a multi-reflecting optical system according to claim 1, wherein the iterative optimization process is as follows:

Generating a series of residence points with proper intervals according to the surface to be repaired, and calculating initial residence time T ₀ by combining a residence function R:

T₀＝H/R；

the initial residual error E ₀ is:

E₀＝H-T₀*R；

Further approximating the residual error, the i-th iteration finds the residual time t _i as:

t_i＝E_i-1/R；

the new dwell time T _i and residual error E _i after this iteration are:

T_i＝T_i-1+λt_i；

E_i＝H-(T_i+λt_i)*R；

And precisely solving the value of T step by step through an iterative optimization process until the RMS of the residual error is smaller than a preset threshold value, thereby obtaining the residence time T of each residence point.