CN115219434B - Lens-free coaxial holographic Mueller matrix imaging system and imaging method - Google Patents
Lens-free coaxial holographic Mueller matrix imaging system and imaging method Download PDFInfo
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Abstract
The invention discloses a lens-free coaxial holographic Mueller matrix imaging system and an imaging method, wherein the system comprises a light source, a polarization state generator, a polarization state analyzer and an image sensor, the polarization state generator and the polarization state analyzer are symmetrical in structure and are composed of a linear polaroid and two liquid crystal phase retarders, a sample to be detected is arranged between the polarization state generator and the polarization state analyzer, and a coaxial holographic diffraction pattern is acquired by the image sensor. According to the method, different polarization state combinations are formed by controlling the voltages of the liquid crystal phase retarder in the polarization state generator and the polarization state analyzer, different coaxial holographic diffraction patterns are obtained by the image sensor, and a Mueller matrix image of a sample to be detected can be obtained based on the coaxial holographic diffraction patterns. The invention eliminates the vibration error caused by mechanical rotation in the traditional Mueller matrix microscopic imaging technology based on the rotary wave plate method, and remarkably improves the imaging speed.
Description
Technical Field
The invention relates to the field of Mueller matrix imaging, in particular to a lens-free coaxial holographic Mueller matrix imaging system and an imaging method.
Background
Mueller matrix imaging (Mueller matrix imaging) is a quantitative imaging modality that can reveal the structure and optical properties of the media. As a label-free, non-invasive detection modality, mueller matrix imaging has unique advantages in viewing biological tissue, materials and other samples, and can provide a complete mathematical characterization of the polarization properties of an object. As an important research direction of the mueller matrix imaging, a mueller matrix microscope has been widely studied in recent years. Mueller matrix microscopes were developed on the basis of a common optical microscope by adding polarization state generators and analyzers (PSG and PSA) in the optical path. However, this lens-based imaging approach suffers from several significant drawbacks such as its limited spatial bandwidth product (difficult to have both large field of view and high resolution), bulkiness, and high cost of polarizing optics (e.g., the use of a non-stressed objective lens). In addition, PSG and PSA are typically composed of a rotatable linear polarizer and a rotatable quarter-wave plate, which can lead to problems of mechanical vibration, slow imaging speed, etc.
Compared with the traditional microscope based on lenses, the lens-free holographic imaging has the outstanding advantages of large spatial bandwidth product, low cost, compact volume and the like. Thus, it has rapidly combined with other imaging techniques such as fluorescence imaging, phase contrast, optofluidic, and the like. Among the various previous studies on lensless holographic imaging, there have been few studies in combination with polarization imaging, and a small number of related efforts include quantitative measurement of birefringence parameters of polarization sensitive materials based on lensless holographic, on-chip differential interference contrast microscopy using birefringent crystals and lensless digital holography, lensless imaging of plant samples using cross-polarized illumination, and the like. However, as a special polarization imaging method capable of detecting the complete polarization characteristics of a sample, there has been no report so far that the mueller matrix imaging technique is integrated into a lens-free coaxial holographic imaging system to provide a mueller matrix image with high resolution and a large field of view. Indeed, the lensless holographic imaging technique is particularly suited for mueller matrix imaging with its unique advantages.
Disclosure of Invention
The invention aims to provide a lens-free coaxial holographic Mueller matrix imaging system and an imaging method based on a liquid crystal variable phase retarder (LCVR), which are used for solving the problems of small space bandwidth product, high cost and large volume caused by imaging lenses in a Mueller matrix microscope in the prior art; and problems of slow imaging speed, mechanical vibration, alignment error and the like caused by adopting a mechanical rotation mode to carry out polarization modulation.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
The utility model provides a no lens coaxial holographic mueller matrix imaging system, includes light source, image sensor, still includes polarization state generator, polarization state analyzer, light source, polarization state generator, polarization state analyzer, image sensor are the optical axis distribution altogether in proper order, and the sample that awaits measuring is placed in between polarization state generator, the polarization state analyzer, wherein:
The polarization state generator comprises a first linear polaroid, a first liquid crystal phase retarder and a second liquid crystal phase retarder which are sequentially distributed along a light path common optical axis, wherein an included angle between the polarization direction of the first linear polaroid and the fast axis direction of the first liquid crystal phase retarder is 45 degrees, and an included angle between the polarization direction of the first linear polaroid and the fast axis direction of the second liquid crystal phase retarder is 0 degree;
The polarization state analyzer is symmetrical to the polarization state generator in structure, and comprises a third liquid crystal phase retarder, a fourth liquid crystal phase retarder and a second linear polarizer which are sequentially distributed along the optical path common optical axis, wherein an included angle between the polarization direction of the second linear polarizer and the fast axis direction of the third liquid crystal phase retarder is 0 degree, and an included angle between the polarization direction of the second linear polarizer and the fast axis direction of the fourth liquid crystal phase retarder is 45 degrees;
The emergent light of the light source sequentially passes through a first linear polarizer, a first liquid crystal phase retarder and a second liquid crystal phase retarder in the polarization state generator and then reaches a sample to be detected, diffraction light is formed through the sample to be detected, and then sequentially passes through a third liquid crystal phase retarder, a fourth liquid crystal phase retarder and a second linear polarizer in the polarization state analyzer and then reaches an image sensor, so that a coaxial holographic diffraction pattern is formed on the image sensor.
Further, the device also comprises a collimation beam expander, wherein the collimation beam expander is coaxially arranged between the light source and the polarization state generator, and the emergent light of the light source reaches the polarization state generator after passing through the collimation beam expander.
Further, in the polarization state generator, the first linear polarizer, the first liquid crystal phase retarder and the second liquid crystal phase retarder are laminated into a monolithic structure.
Further, in the polarization state analyzer, the third liquid crystal phase retarder, the fourth liquid crystal phase retarder, and the second linear polarizer are laminated into a unitary structure.
Further, the image sensor is closely attached to the whole structure of the polarization state analyzer.
Further, the image sensor further comprises a thermoelectric cooler, wherein the thermoelectric cooler is closely attached to the non-light-receiving surface of the image sensor.
A Mueller matrix imaging method of a lens-free coaxial holographic Mueller matrix imaging system comprises the following steps:
step 1, respectively applying different driving voltages to a polarization state analyzer and a liquid crystal phase retarder in the polarization state generator to obtain different polarization state combinations of the polarization state analyzer, wherein each polarization state in the polarization state combinations of the polarization state analyzer and the polarization state analyzer is paired in pairs, and the specific process is as follows:
setting voltages applied to a first liquid crystal phase retarder and a second liquid crystal phase retarder in the polarization state generator as V1 and V2 respectively, and generating phase delays as delta 1 and delta 2 respectively; the voltages applied to the third and fourth liquid crystal retarders in the polarization state analyzer are V3 and V4, respectively, and the resulting phase delays are δ3 and δ4, respectively. Then:
when δ1=pi+2npi, (n∈n), the polarization state generator generates horizontal linearly polarized light, denoted as PSG (H);
When δ1=2npi, (n∈n), the polarization state generator generates vertical linearly polarized light, denoted as PSG (V);
when δ1=δ2=pi/2+npi, (n∈n), the polarization state generator generates +45° linearly polarized light, denoted PSG (+45°);
When δ1=pi/2+npi, δ2= -pi/2+npi (n∈n), the polarization state generator generates-45 ° linearly polarized light, denoted PSG (-45 °);
When δ1=pi/2+npi, δ2=pi+npi (n∈n), the polarization state generator generates left-handed circularly polarized light, denoted as PSG (L);
when δ1=pi/2+npi, δ2=npi (n∈n), the polarization state generator generates right-handed circularly polarized light, denoted as PSG (R);
when δ4=pi+2npi, (n∈n), the polarization state analyzer detects horizontally linearly polarized light, denoted PSA (H);
When δ4=2npi, (n∈n), the polarization state analyzer detects vertically linearly polarized light, denoted PSA (V);
When δ3=δ4=pi/2+npi, (n∈n), the polarization state analyzer detects +45° linearly polarized light, denoted PSA (+45°);
when δ3=pi/2+npi, δ4= -pi/2+npi (n∈n), the polarization state analyzer detects-45 ° linearly polarized light, denoted PSA (-45 °);
when δ4=pi/2+npi, δ3=pi+npi (n∈n), the polarization state analyzer detects left-handed circularly polarized light, denoted PSA (L);
When δ4=pi/2+npi, δ3=npi (n∈n), the polarization state analyzer detects right-handed circularly polarized light, denoted PSA (R);
The polarization state generator and the polarization state analyzer are paired in pairs to generate 36 different polarization state pairs, namely ：PSG(H)—PSA(H)、PSG(H)—PSA(V) 、PSG(H)—PSA(+45°) 、PSG(H)—PSA(-45°) 、PSG(H)—PSA(L) 、PSG(H)—PSA(R) 、PSG(V)—PSA(H) 、PSG(V)—PSA(V) 、PSG(V)—PSA(+45°) 、PSG(V)—PSA(-45°) 、PSG(V)—PSA(L) 、PSG(V)—PSA(R) 、PSG(+45°)—PSA(H) 、PSG(+45°)—PSA(V) 、PSG(+45°)—PSA(+45°) 、PSG(+45°)—PSA(-45°) 、PSG(+45°)—PSA(L) 、PSG(+45°)—PSA(R) 、PSG(-45°)—PSA(H) 、PSG(-45°)—PSA(V) 、PSG(-45°)—PSA(+45°) 、PSG(-45°)—PSA(-45°) 、PSG(-45°)—PSA(L) 、PSG(-45°)—PSA(R) 、PSG(L)—PSA(H) 、PSG(L)—PSA(V) 、PSG(L)—PSA(+45°)、PSG(L)—PSA(-45°) 、PSG(L)—PSA(L) 、PSG(L)—PSA(R) 、PSG(R)—PSA(H) 、PSG(R)—PSA(V) 、PSG(R)—PSA(+45°) 、PSG(R)—PSA(-45°) 、PSG(R)—PSA(L) 、PSG(R)—PSA(R).
Step 2, when the image sensor is matched with each polarization state, collecting 36 frames of coaxial holographic diffraction patterns corresponding to the sample to be detected;
step 3, respectively calculating 36 frame intensity images of a sample to be detected of the sample to be detected according to the 36 frame coaxial holographic diffraction patterns obtained in the step 2;
And 4, calculating by adopting a calculation method proposed by the university of Qinghai Du E et al in Journal of Innovation in Optical HEALTH SCIENCE 2014, 7 th volume and1 st phase article with the name of "Characteristic features of mueller matrix patterns for polarization scattering model of biological tissues" on the basis of the 36-frame intensity image of the sample to be detected obtained in the step 3, so as to obtain a Mueller matrix image of the sample to be detected.
Further, in step 1, the polarization state combination includes a horizontal linear polarization state, a vertical linear polarization state, +45° linear polarization state, -45 ° linear polarization state, a left-hand circular polarization state, and a right-hand circular polarization state.
Specifically, according to the theory presented by Peinado A et al in Optics Express 2010, volume 18, 10 entitled "Optimization and performance criteria of a Stokes polarimeter based on two variable retarders", the multiple equations corresponding to different polarization state combination methods have different condition numbers, when the number of polarization states used by the polarization state generator and the polarization state analyzer is greater than or equal to 4, if the polyhedron enclosed by the points corresponding to the polarization states on the bungjia sphere is a regular polyhedron, the condition number of the equations measured by using the set of polarization states can reach the minimum valueAnd the variance of the measured value becomes smaller as the number of polarization states increases. To minimize the condition number of the system of linear equations, we should choose points that can be connected on the bungqin to form a regular polyhedron to measure. Meanwhile, although a smaller variance can be obtained by increasing the number of measurements, doing so affects the overall measurement speed. In order to achieve the condition number and the measurement speed, the invention selects 36 times of imaging measurement methods, namely, six polarization states of a horizontal linear polarization state, a vertical linear polarization state, a +45 DEG linear polarization state, -45 DEG linear polarization state, a left-hand circular polarization state and a right-hand circular polarization state of a polarization state generator and a polarization state analyzer are matched with each other. The six polarization states form a regular octahedron by surrounding corresponding points on the Ponga sphere, so that the minimum condition number rule is met, the variance is reduced, and the measurement speed of the Mueller matrix is ensured.
Further, in step 3, the intensity image of the sample to be measured is calculated from the coaxial hologram diffraction pattern according to the back propagation angular spectrum reconstruction method based on the angular spectrum theory as proposed in the Introduction to Fourier Optics fourth edition published by j.w. Goodman et al in 2017, in combination with the autofocus algorithm as proposed in the article entitled "Diatom autofocusing in brightfield microscopy: a comparative study" in the Proceedings 15th International Conference on Pattern Recognition of j.l. Pech-Pacheco et al.
Further, in step 2, temperature control is provided to the image sensor by a thermoelectric cooler.
Compared with the prior art, the invention has the advantages that:
The invention adopts a liquid crystal phase retarder without mechanical movement to form a polarization state generator and a polarization state analyzer, utilizes voltage control to produce a group of polarization state combinations, and combines a lens-free imaging technology to realize the acquisition of digital coaxial holograms under different polarization states, thereby calculating and generating a Mueller matrix image.
The invention eliminates the vibration error caused by mechanical rotation in the traditional Mueller matrix microscopic imaging technology based on the rotary wave plate method, and simultaneously the response time of the liquid crystal phase retarder under the voltage control is far less than the time required by mechanical rotation in the wave plate rotary method, thereby obviously improving the imaging speed. Because of combining the lens-free imaging technology, the whole system has the advantages of large space bandwidth product, compact structure and low cost, and is very suitable for constructing a polarization imaging system on a lens-free sheet.
Drawings
FIG. 1 is a schematic diagram of a lens-free coaxial holographic Mueller matrix imaging system according to the present invention.
FIG. 2 is a schematic diagram of a polarization state generator according to the present invention.
Fig. 3 is an exploded view of the structure of the portion a in fig. 1.
Detailed Description
The invention will be further described with reference to the drawings and examples.
As shown in fig. 1,2 and 3, the lens-free coaxial holographic mueller matrix imaging system of the present embodiment includes an optical fiber coupled semiconductor laser 1 as a light source, a collimator beam expander 2, a polarization state generator 3, a polarization state analyzer 5, an image sensor 6, and a thermoelectric cooler 7. The optical fiber coupling semiconductor laser 1, the collimation beam expander 2, the polarization state generator 3, the polarization state analyzer 5 and the image sensor 6 are sequentially distributed on the same optical axis, and the sample4 to be measured is arranged between the polarization state generator 3 and the polarization state analyzer 5.
Specifically, the polarization state generator 3 and the polarization state analyzer 5 have the same structure and are symmetrical to each other. The polarization state generator 3 comprises a first linear polaroid 31, a first liquid crystal phase retarder 32 and a second liquid crystal phase retarder 33 which are sequentially distributed along the optical path common axis, and the first linear polaroid 31, the first liquid crystal phase retarder 32 and the second liquid crystal phase retarder 33 are laminated to form an integral layer structure. The polarization analyzer 5 includes a third liquid crystal phase retarder 51, a fourth liquid crystal phase retarder 52, and a second linear polarizer 53 sequentially distributed along the optical path common axis, and the same third liquid crystal phase retarder 51, fourth liquid crystal phase retarder 52, and second linear polarizer 53 are laminated to form a monolithic layer structure.
In this embodiment, the angle between the polarization direction of the first linear polarizer 31 and the fast axis direction of the first liquid crystal retarder 32 in the polarization state generator 3 is 45 °, the angle between the polarization direction of the first linear polarizer 31 and the fast axis direction of the second liquid crystal retarder 33 is 0 °, the angle between the polarization direction of the second linear polarizer 53 and the fast axis direction of the third liquid crystal retarder 51 in the polarization state analyzer 5 is 0 °, and the angle between the polarization direction of the second linear polarizer 53 and the fast axis direction of the fourth liquid crystal retarder 52 is 45 °.
The sample 4 to be measured is in close contact with the third liquid crystal retarder 51 in the polarization state analyzer 5, and the image sensor 6 is in close contact with the second linear polarizer 53 in the polarization state analyzer 5. The thermoelectric cooler 7 is closely attached to the non-light-receiving surface of the image sensor 6, and the temperature of the image sensor 6 can be controlled by a circuit provided with the thermoelectric cooler 7.
In this embodiment, the optical fiber coupled semiconductor laser 1 is used as an illumination device, the light beam emitted from the optical fiber coupled semiconductor laser 1 is collimated and expanded by the collimating and expanding device 2, and then polarized by the polarization state generator 3 to form polarized light, when the polarized light reaches the sample to be measured, the polarized light interacts with the sample to be measured 4 to form diffracted light, and after the diffracted light passes through the polarization state generator 5, a coaxial holographic diffraction pattern is formed on the image sensor 6. The introduction of the collimating expander 2 is to ensure perpendicularity when incident on the polarization state generator 3 and the polarization state analyzer 5, eliminate angle dependence of the liquid crystal retarder phase retardation, and ensure unit imaging magnification.
The muller matrix imaging method based on the lens-free coaxial holographic muller matrix imaging system comprises the following steps:
Step 1, carefully calibrating the phase delay-voltage curves of the first liquid crystal phase retarder 32, the second liquid crystal phase retarder 33 in the polarization state generator 3, and the third liquid crystal phase retarder 51, the fourth liquid crystal phase retarder 52 in the polarization state analyzer 5;
Then, a set of appropriate driving voltages are sequentially applied to the polarization state generator 3 and the polarization state analyzer 5 to obtain a set of different polarization state combinations including a horizontal linear polarization state, a vertical linear polarization state, +45° linear polarization state, -45 ° linear polarization state, a left-hand circular polarization state, and a right-hand circular polarization state, each polarization state of the polarization state combinations of the polarization state generator 3 and the polarization state analyzer 5 being pairwise paired.
Specifically, according to the theory presented by Peinado A et al in Optics Express 2010, volume 18, 10 entitled "Optimization and performance criteria of a Stokes polarimeter based on two variable retarders", the multiple equations corresponding to different polarization state combination methods have different condition numbers, when the number of polarization states used by the polarization state generator and the polarization state analyzer is greater than or equal to 4, if the polyhedron enclosed by the points corresponding to the polarization states on the bungjia sphere is a regular polyhedron, the condition number of the equations measured by using the set of polarization states can reach the minimum valueAnd the variance of the measured value becomes smaller as the number of polarization states increases. To minimize the condition number of the system of linear equations, we should choose points that can be connected on the bungqin to form a regular polyhedron to measure. Meanwhile, although a smaller variance can be obtained by increasing the number of measurements, doing so affects the overall measurement speed. In order to achieve the condition number and the measurement speed, the invention selects 36 times of imaging measurement methods, namely, six polarization states of a horizontal linear polarization state, a vertical linear polarization state, a +45 DEG linear polarization state, -45 DEG linear polarization state, a left-hand circular polarization state and a right-hand circular polarization state of a polarization state generator and a polarization state analyzer are matched with each other. The six polarization states form a regular octahedron by surrounding corresponding points on the Ponga sphere, so that the minimum condition number rule is met, the variance is reduced, and the measurement speed of the Mueller matrix is ensured.
Setting voltages applied to a first liquid crystal phase retarder and a second liquid crystal phase retarder in the polarization state generator as V1 and V2 respectively, and generating phase delays as delta 1 and delta 2 respectively; the voltages applied to the third and fourth liquid crystal retarders in the polarization state analyzer are V3 and V4, respectively, and the phase delays generated by the voltages are δ3 and δ4, respectively, then:
when δ1=pi+2npi, (n∈n), the polarization state generator generates horizontal linearly polarized light, denoted as PSG (H);
When δ1=2npi, (n∈n), the polarization state generator generates vertical linearly polarized light, denoted as PSG (V);
when δ1=δ2=pi/2+npi, (n∈n), the polarization state generator generates +45° linearly polarized light, denoted PSG (+45°);
When δ1=pi/2+npi, δ2= -pi/2+npi (n∈n), the polarization state generator generates-45 ° linearly polarized light, denoted PSG (-45 °);
When δ1=pi/2+npi, δ2=pi+npi (n∈n), the polarization state generator generates left-handed circularly polarized light, denoted as PSG (L);
when δ1=pi/2+npi, δ2=npi (n∈n), the polarization state generator generates right-handed circularly polarized light, denoted as PSG (R);
when δ4=pi+2npi, (n∈n), the polarization state analyzer detects horizontally linearly polarized light, denoted PSA (H);
When δ4=2npi, (n∈n), the polarization state analyzer detects vertically linearly polarized light, denoted PSA (V);
When δ3=δ4=pi/2+npi, (n∈n), the polarization state analyzer detects +45° linearly polarized light, denoted PSA (+45°);
when δ3=pi/2+npi, δ4= -pi/2+npi (n∈n), the polarization state analyzer detects-45 ° linearly polarized light, denoted PSA (-45 °);
when δ4=pi/2+npi, δ3=pi+npi (n∈n), the polarization state analyzer detects left-handed circularly polarized light, denoted PSA (L);
When δ4=pi/2+npi, δ3=npi (n∈n), the polarization state analyzer detects right-handed circularly polarized light, denoted PSA (R);
The polarization state generator and the polarization state analyzer are paired in pairs to generate 36 different polarization state pairs, namely ：PSG(H)—PSA(H)、PSG(H)—PSA(V) 、PSG(H)—PSA(+45°) 、PSG(H)—PSA(-45°) 、PSG(H)—PSA(L) 、PSG(H)—PSA(R) 、PSG(V)—PSA(H) 、PSG(V)—PSA(V) 、PSG(V)—PSA(+45°) 、PSG(V)—PSA(-45°) 、PSG(V)—PSA(L) 、PSG(V)—PSA(R) 、PSG(+45°)—PSA(H) 、PSG(+45°)—PSA(V) 、PSG(+45°)—PSA(+45°) 、PSG(+45°)—PSA(-45°) 、PSG(+45°)—PSA(L) 、PSG(+45°)—PSA(R) 、PSG(-45°)—PSA(H) 、PSG(-45°)—PSA(V) 、PSG(-45°)—PSA(+45°) 、PSG(-45°)—PSA(-45°) 、PSG(-45°)—PSA(L) 、PSG(-45°)—PSA(R) 、PSG(L)—PSA(H) 、PSG(L)—PSA(V) 、PSG(L)—PSA(+45°)、PSG(L)—PSA(-45°) 、PSG(L)—PSA(L) 、PSG(L)—PSA(R) 、PSG(R)—PSA(H) 、PSG(R)—PSA(V) 、PSG(R)—PSA(+45°) 、PSG(R)—PSA(-45°) 、PSG(R)—PSA(L) 、PSG(R)—PSA(R).
And 2, during each polarization state pairing period, enabling the image sensor 6 to collect 36 frames of coaxial holographic diffraction patterns corresponding to the sample 4 to be detected.
And 3, adopting a back propagation method based on an angular spectrum method, and judging the distance between the sample 4 to be detected and the image sensor 6 in the coaxial holographic diffraction pattern by using a proper automatic focusing algorithm, so that an intensity image of the object is reconstructed in the coaxial holographic diffraction pattern of the sample 4 to be detected.
Specifically, the intensity image of the sample to be measured is calculated from the in-line hologram diffraction pattern according to the back propagation angular spectrum reconstruction method based on the angular spectrum theory as proposed in the fourth edition of Introduction to Fourier Optics published by j.w. Goodman et al in 2017, in combination with the autofocus algorithm as proposed in the article entitled "Diatom autofocusing in brightfield microscopy: a comparative study" in Proceedings 15th International Conference on Pattern Recognition by j.l. Pech-Pacheco et al.
And 4, calculating by adopting a calculation method proposed by the university of Qinghai Du E et al in Journal of Innovation in Optical HEALTH SCIENCE 2014, 7 th volume and1 st phase article with the name of "Characteristic features of mueller matrix patterns for polarization scattering model of biological tissues" on the basis of the 36-frame intensity image of the sample to be detected obtained in the step 3, so as to obtain a Mueller matrix image of the sample to be detected.
In addition, a temperature control circuit based on a thermoelectric cooler 7 is added to the bottom of the image sensor 6 and set to room temperature to prevent the image sensor 6 from heating to interfere with the polarization state analyzer 5 placed in close contact therewith.
The embodiments of the present invention are merely described in terms of preferred embodiments of the present invention, and are not intended to limit the spirit and scope of the present invention, and various modifications and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope of the present invention, and the technical content of the present invention as claimed is fully described in the claims.
Claims (10)
1. The utility model provides a no lens coaxial holographic mueller matrix imaging system, includes light source, image sensor, its characterized in that still includes polarization state generator, polarization state analyzer, light source, polarization state generator, polarization state analyzer, image sensor are the optical axis distribution altogether in proper order, and the sample that awaits measuring is arranged in between polarization state generator, the polarization state analyzer, wherein:
the polarization state generator comprises a first linear polaroid, a first liquid crystal phase retarder and a second liquid crystal phase retarder which are sequentially distributed along a light path common optical axis, wherein an included angle phi 45 degrees is formed between the polarization direction of the first linear polaroid and the fast axis direction of the first liquid crystal phase retarder, and an included angle phi 0 degree is formed between the polarization direction of the first linear polaroid and the fast axis direction of the second liquid crystal phase retarder;
The polarization state analyzer is symmetrical to the polarization state generator in structure, and comprises a third liquid crystal phase retarder, a fourth liquid crystal phase retarder and a second linear polarizer which are sequentially distributed along the optical path common optical axis, wherein an included angle between the polarization direction of the second linear polarizer and the fast axis direction of the third liquid crystal phase retarder is phi 0 degrees, and an included angle between the polarization direction of the second linear polarizer and the fast axis direction of the fourth liquid crystal phase retarder is phi 45 degrees;
The emergent light of the light source sequentially passes through a first linear polarizer, a first liquid crystal phase retarder and a second liquid crystal phase retarder in the polarization state generator and then reaches a sample to be detected, diffraction light is formed through the sample to be detected, and then sequentially passes through a third liquid crystal phase retarder, a fourth liquid crystal phase retarder and a second linear polarizer in the polarization state analyzer and then reaches an image sensor, so that a coaxial holographic diffraction pattern is formed on the image sensor.
2. The lens-free coaxial holographic mueller matrix imaging system of claim 1, further comprising a collimating and beam expander, wherein the collimating and beam expander is coaxially disposed between the light source and the polarization state generator, and wherein the outgoing light from the light source passes through the collimating and beam expander and reaches the polarization state generator.
3. The lens-free coaxial holographic mueller matrix imaging system of claim 1, wherein in the polarization state generator, the first linear polarizer, the first liquid crystal phase retarder, and the second liquid crystal phase retarder are laminated as a unitary structure.
4. The lens-free coaxial holographic mueller matrix imaging system of claim 1, wherein in the polarization state analyzer, the third liquid crystal phase retarder, the fourth liquid crystal phase retarder, and the second linear polarizer are laminated as a unitary structure.
5. The lens-free coaxial holographic mueller matrix imaging system of claim 4, wherein the image sensor is in close proximity to the overall structure of the polarization state analyzer.
6. The lens-free coaxial holographic mueller matrix imaging system of claim 1, further comprising a thermoelectric cooler in close proximity to a non-light receiving surface of the image sensor.
7. A muller matrix imaging method based on a lens-free coaxial holographic muller matrix imaging system of any one of claims 1 to 6, comprising the steps of:
Step 1, respectively applying different driving voltages to a polarization state analyzer and a liquid crystal phase retarder in the polarization state generator to obtain different polarization state combinations of the polarization state analyzer, wherein each polarization state in the polarization state combinations of the polarization state analyzer and the polarization state analyzer is paired in pairs;
step 2, when the image sensor is matched with each polarization state, acquiring a coaxial holographic diffraction pattern corresponding to the sample to be detected;
Step 3, respectively calculating intensity images of a sample to be detected of the sample to be detected according to the plurality of coaxial holographic diffraction patterns obtained in the step 2;
and 4, calculating a Mueller matrix image of the sample to be measured by using the intensity images of the samples to be measured obtained in the step 3.
8. The method of claim 7, wherein in step 1, the polarization state combination includes a horizontal linear polarization state, a vertical linear polarization state, +45° linear polarization state, -45 ° linear polarization state, a left-hand circular polarization state, and a right-hand circular polarization state.
9. The method according to claim 7, wherein in step3, the intensity image of the sample to be measured is calculated from the coaxial hologram by combining the back propagation method based on the angular spectrum method with an autofocus algorithm.
10. The method of claim 7, wherein in step 2, temperature control is provided to the image sensor by a thermoelectric cooler.
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