Full-field complex amplitude lens-free imaging method based on axial movement of objectTechnical Field
The invention relates to the technical field of coherent diffraction imaging, in particular to a full-field complex amplitude lens-free imaging method based on axial movement of an object.
Background
Conventional stack imaging employs size-limited light to illuminate an imaging target, and multiple diffraction images are acquired by laterally moving the illumination light or imaging target and reconstruction of the imaging target and illumination light is achieved. However, due to the limited size of the illumination light, a high dynamic range camera is required to realize simultaneous acquisition of the bright area features and the dark area features; and the adjacent diffraction images need to ensure a certain overlapping rate, so that the number of diffraction images needing to be acquired is larger. While layered imaging based on extended illumination has also evolved, the introduction of scattering elements is required to provide diversity in the measurements.
Disclosure of Invention
In order to solve the problems, the invention provides a full-field complex amplitude lens-free imaging method based on the axial movement of an object, which realizes the complex amplitude reconstruction of the object and illumination light.
In order to achieve the above object, the present invention provides the following solutions:
A full-field complex amplitude lens-free imaging method based on axial movement of an object, the imaging method being applied to an imaging system comprising: the device comprises a first translation stage, an array detector and a second translation stage; the first translation stage is used for placing an imaging target, and the second translation stage is used for placing the array detector;
the imaging method comprises the following steps:
moving the first translation stage to enable the imaging target to be far away from the array detector, and acquiring an imaging target plane where the imaging target corresponding to the diffraction image acquired during each movement is located;
moving the imaging target out of the imaging system and then moving the second translation stage to enable the array detector to be far away from illumination light, and acquiring an array detector plane where the array detector corresponding to the illumination image acquired during each movement is located;
Acquiring a complex amplitude transmission function of an imaging target of the imaging target and a complex amplitude wavefront of illumination light on an Mth imaging target plane;
updating the complex amplitude wavefront of the illumination light at the Mth imaging target plane based on the complex amplitude wavefront of the illumination light at the Mth imaging target plane and the array detector plane;
calculating the complex amplitude wave front of each imaging target plane according to the complex amplitude wave front of the updated illumination light on the Mth imaging target plane;
And updating the complex amplitude transmission function of the imaging target and the complex amplitude wave front of the updated illumination light on the Mth imaging target plane again based on the complex amplitude wave front of each imaging target plane to obtain the reconstructed complex amplitude transmission function of the imaging target and the complex amplitude wave front of the reconstructed illumination light on the Mth imaging target plane.
Optionally, updating the complex amplitude wavefront of the illumination light in the mth imaging target plane based on the complex amplitude wavefront of the illumination light in the mth imaging target plane and the array detector plane specifically includes:
For the kth imaging target plane SPk, the complex amplitude wavefront of the illumination light on the mth imaging target plane is transmitted to the 1 st array detector plane DP1 through diffraction calculation, a first complex amplitude wavefront Pd1 of the illumination light on the 1 st array detector plane DP1 is obtained, the phase of the first complex amplitude wavefront Pd1 is kept unchanged, and the amplitude of the first complex amplitude wavefront Pd1 is updated to beAnd obtaining updated first complex amplitude wavefront Pd1 ', wherein B1 is an illumination light image acquired at the 1 st array detector plane DP1, continuously transmitting the updated first complex amplitude wavefront Pd1 ' to the second array detector plane DP2, obtaining a second complex amplitude wavefront Pd2 of illumination light at the 2 nd array detector plane DP2, maintaining the phase unchanged, updating the amplitude, obtaining updated second complex amplitude wavefront Pd2 ', until obtaining updated N complex amplitude wavefront PdN ' of illumination light at the N array detector plane DPN, and then, returning PdN ' to the M imaging target plane through diffraction calculation to obtain a complex amplitude wavefront of returned illumination light at the M imaging target plane, and updating the complex amplitude wavefront of illumination light at the M imaging target plane through the complex amplitude wavefront of returned illumination light at the M imaging target plane.
Optionally, a calculation formula for updating the complex amplitude wavefront of the illumination light on the mth imaging target plane by the complex amplitude wavefront of the returned illumination light on the mth imaging target plane is as follows:
Wherein PM 'represents the complex amplitude wavefront of the updated illumination light at the Mth imaging target plane, PM represents the complex amplitude wavefront of the illumination light at the Mth imaging target plane, PM' represents the complex amplitude wavefront of the returned illumination light at the Mth imaging target plane,Representing the complex amplitude wavefront of the denoised illumination light at the mth imaging target plane, a representing the weight, and TV representing the total variation denoising.
Optionally, calculating a complex amplitude wavefront of each imaging target plane according to the updated complex amplitude wavefront of the illumination light at the mth imaging target plane specifically includes:
for the kth imaging target plane SPk, the updated complex amplitude wavefront of the illumination light at the mth imaging target plane is transferred to the kth imaging target plane SPk through diffraction calculation, so as to obtain the complex amplitude wavefront of the illumination light at the kth imaging target plane SPk.
Optionally, updating the complex amplitude transmission function of the imaging target and the updated complex amplitude wavefront of the illumination light at the mth imaging target plane again based on the complex amplitude wavefront of each imaging target plane specifically includes:
calculating the emergent wave front of the kth imaging target plane SPk according to the complex amplitude wave front of the illumination light on the kth imaging target plane SPk;
Transmitting the emergent wave front of the kth imaging target plane SPk to the first array detector plane through diffraction calculation to obtain the diffraction wave front of the kth imaging target plane SPk, updating the amplitude of the diffraction wave front of the kth imaging target plane SPk, and obtaining the diffraction wave front of the updated kth imaging target plane SPk;
The diffraction wave front of the updated kth imaging target plane SPk is transmitted back to the kth imaging target plane SPk through diffraction calculation, and the emergent wave front of the updated kth imaging target plane SPk is obtained;
Updating the complex amplitude transmission function of the imaging target based on the updated exit wavefront of the kth imaging target plane SPk, and the complex amplitude wavefront of the illumination light at the kth imaging target plane SPk;
And updating the complex amplitude wavefront of the updated illumination light on the Mth imaging target plane again according to the complex amplitude wavefront of the updated illumination light on the kth imaging target plane SPk.
Optionally, the calculation formula of the outgoing wavefront of the kth imaging target plane SPk is as follows:
ψk＝O·Pk
Where ψk denotes the outgoing wavefront of the kth imaging target plane SPk, PK denotes the complex amplitude wavefront of the illumination light at the kth imaging target plane SPk, and O denotes the imaging target complex amplitude transmission function.
Optionally, the calculation formula for updating the complex amplitude transmission function of the imaging target and the complex amplitude wavefront of the illumination light at the kth imaging target plane SPk based on the updated exit wavefront of the kth imaging target plane SPk is as follows:
Wherein, O ' represents an updated imaging target complex amplitude transmission function, O represents an imaging target complex amplitude transmission function, ψ 'k represents an exit wavefront of an updated k imaging target plane SPk, ψk represents an exit wavefront of a k imaging target plane SPk, Pk represents a complex amplitude wavefront of illumination light at a k imaging target plane SPk, Pk ' represents a complex amplitude wavefront of updated illumination light at a k imaging target plane SPk, and α and β are both weight coefficients.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
The invention adopts expansion illumination, which reduces the requirement on the dynamic range of the array detector; the imaging target and the array detector are moved in the optical axis direction to provide measurement diversity without introducing a scattering element, so that the acquisition quantity of diffraction images is reduced; meanwhile, in order to assist in reconstruction of illumination light, illumination light without an imaging target is collected on the basis of collecting diffraction images; and finally, providing a corresponding iterative reconstruction algorithm to realize the complex amplitude reconstruction of the object and the illumination light.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of an imaging system provided by the present invention.
FIG. 2 is a flow chart of a full-field complex amplitude lensless imaging method based on axial movement of an object provided by the invention;
FIG. 3 is a terahertz imaging result of letters on a PP plastic plate, where FIG. 3 (a) is an imaging sample; FIGS. 3 (b) -3 (d) are diffraction images corresponding to the first three imaging target planes; FIG. 3 (e) is the result of amplitude reconstruction of an imaged object; fig. 3 (f) is a phase reconstruction result of an imaging target; fig. 3 (g) is relative height information extracted from the phase reconstruction.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide a full-field complex amplitude lens-free imaging method based on axial movement of an object, which realizes complex amplitude reconstruction of the object and illumination light.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
The full-field complex amplitude lens-free imaging method based on the axial movement of an object provided by the invention is applied to an imaging system shown in fig. 1, and the imaging system comprises: a first translation stage 3, an array detector 4, and a second translation stage 5; the first translation stage 3 is used for placing the imaging target 2 and the second translation stage 5 is used for placing the array detector 4.
As shown in fig. 2, the full-field complex amplitude lens-free imaging method based on the axial movement of an object provided by the invention comprises the following steps:
s1: and moving the first translation stage to enable the imaging target to be far away from the array detector, and acquiring an imaging target plane where the imaging target corresponding to the diffraction image acquired during each movement is located.
The imaging target 2 is placed in the imaging system and the distance z1 of the imaging target 2 from the array detector 4 in the initial state is recorded. The first translation stage 3 is controlled to move the imaging target 2 away from the array detector 4, and a diffraction image Ii is acquired each time the imaging target 2 is moved, where i= … M. Each movement is a distance deltaz1. The plane of the imaging target 2 corresponding to the diffraction image Ii is SPi, where i= … M.
S2: and moving the second translation stage to enable the array detector to be far away from the illumination light after the imaging target is moved out of the imaging system, and acquiring an array detector plane where the array detector corresponding to the illumination image acquired during each movement is located.
The imaging target 2 is moved out of the imaging system, the second translation stage 5 is controlled to move the array detector 4 away from the illumination light 1, and an illumination image Bj is acquired each time the array detector 4 is moved, where j= … N. Each movement is a distance deltaz2. The plane of the array detector 4 corresponding to the illumination image Bj is DPj, where j= … N.
S3: an imaging target complex amplitude transmission function of the imaging target and a complex amplitude wavefront of the illumination light at an Mth imaging target plane are acquired.
The initial imaging target complex amplitude transmission function O and the complex amplitude wavefront PM of the illumination light at the mth imaging target plane SPM are set to 1. Setting reconstruction weight coefficients a, alpha and beta; the number of reconstruction iterations n_iter is set.
S4: the complex amplitude wavefront of the illumination light at the mth imaging target plane is updated based on the complex amplitude wavefront of the illumination light at the mth imaging target plane and the array detector plane.
S5: and calculating the complex amplitude wave front of each imaging target plane according to the complex amplitude wave front of the updated illumination light on the Mth imaging target plane.
S6: and updating the complex amplitude transmission function of the imaging target and the complex amplitude wave front of the updated illumination light on the Mth imaging target plane again based on the complex amplitude wave front of each imaging target plane to obtain the reconstructed complex amplitude transmission function of the imaging target and the complex amplitude wave front of the reconstructed illumination light on the Mth imaging target plane.
The steps S4-S6 specifically comprise:
And (3) randomly and randomly arranging planes of M imaging targets, and executing steps 1-5 for planes SPk of each imaging target in the arrangement, wherein k is [1, M ].
Step 1: transmitting PM to the 1 st array detector plane DP1 through diffraction calculation to obtain a first complex amplitude wavefront Pd1 of illumination light on the 1 st array detector plane DP1, keeping the phase of Pd1 unchanged, and updating the amplitude to bePd1' was obtained. The transfer of Pd1 'to the next detector plane DP2 is continued with the phase unchanged, updating the amplitude until the last detector plane DPN gets an updated wavefront PdN'. Then, pdN 'is transmitted back to the Mth imaging target plane SPM through diffraction calculation, so that a complex amplitude wavefront PM' of the transmitted illumination light on the Mth imaging target plane is obtained, and the PM is updated according to the formula (1) and the formula (2):
wherein PM 'represents the complex amplitude wavefront of the updated illumination light at the Mth imaging target plane, PM represents the complex amplitude wavefront of the illumination light at the Mth imaging target plane, PM' represents the complex amplitude wavefront of the returned illumination light at the Mth imaging target plane,The complex amplitude wave front of the denoised illumination light on the Mth imaging target plane is represented, and a is a weight coefficient.
Step 2: pM "is passed to the imaging target plane SPk by diffraction calculations, resulting in a complex amplitude wavefront Pk of the illumination light at the kth imaging target plane SPk. The outgoing wavefront ψk of the imaging object plane is then obtained according to equation (3).
ψk＝O·Pk (3)
Step 3: and transmitting the phik to the detector plane DP1 through diffraction calculation to obtain a diffraction wave front phik of the kth imaging target plane SPk. Maintaining the phase of ψk unchanged and updating its amplitude toResulting in an updated diffraction wavefront ψk' of the kth imaging object plane SPk.
Step 4: and returning the psik 'to the imaging target plane SPk through diffraction calculation to obtain an updated emergent wave front psik'. Updating O and Pk by the formula (4) and the formula (5).
Wherein, O ' represents an updated imaging target complex amplitude transmission function, O represents an imaging target complex amplitude transmission function, ψ 'k represents an updated exit wavefront of the kth imaging target plane SPk, ψk represents an exit wavefront of the kth imaging target plane SPk, Pk represents a complex amplitude wavefront of illumination light at the kth imaging target plane SPk, Pk ' represents a complex amplitude wavefront of the updated illumination light at the kth imaging target plane SPk, x represents conjugation, and α and β are weight coefficients.
Step 5: the updated PM '"is obtained by diffraction calculation back to the imaging target plane SPM for Pk'.
Steps 1-5 are sub-iterative processes for a certain imaging target plane. Steps S1-S6 are then iterations for all imaging object planes. The reconstructed O and PM are obtained after performing the iteration N_iter times.
Imaging in the terahertz wave band is taken as an example to show the technical effect of the invention. The imaging operating frequency is 2.52THz, the number of imaging target planes m=10, the number of array detector planes n=2, the imaging target movement pitch Δz1 =0.5 mm, and the array detector movement pitch Δz2 =1 mm. Fig. 3 shows the terahertz imaging result of letters on PP plastic plates. Fig. 3 (b) -3 (d) are diffraction images corresponding to the first three imaging target planes, fig. 3 (e) and 3 (f) are complex amplitude reconstruction results of the imaging target, and fig. 3 (g) is a relative height distribution extracted from fig. 3 (f). The full-field complex amplitude imaging can be obtained by only 10 diffraction images, and compared with the traditional mode, the number of the collected diffraction images is reduced by about 1 order of magnitude. At the same time, due to the reconstruction of the illumination light, the reconstructed imaging target is not affected by the non-uniform illumination.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.