A method and system for chromatic aberration compensation in dual-wavelength digital holography

Abstract

The application relates to a chromatic aberration compensation method in dual-wavelength digital holography, which comprises the following steps: obtaining a dual-wavelength interference pattern containing two wavelengths simultaneously; calculating the complex amplitudes of the two wavelengths at the camera plane; performing numerical propagation of the object wavefronts of the two wavelengths in a set defocus range by using an angular spectrum propagation algorithm to obtain the complex amplitudes of the two wavelengths at different axial positions in the defocus range; calculating the corresponding single-wavelength phase distributions in the defocus range; calculating the dual-wavelength synthetic phase distribution under all combinations of the two wavelengths at different axial positions; obtaining the gradient value of the dual-wavelength synthetic phase distribution when the two wavelengths are at different axial propagation positions; and subtracting the two single-wavelength phases according to the minimum position of the gradient value of the dual-wavelength synthetic phase distribution to obtain the chromatic aberration compensated dual-wavelength synthetic phase. The chromatic aberration compensation method in dual-wavelength digital holography can greatly improve the phase measurement accuracy.

Description

Technical Field

[0001] The present 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, there is a need to perform three-dimensional topography measurements on objects such as MEMS devices and semiconductor chips, whose surface heights vary 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 an object, thereby obtaining three-dimensional information about the object. This technique offers advantages such as high precision, non-contact with samples, non-destructiveness, non-interference, ease of use, no need to stain biological samples, and ease of integration with other instruments. Dual-wavelength digital holography, building on digital holography, uses two light waves of different wavelengths to perform interferometric measurements through wavelength synthesis, significantly extending the range of interferometric measurements. It has wide applications in microelectromechanical (MEMS) testing and medical bioassays.

[0003] However, dual-wavelength digital holography requires recording a set of two-wavelength interference patterns when performing microscopic phase measurement on 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 two-wavelength interference pattern 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 from the two-wavelength interference pattern will introduce errors to the dual-wavelength synthetic phase measurement.

[0004] To address chromatic aberration, existing methods include improving the optical system, adding achromatic elements, or using numerical processing 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, the need for two cameras to perform measurements simultaneously increases the difficulty of experimental debugging and the requirements for camera matching.

[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, the manufacturing cost of these optical elements is high and increases the design difficulty in complex optical systems. In actual applications, due to the errors of optical elements and the non-ideality of experimental systems, the chromatic aberration problem is difficult to completely eliminate, and the complex optical system further exacerbates 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 defocused wavelengths in the hologram, believing that after the chromatic aberration is compensated, no circular fringes will appear in the final phase image. 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 optimal focus state of the object at different wavelengths must 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 capture 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] Obtain a dual-wavelength interferogram containing two wavelengths simultaneously;

[0011] Receive the dual-wavelength interferogram and calculate the complex amplitudes of the 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, and the complex amplitudes of the two wavelengths at different axial positions within the defocus range are obtained;

[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 the two wavelengths at different axial positions based on the single-wavelength phase distribution corresponding to each wavelength;

[0015] Calculating the gradient values ​​of all dual-wavelength composite phase distributions 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 a 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

[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 {} denotes inverse Fourier transform; (u, v) is the frequency domain coordinate corresponding to the spatial coordinate; subscripts m, n = 1, 2, ..., M denote 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 composite 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 emitting a second initial light beam;

[0032] a first beam splitter, disposed in an emitting direction of the first initial light beam and the second initial light beam, and combining the first initial light beam and the second initial light beam to obtain a combined light beam;

[0033] a second beam splitter, disposed in an emitting direction of the combined light beam, and splitting the combined light beam into a first split light beam and a second split light beam;

[0034] a third beam splitter, disposed in an emitting direction of the first split beam, to split the first split beam into a first regulated incident beam and a second regulated incident beam;

[0035] a first plane reflecting mirror, disposed in an exit direction of the first regulated incident light beam, and reflecting the first regulated incident light beam to form a first regulated exit light beam;

[0036] a second plane reflector, arranged in the direction of the second regulated incident light beam, reflecting 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 exits the third beam splitter;

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

[0042] An amplitude calculation module is used to receive the dual-wavelength interference pattern and calculate the complex amplitudes of the two different wavelengths at the camera plane;

[0043] The 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 wavefront 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;

[0044] Single wavelength phase distribution module, 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 based on the single-wavelength phase distribution corresponding to each wavelength;

[0046] A gradient calculation module is used to calculate the gradient value of all dual-wavelength composite phase distributions to obtain the dual-wavelength composite 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 the two single-wavelength phases corresponding to the minimum position of the dual-wavelength composite phase distribution gradient value.

[0048] Furthermore, the first plane mirror and the second plane mirror are movable and rotatable; the beam path can be changed by movement to change the focusing distance of the reference beam; the direction of the reference beam emission 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 controlled 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 controlled 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 this application.

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

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

[0055] Figure 5 for Figure 2 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 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 existing chromatic aberration compensation methods for dual-wavelength digital holography and found that the poor chromatic aberration compensation results from the overly separate back-end analysis of the dual-wavelength interference pattern from the system used to obtain it, resulting in high costs and large errors. To address this, the applicant attempted to control the formation of the interfering beams by using multiple beam splitters and to configure rotatable reflectors to control the variation of interference parameters. This allowed the back-end analysis of the dual-wavelength interference pattern to be integrated with the front-end optical system used to obtain 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 are not limited to the specific types and models of the two light sources. It is only necessary 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 that transmits a beam with part of the energy of the first initial light beam and reflects a beam with the remaining 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 beam with part of the energy of the first initial light beam and transmits a beam with the remaining energy of the second initial light beam, and it is only necessary to combine the first initial light beam with the second initial light beam.

[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 beam, and splits it to obtain a first regulated incident beam and a second regulated incident beam. The first plane reflector 41 is arranged in the exit direction of the first regulated incident 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 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 beam at a certain energy ratio; the first polarizer 31 filters out the beam component of the first regulated incident beam containing the wavelength of the second laser light source 12, and the second polarizer 32 filters out the beam component of the second regulated incident beam containing the wavelength of the first laser light source 11.

[0062] Specifically, the first plane reflective mirror 41 and the second plane reflective mirror 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 beam, the other beam of outgoing light is irradiated on the surface of the sample A to be measured. The fourth beam splitter 24 is arranged between the second beam splitter 22 and the sample A to be measured. 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 measured. The second tube lens 52 is arranged in the outgoing direction of the object beam to focus the object beam.

[0064] The fifth beam splitter 25 is positioned in the direction of the reference beam from the third beam splitter 23 and the object beam from the fourth beam splitter 24, combining the reference beam and the object beam to form an interference beam. The camera 70 is positioned in the direction of the emission of the interference beam. Similarly, the fourth beam splitter 24 and the fifth beam splitter 25 are both ordinary beam splitters that 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 it to obtain a dual-wavelength composite 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 mirror 41 and the second plane mirror 42 are adjusted so that the interference patterns of the two wavelengths are orthogonal to each other in the carrier frequency direction. The interference patterns are simultaneously received by the camera 70, resulting in a dual-wavelength interference pattern containing dual-wavelength orthogonal spatial carrier frequency interference fringes. The dual-wavelength composite 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, is reflected by the first plane reflector 41, and is 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, is reflected by the second plane reflector 42, and is 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 enters the fourth beam splitter 24, and is transmitted through the fourth beam splitter 24 to form an observation beam; the observation 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 beam containing surface information of the sample A to be tested; the information beam propagates in the opposite direction of the observation beam, is collimated by the objective lens 60, and is reflected by the fourth beam splitter 24 to form an object 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, which 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 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 step size 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 and 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. The complex amplitude of the object at different defocus planes is obtained by inverse Fourier transforming back to the spatial domain. and

[0076]

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

[0078] For the defocus range D = 4mm, the range of 2mm in axial direction from the initial position is selected, i.e. taking the original hologram position as 0mm, starting from d1 = -2mm to d2 = 2mm, the complex amplitude of the two wavelengths is calculated every step = 0.1mm, and the complex amplitude distribution of the two wavelengths at M positions is obtained M The single-wavelength phase distribution module is configured to calculate the single-wavelength phase distribution corresponding to the complex amplitude of each position Wherein, M = floor[(d m -d0) / step]+1, floor represents the floor function, and M = 41 at this time.

[0079] The two-wavelength phase distribution module is configured to calculate the two-wavelength synthetic phase distribution under all combinations of different axial positions of the two wavelengths. The single-wavelength phase distribution of each wavelength λ1 is subtracted from the single-wavelength phase distribution of the wavelength λ2 at all axial positions, i.e. M 2 two-wavelength synthetic phase distributions

[0080]

[0081] The gradient calculation module is configured to calculate the gradient value of all to obtain the two-wavelength synthetic phase distribution gradient value G m,n at different axial propagation positions m, n of the two wavelengths:

[0082]

[0083] Wherein, X and Y represent the number of pixels of the image in the longitudinal direction and the transverse direction.

[0084] Please refer to Figure 4 , Figure 4 The figure shows the gradient value image of the two-wavelength synthetic phase at all axial position combinations obtained by the chromatic aberration compensation method in the two-wavelength digital holography of the present application.

[0085] Due to the influence of dispersion, the refractive index of different wavelengths in the same plane is different, so the focal length when focusing is also different. When the light waves of two 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 out of focus, or the two wavelengths to be out of focus together, thereby generating additional phase wrapping in the two-wavelength synthetic phase distribution, and increasing the gradient value of the two-wavelength synthetic phase. Therefore, the axial propagation positions of the two wavelengths when the gradient value of the two-wavelength synthetic phase reaches the minimum can be determined, and the two wavelengths are respectively in the focusing position at this time, and the two-wavelength synthetic phase is affected by the chromatic aberration the least. 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 = 639 nm.

[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. To verify the actual effect of the chromatic aberration compensation system in the dual-wavelength digital holography of this 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 this application. Figure 6 , Figure 6 The comparison of the measurement results with the uncompensated results is shown, 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 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 after the chromatic aberration compensation system in the dual-wavelength digital holography of this application compensates, the dual-wavelength synthetic phase image is well distributed, the data fluctuation is stable, and the dual-wavelength synthetic phase can be accurately obtained.

[0087] The above-described embodiments merely represent the best modes of carrying out the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that variations and modifications are possible, as would be apparent to those skilled in the art, without departing from the spirit of the present invention, and the present invention is intended to encompass such variations and modifications.

Claims

1. A method for compensating chromatic aberration in dual-wavelength digital holography, characterized by: include: Obtain a dual-wavelength interferogram containing two wavelengths simultaneously; Receive the dual-wavelength interferogram and calculate the complex amplitudes of the 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, and the complex amplitudes of the two wavelengths at different axial positions within the defocus range are obtained; 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 the two wavelengths at different axial positions based on the single-wavelength phase distribution corresponding to each wavelength; Calculating the gradient values ​​of all dual-wavelength composite phase distributions 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; 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 wavelength The complex amplitude at different axial positions within the defocus range, is the wavelength complex amplitude at different axial positions within the defocus range; represents the Fourier transform, represents the inverse Fourier transform; is the frequency domain coordinate corresponding to the spatial coordinate; subscripts m, n = 1, 2, ..., M, represent the propagation position number; The propagation position sequence number satisfies: , where floor represents rounding down, and M=41; Each wavelength The single wavelength phase distribution is subtracted from the wavelength The single wavelength phase distribution at all axial positions is obtained Dual-wavelength synthetic phase distribution : in, is the wavelength The corresponding single wavelength phase distribution, is the wavelength The corresponding single wavelength phase distribution; For all The gradient value is calculated to obtain the dual-wavelength composite phase distribution gradient value when the two wavelengths are at different axial propagation positions m and n. : Where X and Y represent the number of pixels in the vertical and horizontal directions of the image.

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= ~ =4mm, where D is the defocus range, d is the imaging plane distance, and M is a natural number.

3. A chromatic aberration compensation system in dual-wavelength digital holography, characterized by: include: A first laser light source continuously emits a first initial light beam; a second laser light source, continuously emitting a second initial light beam; a first beam splitter, disposed in an emitting direction of the first initial light beam and the second initial light beam, and combining the first initial light beam and the second initial light beam to obtain a combined light beam; a second beam splitter, disposed in an emitting direction of the combined light beam, and splitting the combined light beam into a first split light beam and a second split light beam; a third beam splitter, disposed in an emitting direction of the first split beam, to split the first split beam into a first regulated incident beam and a second regulated incident beam; a first plane reflecting mirror, disposed in an exit direction of the first regulated incident light beam, and reflecting the first regulated incident light beam to form a first regulated exit light beam; a second plane reflecting mirror, disposed in the direction of the second regulated incident light beam, reflecting 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 exits the third beam splitter; a fourth beam splitter, arranged in the emitting direction of the second split beam, transmitting the second split beam and irradiating it on the surface of the sample to be tested, and reflecting the beam reflected back from the surface of the sample to be tested again to form an object 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 beam and receives the interference beam to obtain a dual-wavelength interference pattern; a processor, receiving the dual-wavelength interferogram and analyzing it to obtain the dual-wavelength composite phase after chromatic aberration compensation; The processor includes: An amplitude calculation module is used to receive the dual-wavelength interference pattern and calculate the complex amplitudes of the two different wavelengths at the camera plane; The 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 wavefront 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; Single wavelength phase distribution module, 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 based on the single-wavelength phase distribution corresponding to each wavelength; A gradient calculation module is used to calculate the gradient value of all dual-wavelength composite phase distributions to obtain the dual-wavelength composite 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 the two single-wavelength phases corresponding to the minimum position of the dual-wavelength composite phase distribution gradient value.

4. The chromatic aberration compensation system in dual-wavelength digital holography according to claim 3, characterized in that: The first plane reflecting mirror and the second plane reflecting mirror are movable and rotatable; the beam path can be changed by moving to change the focusing distance of the reference beam; the direction of the reference beam emission can be changed by rotating to make the interference beam form off-axis interference.

5. The chromatic aberration compensation system in dual-wavelength digital holography according to claim 4, 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 controlled 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 controlled incident light beam.

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