阅读说明：本技术 一种叠层衍射成像装置及方法 (Laminated diffraction imaging device and method ) 是由 史祎诗 张书源 张峻浩 苗栋 于 2020-12-14 设计创作，主要内容包括：本发明涉及一种叠层衍射成像装置及方法。该装置包括：CCD相机、旋转台、探针和分辨率板；旋转台的中心开设有第一通孔,探针的中心开设有第二通孔,探针固定于旋转台的平面上,且探针的中心与旋转台的中心不重叠；分辨率板、旋转台和CCD相机依次间隔固定,光路依次经过分辨率板、探针和旋转台后到达CCD相机,分辨率板待测区域的中心、旋转台的中心和CCD相机中心均与光路同轴；旋转台在与光路垂直的方向可旋转；分辨率板、探针和CCD相机之间满足菲涅尔衍射条件。本发明可以提高叠层衍射成像的分辨率。(The invention relates to a laminated diffraction imaging device and a method. The device includes: a CCD camera, a rotating platform, a probe and a resolution plate; the center of the rotating platform is provided with a first through hole, the center of the probe is provided with a second through hole, the probe is fixed on the plane of the rotating platform, and the center of the probe is not overlapped with the center of the rotating platform; the resolution plate, the rotating platform and the CCD camera are fixed at intervals in sequence, the light path reaches the CCD camera after passing through the resolution plate, the probe and the rotating platform in sequence, and the center of the area to be measured of the resolution plate, the center of the rotating platform and the center of the CCD camera are all coaxial with the light path; the rotating platform can rotate in the direction vertical to the light path; fresnel diffraction conditions are met among the resolution plate, the probe and the CCD camera. The invention can improve the resolution of the laminated diffraction imaging.)

1. A stacked diffraction imaging apparatus, comprising: a CCD camera, a rotating platform, a probe and a resolution plate;

the center of the rotating platform is provided with a first through hole, the center of the probe is provided with a second through hole, the probe is fixed on the plane of the rotating platform, and the center of the probe is not overlapped with the center of the rotating platform;

the resolution plate, the rotating platform and the CCD camera are fixed at intervals in sequence, a light path sequentially passes through the resolution plate, the probe and the rotating platform and then reaches the CCD camera, and the center of a region to be measured of the resolution plate, the center of the rotating platform and the center of the CCD camera are all coaxial with the light path; the rotating platform can rotate in the direction vertical to the light path; fresnel diffraction conditions are met among the resolution plate, the probe and the CCD camera.

2. The stacked diffraction imaging apparatus of claim 1, wherein an off-center distance of the probe is smaller than a radius of the second through hole; the eccentric distance of the probe is the distance between the center of the probe and the center of the rotating table.

3. The stacked diffraction imaging apparatus of claim 1, wherein the CCD camera is connected to a computer for recording diffraction patterns.

4. The stacked diffractive imaging apparatus according to claim 3, wherein said rotary stage rotates in a clockwise direction.

5. The stacked diffraction imaging apparatus of claim 4, wherein the unit of rotation of the rotary stage is 90 degrees, and a diffraction pattern is recorded every 90 degrees of rotation.

6. A stacked diffraction imaging method applied to the stacked diffraction imaging apparatus according to any one of claims 1 to 5, the stacked diffraction imaging method comprising:

acquiring a plurality of diffraction images of a sample to be detected;

and recovering the plurality of diffraction images based on an ePIE algorithm to obtain the parameters of the sample to be detected.

7. The stacked diffraction imaging method according to claim 6, wherein the acquiring a plurality of diffraction images of the sample to be measured specifically comprises:

rotating the rotary table according to the rotation unit of the rotary table, and recording a diffraction image every time the rotary table rotates one rotation unit; after the rotating table rotates for one circle, a plurality of diffraction images are obtained.

8. The stacked diffraction imaging method according to claim 7, wherein the recovering of the plurality of diffraction images based on the ePIE algorithm to obtain the parameter of the sample to be measured specifically comprises:

for the current iteration of the current round, obtaining the complex amplitude distribution of the sample to be detected and the pure amplitude distribution of the probe; each round comprises N iterations, N being the number of diffraction images;

calculating to obtain an initial emergent field based on the complex amplitude distribution of the sample to be detected and the pure amplitude distribution of the probe;

performing Fresnel diffraction on the initial emergent field to obtain light field distribution;

judging whether the light field distribution is consistent with the diffraction image corresponding to the current iteration;

when the light field distribution is consistent with the diffraction image corresponding to the current iteration, determining the complex amplitude distribution of the sample to be detected corresponding to the current iteration as the parameter of the sample to be detected;

when the light field distribution is inconsistent with the diffraction image corresponding to the current iteration, replacing the amplitude of the light field distribution with the intensity information in the diffraction image corresponding to the current iteration to obtain updated light field distribution;

performing Fresnel inverse transformation on the updated light field distribution to obtain an object plane emergent field;

updating the complex amplitude distribution of the sample to be tested and the pure amplitude distribution of the probe based on the complex amplitude distribution of the sample to be tested, the pure amplitude distribution of the probe and the object plane emergent field of the current iteration to obtain the updated complex amplitude distribution of the sample to be tested and the pure amplitude distribution of the probe;

judging whether the current iteration times reach the maximum iteration times of the current round or not;

if the current iteration number reaches the maximum iteration number of the current round, taking the updated complex amplitude distribution of the sample to be detected and the updated pure amplitude distribution of the probe as the initial value of the complex amplitude distribution of the sample to be detected and the initial value of the pure amplitude distribution of the probe in the next round, returning to the step of obtaining the complex amplitude distribution of the sample to be detected and the pure amplitude distribution of the probe, and entering the next round;

and if the current iteration times do not reach the maximum iteration times of the current round, taking the updated complex amplitude distribution of the sample to be detected and the updated pure amplitude distribution of the probe as the complex amplitude distribution of the sample to be detected and the pure amplitude distribution of the probe of the next iteration, returning to the step of obtaining the complex amplitude distribution of the sample to be detected and the pure amplitude distribution of the probe, and entering the next iteration.

9. The laminated diffraction imaging method according to claim 8, wherein the updating of the complex amplitude distribution of the sample to be measured and the pure amplitude distribution of the probe based on the complex amplitude distribution of the sample to be measured, the pure amplitude distribution of the probe, and the object plane exit field of the current iteration to obtain the updated complex amplitude distribution of the sample to be measured and the updated pure amplitude distribution of the probe specifically includes:

using formulasUpdating the complex amplitude distribution of the sample to be detected; in the formula, Object_j+1(r) is the updated complex amplitude distribution of the sample to be measured; object (Object)_j(r) is the complex amplitude distribution of the sample to be measured of the current iteration; psi'_j(r) is an object plane exit field; psi_j(r) is the initial exit field;is the conjugate of the complex amplitude function of the probe;the square of the complex amplitude function digital model of the probe; r_s(j)The rotation vector of the probe corresponding to the diffraction image of the current iteration relative to the sample to be detected;

using formulasUpdating the pure amplitude distribution of the probe; in the formula, Probe_j+1(r) is the net amplitude distribution of the updated probe; probe_j(r) is the pure amplitude distribution of the probe for the current iteration;is the conjugate of the objective function;is the square of the objective function modulus.

Technical Field

The invention relates to the field of diffraction imaging, in particular to a laminated diffraction imaging device and method.

Background

Laminated diffraction imaging, as a lens-free phase imaging technique, has been studied with many results in microscopic imaging, and has become one of the mainstream imaging techniques. In the existing stacked diffraction imaging technology, a probe or an object needs to be translated in x-y two dimensions in the imaging process to scan to obtain a plurality of mutually overlapped diffraction patterns so as to restore excellent results. However, the x-y two-dimensional translation introduces translation errors in two directions, and the stacked diffraction imaging algorithm needs to iterate many times, and after completing one scan of the area to be imaged, the stack diffraction imaging algorithm needs to translate back to the position of the first scan, the reset operation is useless for the kernel of diffraction recovery, only simple reset is performed, and extra return errors which are extremely difficult to eliminate are introduced, and the two errors greatly influence the resolution of the stacked diffraction imaging.

Disclosure of Invention

The invention aims to provide a laminated diffraction imaging device and a method, which are used for reducing imaging errors and improving the resolution of laminated diffraction imaging.

In order to achieve the purpose, the invention provides the following scheme:

a stacked diffraction imaging apparatus comprising: a CCD camera, a rotating platform, a probe and a resolution plate;

the center of the rotating platform is provided with a first through hole, the center of the probe is provided with a second through hole, the probe is fixed on the plane of the rotating platform, and the center of the probe is not overlapped with the center of the rotating platform;

the resolution plate, the rotating platform and the CCD camera are fixed at intervals in sequence, a light path sequentially passes through the resolution plate, the probe and the rotating platform and then reaches the CCD camera, and the center of a region to be measured of the resolution plate, the center of the rotating platform and the center of the CCD camera are all coaxial with the light path; the rotating platform can rotate in the direction vertical to the light path; fresnel diffraction conditions are met among the resolution plate, the probe and the CCD camera.

Optionally, the eccentric distance of the probe is smaller than the radius of the second through hole; the eccentric distance of the probe is the distance between the center of the probe and the center of the rotating table.

Optionally, the CCD camera is connected to a computer, and the computer is used to record diffraction patterns.

Optionally, the rotating table rotates in a clockwise direction.

Optionally, the unit of rotation of the rotating table is 90 degrees, and a diffraction pattern is recorded every 90 degrees of rotation.

The invention also provides a laminated diffraction imaging method, which is applied to the laminated diffraction imaging device and comprises the following steps:

acquiring a plurality of diffraction images of a sample to be detected;

and recovering the plurality of diffraction images based on an ePIE algorithm to obtain the parameters of the sample to be detected.

Optionally, the obtaining of multiple diffraction images of the sample to be detected specifically includes:

rotating the rotary table according to the rotation unit of the rotary table, and recording a diffraction image every time the rotary table rotates one rotation unit; after the rotating table rotates for one circle, a plurality of diffraction images are obtained.

Optionally, the recovering the plurality of diffraction images based on the ePIE algorithm to obtain the parameter of the sample to be detected specifically includes:

for the current iteration of the current round, obtaining the complex amplitude distribution of the sample to be detected and the pure amplitude distribution of the probe; each round comprises N iterations, N being the number of diffraction images;

calculating to obtain an initial emergent field based on the complex amplitude distribution of the sample to be detected and the pure amplitude distribution of the probe;

performing Fresnel diffraction on the initial emergent field to obtain light field distribution;

judging whether the light field distribution is consistent with the diffraction image corresponding to the current iteration;

when the light field distribution is consistent with the diffraction image corresponding to the current iteration, determining the complex amplitude distribution of the sample to be detected corresponding to the current iteration as the parameter of the sample to be detected;

when the light field distribution is inconsistent with the diffraction image corresponding to the current iteration, replacing the amplitude of the light field distribution with the intensity information in the diffraction image corresponding to the current iteration to obtain updated light field distribution;

performing Fresnel inverse transformation on the updated light field distribution to obtain an object plane emergent field;

updating the complex amplitude distribution of the sample to be tested and the pure amplitude distribution of the probe based on the complex amplitude distribution of the sample to be tested, the pure amplitude distribution of the probe and the object plane emergent field of the current iteration to obtain the updated complex amplitude distribution of the sample to be tested and the pure amplitude distribution of the probe;

judging whether the current iteration times reach the maximum iteration times of the current round or not;

if the current iteration number reaches the maximum iteration number of the current round, taking the updated complex amplitude distribution of the sample to be detected and the updated pure amplitude distribution of the probe as the initial value of the complex amplitude distribution of the sample to be detected and the initial value of the pure amplitude distribution of the probe in the next round, returning to the step of obtaining the complex amplitude distribution of the sample to be detected and the pure amplitude distribution of the probe, and entering the next round;

and if the current iteration times do not reach the maximum iteration times of the current round, taking the updated complex amplitude distribution of the sample to be detected and the updated pure amplitude distribution of the probe as the complex amplitude distribution of the sample to be detected and the pure amplitude distribution of the probe of the next iteration, returning to the step of obtaining the complex amplitude distribution of the sample to be detected and the pure amplitude distribution of the probe, and entering the next iteration.

Optionally, the updating is performed on the complex amplitude distribution of the sample to be detected and the pure amplitude distribution of the probe based on the complex amplitude distribution of the sample to be detected, the pure amplitude distribution of the probe, and the object plane exit field of the current iteration, so as to obtain the updated complex amplitude distribution of the sample to be detected and the updated pure amplitude distribution of the probe, and the updating specifically includes:

using formulasUpdating the complex amplitude distribution of the sample to be detected; in the formula, Object_j+1(r) is the updated complex amplitude distribution of the sample to be measured; object (Object)_j(r) is the complex amplitude distribution of the sample to be measured of the current iteration;emitting a field for an object plane; psi_j(r) is the initial exit field;is the conjugate of the complex amplitude function of the probe;the square of the complex amplitude function digital model of the probe; r_s(j)The rotation vector of the probe corresponding to the diffraction image of the current iteration relative to the sample to be detected;

using formulasUpdating the pure amplitude distribution of the probe; in the formula, Probe_j+1(r) is the net amplitude distribution of the updated probe; probe_j(r) is the pure amplitude distribution of the probe for the current iteration;is the conjugate of the objective function;is the square of the objective function modulus.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects:

according to the invention, two-dimensional translation in the prior art is replaced by rotation, so that displacement errors can be reduced, return errors can be eliminated, and the resolution of laminated diffraction imaging can be further improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 is a schematic diagram of a stacked diffraction imaging apparatus according to the present invention;

FIG. 2 is a first side view of a stacked diffractive imaging device of the present invention;

FIG. 3 is a second side view of a stacked diffractive imaging device of the present invention;

FIG. 4 is a schematic flow chart of a stacked diffraction imaging method of the present invention;

FIG. 5 is a schematic diagram of the initial position of a probe in a simulation example of the present invention;

FIG. 6 is a schematic diagram of an illumination process in a simulation example of the present invention;

FIG. 7 is a schematic diagram of the amplitude and phase of an object under test according to a simulation example of the present invention;

FIG. 8 is a schematic diagram of the amplitude and phase recovered by the method of the present invention in an example of simulation of the present invention;

FIG. 9 is a diffraction pattern of a probe in a simulation example of the present invention;

FIG. 10 is a schematic diagram of the amplitude and phase of the probe recovered by the method of the present invention in the simulation example of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

Fig. 1 is a schematic structural diagram of a stacked diffraction imaging device of the present invention, fig. 2 is a first side view of the stacked diffraction imaging device of the present invention, and fig. 3 is a second side view of the stacked diffraction imaging device of the present invention. As shown in fig. 1 to 3, the stacked diffraction imaging apparatus of the present invention includes: a CCD camera 1, a rotary table 2, a probe 3 and a resolution plate 4.

First through-hole has been seted up at revolving stage 2's center, the second through-hole has been seted up at the center of probe 3, probe 3 off-centre is fixed in on revolving stage 2's the plane, promptly the center of probe 3 with revolving stage 2's center does not overlap. Specifically, if the circular hole probe 3 with the radius of the second through hole being 1.5mm is selected, the eccentric distance between the probe 3 and the rotating platform 2 is 1.2mm, and the eccentric distance is smaller than the radius of the circular hole, so that no leakage area exists after the multiple rotary diffraction patterns are spliced. The specific process of fixing the probe 3 on the turntable 2 is as follows: firstly, fixing a grid on the back side of the rotating platform 2, inserting a marker post at the position of 1.2mm eccentric to the grid, penetrating the center of a round hole of the probe 3 into the marker post, fixing the probe 3 on the rotating platform 2 through a screw or other dark visits, removing the grid, and finishing the fixation of the probe 3 on the rotating platform 2. In a specific application, the outer diameter of the probe 3 is smaller than the outer diameter of the turntable 2, so that the rotation scale can be seen clearly when the turntable 2 rotates.

Resolution ratio board 4 the revolving stage 2 with CCD camera 1 is fixed at the interval in proper order, and the light path passes through in proper order resolution ratio board 4 probe 3 with reach behind the revolving stage 2 CCD camera 1, the center in the region that the resolution ratio board 4 awaits measuring the center of revolving stage 2 with the CCD center all with the light path is coaxial, as shown in fig. 2 and fig. 3. The rotary table 2 is rotatable in a direction perpendicular to the optical path; fresnel diffraction conditions are met among the resolution plate 4, the probe 3 and the CCD.

Specifically, after the light path is collimated into a beam of standard plane wave, the CCD camera 1 used for acquiring the diffraction pattern is coaxially fixed with the light path, a region with characteristics on a standard resolution plate 4 is selected as a region to be measured, the resolution plate 4 is placed at a position 8cm in front of the CCD (the distance can be any and the Fresnel diffraction condition can be met), and the resolution plate 4 is adjusted, so that the center of the region to be measured, the center of the CCD and the center of the light path are coaxial. When the diffraction pattern is collected, the rotating platform 2 with the probe 3 eccentrically fixed is placed at the position 3cm behind the resolution plate 4 (the distance can be any and the Fresnel diffraction condition is met), the center of the rotating platform 2 is coaxial with the center of the light path (the center of the probe 3 is deviated from the center of the light path by about 1.2mm), the CCD is connected with a computer, the current diffraction pattern is recorded, and then the rotating platform 2 is rotated once in the clockwise direction without rotating, and one diffraction pattern is recorded. For example, if the unit of rotation is 90 degrees, one diffraction pattern is recorded for every 90 degrees of rotation, and a total of 4 diffraction patterns are obtained for one rotation.

Based on the diffraction pattern acquired by the device, the invention also provides a laminated diffraction imaging method, and fig. 4 is a flow schematic diagram of the laminated diffraction imaging method. As shown in fig. 4, the stacked diffraction imaging method of the present invention comprises the steps of:

first, a plurality of diffraction images of the sample 5 to be measured are acquired. Specifically, the rotary table is rotated in units of rotation of the rotary table, one diffraction image is recorded for each rotation of the rotary table, and after one rotation of the rotary table, N diffraction images are obtained. And then, based on the N diffraction images, recovering by adopting an ePIE algorithm to obtain the parameters of the sample 5 to be detected. The specific process is as follows:

defining j to represent the current iteration times, wherein the jth iteration corresponds to the jth diffraction image; r_s(j)Representing the rotation vector of the probe corresponding to the jth diffraction image relative to the sample 5 to be detected; r represents a spatial domain coordinate; u denotes the fresnel domain coordinates. The illumination probe (round hole) is incident on a sample 5 to be measured with a complex amplitude distribution function of object (r), and the transmitted light propagates for a certain distance and then has a light intensity distribution I on a Fresnel domain_s(j)(u). Rotating the illumination probe to scan the relative displacement of the object while ensuring a certain overlap between adjacent scanning positions, and recording the light intensity distribution I of the transmitted light in the Fresnel domain after the transmitted light is transmitted for a certain distance_j(u)。

First, the complex amplitude distribution of the sample 5 to be measured and the pure amplitude distribution of the probe are assigned initial values.

For the j iteration of the current round, dividing the Object according to the complex amplitude of the sample 5 to be measured of the current iteration_j(r) and pure amplitude distribution Probe of the Probe_j(r) calculating to obtain an initial emergent field of

ψ_j(r)＝Object_j(r)*Probe_j(r-R_s(j))

In the formula, #_j(r) is the initial exit field; probe_j(r-R_s(j)) As a function of the complex amplitude of the probe.

The initial emergent field is diffracted by Fresnel with a certain distance to obtain the corresponding light field distribution

In the formula, #_j(u) is the light field distribution; fresnel {. is a Fresnel transformation function; a. the_j(u) is an amplitude term; i is an imaginary unit;is the phase of the diffraction pattern.

Using the known intensity information I of the current jth diffraction pattern_j(u) substituting amplitudes in the light field distribution to obtain an updated light field distribution

In formula (II), psi'_j(u) is the updated light field distribution.

The updated light field distribution is subjected to Fresnel inverse transformation to obtain a new object plane emergent field

ψ′_j(r)＝iFresnel{ψ′_j(u)}

In formula (II), psi'_j(r) is an object plane exit field; iFresnel {. is the inverse Fresnel transform function.

Updating complex amplitude distribution functions of objects and probes

Wherein the content of the first and second substances,the max is to prevent the denominator from being zero in matlab and the algorithm from reporting errors.

This is repeated until all recorded diffraction patterns have been used, and a round is considered complete. After a plurality of rounds of iteration, when the light field distribution of the current iteration is consistent with the diffraction image corresponding to the current iteration, namely the autocorrelation coefficient of the corresponding recovered diffraction pattern and the recorded diffraction pattern exceeds a set threshold value, the iteration is terminated, and the complex amplitude distribution of the sample 5 to be measured corresponding to the current iteration is determined as the parameter of the sample 5 to be measured.

For example, knowing the intensities (amplitudes) of six truly collected diffraction patterns at different rotation positions, randomly setting the amplitudes and phases of the sample 5, performing fresnel diffraction to obtain a diffraction pattern, performing amplitude replacement with the actual diffraction pattern, performing inverse fresnel diffraction on the replaced diffraction pattern, performing the above operation on all six positions, regarding as an iteration, and repeating the operation until the guessed diffraction pattern obtained after the sample 5 diffracts is consistent with the actual diffraction pattern (or the error is smaller than a threshold), and terminating the iteration.

A simulation example is provided below to further illustrate the solution of the present invention.

In this example, the initial position of the probe is shown in fig. 5, the illumination process is shown in fig. 6, the object to be measured is shown in fig. 7, the left part is shown by the amplitude, and the right part is shown by the phase. In this example, the unit of rotation is 60 °, one diffraction pattern is recorded for each 60 ° rotation, and six diffraction patterns are recorded. Based on six diffraction patterns, the scheme of the invention is adopted to recover the object to be detected, the obtained amplitude and phase are shown in fig. 8, the left part in fig. 8 is an amplitude schematic diagram obtained by recovery, and the right part is a phase schematic diagram obtained by recovery.

The diffraction pattern of the probe is shown in FIG. 9, in which 4 portions are 4 diffraction patterns of the probe recorded in sequence. FIG. 9 is a diffraction pattern of a probe in a simulation example of the present invention. The scheme of the invention is adopted to recover the probe to be detected, the obtained amplitude and phase are shown in fig. 10, the left part in fig. 10 is the amplitude schematic obtained by recovery, and the right part is the phase schematic obtained by recovery.

The invention changes the traditional snake-shaped x-y scanning mode into rotary scanning, only needs a rotary table, rotates the probe along one direction according to a fixed angle, controls the overlapping rate, and can reduce the two-dimensional translation error into one-dimensional rotation error. Meanwhile, the method automatically resets to the initial position after completing one-time scanning, thereby omitting the traditional resetting process, having good imaging quality and easy operation.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.

The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.