Chromatic aberration compensation method and system in dual-wavelength digital holography

Abstract

The invention relates to a chromatic aberration compensation method in dual-wavelength digital holography. The chromatic aberration compensation method comprises the following steps: obtaining a dual-wavelength interferogram containing two wavelengths at the same time; calculating to obtain complex amplitudes of two different wavelengths at a camera plane; performing numerical propagation on the object wavefront of the two wavelengths in a set defocus range by using an angular spectrum propagation algorithm to obtain complex amplitudes of the two wavelengths at different axial positions in the defocus range; calculating corresponding single wavelength phase distribution in the defocus range; calculating dual-wavelength synthetic phase distribution of the two wavelengths under all combinations of different axial positions; solving a gradient value to obtain a dual-wavelength synthetic phase distribution gradient value when the two wavelengths are located at different axial propagation positions; and subtracting the two single-wavelength phases corresponding to the minimum position of the dual-wavelength synthesis phase distribution gradient value to obtain a dual-wavelength synthesis phase after chromatic aberration compensation. By adopting the chromatic aberration compensation method in the dual-wavelength digital holography, the phase measurement precision can be greatly improved.

Description

Technical Field

[0001] The invention relates to the field of digital holographic three-dimensional measurement, and in particular to a chromatic aberration compensation method in dual-wavelength digital holography. Background Art

[0002] With the development of precision manufacturing, it is necessary to perform three-dimensional morphology measurement on some objects such as MEMS devices and semiconductor chips whose surface height jumps from hundreds of nanometers to hundreds of microns. Existing digital holography uses the principle of interference to measure the optical phase of light waves modulated by objects, and then obtains three-dimensional information of objects. It has the advantages of high precision, no contact with samples, non-destructive, non-interventional, easy to use, no need to dye biological samples, and easy to use with other instruments. Dual-wavelength digital holography uses two light waves of different wavelengths on the basis of digital holography to perform interference measurement through wavelength synthesis, which can greatly extend the range of interference measurement; it has a wide range of applications in micro-electromechanical detection and medical biological detection.

[0003] However, dual-wavelength digital holography requires recording a set of interference patterns at two wavelengths for microscopic phase measurement of samples. Due to the dispersion characteristics of the optical device itself, chromatic aberration will occur when the two wavelengths are imaged in the same plane. That is, in the interference pattern of the two wavelengths obtained on a camera plane, only one wavelength of the object wavefront is actually in focus, while the object wavefront of the other wavelength is defocused. Therefore, the defocused phase image calculated by the interference pattern of the two wavelengths will bring errors to the dual-wavelength synthetic phase measurement.

[0004] In order to solve the chromatic aberration problem, existing methods include improving the optical system, adding achromatic elements or using numerical processing methods to compensate. For example, Indian scholar Ibrahim improved the optical system by using two identical cameras and two bandpass filters to capture two holograms in real time; however, this method is equivalent to using two Mach-Zehnder interferometers, which increases the complexity of the system. In addition, since two cameras are required to measure simultaneously, the difficulty of experimental debugging and camera matching requirements are also increased accordingly.

[0005] In addition, adding achromatic elements such as achromatic lenses to the optical system can reduce the focus differences of different wavelengths to a certain extent; however, these optical elements are expensive to manufacture and increase the design difficulty in complex optical systems. In practical applications, due to the errors of optical elements and the non-ideality of experimental systems, chromatic aberration is difficult to completely eliminate, and complex optical systems further increase this problem.

[0006] The method using numerical processing is to post-process the recorded interference pattern through numerical algorithms to eliminate or reduce the impact of chromatic aberration on measurement accuracy. For example, Italian scholar Ferraro proposed numerically refocusing the wavelengths that are out of focus in the hologram, believing that no circular fringes will appear in the final phase diagram after the chromatic aberration is compensated. However, this method requires that at least one wavelength corresponding to the corresponding defocus distance be known in advance, and in real-time changing experiments, the best focusing state of the object at different wavelengths needs to be judged by the naked eye, which can easily lead to misjudgment of the focal plane and affect the accuracy of phase measurement.

[0007] In summary, the chromatic aberration compensation method in dual-wavelength digital holography in the prior art still has problems such as complex system, high manufacturing cost or inaccurate measurement. Summary of the invention

[0008] Based on this, the purpose of the present invention is to provide a chromatic aberration compensation method in dual-wavelength digital holography, which can simultaneously collect spatial carrier frequency interference patterns of two wavelengths in an off-axis form on the same camera, and after calculation, it can achieve high-precision chromatic aberration compensation of the dual-wavelength synthetic phase in a low-cost optical path system.

[0009] A method for compensating chromatic aberration in dual-wavelength digital holography, comprising:

[0010] A dual-wavelength interference pattern containing two wavelengths simultaneously is obtained;

[0011] Receive the dual-wavelength interference pattern and calculate the complex amplitudes of two different wavelengths at the camera plane;

[0012] Combining the complex amplitudes of the two wavelengths at the camera plane, the angular spectrum propagation algorithm is used to numerically propagate the object wavefronts of the two wavelengths within the set defocus range to obtain the complex amplitudes of the two wavelengths at different axial positions within the defocus range.

[0013] Calculate the corresponding single wavelength phase distribution according to the complex amplitude at each position within the defocus range;

[0014] Calculate the dual-wavelength composite phase distribution under all combinations of two wavelengths at different axial positions according to the single-wavelength phase distribution corresponding to each wavelength;

[0015] The gradient values ​​of all dual-wavelength composite phase distributions are calculated to obtain the dual-wavelength composite phase distribution gradient values ​​when the two wavelengths are at different axial propagation positions;

[0016] The dual-wavelength composite phase after chromatic aberration compensation is obtained by subtracting the two single-wavelength phases corresponding to the minimum position of the dual-wavelength composite phase distribution gradient value.

[0017] Furthermore, the defocus range is set to D = d1 ~ d M=4mm, where D is the defocus range, d is the imaging plane distance, and M is a natural number.

[0018] Furthermore, the complex amplitude of the light field is transformed into the frequency domain by two-dimensional Fourier transform. A phase factor related to the propagation distance is introduced into the frequency domain to represent the influence of different propagation distances. The complex amplitude of the object at different defocus planes is obtained by inverse Fourier transform back to the spatial domain. and

[0019]

[0020] in, is the complex amplitude of wavelength λ1 at different axial positions within the defocus range, is the complex amplitude of wavelength λ2 at different axial positions within the defocus range; F{} represents Fourier transform, F -1 {} represents inverse Fourier transform; (u, v) is the frequency domain coordinate corresponding to the spatial coordinate; the subscript m, n = 1, 2, ..., M, represents the propagation position number.

[0021] Furthermore, the propagation position sequence number satisfies:

[0022] M=floor[(d m -d0) / step]+1, where floor represents rounding down, and M=41.

[0023] Furthermore, the single-wavelength phase distribution of each wavelength λ1 is subtracted from the single-wavelength phase distribution of wavelength λ2 at all axial positions, and M is obtained. 2 Dual wavelength synthetic phase distribution

[0024]

[0025] in, is the single wavelength phase distribution corresponding to wavelength λ1, is the single wavelength phase distribution corresponding to wavelength λ2.

[0026] Furthermore, for all The gradient value is calculated to obtain the dual-wavelength synthetic phase distribution gradient value G when the two wavelengths are at different axial propagation positions m and n. m,n :

[0027]

[0028] Where X and Y represent the number of pixels in the vertical and horizontal directions of the image.

[0029] The present invention also provides a chromatic aberration compensation system in dual-wavelength digital holography, comprising:

[0030] A first laser light source continuously emits a first initial light beam;

[0031] A second laser light source continuously emits a second initial light beam;

[0032] A first beam splitter is arranged in the emission direction of the first initial light beam and the second initial light beam, and combines the first initial light beam and the second initial light beam to obtain a combined light beam;

[0033] A second beam splitter is arranged in the emission direction of the combined light beam, and splits the combined light beam into a first split light beam and a second split light beam;

[0034] A third beam splitter is arranged in an emitting direction of the first split light beam, and splits the first split light beam to obtain a first regulated incident light beam and a second regulated incident light beam;

[0035] A first plane reflector, disposed in the direction of the first regulated incident light beam, reflects the first regulated incident light beam to form a first regulated outgoing light beam;

[0036] A second plane reflector is arranged in the direction of the second regulated incident light beam, and reflects the second regulated incident light beam to form a second regulated outgoing light beam; the second regulated outgoing light beam is combined with the first regulated outgoing light beam in the third beam splitter to form a reference light beam and then out of the third beam splitter;

[0037] a fourth beam splitter, arranged in the emitting direction of the second split light beam, transmitting the second split light beam and irradiating it on the surface of the sample to be tested, and reflecting the light beam reflected back from the surface of the sample to be tested again to form an object light beam;

[0038] a fifth beam splitter, arranged in the emission direction of the reference beam and the object beam, and combining the reference beam and the object beam to form an interference beam;

[0039] A camera is arranged in the emission direction of the interference light beam, and receives the interference light beam to obtain a dual-wavelength interference pattern;

[0040] The processor receives the dual-wavelength interference pattern and analyzes it to obtain the dual-wavelength synthetic phase after chromatic aberration compensation.

[0041] Furthermore, the processor comprises:

[0042] An amplitude calculation module, used for receiving a dual-wavelength interference pattern and calculating the complex amplitudes of two different wavelengths at a camera plane;

[0043] An amplitude distribution module is used to combine the complex amplitudes of the two wavelengths at the camera plane, and use the angular spectrum propagation algorithm to numerically propagate the object wavefronts of the two wavelengths within a set defocus range to obtain the complex amplitudes of the two wavelengths at different axial positions within the defocus range;

[0044] A single wavelength phase distribution module is used to calculate the corresponding single wavelength phase distribution according to the complex amplitude at each position within the defocus range;

[0045] A dual-wavelength phase distribution module is used to calculate the dual-wavelength composite phase distribution under all combinations of two wavelengths at different axial positions according to the single-wavelength phase distribution corresponding to each wavelength;

[0046] A gradient calculation module, used for calculating the gradient value of all dual-wavelength synthetic phase distributions to obtain the dual-wavelength synthetic phase distribution gradient value when the two wavelengths are at different axial propagation positions;

[0047] The chromatic aberration compensation module is used to obtain the dual-wavelength composite phase after chromatic aberration compensation by subtracting two single-wavelength phases corresponding to the minimum position of the dual-wavelength composite phase distribution gradient value.

[0048] Furthermore, the first plane reflector and the second plane reflector are movable and rotatable; the beam distance can be changed by movement to change the focusing distance of the reference beam; the emission direction of the reference beam can be changed by rotation to make the interference beam form off-axis interference.

[0049] Furthermore, it also includes a first polarizer and a second polarizer, the first polarizer is arranged between the first plane reflector and the third beam splitter, and filters out the beam component containing the wavelength of the second laser light source in the first regulated incident light beam; the second polarizer is arranged between the second plane reflector and the third beam splitter, and filters out the beam component containing the wavelength of the first laser light source in the second regulated incident light beam.

[0050] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a schematic diagram of the structure of the chromatic aberration compensation system in the dual-wavelength digital holography of the present application.

[0052] Figure 2 This is a flow chart of the chromatic aberration compensation method in dual-wavelength digital holography of the present application.

[0053] Figure 3 for Figure 1 A schematic diagram of the structure of the processor in the chromatic aberration compensation system in the dual-wavelength digital holography.

[0054] Figure 4 for Figure 2 Schematic diagram of the gradient value image of the dual-wavelength synthetic phase at all axial position combinations in the chromatic aberration compensation method in the dual-wavelength digital holography.

[0055] Figure 5 for Figure 2 A schematic diagram of the phase distribution of two wavelengths focused at the minimum value of the dual-wavelength synthetic phase gradient value in the chromatic aberration compensation method in the dual-wavelength digital holography.

[0056] Figure 6 for Figure 2 Schematic diagram comparing the dual-wavelength synthetic phase measurement results of a step object in the chromatic aberration compensation method in dual-wavelength digital holography with the results of conventional measurement without chromatic aberration compensation. DETAILED DESCRIPTION

[0057] The applicant carefully analyzed the existing chromatic aberration compensation methods in dual-wavelength digital holography and found that the reason for the poor chromatic aberration compensation effect is that the back-end analysis of the dual-wavelength interference pattern and the system for obtaining the dual-wavelength interference pattern are too separated, resulting in high costs and large errors. To this end, the applicant tried to control the formation of interference beams through multiple beam splitters and set a rotatable reflector to control the change of interference parameters, so that the back-end analysis of the dual-wavelength interference pattern can be combined with the front-end optical system for obtaining the dual-wavelength interference pattern.

[0058] See also Figure 1 The chromatic aberration compensation system in the dual-wavelength digital holography includes a first laser light source 11, a second laser light source 12, a first beam splitter 21, a second beam splitter 22, a third beam splitter 23, a fourth beam splitter 24, a fifth beam splitter 25, a first polarizer 31, a second polarizer 32, a first plane mirror 41, a second plane mirror 42, a first tube lens 51, a second tube lens 52, an objective lens 60, a camera 70 and a processor (not shown).

[0059] The first laser light source 11 continuously emits a first initial light beam, and the second laser light source 12 continuously emits a second initial light beam, and the first initial light beam and the second initial light beam have different wavelengths; the first beam splitter 21 is arranged in the direction of the first initial light beam emitted by the first laser light source 11 and the second initial light beam emitted by the second laser light source 12, and the first initial light beam is perpendicular to the second initial light beam. It can be understood that the positions of the first laser light source 11 and the second laser light source 12 are interchangeable, and the specific types and models of the two light sources are not limited, and it is only necessary to satisfy that the wavelengths of the light beams emitted by the first laser light source 11 and the second laser light source 12 are different. The first beam splitter 21 is an ordinary beam splitter, which transmits a light beam with a part of the energy of the first initial light beam and reflects a light beam with the rest of the energy of the second initial light beam. It can be understood that when the positions of the first laser light source 11 and the second laser light source 12 are interchanged, the first beam splitter 21 reflects a light beam with a part of the energy of the first initial light beam and transmits a light beam with the rest of the energy of the second initial light beam, and it is only necessary to satisfy that the first initial light beam and the second initial light beam are combined.

[0060] The second beam splitter 22 is arranged in the direction of the output light after the first beam splitter 21 combines the beams, and splits the light beam from the first beam splitter 21 to obtain a first split light beam and a second split light beam; the third beam splitter 23 is arranged in the direction of the first split light beam, and the fourth beam splitter 24 is arranged in the direction of the second split light beam; the second beam splitter 22 is an ordinary beam splitter, which splits the light beam from the first beam splitter 21 at a certain energy ratio.

[0061] The third beam splitter 23 is arranged in the direction of the first split light beam, and splits it to obtain a first regulated incident light beam and a second regulated incident light beam. The first plane reflector 41 is arranged in the exit direction of the first regulated incident light beam, and the first polarizer 31 is arranged between the first plane reflector 41 and the third beam splitter 23; the second plane reflector 42 is arranged in the exit direction of the second regulated incident light beam, and the second polarizer 32 is arranged between the second plane reflector 42 and the third beam splitter 23; the third beam splitter 23 is an ordinary beam splitter, which splits the incident light beam at a certain energy ratio; the first polarizer 31 filters out the beam component containing the wavelength of the second laser light source 12 in the first regulated incident light beam, and the second polarizer 32 filters out the beam component containing the wavelength of the first laser light source 11 in the second regulated incident light beam.

[0062] Specifically, the first plane reflector 41 and the second plane reflector 42 are movable and rotatable, and the direction in which the reference beam is emitted can be changed by rotation.

[0063] After the second beam splitter 22 splits the light, the other outgoing light beam is irradiated on the surface of the sample A to be tested. The fourth beam splitter 24 is arranged between the second beam splitter 22 and the sample A to be tested. The first tube lens 51 is arranged between the fourth beam splitter 24 and the second beam splitter 22. The objective lens 60 is arranged between the fourth beam splitter 24 and the sample A to be tested. The second tube lens 52 is arranged in the outgoing direction of the object light beam to focus the object light beam.

[0064] The fifth beam splitter 25 is arranged in the direction of the reference beam from the third beam splitter 23 and the object beam from the fourth beam splitter 24, and the reference beam and the object beam are combined to obtain an interference beam, and the camera 70 is arranged in the emission direction of the interference beam. Similarly, the fourth beam splitter 24 and the fifth beam splitter 25 are both ordinary beam splitters, which split the incident light beam at a certain energy ratio.

[0065] The processor is connected to the camera, receives a dual-wavelength interference pattern containing both wavelengths λ1 and λ2, and analyzes to obtain a dual-wavelength synthetic phase after chromatic aberration compensation. Specifically, the wavelength of the first laser light source 11 is λ1=532nm, and the wavelength of the second laser light source 12 is λ2=639nm. The first plane reflector 41 and the second plane reflector 42 are adjusted so that the interference patterns of the two wavelengths are mutually orthogonal in the carrier frequency direction and are simultaneously received by the camera 70, thereby obtaining a dual-wavelength interference pattern containing dual-wavelength orthogonal spatial carrier frequency interference fringes. The dual-wavelength synthetic phase after chromatic aberration compensation is obtained by analyzing the dual-wavelength interference pattern.

[0066] The following describes in detail the light beam propagation process in the chromatic aberration compensation system in the dual-wavelength digital holography of the present application.

[0067] The first laser light source 11 emits a first initial light beam, and the second laser light source 12 emits a second initial light beam; the first beam splitter 21 receives the first initial light beam and the second initial light beam and combines them to form a combined light beam; the combined light beam is transmitted through the second beam splitter 22 to form a first split light beam, and the combined light beam is reflected by the second beam splitter 22 to form a second split light beam.

[0068] The first split light beam is incident on the third beam splitter 23, and is reflected by the third beam splitter 23 to form a first regulated incident light beam. The first regulated incident light beam is transmitted through the first polarizer 31 to form a first filtered light beam. The first filtered light beam is irradiated on the first plane reflector 41, and is reflected by the first plane reflector 41 and then transmitted through the first polarizer 31 again to form a first regulated output light beam. The first split light beam is transmitted through the third beam splitter 23 to form a second regulated incident light beam. The second regulated incident light beam is transmitted through the second polarizer 32 to form a second filtered light beam. The second filtered light beam is irradiated on the second plane reflector 41, and is reflected by the second plane reflector 42 and then transmitted through the second polarizer 32 again to form a second regulated output light beam. The third beam splitter 23 receives the first regulated output light beam and the second regulated output light beam and combines them to form a reference light beam that exits the third beam splitter 23.

[0069] The second split light beam is converged by the first tube lens 51 and then incident on the fourth beam splitter 24, and is transmitted through the fourth beam splitter 24 to form an observation light beam; the observation light beam is irradiated on the surface of the sample A to be tested after passing through the objective lens 60, and is reflected to form an information light beam containing the surface information of the sample A to be tested; the information light beam propagates in the opposite direction of the observation light beam, is collimated by the objective lens 60, and is reflected by the fourth beam splitter 24 to form an object light beam, and is focused again by the second tube lens 52.

[0070] The fifth beam splitter 25 receives the reference beam and the object beam and combines them to form an interference beam. The camera 70 receives the interference beam to obtain a dual-wavelength interference pattern. The dual-wavelength interference pattern simultaneously includes beam components of different wavelengths emitted by the first laser light source 11 and the second laser light source 12.

[0071] The processor receives a dual-wavelength interference pattern containing two different wavelengths at the same time and analyzes it to obtain a dual-wavelength synthetic phase after chromatic aberration compensation.

[0072] Please combine Figure 2 and Figure 3 The processor includes an amplitude calculation module, an amplitude distribution module, a single-wavelength phase distribution module, a dual-wavelength phase distribution module, a gradient calculation module and a chromatic aberration compensation module.

[0073] The amplitude calculation module is used to calculate the complex amplitudes of the two wavelengths at the camera plane using the Fourier transform method for the received dual-wavelength interference pattern. and the corresponding single wavelength phase

[0074] Through repeated experiments, it can be observed that the defocus distance of the two wavelengths of the dual-wavelength digital holographic system of the present application on the camera plane is within ±2mm. Therefore, in the dual-wavelength digital holographic system, the defocus range of the two wavelengths is uniformly set to D = d1 ~ d M =4mm, and in steps of step = 0.1mm from the camera plane distance d1 = -2mm to d M =2mm, where M is a natural number.

[0075] The amplitude distribution module is used to numerically propagate the two-wavelength object wavefront within the defocus range D using the angular spectrum propagation algorithm to obtain the complex amplitudes of the two wavelengths at different axial positions within the defocus range D. Specifically, the complex amplitude of the light field is subjected to a two-dimensional Fourier transform, converted to the frequency domain, a phase factor related to the propagation distance is introduced in the frequency domain to represent the influence of different propagation distances, and the complex amplitude of the object under different defocus planes is obtained by inverse Fourier transforming back to the spatial domain. and

[0076]

[0077] Where F{} represents Fourier transform, F -1 {} represents inverse Fourier transform; (u, v) is the frequency domain coordinate corresponding to the spatial coordinate; the subscript m, n = 1, 2, ..., M, represents the propagation position number.

[0078] For the defocus range D = 4 mm, a range of 2 mm is selected from the initial position in the axial direction, that is, the original hologram position is 0 mm, starting from d1 = -2 mm to d M =2mm The complex amplitude of the dual wavelength is calculated every step of step=0.1mm, and the complex amplitude distribution at M positions is obtained for both wavelengths. as well as The single wavelength phase distribution module is used to calculate the single wavelength phase distribution corresponding to the complex amplitude at each position. Where M = floor[(d m -d0) / step]+1, floor means round down, in this case M=41.

[0079] The dual-wavelength phase distribution module is used to calculate the dual-wavelength composite phase distribution under all combinations of two wavelengths at different axial positions. The single-wavelength phase distribution of each wavelength λ1 is subtracted from the single-wavelength phase distribution of wavelength λ2 at all axial positions, and M is obtained. 2 Dual wavelength synthetic phase distribution

[0080]

[0081] The gradient calculation module is used to calculate all The gradient value is calculated to obtain the dual-wavelength synthetic phase distribution gradient value G when the two wavelengths are at different axial propagation positions m and n. m,n :

[0082]

[0083] Where X and Y represent the number of pixels in the vertical and horizontal directions of the image.

[0084] See also Figure 4 , Figure 4 The dual-wavelength synthetic phase gradient value images at all axial position combinations obtained by the chromatic aberration compensation method in the dual-wavelength digital holography of the present application are shown.

[0085] Due to the influence of dispersion, different wavelengths have different refractive indices on the same plane, so the focal lengths when focusing are also different. When two light waves of different wavelengths are imaged on the same camera plane, the wavefronts of the two wavelengths cannot be focused on the camera plane at the same time. This will cause the wavefront of a certain wavelength to be defocused, or the two wavelengths to be defocused together, thereby generating additional phase wrapping in the dual-wavelength composite phase distribution, increasing the gradient value of the dual-wavelength composite phase. Therefore, by finding the axial propagation positions of the two wavelengths when the gradient value of the dual-wavelength composite phase reaches the minimum, it can be determined that the two wavelengths are in their respective focus positions, and at this time, the dual-wavelength composite phase is least affected by chromatic aberration. Please refer to Figure 5 , Figure 5 The phase distribution of the two wavelengths focused at the minimum value of the dual-wavelength synthetic phase gradient is shown, where Figure 5 Figure a shows the phase distribution corresponding to wavelength λ1=532nm. Figure 5 Figure b shows the phase distribution corresponding to wavelength λ2=639nm.

[0086] The chromatic aberration compensation module is used to calculate the dual-wavelength composite phase after chromatic aberration compensation. Specifically, find G m,n The minimum value of G p,q , and its corresponding subscript numbers p, q, indicate that the wavelength λ1 is at the pth propagation position and the wavelength λ2 is at the qth propagation position when the optimal propagation distance is reached, that is, and The two wavelengths are respectively the single wavelength phase distributions when they are focused. The dual wavelength composite phase is obtained by subtracting the single wavelength phases corresponding to the two serial numbers. That is, the dual-wavelength composite phase after chromatic aberration compensation. In order to verify the actual effect of the chromatic aberration compensation system in the dual-wavelength digital holography of the present application, the dual-wavelength composite phase of the step object is measured using the chromatic aberration compensation system in the dual-wavelength digital holography of the present application. Figure 6 , Figure 6 The measurement results are compared with the uncompensated results, where Figure 6 Figure a shows the phase distribution of dual-wavelength measurement without chromatic aberration compensation; Figure 6 Figure b in the figure is Figure 6 Figure a is a cross-sectional view along the step direction; Figure 6 Figure c in the figure shows the phase distribution of dual-wavelength measurement after chromatic aberration compensation; Figure 6 The d figure in Figure 6 Figure c is a cross-sectional view along the step direction. It can be seen that the dual-wavelength synthetic phase image after compensation by the chromatic aberration compensation system in the dual-wavelength digital holography of the present application has a good distribution, stable data fluctuation, and can accurately obtain the dual-wavelength synthetic phase.

[0087] The above-mentioned embodiments only express the best implementation mode of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims

1. A method for compensating chromatic aberration in dual-wavelength digital holography, characterized in that: include: A dual-wavelength interference pattern containing two wavelengths simultaneously is obtained; Receive the dual-wavelength interference pattern and calculate the complex amplitudes of two different wavelengths at the camera plane; Combining the complex amplitudes of the two wavelengths at the camera plane, the angular spectrum propagation algorithm is used to numerically propagate the object wavefronts of the two wavelengths within the set defocus range to obtain the complex amplitudes of the two wavelengths at different axial positions within the defocus range. Calculate the corresponding single wavelength phase distribution according to the complex amplitude at each position within the defocus range; Calculate the dual-wavelength composite phase distribution under all combinations of two wavelengths at different axial positions according to the single-wavelength phase distribution corresponding to each wavelength; The gradient values ​​of all dual-wavelength composite phase distributions are calculated to obtain the dual-wavelength composite phase distribution gradient values ​​when the two wavelengths are at different axial propagation positions; The dual-wavelength composite phase after chromatic aberration compensation is obtained by subtracting the two single-wavelength phases corresponding to the minimum position of the dual-wavelength composite phase distribution gradient value.

2. The chromatic aberration compensation method in dual-wavelength digital holography according to claim 1, characterized in that: The defocus range is set to D = d1 ~ d M =4mm, where D is the defocus range, d is the imaging plane distance, and M is a natural number.

3. The chromatic aberration compensation method in dual-wavelength digital holography according to claim 2, characterized in that: The complex amplitude of the light field is transformed into the frequency domain by two-dimensional Fourier transform. A phase factor related to the propagation distance is introduced in the frequency domain to represent the influence of different propagation distances. The complex amplitude of the object at different defocus planes is obtained by inverse Fourier transform back to the spatial domain. and in, is the complex amplitude of wavelength λ1 at different axial positions within the defocus range, is the complex amplitude of wavelength λ2 at different axial positions within the defocus range; F{} represents Fourier transform, F -1 {} represents inverse Fourier transform; (u, v) is the frequency domain coordinate corresponding to the spatial coordinate; the subscript m, n = 1, 2, ..., M, represents the propagation position number.

4. The chromatic aberration compensation method in dual-wavelength digital holography according to claim 3, characterized in that: The propagation position sequence number satisfies: M=floor[(d m -d0) / step]+1, where floor represents rounding down, and M=41.

5. The chromatic aberration compensation method in dual-wavelength digital holography according to claim 4, characterized in that: Subtract the single wavelength phase distribution of wavelength λ2 at all axial positions from the single wavelength phase distribution of each wavelength λ1, and we can get M 2 Dual wavelength synthetic phase distribution in, is the single wavelength phase distribution corresponding to wavelength λ1, is the single wavelength phase distribution corresponding to wavelength λ2.

6. The chromatic aberration compensation method in dual-wavelength digital holography according to claim 5, characterized in that: For all The gradient value is calculated to obtain the dual-wavelength synthetic phase distribution gradient value G when the two wavelengths are at different axial propagation positions m and n. m,n : Where X and Y represent the number of pixels in the vertical and horizontal directions of the image.

7. A chromatic aberration compensation system in dual-wavelength digital holography, characterized in that: include: A first laser light source continuously emits a first initial light beam; A second laser light source continuously emits a second initial light beam; A first beam splitter is arranged in the emission direction of the first initial light beam and the second initial light beam, and combines the first initial light beam and the second initial light beam to obtain a combined light beam; A second beam splitter is arranged in the emission direction of the combined light beam, and splits the combined light beam into a first split light beam and a second split light beam; A third beam splitter is arranged in an emitting direction of the first split light beam, and splits the first split light beam to obtain a first regulated incident light beam and a second regulated incident light beam; A first plane reflector, disposed in the direction of the first regulated incident light beam, reflects the first regulated incident light beam to form a first regulated outgoing light beam; A second plane reflector is arranged in the direction of the second regulated incident light beam, and reflects the second regulated incident light beam to form a second regulated outgoing light beam; The second regulated output light beam is combined with the first regulated output light beam in the third beam splitter to form a reference light beam and then outputs the reference light beam through the third beam splitter; a fourth beam splitter, arranged in the emitting direction of the second split light beam, transmitting the second split light beam and irradiating it on the surface of the sample to be tested, and reflecting the light beam reflected back from the surface of the sample to be tested again to form an object light beam; a fifth beam splitter, arranged in the emission direction of the reference beam and the object beam, and combining the reference beam and the object beam to form an interference beam; A camera is arranged in the emission direction of the interference light beam, and receives the interference light beam to obtain a dual-wavelength interference pattern; The processor receives the dual-wavelength interference pattern and analyzes it to obtain the dual-wavelength synthetic phase after chromatic aberration compensation.

8. The chromatic aberration compensation system in dual-wavelength digital holography according to claim 7, characterized in that: The processor comprises: An amplitude calculation module, used for receiving a dual-wavelength interference pattern and calculating the complex amplitudes of two different wavelengths at a camera plane; An amplitude distribution module is used to combine the complex amplitudes of the two wavelengths at the camera plane, and use the angular spectrum propagation algorithm to numerically propagate the object wavefronts of the two wavelengths within a set defocus range to obtain the complex amplitudes of the two wavelengths at different axial positions within the defocus range; A single wavelength phase distribution module is used to calculate the corresponding single wavelength phase distribution according to the complex amplitude at each position within the defocus range; A dual-wavelength phase distribution module is used to calculate the dual-wavelength composite phase distribution under all combinations of two wavelengths at different axial positions according to the single-wavelength phase distribution corresponding to each wavelength; A gradient calculation module, used for calculating the gradient value of all dual-wavelength synthetic phase distributions to obtain the dual-wavelength synthetic phase distribution gradient value when the two wavelengths are at different axial propagation positions; The chromatic aberration compensation module is used to obtain the dual-wavelength composite phase after chromatic aberration compensation by subtracting two single-wavelength phases corresponding to the minimum position of the dual-wavelength composite phase distribution gradient value.

9. The chromatic aberration compensation system in dual-wavelength digital holography according to claim 8, characterized in that: The first plane reflecting mirror and the second plane reflecting mirror are movable and rotatable; the beam distance can be changed by moving, so as to change the focusing distance of the reference beam; the emission direction of the reference beam can be changed by rotating, so as to make the interference beam form off-axis interference.

10. The chromatic aberration compensation system in dual-wavelength digital holography according to claim 9, characterized in that: It also includes a first polarizer and a second polarizer. The first polarizer is arranged between the first plane reflector and the third beam splitter to filter out the beam component containing the wavelength of the second laser light source in the first regulated incident light beam; the second polarizer is arranged between the second plane reflector and the third beam splitter to filter out the beam component containing the wavelength of the first laser light source in the second regulated incident light beam.

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