CN111366536A - Vertical single-optical-element rotary type Mueller matrix imaging measuring device and method - Google Patents
Vertical single-optical-element rotary type Mueller matrix imaging measuring device and method Download PDFInfo
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Abstract
The invention discloses a measuring device and method for vertical single-optical-element rotary Mueller matrix imaging, and belongs to the technical field of polarized optical measurement and microscopic imaging. The device comprises a light source, a reflector, a polarization modulation unit, a sample measuring unit, a polarization demodulation unit, a light detector and a calculator which are sequentially arranged along a light path. The invention utilizes the Stokes-Mueller calculus principle to establish the relation between the sample to be measured and the light intensity of the change measured by the light detector, adopts a measuring device of Mueller matrix imaging to measure the full Mueller matrix of the sample to be measured, and further obtains all optical anisotropy parameters of the sample to be measured. The invention overcomes the problems of complex operation, low measurement precision and the like in the processes of measurement, transformation solving and the like of polynomial Fourier coefficients, improves the measurement speed and precision, and can realize the nondestructive, rapid and accurate measurement of the structural morphology and the optical anisotropy parameters of the sample.
Description
Technical Field
The invention relates to the technical field of polarized optical measurement and microscopic imaging, in particular to a measuring device and a measuring method for vertical single optical element rotary type Mueller matrix imaging, namely a measuring method for vertical single optical element rotary type Mueller matrix imaging, which is used for measuring full Mueller matrix elements and optical anisotropic parameters of a sample by adopting the measuring device.
Background
In recent years, with rapid development in the technical fields of semiconductor devices, nanomaterials, thin film materials, nano biomedicine and the like, various functional materials have changed from original two-dimensional planar structures to complex three-dimensional structures, and the inherent optical properties of the functional materials are changed with the change of the material structures. The optical parameters are the most important optical properties of the anisotropic material, which can directly reflect the final properties of the material. Therefore, it is very important to perform high-resolution, non-destructive, and accurate measurement of the optical properties of anisotropic materials.
At present, a commonly used measurement method is to calculate a fourier coefficient of a polarized light intensity after being reflected (or transmitted) by a sample according to an experimentally measured change of the polarized light intensity by using a mueller matrix ellipsometer and based on a demodulation principle of fourier transform, so as to obtain a mueller matrix element of the sample. However, in the conventional mueller matrix measurement method, a dual-optical-element rotary mueller matrix ellipsometer is adopted, that is, a compensator in a polarization system and a compensator in an analyzer are required to move at a certain speed ratio (usually, 5 ω: m ω, ω is a motion angular velocity of the polarization system and the analyzer, m is a non-zero integer and is not equal to 5 or 10) to generate different modulation frequencies, so that in order to obtain a complete calibration result, at least 25 fourier coefficients are required to be solved in a test process to obtain all mueller matrix elements, and the measurement period is long, and the calibration calculation process is complex. In the conventional mueller matrix measurement technology, a transmissive full mueller matrix spectroscopic ellipsometer disclosed in patent CN201310040729.7 adopts a transmissive structure, but in the detection process, because the polarizing arm and the polarization analyzing arm are symmetric along the sample stage, the finally detected transmitted light intensity contains a part of reflected light intensity, which has a certain influence on the measurement accuracy. More importantly, the existing mueller matrix ellipsometer can only realize spectral measurement and microscopic imaging of the geometric morphology of a sample, and the existing method for measuring the optical properties of the sample is only to analyze the mueller matrix elements of the sample, but actually, the matrix elements capable of directly reflecting the optical properties of the sample should be an obtained inversion matrix of the mueller matrix elements of the sample to be measured, and in addition, research on measurement and analysis of the optical anisotropy parameters of the sample by using the mueller matrix polarizer and pseudo color imaging of the measured optical anisotropy parameters is not developed at present.
Disclosure of Invention
The invention aims to provide a vertical single-optical-element rotary type mueller matrix imaging measuring device and method aiming at the defects of the prior art, and the device solves the problems of complex operation, low measurement precision and the like in the processes of measurement, transformation solving and the like of polynomial Fourier coefficients and the like because the finally detected transmission light intensity contains partial reflection light intensity components on the basis of a double-optical-element rotary type mueller matrix ellipsometer for measuring transmission type full mueller matrix elements of a sample, and can quickly and efficiently measure the full mueller matrix elements of the sample.
The invention also aims to provide a method for measuring the Mueller matrix imaging of the sample based on the Stokes-Mueller calculus integral principle, which can get rid of the speed limitation of a double-optical element rotation mode and the fuzzy analysis of the optical properties of the sample in the measurement process compared with the traditional measuring method based on the Fourier transform principle, and can realize the nondestructive, rapid and accurate measurement of the structural morphology and the optical anisotropy parameters of the sample.
The specific technical scheme for realizing the purpose of the invention is as follows:
a vertical single optical element rotary type Mueller matrix imaging measuring device is characterized by comprising a light source, a reflector, a polarization modulation unit, a sample measuring unit, a polarization demodulation unit, a light detector and a computer; the light source and the reflector are arranged on the same straight line along the light path; the polarization modulation unit, the sample measuring unit, the polarization demodulation unit and the light detector are arranged on the same straight line along a light path; the light source and the reflector are arranged in the direction vertical to the light paths of the polarization modulation unit, the sample measuring unit, the polarization demodulation unit and the light detector; the polarization modulation unit is sequentially provided with a polarizer and a first compensator along the direction of a light path and modulates the polarization state of the incident light emitted to the sample measurement unit by the light source and the reflector; the sample measuring unit is sequentially provided with a sample stage and an infinite correction microscope objective along the direction of an optical path; the polarization demodulation unit is sequentially provided with a second compensator and an analyzer along the direction of the light path and demodulates the polarization state of the transmission light emitted by the sample measurement unit; the computer is connected with the first compensator, the second compensator and the light detector; wherein:
the light emitted by the light source passes through the reflector and then emits incident light to the sample measuring unit;
the sample stage is a three-dimensional displacement adjusting platform;
the light detector is an image acquisition detector that receives the transmitted light demodulated by the polarization demodulation unit.
The first compensator is a high-precision rotating table with a fixed rotating angle and is provided with an achromatic quarter-wave plate; the second compensator is a high-precision rotating platform which is set to rotate at a constant speed and is provided with an achromatic quarter-wave plate.
The computer calculates the change of the polarization angle generated when the second compensator rotates at a constant speed and the change of the measured light intensity received by the light detector, calculates the full Mueller matrix elements of the sample, calculates the optical anisotropy parameters of the sample according to the full Mueller matrix elements of the sample, and controls the rotation motion angles and speeds of the first compensator and the second compensator and stores and displays the calculated full Mueller matrix elements and optical anisotropy parameters of the sample.
The optical path of the measuring device is defined in an XYZ coordinate system and satisfies the right-hand rule: the incident direction of light, namely a main optical axis is a Z axis, the direction vertical to the main optical axis is a Y axis, and the direction vertical to a plane formed by Y, Z axes is an X axis;
the included angle between the transmission axis of the polarizer and the X axis is 0 degree, and the included angle between the fast axis of the achromatic quarter-wave plate of the first compensator and the fast axis of the achromatic quarter-wave plate of the second compensator and the transmission axis of the polarizer is 0 degree.
The fast axis of the achromatic quarter wave plate is located in the XY plane and is rotatable about the Z axis.
A vertical single optical element rotary type Mueller matrix imaging measurement method comprises the following steps:
step 4, controlling the second compensator to rotate at a constant speed by using the computer, and simultaneously controlling the light detector to measure and collect the variable light intensity generated by the constant speed rotation of the second compensator and perform real-time sample imaging preview;
and 7, performing pseudo color imaging on the structural morphology characteristics and the optical anisotropy parameters of the sample by using the computer.
Compared with the prior art, the vertical single optical element rotary type Mueller matrix imaging measuring device has the following beneficial effects:
(1) the vertical single-optical-element rotary-type Mueller matrix imaging measuring device provided by the invention can overcome the problems of complex operation, complicated solution and low measuring efficiency and effectiveness caused by the fact that a plurality of Fourier coefficients need to be measured and solved and transformed in the measuring process of a double-optical-element rotary-type Mueller matrix ellipsometer according to the rotating mode of a single optical element, so that the measuring process is quicker, and the accuracy of the measuring result is ensured.
(2) The vertical single-optical-element rotary-type Mueller matrix imaging measuring device provided by the invention can solve the problem of low measurement accuracy caused by the fact that a transmission type Mueller matrix ellipsometer contains a part of reflected light intensity component in the detected transmission light intensity in the measurement in the prior art according to the mode that a single optical element rotates, so that the measurement accuracy can be improved.
(3) The measurement method based on the vertical single-optical-element rotary Mueller matrix imaging can get rid of the speed limitation of a double-optical-element rotary mode and the fuzzy analysis of the optical properties of a sample in the measurement process, so that the measurement speed and the accuracy of the measurement result are improved, and the nondestructive, rapid and accurate measurement of the structural morphology and the optical anisotropy parameters of the sample can be realized.
Drawings
FIG. 1 is a schematic diagram of the structure of the apparatus of the present invention.
Detailed Description
Referring to fig. 1, the present invention will be described in further detail with reference to the following embodiments.
The rotation of the single optical element in the present invention means that, during the operation of the measurement apparatus for mueller matrix imaging provided by the present invention, the first compensator 302 in the polarization modulation unit 3 is set to have a fixed rotation angle, and the second compensator 501 in the polarization demodulation unit 5 is set to rotate at a constant speed.
The non-normalized Mueller matrix of the sample to be tested is expressed as follows:
wherein M issNon-normalized Mueller matrix, m, representing samplesij(i, j ═ 0,1,2,3) represents the 16 non-normalized mueller matrix elements of the samples to be tested.
The non-normalized mueller matrix of the sample to be measured can be solved by associating the stokes vector of the light intensity which is measured by the light detector 6 and changes of the light intensity which is measured by the light source 1 and the stokes vector of the incident light which is emitted by the light source 1 with the changed mueller matrices of the first compensator 302 and the second compensator 501 due to the rotation motion:
Sout(t)＝Mp2Mc2(t)MsMc1Mp1Sin(4)
wherein S isinRepresenting the Stokes vector of the incident light emitted by the light source 1 via the mirror 2, Mp1A Mueller matrix, M, representing said polarizer 301c1A Mueller matrix, M, representing said first compensator 302sMuller matrix representing samples to be tested, Mc2(t) represents a time-varying mueller matrix, M, generated by the second compensator 501 during uniform rotationp2Representing the mueller matrix of the analyzer 502.
The mueller matrices of the polarizer 301 and the analyzer 502 have a certain mueller matrix form at a fixed angle, and therefore can be directly substituted as known quantities in the measurement and calculation process; the first compensator 302 and the second compensator 501 have a changing mueller matrix due to the rotation motion:
in the above formula, the first and second carbon atoms are,
SX≡sin(X) (2a)
CX≡cos(X) (2b)
wherein M isCi(θ，δ)(i is 1,2) respectively representing the mueller matrices of the first compensator 302 and the second compensator 501, δ is the retardation introduced by the compensators, θ is the included angle formed by the fast axis of the achromatic quarter-wave plate in the first compensator 302 and the second compensator 501 and the transmission axis of the polarizer 301, and S is the retardation introduced by the compensatorsXDenotes the abbreviation of a sine function sin (X), X being 2 theta or delta, CXDenotes the abbreviation of the cosine function cos (X), X being 2 theta or delta. In commercial achromatic compensators, δ will still vary with wavelengthWith slight variations. Due to the rotational setting, θ also changes during the measurement. Its variation with time is given by:
θ(t)＝ωt+φ (3)
where ω is the angular velocity, which is constant during the measurement, t is the measurement time and φ is the phase, i.e. the initial direction of the compensator.
Compared with the Fourier transform principle, the Stokes-Muller calculus principle is used as a simpler and popular and understandable transformation principle for solving the Mueller matrix of the sample, and plays an important role in the process of calculating and evaluating the Mueller matrix of the sample to be detected.
According to the stokes-mueller calculus principle, since the light intensity reaching the light detector 6 during measurement and calculation can be given by the first element of the stokes vector in equation (4), it can be expressed as:
thus when expressed in vector form, the above formula can be expressed as:
I(i)＝BT(i)A (9)
wherein I (i) represents the intensity recorded at the ith measurement, SXDenotes the abbreviation of a sine function sin (X), X being 2 theta or delta, CXDenotes the abbreviation of cosine function cos (X), X is 2 theta or delta, delta is the retardation introduced by the compensator, theta is the included angle between the fast axis of the achromatic quarter-wave plate in the first compensator 302 and the second compensator 501 and the transmission axis of the polarizer 301, m isij(i, j ═ 0,1,2,3) represents the 16 non-normalized mueller matrix elements of the sample to be measured, a is the vector containing the 16 non-normalized mueller matrix elements of the sample, b (i) is the base vector evolving with the delay of the compensator and the direction of the fast axis of the quarter-wave plate. In the above equation, T represents a transposed matrix. If a new dimension is added, the formula can be generalized to include all intensities recorded over the number of measurements in the same calculation:
I＝BTA (10)
where I is a vector containing the intensity of I measurements, where B is no longer a vector but a matrix of size I × 16.
Therefore, according to the stokes-mueller calculus form, the modulation frequency change introduced by the rotary compensator can be analyzed through the light intensity change, and the mueller matrix of the sample to be measured is calculated.
The optical properties of the sample can be expressed in a Mueller matrix form of 4 × 4, wherein 6 independent property parameters including LB, LB ', LD, LD', CB and CD are contained, and the matrix representation of the properties of the sample can be obtained by the normalized Mueller matrix inversion transformation.
Wherein L isSAll optical property parameter matrixes of the sample to be detected are represented, A is a normalized parameter and has no practical significance; LB and LB' represent the linear birefringence of the sample; LD and LD' represent linear dichroism of the sample; CB represents the circular birefringence of the sample; CD represents the circular dichroism of the sample.
The normalized Mueller matrix of the sample to be detected can be obtained by dividing the non-normalized Mueller matrix by the first Mueller matrix element:
the method for measuring the optical anisotropy parameters of the sample to be measured is based on the Stokes-Muller calculus principle.
The invention discloses a vertical single-optical-element rotary-type Mueller matrix imaging measuring device which is shown in figure 1, and comprises a light source 1, a reflector 2, a polarization modulation unit 3, a sample measuring unit 4, a polarization demodulation unit 5, a light detector 6 and a computer 7; the light source 1 and the reflector 2 are arranged on the same straight line along a light path; the polarization modulation unit 3, the sample measuring unit 4, the polarization demodulation unit 5 and the light detector 6 are arranged on the same straight line along the light path; the light source 1 and the reflector 2 are arranged in the direction perpendicular to the light paths of the polarization modulation unit 3, the sample measuring unit 4, the polarization demodulation unit 5 and the light detector 6; the polarization modulation unit 3 is sequentially provided with a polarizer 301 and a first compensator 302 along the light path direction, and modulates the polarization state of the incident light emitted from the light source 1 and the reflector 2 to the sample measurement unit 3; the sample measuring unit 4 is sequentially provided with a sample stage 401 and an infinity corrected microscope objective 402 along the optical path direction; the polarization demodulation unit 5 is provided with a second compensator 501 and an analyzer 502 in sequence along the direction of the light path, and demodulates the polarization state of the transmission light emitted by the sample measurement unit 4; the computer 7 is connected with the first compensator 302, the second compensator 501 and the light detector 6; wherein:
the light emitted by the light source 1 is transmitted to the sample measuring unit 4 after passing through the reflector 2;
the sample stage 401 is a three-dimensional displacement adjusting platform;
the photodetector 6 is an image acquisition detector that receives the transmitted light demodulated by the polarization demodulation unit 5.
The first compensator 302 is a high-precision rotating table with a fixed rotating angle and is provided with an achromatic quarter-wave plate; the second compensator 501 is a high-precision rotary table that is set to rotate at a constant speed and is equipped with an achromatic quarter-wave plate.
The computer 7 calculates a change of a polarization angle generated when the second compensator 501 rotates at a constant speed and a change of a measured light intensity received by the light detector 6, calculates an all-muller matrix element of the sample, and calculates an optical anisotropy parameter of the sample according to the all-muller matrix element of the sample, and the computer 7 controls a rotational motion angle and a rotational motion speed of the first compensator 302 and the second compensator 501 and stores and displays the calculated all-muller matrix element and the calculated optical anisotropy parameter of the sample.
The optical path of the measuring device is defined in an XYZ coordinate system and satisfies the right-hand rule: the incident direction of light, namely a main optical axis is a Z axis, the direction vertical to the main optical axis is a Y axis, and the direction vertical to a plane formed by Y, Z axes is an X axis;
the included angle between the transmission axis of the polarizer 301 and the X axis is 0 degree, and the included angle between the fast axes of the achromatic quarter-wave plates of the first compensator 302 and the second compensator 501 and the transmission axis of the polarizer 301 is 0 degree.
The fast axis of the achromatic quarter wave plate is located in the XY plane and is rotatable about the Z axis.
The method is implemented according to the following steps of:
And 2, placing a sample to be measured on the sample table 401 of the vertical single-optical-element rotary Mueller matrix imaging measuring device, and rotating a three-dimensional adjusting screw button of the sample table 401 to adjust the height and the direction of the sample table 401, so as to ensure that a light intensity signal received by the light detector 6 reaches the maximum value, and present the clearest image of the sample to be measured on a display screen of the computer 7.
And 3, controlling the high-precision rotating table of the first compensator 302 in the Mueller matrix imaging three-dimensional measuring device to rotate to a set displacement angle through the program command of the computer 7 in the Mueller matrix imaging measuring device.
And 4, controlling a high-precision rotating platform of the second compensator 501 in the mueller matrix imaging measuring device to rotate at a constant speed by a program instruction of the computer 7 in the mueller matrix imaging measuring device, controlling the light detector 6 to measure and collect the variable light intensity generated by the constant speed rotation of the second compensator 501 by using the computer 7 in the mueller matrix imaging measuring device, and imaging and previewing the real-time morphological characteristics of the sample on a display screen of the computer 7.
5.1, calculating a changed Mueller matrix M of the first compensator 302 and the second compensator 501 in the measuring device for imaging the Mueller matrix due to the rotation motionCi(θ，δ)：
In the above formula, the first and second carbon atoms are,
SX≡sin(X) (2a)
CX≡cos(X) (2b)
wherein M isCi(θ，δ)(i is 1,2) is the mueller matrix of the first compensator 302 and the second compensator 501, respectively, and represents that δ is the retardation introduced by the compensators, θ is the angle formed by the fast axis of the achromatic quarter-wave plate in the first compensator 302 and the second compensator and the transmission axis of the polarizer 301, and S isXDenotes the abbreviation of a sine function sin (X), X being 2 theta or delta, CXDenotes the abbreviation of the cosine function cos (X), X being 2 theta or delta. In commercial achromatic compensators, δ will still vary slightly with wavelength. Because of the rotational setting, θ also changes during the measurement, and its variation with time is given by:
θ(t)＝ωt+φ (3)
where ω is the angular velocity, which is constant during the measurement, t is the measurement time and φ is the phase, i.e. the initial direction of the compensator.
5.2 calculating the light detection in a measuring device for Mueller matrix imagingStokes vector S of the time-varying light intensity measured by the device 6out(t)：
Sout(t)＝Mp2Mc2(t)MsMc1Mp1Sin(4)
Wherein S isinRepresenting the Stokes vector of the incident light emitted by the light source 1 via the mirror 2, Mp1A Mueller matrix, M, representing said polarizer 301c1A Mueller matrix, M, representing said first compensator 302sMuller matrix representing samples to be tested, Mc2(t) represents a time-varying mueller matrix, M, generated by the second compensator 501 during uniform rotationp2A Mueller matrix representing said analyzer 502, a Mueller matrix M of said polarizer 301 and said analyzer 502p1，Mp2At a fixed angle, the image has a certain mueller matrix form.
5.3, obtaining the changed light intensity according to the calculation and the changed Mueller matrix M generated by the first compensator 302 and the second compensator 501 due to the rotation motionCi(θ，δ)(i-1, 2) calculating the non-normalized Mueller matrix M of the sample to be measureds：
Wherein M issNon-normalized Mueller matrix, m, representing the sample to be testedij(i, j ═ 0,1,2,3) represents the 16 non-normalized mueller matrix elements of the samples to be tested.
According to the stokes-mueller calculus principle, since the light intensity reaching the light detector 6 during measurement and calculation can be given by the first element of the stokes vector in equation (4), it can be expressed as:
thus when expressed in vector form, the above formula can be expressed as:
I(i)＝BT(i)A (9)
wherein I (i) represents the intensity recorded at the ith measurement, SXDenotes the abbreviation of a sine function sin (X), X being 2 theta or delta, CXDenotes the cosine function cos (X), X is 2 theta or delta, delta is the retardation introduced by the compensator, theta is the angle formed by the fast axis of the achromatic quarter-wave plate in the first compensator 302 and the second compensator and the transmission axis of the polarizer 301, mij(i, j ═ 0,1,2,3) represents the 16 non-normalized mueller matrix elements of the sample to be measured, a is the vector containing the 16 non-normalized mueller matrix elements of the sample, b (i) is the basic vector evolving with the orientation of the retardation of the compensator and the fast axis of the achromatic quarter-wave plate. In the above equation, T represents a transposed matrix. If a new dimension is added, the formula can be generalized to include all intensities recorded over the number of measurements in the same calculation:
I＝BTA (10)
where I is a vector containing the intensity of I measurements, where B is no longer a vector but a matrix of size I × 16.
The intensity I matrix is thus obtained after a number of measurements collected by the photodetector:
I＝[I1I2I3...In]T(11)
wherein I represents a matrix of multiple light intensity values collected by the photodetector, Ii(i ═ 1,2,3.. n) denotes the light intensity value measured by the light detector at a single time, and T denotes a transposed matrix.
After a plurality of measurements, a coefficient B matrix which evolves along the directions of the retardation of the compensator and the fast axis of the achromatic quarter-wave plate can be obtained:
B＝[b1b2b3...bn](12)
wherein B represents a coefficient matrix evolving with the compensator retardation and the change of direction of the fast axis of the achromatic quarter-wave plate, Bi(i ═ 1,2,3.. n) represents a matrix of coefficients evolving from a change in direction of the single pass compensator retardance and the achromatic quarter-wave plate fast axis.
Then, inverse matrix calculation is carried out on the coefficient B matrix:
W＝inv(B) (13)
where W represents an inverse matrix of the coefficient B matrix, and inv represents inverse matrix calculation performed on the coefficient B matrix.
In conjunction with the intensity matrix I, an expression for A can be derived from equation (8):
A＝W*I (14)
therefore, according to the stokes-mueller calculus form, the modulation frequency change introduced by the rotary compensator can be analyzed through the light intensity change, and the mueller matrix of the sample to be measured is calculated.
6.1, calculating the normalized Mueller matrix M of the sample to be measureds'：
Wherein M iss' denotes the normalized Mueller matrix, m ' of the sample to be tested 'ij(i, j ═ 0,1,2,3) denotes the normalized mueller matrix elements of the samples to be tested, mij(i, j ═ 0,1,2,3) represents the 16 non-normalized mueller matrix elements of the samples to be tested.
6.2 normalized Mueller matrix M for sample to be testeds' analysis and inversion change are carried out to obtain all optical property parameter matrixes L of the sample to be measuredS:
Wherein L isSExpressing that all optical property parameter matrixes of the sample to be detected are obtained, wherein A is a normalized parameter and has no practical significance; LB and LB' represent the linear birefringence of the sample; LD and LD' represent linear dichroism of the sample; CB represents the circular birefringence of the sample; CD represents the circular dichroism of the sample.
And 7, performing pseudo color imaging on the structural morphology characteristics and the optical anisotropy parameters of the sample by using the calculating and analyzing unit 7.
The key point of the device provided by the embodiment of the invention is that a single optical element rotating mode is adopted on the basis of a stokes-muller calculus form, specifically, a fixed displacement angle is set for the first compensator 302 in the polarization modulation unit 3, a rotating type which moves at a constant speed is adopted for the second compensator 501 in the polarization demodulation unit 5, an equation is established for the light intensity collected by the light detector 6 and the muller matrix equation of the polarizer 301, the first compensator 302, the second compensator 501 and the analyzer 502 in the measuring device for imaging the muller matrix, so that the non-normalized muller matrix of the sample to be measured is solved, and further, the normalized muller matrix of the sample to be measured is analyzed and inverted to obtain all optical anisotropy parameters of the sample to be measured.
The device provided by the invention can overcome the problems of complex operation, complicated solution and low measurement efficiency and effectiveness caused by the fact that a plurality of Fourier coefficients need to be measured and solved and transformed in the measurement process of the dual-optical-element rotary-type muller matrix ellipsometer, and ensures that the finally detected transmitted light intensity contains a part of reflected light intensity component to cause low measurement accuracy on the basis of simultaneously obtaining 16 full muller matrix elements of a sample to be measured in one measurement through the dual-optical-element rotary-type muller matrix ellipsometer for measuring the transmission-type full muller matrix elements of the sample in the prior art, thereby improving the measurement speed and the measurement accuracy.
The present invention is not limited to the above-described embodiments, but the present invention should not be limited to the disclosure of the embodiments and the drawings. Therefore, any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A vertical single optical element rotary type Mueller matrix imaging measuring device is characterized by comprising a light source, a reflector, a polarization modulation unit, a sample measuring unit, a polarization demodulation unit, a light detector and a calculator, wherein the light source is used for emitting light;
the light source and the reflector are arranged on the same straight line along the light path;
the polarization modulation unit, the sample measuring unit, the polarization demodulation unit and the light detector are arranged on the same straight line along a light path;
the light source and the reflector are arranged in the direction vertical to the light paths of the polarization modulation unit, the sample measuring unit, the polarization demodulation unit and the light detector;
the polarization modulation unit is sequentially provided with a polarizer and a first compensator along the direction of a light path and modulates the polarization state of the incident light emitted to the sample measurement unit by the light source and the reflector;
the sample measuring unit is sequentially provided with a sample stage and an infinite correction microscope objective along the direction of an optical path;
the polarization demodulation unit is sequentially provided with a second compensator and an analyzer along the direction of the light path and demodulates the polarization state of the transmission light emitted by the sample measurement unit;
the computer is connected with the first compensator, the second compensator and the light detector; wherein:
the light emitted by the light source passes through the reflector and then emits incident light to the sample measuring unit;
the sample stage is a three-dimensional displacement adjusting platform;
the light detector is an image acquisition detector that receives the transmitted light demodulated by the polarization demodulation unit.
2. A measuring device according to claim 1, characterized in that the first compensator is a device provided with a high precision rotary table of fixed rotation angle and fitted with an achromatic quarter wave plate; the second compensator is a high-precision rotating platform which is set to rotate at a constant speed and is provided with an achromatic quarter-wave plate.
3. The measuring device according to claim 1, wherein the computer calculates a change in a polarization angle generated when the second compensator rotates at a constant speed and a change in a measured light intensity received by the light detector, calculates an all-muller matrix element of the sample, and calculates an optical anisotropy parameter of the sample according to the all-muller matrix element of the sample, and the computer controls a rotational motion angle and a rotational motion speed of the first compensator and the second compensator and stores and displays the calculated all-muller matrix element and the calculated optical anisotropy parameter of the sample.
4. A measuring device as claimed in claim 1, characterized in that the optical path of the device is defined in an XYZ coordinate system and satisfies the right-hand rule: the incident direction of light, namely a main optical axis is a Z axis, the direction vertical to the main optical axis is a Y axis, and the direction vertical to a plane formed by Y, Z axes is an X axis;
the included angle between the transmission axis of the polarizer and the X axis is 0 degree, and the included angle between the fast axis of the achromatic quarter-wave plate of the first compensator and the fast axis of the achromatic quarter-wave plate of the second compensator and the transmission axis of the polarizer is 0 degree.
5. A measurement device as claimed in claim 2, wherein the fast axis of the achromatic quarter waveplate lies in the XY plane and is rotatable about the Z axis.
6. A method for measuring vertical single-optical element rotary mueller matrix imaging using the apparatus of claim 1, comprising the steps of:
step 1, turning on the light source, and simultaneously turning on the computer and signal power supplies of the first compensator, the second compensator and the light detector;
step 2, placing a sample to be detected on the sample table, and adjusting the height and the direction of the sample table; ensuring that the light detector can present a clear image of the sample to be detected;
step 3, controlling the first compensator to rotate to a set displacement angle by using the computer;
step 4, controlling the second compensator to rotate at a constant speed by using the computer, and simultaneously controlling the light detector to measure and collect the variable light intensity generated by the constant speed rotation of the second compensator and perform real-time sample imaging preview;
step 5, calculating the variation light intensity measured by the light detector through the computer to obtain the non-normalized Mueller matrix elements of the sample to be measured;
step 6, analyzing and inverting the non-normalized Mueller matrix elements of the to-be-detected sample obtained through calculation through the computer to obtain all optical anisotropy parameter matrixes of the to-be-detected sample;
and 7, performing pseudo color imaging on the structural morphology characteristics and the optical anisotropy parameters of the sample by using the computer.
7. The measurement method according to claim 6, wherein the step 5 comprises:
a. calculating a change Mueller matrix M of the first compensator and the second compensator due to the rotation motionCi(θ，δ)：
In the above formula, the first and second carbon atoms are,
SX≡sin(X) (2a)
CX≡cos(X) (2b)
wherein M isCi(θ，δ)(i is 1,2) is the Mueller matrix of the first and second compensators, delta is the retardation introduced by the compensators, theta is the included angle formed by the fast axis of the achromatic quarter-wave plate and the transmission axis of the polarizer in the first and second compensators, and S is the retardation introduced by the compensatorsXDenotes the abbreviation of a sine function sin (X), X being 2 theta or delta, CXDenotes the abbreviation of the cosine function cos (X), X being 2 θ or δ; in commercial achromatic compensators, δ will still vary slightly with wavelength; because of the rotational setting, θ also changes during the measurement, and its variation with time is given by:
θ(t)＝ωt+φ (3)
where ω is the angular velocity, which is constant during the measurement, t is the measurement time, and φ is the phase, i.e. the initial direction of the compensator;
b. calculating a Stokes vector S of the time-varying light intensity measured by the light detectorout(t)：
Sout(t)＝Mp2Mc2(t)MsMc1Mp1Sin(4)
Wherein S isinA Stokes vector, M, representing incident light from the light source via the mirrorp1Mueller matrix, M, representing said polarizerc1Mueller matrix, M, representing said first compensatorsMuller matrix representing samples to be tested, Mc2(t) a time-varying Mueller matrix, M, generated by the second compensator at constant speed rotationp2A Mueller matrix representing said analyzer, a Mueller matrix M of said polarizer and said analyzerp1，Mp2The mode of the determined Mueller matrix is adopted at a fixed angle;
c. according to the calculated changed light intensity and the changed Mueller matrix M generated by the first compensator and the second compensator due to the rotary motionCi(θ，δ)(i-1, 2) calculating the non-normalized Mueller matrix M of the sample to be measureds：
Wherein M issNon-normalized Mueller matrix, m, representing the sample to be testedij(i, j ═ 0,1,2,3) represents the 16 non-normalized mueller matrix elements of the samples to be tested.
8. The measurement method according to claim 6, wherein the step 6 comprises:
a. calculating the normalized Mueller matrix M of the sample to be measureds'：
Wherein M iss' denotes the normalized Mueller matrix, m ' of the sample to be tested 'ij(i, j ═ 0,1,2,3) 16 normalized mueller matrix elements for the samples to be tested, mij(i, j ═ 0,1,2,3) 16 unnormalized mueller matrix elements of the sample to be tested;
b. normalized full Mueller matrix M for sample to be testeds' analysis and inversion change are carried out to obtain all optical property parameter matrixes L of the sample to be measuredS：
Wherein L isSAll optical property parameter matrixes of the sample to be detected are represented, A is a normalized parameter and has no practical significance; LB and LB' represent the linear birefringence of the sample; LD and LD' represent linear dichroism of the sample; CB represents the circular birefringence of the sample; CD represents the circular dichroism of the sample.
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