CN106990694B - Non-iterative phase recovery device and method under partially-dry-light illumination - Google Patents
Non-iterative phase recovery device and method under partially-dry-light illumination Download PDFInfo
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Abstract
The invention relates to a non-iterative phase recovery device and a non-iterative phase recovery method under the illumination of partial coherent light, and the non-iterative phase recovery device comprises a partial coherent light generating unit and an object phase measuring unit, wherein the partial coherent light generating unit comprises a laser, a beam expander, a focusing lens, a rotating ground glass sheet, a collimating lens and a Gaussian filter sheet, and a spiral phase plate can be arranged between the beam expander and the focusing lens; the object phase measuring unit comprises a beam splitter, a spatial light modulator, a reflector, a porous array plate, a Fourier lens, a charge coupling element and a computer. Compared with an iterative algorithm, the method has the advantages that the recovery process is faster, and real-time object information recovery can be realized; compared with a mode expansion method, the method has wider application range and can realize the object information recovery under the illumination of the part of coherent light with unknown associated structure; meanwhile, the method can be widely applied to lens-free diffraction imaging of X rays; the device has the advantages of simplicity, wide application range, high recovery speed and the like, and has important application prospect.
Description
Technical Field
The invention relates to the technical field of optics, in particular to a non-iterative phase recovery device and a non-iterative phase recovery method under the illumination of partial dry light.
Background
For an unknown object containing amplitude and phase information, the object amplitude information can be directly observed through a charge coupled device, but the phase information cannot be directly obtained, so how to obtain the phase information of the unknown object from the intensity information becomes an important subject of research. The technology of acquiring object phase information from intensity information is called a wavefront detection technology or phase retrieval, and the method of acquiring object phase information by a diffraction or interference method to realize two-dimensional and three-dimensional imaging is called coherent diffraction imaging. With the rapid development of coherent diffraction imaging technology, the resolution has reached nanometer level, and the recovery device is increasingly intelligent and real-time.
In the study of wavefront sensing technology and phase recovery, it is mostly assumed that the illumination light source is completely coherent light, but in practical applications, such as high-resolution wavefront sensing, x-rays or electron beams are often used as the light source for phase recovery, which are not completely coherent light. In addition, spatial coherence is reduced when a beam of fully coherent light is transmitted through a medium, and in these cases, it is still treated as fully coherent light, which can be problematic.
There are many ways to achieve phase recovery, and first in 1952, David Sayre proposed using shannon's theorem to achieve phase recovery by measuring higher density light intensity. To date, a series of methods for phase recovery have been developed, such as hartmann wavefront sensing technology, holographic interference technology, computational phase recovery technology, and stacking technology.
The Hartmann wavefront sensing technology is mainly used for recovering phase information by measuring wavefront slope (Platt B C, Shack R.History and principles of Shack-Hartmann wave front sensing [ J ]. Journal of reflective surface, 2001,17(5): S573-S577). The Shack Hartmann sensor is based on the technology and comprises a micro lens array and a charge coupled element, and the wavefront is reconstructed by measuring the coordinates of a light spot focused on the charge coupled element through a micro lens and calculating a Zernike coefficient by using a Zernike polynomial method. The technology has high recovery speed and high sensitivity, and is widely applied to the fields of high-resolution imaging of astronomical telescopes, resolution imaging of human eye retinal cells and the like.
The holographic interference technology is a technology for recovering an object wave light field by using an interference principle (Eisebitt S, L ü ning J, Schlotter W F, et al. lens imaging of magnetic nanostructured by X-ray spectro-hology [ J ] Nature,2004,432(7019): 885. 888.), and is divided into two processes of shooting and recovering, when one beam of reference light interferes with the object light, the phase and amplitude information of the object is recorded in an interference pattern, and the reference light is used for irradiating the holographic interference pattern, so that the light field information of the object light can be recovered, and the phase and amplitude information of the object can be extracted. With the rapid development of holographic interference technology, a charge coupled device is used to record interference patterns, and a computer is used to perform a phase recovery process, so that the technology becomes a digital holographic technology and is widely applied to the aspects of three-dimensional image reconstruction, digital microscopic imaging, nondestructive inspection of materials, medical diagnosis and the like.
Compared with the former two methods, the calculation phase recovery method has wider application range and is applicable to both visible light and extreme ultraviolet wave bands. The recovery method is proposed in 1972 (Gerchberg R W.A practical algorithm for the determination of phase from image and diffraction plane images [ J ]. Optik,1972,35:237.), and the recovery method can be used in an imaging system taking X-rays or free electron beams as light sources to realize lens-free diffraction imaging and phase recovery, thereby reducing errors of the imaging system and simplifying the system structure, and has great prospect. Another stacked imaging technique (Rodenburg J M, Faulkner H M L.A phase diffraction for shifting and drilling J. Applied physics letters,2004,85(20): 4795-.
However, these techniques have certain disadvantages and drawbacks, and the iterative algorithm for calculating the phase recovery method requires a large number of iterations and iteration time, and for complex phase objects, the information cannot be recovered quickly and in real time, and even a unique solution cannot be obtained. In addition, when the existing iterative algorithm processes the partially coherent light, the cross-correlation function of the light source is assumed to be gaussian scherrer model, and the processing is performed by using the mode expansion, however, under the condition of very low coherence, a large number of modes are needed to correctly recover the phase information, and for the light source with unknown correlation function, the mode expansion method is not applicable any more.
Based on the defects in the aspect of object information recovery under the partial coherent light illumination, the patent innovatively provides a novel non-iterative method for phase information recovery under the partial coherent light illumination.
Disclosure of Invention
In order to solve the above technical problems, an object of the present invention is to provide a non-iterative phase recovery apparatus and method under partially-coherent illumination, which avoids the redundancy and complexity of iterative algorithms, overcomes the drawbacks of mode expansion methods, and can realize correct and real-time recovery of phase object information under illumination of light sources with complicated or even unknown conventional correlation or correlation structures.
The non-iterative phase recovery device under the illumination of the partial coherent light comprises a partial coherent light generation unit and an object phase measurement unit, wherein the object phase measurement unit comprises
A beam splitter for transmitting the partially coherent light generated by the partially coherent light generation unit and reflecting the light beam modulated by the spatial light modulator;
a spatial light modulator, disposed perpendicular to the optical axis of the partially coherent light generating unit, for loading the phase object to be measured and disturbance points for performing phase disturbance on the phase object to be measured, the spatial light modulator reflecting the light transmitted by the beam splitter and allowing the modulated light to be reflected again by the beam splitter;
A porous array plate, through which the light beam reflected by the beam splitter passes, wherein a two-dimensional aperture array arranged periodically is arranged on the porous array plate, a reference aperture is arranged near the center of the array, the reference aperture on the porous array plate is aligned with the light beam reflected by the beam splitter, and the distance between the porous array plate and the spatial light modulator satisfies z ≥ d x L/lambda, wherein d is the interval between the apertures on the porous array plate, L is the size of the widest part of the phase object to be measured, and lambda is the wavelength of the laser light source in the partially coherent light generating unit;
-a fourier lens placed immediately behind the multi-well array plate or capable of having the multi-well array plate located in a front focal plane of the fourier lens for fourier transforming the light beam passing through the multi-well array plate;
-a charge coupled element placed at the fourier plane to capture the light intensity information;
the computer is connected with the spatial light modulator and the charge coupled device, controls phase loading on the spatial light modulator, and performs real-time inverse Fourier transform, screening and inverse transmission processing on the shot light intensity to obtain phase information of the object.
Further, when the purpose is to generate the partial coherent light of the traditional gaussian correlation, the partial coherent light generating unit comprises a laser, a beam expander for expanding a laser beam emitted by the laser, a collimating lens for collimating the laser beam and a gaussian filter for shaping the laser beam, which are sequentially arranged, and the light emitted by the gaussian filter is transmitted through the beam splitter to reach the spatial light modulator.
Further, when the purpose is to generate partially coherent light associated with Laguerre Gauss, the partially coherent light generating unit comprises the laser, a beam expander for expanding a laser beam emitted by the laser, a spiral phase plate for changing the phase of the expanded light, a collimating lens for collimating the light beam and a Gauss filter for shaping the light beam, which are sequentially arranged, and the light emitted by the Gauss filter is transmitted through the beam splitter and reaches the spatial light modulator.
Furthermore, the partially coherent light generating unit further comprises a coherence adjusting assembly, the coherence adjusting assembly comprises a lens for focusing the light beam expanded by the beam expander or the light beam of which the phase is changed by the spiral phase plate, and rotating ground glass for scattering the focused light beam, and the light scattered by the rotating ground glass is collimated by the collimating lens.
Further, the light beam reflected by the beam splitter can be reflected by a mirror onto the porous array plate.
Furthermore, the disturbance point is located at any position of the object with the phase to be measured, the size of the disturbance point is far smaller than that of the object with the phase to be measured, and the phase assignment of the disturbance point is different from that of the original object with the phase to be measured at the position.
Further, a reference small hole is etched on the lightproof substrate through laser, the reference small hole is used as the center of a circle and is respectively shifted to the x direction and the y direction by a certain distance, then a two-dimensional small hole array is symmetrically etched through the laser, the porous array plate is formed, the interval between the two-dimensional small holes needs to satisfy d not more than z lambda/L, wherein z is the distance from an object plane to the porous array plate, L is the size of the widest position of the phase object to be detected, and lambda is the wavelength of a laser light source in the partial coherent light generating unit; the offset is a/2 ≤ Δ x ≤ Δ y ≤ d/2-a/2, wherein a is the size of the two-dimensional pore; the sizes of the reference small holes and the two-dimensional small holes are consistent, and the reference small holes are far smaller than the size of the object to be measured and smaller than one third of the interval of the two-dimensional small holes; the structure of the porous array plate can also be simulated by the spatial light modulator.
Further, the spatial light modulator is a reflective phase-only spatial light modulator.
Further, the beam splitter is a light intensity 50: 50 half mirror.
The invention relates to a method for non-iterative phase recovery by using a non-iterative phase recovery device under the illumination of partial coherent light, which comprises the following steps:
(1) acquiring Gaussian-related partial coherent light or Laguerre Gaussian-related partial coherent light by a partial coherent light generation unit, and changing the size of a light spot focused on the rotating ground glass by adjusting the front and back positions of the lens for focusing on the optical axis to adjust the spatial coherence of a light source;
(2) Transmitting the partially coherent light to the object phase measuring unit, so that the partially coherent light passes through the object to be measured and records light intensity information:
(21) when the partial coherent light is Gaussian-associated partial coherent light, recording the light intensity twice, shooting for the first time, namely loading the object with the phase to be measured: setting the prepared picture as a gray scale image mode, and converting the gray scale value into a corresponding phase when the picture is loaded on the spatial light modulator with pure phase; second shooting, namely placing a disturbance point at any position of the object with the phase to be measured, wherein the size of the disturbance point is far smaller than that of the object with the phase to be measured, and the phase assignment of the disturbance point is different from that of the original object with the phase to be measured at the position; and (3) transmitting the light intensity information obtained by two times of shooting to a computer for processing: firstly, performing Fourier transform on two groups of light intensity information respectively, screening by a screening array, subtracting the screened results, and performing reverse transmission on the subtracted results to extract object phase information; the screening pores of the screening array are periodically arranged two-dimensional pores, and are generated by the computer, and the side length and the interval of each screening pore are consistent with those of the porous array plate;
(22) When the partial coherent light is Laguerre Gaussian associated partial coherent light, recording four light intensities, shooting for the first time, namely loading the object with the phase to be measured: setting the prepared picture as a gray scale image mode, and converting the gray scale value into a corresponding phase when the picture is loaded on the spatial light modulator with pure phase; second shooting, namely placing a disturbance point at any position of the object with the phase to be measured, wherein the size of the disturbance point is far smaller than that of the object with the phase to be measured, and the phase assignment of the disturbance point is different from that of the original object with the phase to be measured at the position; shooting for the third time, namely removing the object with the phase to be detected without removing the disturbance point, namely setting the phase of the area where the original object with the phase to be detected is located to be 0; fourth shooting-removing the disturbance phase; and (3) transmitting the light intensity information of two times obtained by the third shooting and the fourth shooting to a computer for processing: firstly, performing Fourier transform on two groups of light intensity information respectively, screening by a screening array, subtracting the screened results, and performing reverse transmission on the subtracted results to extract cross spectral density information and phase information of the light source; and (3) conveying the twice light intensity information obtained by the first shooting and the second shooting to a computer for processing: firstly, performing Fourier transform on two groups of light intensity information respectively, screening by a screening array, subtracting the screened results, and performing reverse transmission on the subtracted results to extract object phase information influenced by the light source phase; finally, the object phase influenced by the light source phase is used for removing the phase of the light source, so that correct object phase information can be obtained; the screening holes of the screening array are periodically arranged two-dimensional holes, and are generated by the computer, and the side length and the interval of each screening hole are consistent with those of the porous array plate.
By means of the scheme, the invention at least has the following advantages:
aiming at the recovery of object phase information under the condition of partial coherent light illumination, compared with an iterative algorithm, the method is quicker and more real-time, has wider application range compared with the iterative algorithm for processing the partial coherent light by mode expansion, and has unique advantages of the recovery of object phase under the condition of processing the partial coherent light illumination with complex associated structure and even unknown associated structure; the phase recovery device for lens-free diffraction imaging can be expanded to an X-ray imaging system, so that the phase recovery device has extremely important significance in practical application.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.
Drawings
FIG. 1 is a schematic diagram of the structure of a non-iterative phase recovery device under partially coherent light illumination according to the present invention;
FIG. 2 is an example of loading a phase object and perturbations on a spatial light modulator, where FIG. 2(a) is loading only object information and FIG. 2(b) is loading a perturbation on the object information;
FIG. 3(a) is a detailed view of the central portion of a multi-well array plate used in the present invention; FIG. 3(b) is a detailed view of the central portion of the screening array used in the computer recovery.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
The phase recovery method provided by the invention comprises three processes: a partially coherent light source producing a gaussian or special correlation, passed through an object carrying phase information and recorded light intensity and computer processed to recover the phase. The corresponding structural device is shown in figure 1.
Firstly, a partial coherent light source is generated, the partial coherent light source irradiates an object to be measured and then passes through the porous array plate, and the light spot intensity of the Fourier plane is recorded by utilizing the charge coupling element. In general, only two shots are needed to recover the complete phase information of the object to be measured. The first shooting is that after a light source irradiates an object to be measured, the object is transmitted for a certain distance to reach a specially designed porous array plate, and then the charge-coupled element arranged on a Fourier plane records light intensity information; and (4) shooting for the second time, adding a disturbance point in the middle of the object to be detected, and recording light intensity information by the charge coupled device through the same transmission process. After two times of shooting, the object light information is recovered by utilizing the computer program to process. If the light source is not Gaussian associated, the object light information obtained by recovery is influenced by the light source associated structure, under the condition, the object needs to be moved away, the other objects are not changed, the shooting is carried out twice according to the steps, the shooting is processed and recovered by a computer, the cross spectral density equation of the light source is obtained, and finally, the two recovery results are divided to obtain the correct object amplitude and phase information.
The structure of the Gaussian-correlation partially-coherent light generation unit in the invention comprises: the laser beam emitted by the laser 1 is expanded by the beam expander 2, and then is focused on the rotating ground glass sheet 5 by the focusing lens 4, and the emergent light is collimated by the collimating lens 6 and shaped by the Gaussian filter 7. The focusing lens 4 and the rotating ground glass sheet 5 form a coherence degree adjusting system, and the coherence degree of the emergent light can be changed by changing the positions of the focusing lens 4 and the rotating ground glass sheet 5, because the coherence of the emergent light is directly influenced by the size of a light spot focused on the rotating ground glass sheet 5, the larger the focusing light spot is, the lower the coherence is, the smaller the focusing light spot is, and the higher the coherence is. The light beam after passing through the gaussian filter 7 is partially coherent light with gaussian correlation, i.e. the required light source. If a spiral phase plate 3 is placed between the beam expander 2 and the focusing lens 4, and the other is not changed, then the partially coherent light associated with the laguerre gaussian is generated after the gaussian filter 7, i.e. the required partially coherent light source with special association.
The structure of the object phase measuring unit in the invention specifically comprises: after the partially coherent light source is generated, it passes through a beam splitter 8 and is vertically incident on the spatial light modulator 9, where the beam splitter 8 is a light intensity 50: 50, loading an object carrying phase information on a spatial light modulator 9, after passing through the spatial light modulator 9, reflecting light reflected by the spatial light modulator 9 to a porous array plate 13 through a beam splitter 8, wherein the distance between the spatial light modulator 9 and the porous array plate 13 satisfies a formula z being more than or equal to d L/lambda, wherein d is the interval between small holes on the porous array plate 13, L is the size of the widest part of the object to be measured, and lambda is the wavelength of a laser light source. The multi-well array plate 13 is composed of a two-dimensional array of wells arranged periodically, with a reference well in the middle of the array. The light beam reaching the aperture array plate 13 needs to be aligned to the reference aperture, and the fourier lens 12 is placed immediately behind the aperture array plate 13, or the aperture array plate can be placed in the front focal plane of the fourier lens, and finally the intensity information is captured by the charge-coupled device 11 at the fourier plane. The light intensity captured by the CCD is transmitted to the computer 10 for real-time Fourier transform, screening array screening and de-transmission processing to obtain the phase information of the object.
The basis and principle of the invention are as follows:
the source cross spectral density is denoted as W0(ρ1,ρ2) The object to be measured is represented as O (ρ), and after the light source irradiates the object to be measured, the cross spectral density equation transmitted to the porous array plate can be represented as:
W(r1,r2)＝∫∫W0(ρ1,ρ2)O(ρ1)O(ρ2)*P(ρ1,r1)P(ρ2,r2)*dρ1dρ2 (1)
where P (ρ, r) is the transmission term from the object plane to the porous array plate. The multi-well array plate can be represented by a delta function:
M(r)＝δ(r)+∑mnδ(r-rmn) (2)
wherein r ismnWhere (md + Δ x, nd + Δ y) are coordinates of periodic wells on the multi-well array plate, m and n are integers, d is the spacing between array wells, Δ x and Δ y indicate the offset of array wells near the reference well in the x and y directions from the center point, and δ (r) indicates the central reference well. The light intensity I (kappa) reaching the Fourier plane through the porous array plate is subjected to inverse Fourier transform, and the corresponding light is the light passing through the porous array plateCross spectral density equation of field:
wherein r ismn-rpq＝[(m-p)d,(n-q)d]Where p and q are integers. Next, computer program simulation is used to pass the cross-spectral density after the inverse Fourier transform through a screening array that is similar in distribution to the multiwell array plate but lacks a reference well. W (-r) can be filtered out by the screening arraymn0) or W (0, r)mn)*Because the multi-well array is not strictly centered on the reference well, only one cross-spectral density equation can be selected. From equation (3):
Wherein T isO(ρ1,ρ2)＝∫W0(ρ1,ρ2)O(ρ2)*P(ρ2,0)*dρ2At this time, if it is to W (r)mn0) reverse transmission, resulting in TO(ρ1,ρ2)O(ρ1) This is not the correct information to be acquired, and therefore, a second shot is also required. Loading a disturbance, mathematically expressed as C δ (ρ - ρ), on the object to be measured0) Where C is a complex constant, ρ0Is the coordinates of the perturbation. Second shot W' (r)mn0) is expressed as:
subtracting the front and back results to obtain:
at this time, the reverse is performedTo the transmission, only W remains0(ρ1,ρ0)O(ρ1) For the Gaussian-correlated partially coherent light with a phase of 1, the recovered phase is the object O (ρ)1) The carried phase is that when the illumination light source is not Gaussian related but is partially coherent light of special relation, an object needs to be removed from the light path, and W is obtained by the same experiment and processing method0(ρ1,ρ0) And then the front result and the rear result are divided to obtain correct phase information.
The invention is further described with reference to the following drawings and detailed description.
The first embodiment is as follows: and recovering object phase information under Gaussian correlation partial coherent light illumination.
1. Generation of a gaussian-correlated partially coherent light source: the structure of the laser comprises a semiconductor pump solid laser 1 with adjustable power, wherein the laser wavelength emitted by the laser is 532nm, the laser beam emitted by the laser is expanded by a beam expander 2, the expanded beam is focused on a rotating ground glass sheet 5 by a focusing lens 4, the scattered light is collimated by a collimating lens 6, and then is shaped by a Gaussian filter 7. The light coming out of the Gaussian filter is Gaussian related partial coherent light. Here, the focal length of the focusing lens 4 is 80mm, and the focal length of the collimator lens 6 is 150 mm.
1.1, adjusting the spatial coherence of a light source: the space coherence of the light source and the size of the light spot focused on the rotating frosted glass sheet have a direct relation, so the size of the light spot focused on the rotating frosted glass sheet 5 is changed by adjusting the front and back positions of the focusing lens 4 on the optical axis, when the focusing light spot is smaller, the coherence of the emergent light is higher, and conversely, when the focusing light spot is larger, the coherence of the emergent light is lower.
2. Unit for light source passing through object and recording light intensity: the partially coherent light source produced in the previous step is transmitted through a beam splitter 8 to a reflective phase-only spatial light modulator 9. The beam splitter is a light intensity 50: 50, and the reflective spatial light modulator is placed perpendicular to the optical axis of the partially coherent light generating unit. The spatial light modulator 9 is connected to a computer 10, and the computer 10 controls the phase loading on the spatial light modulator. The emergent light after phase modulation passes through the beam splitter again to be reflected, and in order to save the occupied space of the device, the reflected light is reflected again through a reflector 14 and reaches the porous array plate 13 after being transmitted by 1170 mm. The transmission distance of the light beam from the spatial light modulator to the porous array plate needs to meet the condition that z is more than or equal to d x L/lambda, wherein d is the interval of the small holes of the porous array plate, L is the size of the widest position of an object to be detected, and lambda is the wavelength of a laser light source. Immediately behind the multiwell array plate, a Fourier lens 12 with a focal length of 150mm was placed, and a charge-coupled device 11 connected to a computer 10 was placed at the Fourier plane and the intensity recorded.
The whole process needs to record the light intensity twice, and the only difference in the two shooting processes is that the phase loading on the spatial light modulator 9 is different: taking a picture for the first time, and loading an object with a phase to be measured, as shown in fig. 2 (a); and (c) shooting for the second time, and placing a disturbance point in the middle of the object with the phase to be detected, as shown in fig. 2(b), wherein the disturbance point is a square with the side length of 240 micrometers, and the phase assignment of the disturbance point is equal to the phase of the original object to be detected at the position and then 0.8 pi is subtracted, so that the disturbance effect is achieved.
2.1, loading phase information on a reflective spatial light modulator: first, the prepared picture is set to a grayscale map mode. When the picture is loaded on a phase-only spatial light modulator (model Holoeye-Pluto, pixel size 1920 × 1080, pixel size 8 μm), the gray value will be converted into the corresponding phase.
2.2, design of the porous array plate used in the experiment: utilizing laser etching to manufacture a porous array plate with the size of 18mm multiplied by 14mm, wherein the substrate is integrally lightproof, and then punching is carried out, wherein a square small hole with the side length of 54 microns is placed at the position of an original point, and then, the position of the original point is respectively shifted to the x direction and the y direction by delta x being 117 microns and delta y being 117 microns, and the small hole array is symmetrically arranged by taking the square small hole as the center of a circle, as shown in fig. 3(a), wherein 66 small holes are arranged in the x direction, 48 small holes are arranged in the y direction, the side length of each small hole is 54 microns, and the interval d between the small holes is 270 microns. It is noted that Δ x ≠ d/2. (the porous array plate may also be replaced by a transmissive spatial light modulator). In the experiment, the light beam reaching the multi-well array plate is aimed at the reference well.
3. And (3) calculating a recovery phase: the light intensity information obtained by the two shots is transmitted to the computer 10 for processing. Firstly, two groups of light intensity information are respectively subjected to Fourier transform, then are screened by a screening array, secondly, screened results are subtracted, and the subtracted results are subjected to inverse transmission, so that object phase information can be extracted.
3.1, designing a screening array used in computer recovery: the screening array is not an actual object but an array for screening information that is required in the process of the program. The distribution is shown in fig. 3(b), and the only difference from the experimental multi-well array plate is the absence of the middle reference well and the consistency of other parameters.
The second embodiment: and recovering object phase information under the special relevant partial coherent light illumination.
1. Generation of a specially associated partially coherent light source: the structure of the laser comprises a semiconductor pump solid laser 1 with adjustable power, the wavelength of the laser is 532nm, a laser beam emitted by the laser is expanded by a beam expander 2, the expanded beam passes through a spiral phase plate 3 with the topological charge number of 2 and is focused on a rotating ground glass sheet 5 by a focusing lens 4, and the scattered light is collimated by a collimating lens 6 and is shaped by a Gaussian filter 7. Here, the focal length of the focusing lens 4 is 80mm, and the focal length of the collimator lens 6 is 150 mm. The light coming out of the Gaussian filter is partially coherent light associated with Laguerre Gaussian. The partially coherent light of Laguerre Gaussian correlation is used as an illumination light source to illustrate the phase recovery process under the complex correlation structure condition.
1.1, adjusting the spatial coherence of a light source: the space coherence of the light source and the size of the light spot focused on the ground glass sheet have a direct relation, so that the size of the light spot focused on the rotating ground glass sheet 5 is changed by adjusting the front and back positions of the focusing lens 4 on the optical axis, and the coherence of the emergent light is higher when the focusing light spot is smaller, and the coherence of the emergent light is lower when the focusing light spot is larger.
2. Unit for light source passing through object and recording light intensity: the partially coherent light source of laguerre gaussian correlation produced in the previous step is transmitted through a beam splitter 8 to a reflective phase-only spatial light modulator 9. The beam splitter is a half-mirror with light intensity of 50:50, and the reflective spatial light modulator is arranged perpendicular to the optical axis of the partially coherent light generating unit. The spatial light modulator 9 is connected to a computer 10, and the computer 10 controls the phase loading on the spatial light modulator. The emergent light after phase modulation passes through the beam splitter again to be reflected, and in order to save the occupied space of the device, the reflected light is reflected again through a reflector 14 and reaches the porous array plate 13 after being transmitted by 1170 mm. The transmission distance of the light beam from the spatial light modulator to the porous array plate needs to meet the condition that z is more than or equal to d x L/lambda, wherein d is the interval of small holes of the porous array plate, L is the size of the widest position of an object to be measured, and lambda is the wavelength of a laser light source. Immediately behind the multiwell array plate, a Fourier lens 12 with a focal length of 150mm was placed, and a charge-coupled device 11 connected to a computer 10 was placed at the Fourier plane and the intensity recorded.
The whole process requires 4 light intensity recordings, and the only difference in the 4 shooting processes is that the phase loading on the spatial light modulator 9 is different: shooting for the 1 st time, and loading an object to be measured in a phase position, as shown in a figure 2 (a); in the 2 nd shooting, a disturbance point is placed in the middle of the object with the phase to be measured, as shown in fig. 2(b), the disturbance point is a square with the side length of 240 μm, and the phase assignment is equal to the phase of the original object to be measured at the position and then 0.8 pi is subtracted, so that the disturbance effect is achieved; 3, taking a picture, removing a phase object without removing disturbance loading (removing the phase object does not remove the spatial light modulator, but sets the phase of the area where the original object is located to be 0); and 4, taking the picture, and removing the disturbance load.
2.1, loading phase information on a reflective spatial light modulator: first, the prepared picture is set to a grayscale map mode. When the picture is loaded on a phase-only spatial light modulator (model Holoeye-Pluto, pixel size 1920 × 1080, pixel size 8 μm), the gray value will be converted into the corresponding phase.
2.2, design of the porous array plate used in the experiment: utilizing laser etching to manufacture a porous array plate with the size of 18mm multiplied by 14mm, wherein the substrate is integrally lightproof, and then punching is carried out, wherein a square small hole with the side length of 54 microns is placed at the position of an original point, and then, the position of the original point is respectively shifted to the x direction and the y direction by delta x being 117 microns and delta y being 117 microns, and the small hole array is symmetrically arranged by taking the square small hole as the center of a circle, as shown in fig. 3(a), wherein 66 small holes are arranged in the x direction, 48 small holes are arranged in the y direction, the side length of each small hole is 54 microns, and the interval d between the small holes is 270 microns. It is noted that Δ x ≠ d/2. (the porous array plate may also be replaced by a transmissive spatial light modulator). In the experiment, the light beam reaching the multi-well array plate is aimed at the reference well.
3. And (3) calculating a recovery phase: for the 3 rd and 4 th removal phase object shots above: the light intensity information obtained by the two shots is transmitted to the computer 10 for processing. Firstly, two groups of light intensity information are respectively subjected to Fourier transform, then are screened by a screening array, then the screened results are subtracted, and the subtracted results are subjected to inverse transmission, so that the cross spectral density information and the phase information of the light source can be extracted. For the above 1 st and 2 nd shot of the phase-bearing object: the light intensity information obtained by the two shots is transmitted to the computer 10 for processing. Firstly, two groups of light intensity information are respectively subjected to Fourier transform, then are screened by a screening array, then the screened results are subtracted, and the subtracted results are subjected to reverse transmission, so that the phase information of the object influenced by the light source phase can be extracted. And finally, removing the phase of the light source by using the object phase influenced by the phase of the light source, so that correct object phase information can be obtained.
3.1, designing a screening array used in computer recovery: the screening array is not an actual object but an array for screening information that is required in the program processing. The distribution is shown in FIG. 3(b), the only difference from the experimental multi-well array plate is the absence of the middle reference well, and the other parameters are consistent.
The whole process comprises four light intensity records and data processing, and the processing process is simple, so that the whole process consumes extremely short time and can almost realize real-time recovery.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (8)
1. A non-iterative phase recovery device under partially coherent illumination, characterized by: comprises a partially coherent light generation unit and an object phase measurement unit including
A beam splitter for transmitting the partially coherent light generated by the partially coherent light generation unit and reflecting the light beam modulated by the spatial light modulator;
a spatial light modulator, disposed perpendicular to the optical axis of the partially coherent light generating unit, for loading the phase object to be measured and disturbance points for performing phase disturbance on the phase object to be measured, the spatial light modulator reflecting the light transmitted by the beam splitter and allowing the modulated light to be reflected again by the beam splitter;
A porous array plate, through which the light beam reflected by the beam splitter passes, wherein a two-dimensional aperture array arranged periodically is arranged on the porous array plate, a reference aperture is arranged near the center of the array, the reference aperture on the porous array plate is aligned with the light beam reflected by the beam splitter, and the distance between the porous array plate and the spatial light modulator satisfies z ≥ d x L/lambda, wherein d is the interval between the apertures on the porous array plate, L is the size of the widest part of the phase object to be measured, and lambda is the wavelength of the laser light source in the partially coherent light generating unit;
-a fourier lens placed immediately behind the multi-well array plate or capable of having the multi-well array plate located in a front focal plane of the fourier lens for fourier transforming the light beam passing through the multi-well array plate;
-a charge coupled element placed at the fourier plane to capture the light intensity information;
the computer is connected with the spatial light modulator and the charge coupled device, controls phase loading on the spatial light modulator, and performs real-time inverse Fourier transform, screening and inverse transmission processing on the shot light intensity to obtain phase information of the object;
when the purpose is to generate partial coherent light of the traditional Gaussian correlation, the partial coherent light generating unit comprises a laser, a beam expander for expanding a laser beam emitted by the laser, a collimating lens for collimating the light beam and a Gaussian filter for shaping the light beam which are sequentially arranged, and the light emitted by the Gaussian filter transmits through the beam splitter to reach the spatial light modulator;
The partially coherent light generating unit further comprises a coherence adjusting assembly, the coherence adjusting assembly comprises a lens for focusing the light beam with the phase changed by the light beam expanded by the beam expander and rotating ground glass for scattering the focused light beam, and the light scattered by the rotating ground glass is collimated by the collimating lens.
2. The non-iterative phase recovery apparatus under illumination by partially coherent light of claim 1, wherein: when the purpose is to generate Laguerre Gaussian related partial coherent light, the partial coherent light generating unit comprises a laser, a beam expander for expanding a laser beam emitted by the laser, a spiral phase plate for changing the phase of the expanded light, a collimating lens for collimating the light beam and a Gaussian filter for shaping the light beam, which are sequentially arranged, and the light emitted by the Gaussian filter is transmitted through the beam splitter and reaches the spatial light modulator.
3. The non-iterative phase recovery apparatus under illumination by partially coherent light of claim 1, wherein: the beam reflected by the beam splitter may also be reflected by a mirror onto the porous array plate.
4. The apparatus for non-iterative phase recovery under illumination by partially coherent light of claim 1, wherein: the disturbance point is positioned at any position of the phase object to be measured, the size of the disturbance point is far smaller than that of the phase object to be measured, and the phase assignment of the disturbance point is different from that of the original phase object to be measured at the position.
5. The non-iterative phase recovery apparatus under illumination by partially coherent light of claim 1, wherein: etching a reference small hole on a lightproof substrate by laser, and symmetrically laser etching a two-dimensional small hole array by taking the reference small hole as a circle center and respectively offsetting a certain distance to the x direction and the y direction to form the porous array plate, wherein the interval between the two-dimensional small holes needs to satisfy that d is not more than z lambda/L, wherein z is the distance from an object plane to the porous array plate, L is the size of the widest position of a phase object to be detected, and lambda is the wavelength of a laser light source in a partial coherent light generation unit; the offset is a/2 ≤ Δ x ≤ Δ y ≤ d/2-a/2, wherein a is the size of the two-dimensional pore; the sizes of the reference small holes and the two-dimensional small holes are consistent, and the reference small holes are far smaller than the size of the object to be measured and smaller than one third of the interval of the two-dimensional small holes; the porous array plate may be replaced with a transmissive spatial light modulator.
6. The non-iterative phase recovery apparatus under illumination by partially coherent light of claim 1, wherein: the spatial light modulator is a reflective phase-only spatial light modulator.
7. The non-iterative phase recovery apparatus under illumination with partially coherent light according to claim 3, wherein: the beam splitter is a light intensity 50: 50 half mirror.
8. A method of non-iterative phase recovery using a non-iterative phase recovery device under illumination with partially coherent light according to any of claims 1 to 7, comprising the steps of:
(1) acquiring Gaussian-related partial coherent light or Laguerre Gaussian-related partial coherent light through a partial coherent light generation unit, and changing the size of a light spot focused on the rotating ground glass to adjust the spatial coherence of a light source by adjusting the front and back positions of the lens for focusing on an optical axis;
(2) transmitting the partially coherent light to the object phase measuring unit, so that the partially coherent light passes through the object to be measured and records light intensity information:
(21) when the partial coherent light is Gaussian-associated partial coherent light, recording the light intensity twice, shooting for the first time, namely loading the object with the phase to be measured: setting the prepared picture as a gray scale image mode, and converting the gray scale value into a corresponding phase when the picture is loaded on the spatial light modulator with pure phase; second shooting, namely placing a disturbance point at any position of the object with the phase to be measured, wherein the size of the disturbance point is far smaller than that of the object with the phase to be measured, and the phase assignment of the disturbance point is different from that of the original object with the phase to be measured at the position; and (3) transmitting the light intensity information obtained by two times of shooting to a computer for processing: firstly, performing Fourier transform on two groups of light intensity information respectively, screening by a screening array, subtracting the screened results, and performing reverse transmission on the subtracted results to extract object phase information; the screening pores of the screening array are periodically arranged two-dimensional pores, and are generated by the computer, and the side length and the interval of each screening pore are consistent with those of the porous array plate;
(22) When the partial coherent light is Laguerre Gaussian related partial coherent light, recording four light intensities, shooting for the first time, and loading the object with the phase to be measured: setting the prepared picture as a gray scale image mode, and converting the gray scale value into a corresponding phase when the picture is loaded on the spatial light modulator with pure phase; second shooting, namely placing a disturbance point at any position of the object with the phase to be measured, wherein the size of the disturbance point is far smaller than that of the object with the phase to be measured, and the phase assignment of the disturbance point is different from that of the original object with the phase to be measured at the position; shooting for the third time, namely removing the object with the phase to be detected without removing the disturbance point, namely setting the phase of the area where the original object with the phase to be detected is located to be 0; fourth shooting-removing the disturbance phase; and (3) transmitting the light intensity information of two times obtained by the third shooting and the fourth shooting to a computer for processing: firstly, performing Fourier transform on two groups of light intensity information respectively, screening by a screening array, subtracting the screened results, and performing reverse transmission on the subtracted results to extract cross spectral density information and phase information of the light source; and (3) conveying the light intensity information of the two times obtained by the first shooting and the second shooting to a computer for processing: firstly, performing Fourier transform on two groups of light intensity information respectively, screening by a screening array, subtracting the screened results, and performing reverse transmission on the subtracted results to extract object phase information influenced by the light source phase; finally, the object phase influenced by the light source phase is used for removing the phase of the light source, so that correct object phase information can be obtained; the screening pores of the screening array are periodically arranged two-dimensional pores, and are generated by the computer, and the side length and the interval of each screening pore are consistent with those of the porous array plate.
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