Mueller matrix measuring device and calibration method

Abstract

The present application relates to the technical field of optical detection, and specifically provides a Mueller matrix measuring device and a calibration method, which comprises a light source, a polarized light path, a detection polarized light path and a bidirectional light path, wherein the bidirectional light path comprises a light splitting component for splitting polarized modulation light, part of the light beams are emitted to a sample to be measured through the light splitting component, and the light beams pass through the sample to be measured in a forward and reverse direction and are then emitted to the detection polarized light path by the light splitting component; in order to increase the diameter of the light beams, a beam expander can be additionally arranged to increase the diameter of the light beams emitted to the sample to be measured; the present application is designed through the bidirectional light path, so that the measuring light path is completely located on the same side of the sample to be measured, and the Mueller matrix measurement can be realized without penetrating the sample to be measured or arranging an external light path, the problem that the traditional reflection type ellipsometer cannot detect high-thickness samples is solved, and medium interference is avoided; and the measurement error is eliminated with the help of a plane mirror, and the precise calibration of the Mueller matrix is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical detection, and particularly relates to a Mueller matrix measuring device and a calibration method. BACKGROUND

[0002] Polarization property detection technology is an important tool in modern scientific research and industrial applications. By analyzing the polarization state of light, the microstructure and surface properties of matter can be deeply understood, thereby providing researchers with more comprehensive scientific data. Therefore, polarization property detection technology plays an irreplaceable role in the fields of material analysis, environmental monitoring, and biomedical imaging.

[0003] Mueller matrix ellipsometry (MME) is a powerful polarization property detection tool that can obtain all 16 elements of the Mueller matrix of a sample without contact. Common Mueller matrix ellipsometers are mainly divided into two categories: transmission type and reflection type. The transmission type Mueller matrix ellipsometer uses normal incidence to obtain the Mueller matrix through the transmitted light of the sample, while the reflection type Mueller matrix ellipsometer uses oblique incidence to obtain the Mueller matrix through the reflected light of the sample.

[0004] The detection light path of the transmission type Mueller matrix ellipsometer needs to be located on both sides of the sample. If it is used to detect the polarization properties of samples in special working environments such as submarine observation windows, part of the light path needs to be placed outside the submarine cabin, i.e. immersed in seawater. Considering the complex working environment of the deep sea, this scheme has great risks and safety hazards. More importantly, the detection light path needs to pass through seawater, so the detection result will be seriously affected by the optical properties of seawater. The reflection type Mueller matrix ellipsometer cannot perform full-aperture detection on thick samples due to the use of oblique incidence. In addition, due to the size limitation of polarization optical elements, the measurement range of the Mueller matrix ellipsometer cannot meet the measurement requirements of large-aperture samples.

[0005] Therefore, it is urgent to propose a new Mueller matrix measuring device and calibration method to complete the polarization property measurement of large-aperture and high-thickness optical elements in special working environments. SUMMARY

[0006] Therefore, the present application aims to provide a Mueller matrix measuring device and calibration method, which effectively solves the limitation that the prior art cannot perform full-aperture detection on thick samples through a bidirectional light path.

[0007] To achieve the above-mentioned purpose, the technical solution of the present application is as follows:

[0008] The present application provides a Mueller matrix measuring device in the first aspect, comprising: a light source, a polarizing light path, a detection light path, and a bidirectional light path arranged in the exit direction of the polarizing light path.

[0009] The bidirectional optical path comprises a first light splitting component for splitting the polarized modulation light emitted by the polarized optical path;

[0010] The light beam transmitted by the first light splitting component is incident to the sample to be measured, and the transmitted light beam is reflected by the sample to be measured to the first light splitting component, and the light beam is reflected by the first light splitting component into the detection polarized optical path; or the light beam reflected by the first light splitting component is incident to the sample to be measured, and the reflected light beam is reflected by the sample to be measured to the first light splitting component, and the light beam is transmitted by the first light splitting component into the detection polarized optical path.

[0011] Preferably, further comprising: a beam expander arranged between the first light splitting component and the sample to be measured, for expanding the diameter of the light beam emitted to the sample to be measured.

[0012] Preferably, the calculation formula of the unidirectional optical path Mueller matrix calculated by the bidirectional optical path Mueller matrix is:

[0013] ;

[0014] Wherein, is the bidirectional optical path Mueller matrix measured by the Mueller matrix measurement device, is the unidirectional optical path Mueller matrix, is the Mueller matrix of the plane mirror, .

[0015] Preferably, the polarized optical path comprises a polarizer and a rotatable wave plate arranged along the transmission direction of the light beam, the polarizer is used to process the light beam provided by the light source into a light beam with a specific polarization state, and the wave plate adjusts the light beam with the specific polarization state into a light beam with different polarization states by rotating.

[0016] Preferably, the detection polarized optical path comprises a second light splitting component, a first polarization camera, a second polarization camera, and a quarter wave plate arranged between the second light splitting component and the first polarization camera.

[0017] Preferably, the light beam propagating in the bidirectional optical path is perpendicular to the sample to be measured.

[0018] Preferably, the sample to be measured is an optical system or a single optical element.

[0019] Preferably, the light beam is forwardly incident into the optical system and is reversely emitted by the optical system; or the light beam is forwardly incident from the front surface of the single optical element and is reversely emitted from the rear surface of the single optical element.

[0020] The second aspect of the present application provides a Mueller matrix calibration method, comprising:

[0021] S1: measuring the sample to be measured by using the Mueller matrix measurement device to obtain the measured Mueller matrix , and the real Mueller matrix of the sample to be measured is:

[0022] ;

[0023] wherein, is the Mueller matrix of the polarized light path, is the first beam-splitter Mueller matrix of the direction of the light beam emitted by the first beam-splitter towards the sample under test, is the real Mueller matrix of the sample under test, is the first beam-splitter reflection Mueller matrix of the direction of the light beam emitted by the first beam-splitter towards the detection light path, is the Mueller matrix of the detection light path;

[0024] S2: a plane mirror is arranged between the first beam-splitter and the sample under test, and the Mueller matrix measurement device is used again to measure and obtain the Mueller matrix , is:

[0025] ;

[0026] wherein, is the Mueller matrix of the plane mirror;

[0027] S3: the Mueller matrix of the first beam-splitter and the Mueller matrix of the polarized light path are measured separately, and the real Mueller matrix of the sample under test is calibrated using and ;

[0028] S4: the Mueller matrix error in the process of the light beam emitted by the plane mirror towards the detection light path is obtained according to and :

[0029] ;

[0030] S5: the real Mueller matrix of the sample under test is calculated using the measured Mueller matrix and the error :

[0031] .

[0032] The third aspect of the present application provides a Mueller matrix calibration method, comprising:

[0033] a: the measured Mueller matrix of the sample under test is obtained by using the Mueller matrix measurement device according to claim 2, and the expression of the measured Mueller matrix is:

[0034] ;

[0035] wherein, is the Mueller matrix of the polarizing path, is the first beam-splitter Mueller matrix of the light beam in the direction from the first beam-splitter to the sample under test, is the beam expander Mueller matrix of the light beam in the direction from the beam expander to the sample under test, i.e. the forward Mueller matrix of the beam expander, is the real Mueller matrix of the sample under test, is the first beam-splitter reflection Mueller matrix of the light beam in the direction from the first beam-splitter to the detection path, is the Mueller matrix of the detection path, is the beam expander Mueller matrix of the light beam in the direction from the beam expander to the first beam-splitter, i.e. the backward Mueller matrix of the beam expander;

[0036] b: the bidirectional Mueller matrix of the beam expander and the sample under test is:

[0037] ;

[0038] c: a flat mirror is arranged between the first beam-splitter and the beam expander, and the Mueller matrix measurement device is used again to measure the Mueller matrix , is:

[0039] ;

[0040] wherein, is the Mueller matrix of the flat mirror;

[0041] d: the Mueller matrix of the first beam-splitter and the Mueller matrix of the polarizing path are measured separately, and the real Mueller matrix of the sample under test is calibrated using and ;

[0042] e: the Mueller matrix error of the light beam in the process of being emitted from the flat mirror to the detection path is obtained according to and :

[0043] ;

[0044] f: the Mueller matrix of the beam expander and the sample under test is expressed as: using the measured Mueller matrix and the error

[0045] ;

[0046] g: the flat mirror is moved to be between the beam expander and the sample under test, and the Mueller matrix measurement device is used again to measure the Mueller matrix , is:

[0047] ;

[0048] h: the bidirectional Mueller matrix of the beam expander is:

[0049] ;

[0050] and the forward Mueller matrix of the beam expander is calculated from the bidirectional Mueller matrix of the beam expander and the reverse Mueller matrix ;

[0051] j: the forward Mueller matrix of the beam expander is and the reverse Mueller matrix The bidirectional Mueller matrix of the beam expander and the whole sample to be measured is obtained, and the real Mueller matrix of the sample to be measured is:

[0052] .

[0053] Compared with the prior art, the application can achieve the following beneficial effects:

[0054] The application uses a bidirectional optical path design, so that the measurement optical path is completely located on the same side of the sample to be measured, and the device optical path does not need to penetrate the sample to be measured or arrange an external optical path to realize Mueller matrix measurement, thereby avoiding the risk of external optical path in special environments such as deep sea and high pressure, and also avoiding the light passing through seawater or other media, eliminating the interference of the environment medium on the measurement result, and improving the detection reliability. In addition, the bidirectional optical path design is adopted, the light vertically passes through the sample to be measured twice, and a conversion formula from the bidirectional Mueller matrix to the single-direction matrix is proposed by combining a mathematical solving method, so that the real polarization characteristics of the sample are accurately restored, the error introduced by the bidirectional optical path is avoided, the problem that the traditional reflection type ellipsometer cannot detect high-thickness samples due to inclined incidence is effectively solved, and a scheme for full-aperture detection of thick samples is provided.

[0055] The application adds a beam expander in the bidirectional optical path, significantly increases the aperture of the detection light beam, and supports full-aperture polarization characteristic detection of large-aperture optical elements

[0056] The application also provides two corresponding calibration schemes corresponding to the two cases with and without the beam expander, and the calibration method eliminates the errors introduced by the polarizing optical path, the analyzing optical path, the light splitting component, the beam expander and the like by means of the plane mirror optical path, and accurately obtains the real Mueller matrix of the sample to be measured. BRIEF DESCRIPTION OF DRAWINGS

[0057] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. The illustrations are shown in the drawings, wherein:

[0058] Figure 1 is a structural schematic diagram of a Mueller matrix measuring device according to Embodiment 1 of the present application;

[0059] Figure 2 is a Mueller matrix calibration schematic diagram according to Embodiment 2 of the present application;

[0060] Figure 3 is a Mueller matrix calibration schematic diagram according to Embodiment 3 of the present application.

[0061] The reference signs in the drawings include:

[0062] Polarizer 101, wave plate 102, first light splitting assembly 103, beam expander 104, second light splitting assembly 105, quarter wave plate 106, first polarization camera 107, second polarization camera 108, light source 109, plane mirror 110, sample to be measured 111. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not constitute a limitation on the present application. Similar elements in different embodiments use associated similar element numbers. In the following embodiments, many details are described in order to make the present application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials or methods. In some cases, some operations related to the present application are not shown or described in the specification in order to avoid the core part of the present application being overwhelmed by too much description, and it is not necessary for those skilled in the art to describe these related operations in detail according to the description in the specification and general technical knowledge in the art.

[0064] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other to form various embodiments without conflict. Meanwhile, each step or action in the method description can also be sequentially adjusted or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various orders in the specification and the drawings are only for the purpose of clearly describing a certain embodiment, and do not mean a necessary order, unless otherwise stated that a certain order must be followed.

[0065] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" and the like can be explicitly or implicitly included one or more. In the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0066] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0067] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0068] Please refer to Figure 1 In one embodiment 1 of the present application, a Mueller matrix measuring device is provided, mainly including a light source 109, a polarizing light path, a polarized light path, and a two-way light path, wherein the light source 109 is used to provide a measuring light beam. The measuring light beam emitted by the light source 109 enters the polarizing light path for polarization modulation. The polarizing light path is composed of a polarizer 101 and a rotatable wave plate 102. The transmission axis direction of the polarizer 101 is horizontal. The polarizer 101 is coaxially arranged with the wave plate 102. The reference direction of the wave plate 102 is the transmission axis direction of the polarizer 101. The measuring light beam passes through the polarizer 101 and the wave plate 102 in turn. The wave plate 102 is clamped by a precision rotating motor to realize high-precision rotation. With the rotation of the wave plate 102, the measuring light beam is modulated to generate polarization modulation light with different polarization states.

[0069] The light beam is emitted from the polarized light path and enters a bidirectional light path arranged at the rear end of the polarized light path. The bidirectional light path mainly comprises a first light splitting component 103, which is a light splitting prism. The first light splitting component 103 is configured to direct the forward transmission light beam to the sample 111 to be measured and direct the backward transmission light beam reflected by the sample 111 to be measured to the detection polarization light path. Specifically, the first light splitting component 103 can be designed in two ways. In one way, the first light splitting component 103 is configured to transmit the forward transmission light beam emitted from the polarized light path and reflect the backward transmission light beam emitted from the sample 111 to be measured. In this design, the bidirectional light path is coaxial with the polarized light path. After the light beam is emitted from the polarized light path, it is transmitted through the first light splitting component 103 and continues to be transmitted into the sample 111 to be measured. The sample 111 to be measured is generally an optical system or a single optical element with a large thickness. When the sample 111 to be measured is an optical system, the light beam is transmitted along the optical path of the optical system after being incident into the optical system, is reflected at the last end of the optical system, is reflected out of the optical system again, and is transmitted in the optical system in the forward and backward directions. After being emitted from the optical system, the light beam is incident on the first light splitting component 103 again, and the first light splitting component 103 reflects the light beam to the detection polarization light path. If the optical system is completely transmissive, a high-reflection film can be coated on the rear surface of the last element of the optical system to enhance the intensity of the light beam reflected out of the optical system. Similarly, when the sample 111 to be measured is a single optical element, the light beam is incident on the front surface of the single optical element, is reflected by the rear surface of the single optical element, is reflected out of the single optical element again, and is transmitted in the single optical element in the forward and backward directions. After being emitted from the single optical element, the light beam is incident on the first light splitting component 103 again, and the first light splitting component 103 reflects the light beam to the detection polarization light path. A high-reflection film can be coated on the rear surface of the single optical element to enhance the intensity of the light beam reflected out of the single optical element.

[0070] The other design way is that the first light splitting component 103 is configured to reflect the forward transmission light beam emitted from the polarized light path and transmit the backward transmission light beam emitted from the sample 111 to be measured. In this case, the polarized light path and the detection polarization light path are coaxial, and the bidirectional light path is perpendicular to the polarized light path. The specific light beam transmission process is the same as that in the first design way, which will not be described here.

[0071] The light beam is shot to the detection polarized light path by the first light splitting component 103, the detection polarized light path comprises a second light splitting component 105, a quarter-wave plate 106, a first polarization camera 107 and a second polarization camera 108, wherein the second light splitting component 105 is used for splitting the light beam shot into the detection polarized light path. After the light beam enters the detection polarized light path, the light beam is first shot into the second light splitting component 105, and the second light splitting component 105 adopts a light splitting prism with a light splitting ratio of 50:50. The second light splitting component 105 splits the light beam into two light beams, one of which is shot to the quarter-wave plate 106, and the other of which is directly shot to the second polarization camera 108. In the embodiment of the application, four polarization channels (0°, 45°, 90°, 135°) of the second polarization camera 108 and two polarization channels (45°, 135°) of the first polarization camera 107 after passing through the quarter-wave plate 106 are selected, and a total of six polarization channels are obtained. A detection polarization matrix is formed by different polarization channels, all Stokes parameters are obtained by single shooting, and then the Mueller matrix is calculated.

[0072] In order to enhance the applicability of the Mueller matrix measuring device, a light beam adjuster is further arranged on the rear end of the first light splitting component 103, that is, on the light path between the first light splitting component 103 and the to-be-measured sample 111, to adjust the diameter of the light beam shot to the to-be-measured sample 111. Generally, in order to meet the detection of a large-diameter element, the adjuster is a beam expander, which expands the diameter of the light beam to adapt to the measurement of the Mueller matrix of the large-diameter to-be-measured sample 111, and overcomes the disadvantage that the Mueller matrix ellipsometer (MME) cannot detect large-diameter elements.

[0073] In addition, the embodiment of the application realizes that the light source 109, the polarized light path, the detection polarized light path and the bidirectional light path are all arranged on the same side of the to-be-measured sample 111 through the bidirectional light path design, avoids the problem that the traditional light path needs to penetrate the to-be-measured sample 111 or needs to arrange an external light path, and effectively avoids the damage of deep sea or high pressure to the equipment in the special environment of deep sea and high pressure. At the same time, the light does not pass through the seawater medium, the detection result avoids the interference of the medium, and the detection reliability is improved. Moreover, the light beam shot to the to-be-measured sample 111 is in a perpendicular incidence mode, which solves the problem that the traditional reflection type Mueller matrix ellipsometer needs to adopt an oblique incidence mode.

[0074] Since the bidirectional light path is adopted in the application, the detection light beam passes through the to-be-measured sample 111 twice, therefore, the Mueller matrix measured by the Mueller matrix measuring device in the embodiment of the application is essentially a bidirectional light path Mueller matrix, so it is necessary to derive a calculation formula for calculating the unidirectional light path Mueller matrix from the bidirectional light path Mueller matrix. The Mueller matrix construction process in the embodiment of the application is the same as that of the traditional method, and only a brief description is given as follows:

[0075] Based on the Mueller matrix-Stokes vector theory, a theoretical model of the Mueller matrix measuring device is established. The whole optical path of the Mueller matrix measuring device can be described by the Mueller matrix as follows:

[0076] (0.1)

[0077] wherein, is the horizontal linear polarization of the light emitted by the polarizer 101, that is, the Stokes vector of the forward incident light to the sample 111 to be measured, is the bidirectional optical path Mueller matrix of the sample 111 to be measured measured by the Mueller matrix measuring device, delta is the phase retardation of the wave plate 102, theta is the azimuth angle of the wave plate 102, and t represents a time variable, represents the rotation matrix of the wave plate 102, is the polarization state of the light modulated by the wave plate 102 and the sample 111 to be measured, that is, the Stokes vector of the backward emitted light of the sample 111 to be measured.

[0078] The information obtained by the different polarization channels of the first polarization camera 107 and the second polarization camera 108 is the light intensity, which is the first element of the Stokes vector of the emitted light, so that the light intensity information obtained by a single polarization channel in a single measurement is:

[0079] (0.2)

[0080] wherein I represents the light intensity measured by a certain polarization channel, each element in the matrix corresponds to the measurement result of a polarization channel, represents the response coefficient of different polarization channels to each component of the Stokes vector, and each element in the matrix represents the response degree of the corresponding polarization channel to a specific component of the Stokes vector, is the Stokes vector of the emitted light, which represents the polarization state of the emitted light and is used to describe different polarization characteristics of the light.

[0081] In the embodiment of the application, four polarization channels (0°, 45°, 90°, 135°) of the second polarization camera 108 and two polarization channels (45°, 135°) of the first polarization camera 107 after the quarter-wave plate 106 are selected, and a total of six polarization channels are obtained. Therefore, the polarization analyzer matrix P composed of different polarization channels is:

[0082] (0.3)

[0083] Therefore, the measurement process each time can be described as:

[0084] (0.4)

[0085] wherein, is the light intensity vector output by the six polarization channels, and simplifying it can obtain:

[0086] (0.5)

[0087] wherein, is the polarization light intensity detected by the polarization channel i when the wave plate 102 rotates at an angle of θ, constitutes the Mueller matrix of the optical element to be measured. With the continuous rotation of the wave plate 102, the Stokes vector of the incident light constitutes the incident matrix of the system, and the Stokes vector of the outgoing light constitutes the outgoing matrix of the system. The wave plate 102 is rotated at least four times, and 16 equations are constructed to solve the 16 unknowns of the Mueller matrix.

[0088] According to the above, the outgoing light matrix in the reverse transmission process can be calculated as:

[0089] (0.6)

[0090] wherein, is the measured optical path Mueller matrix, represents the incident matrix generated by the rotation of the wave plate 102, represents the outgoing light matrix in the reverse transmission process.

[0091] The formula (0.6) is further adjusted as:

[0092] (0.7)

[0093] The above process is the basic principle of the traditional Mueller matrix polarimeter measurement. However, there is a bidirectional optical path in the Mueller matrix measurement device of the embodiment of the present application, and the light passes through the sample to be measured 111 twice, so the measured optical path Mueller matrix in the above formula (0.7) is actually a bidirectional Mueller matrix, that is, the matrix reflects not only the light emitted from the first light splitting assembly 103 to the sample to be measured 111, but also the light emitted from the sample to be measured 111. The bidirectional Mueller matrix cannot correctly represent the polarization properties of the sample to be measured 111, so it is necessary to calculate the single-directional Mueller matrix from the bidirectional Mueller matrix. Therefore, the Mueller matrix measurement device of the embodiment of the present application measures the measured bidirectional Mueller matrix and the mathematical relationship between the single-directional Mueller matrix is:

[0094] (0.8)

[0095] wherein, and is the single-directional optical path Mueller matrix, The Mueller matrix of the single light path from the first light splitting component 103 to the sample 111, The Mueller matrix of the single light path from the sample 111 to the first light splitting component 103, The Mueller matrix of the plane mirror, specifically,

[0096] (0.9)

[0097] According to the polar decomposition of the Mueller matrix, the Mueller matrix of the single light path through the sample 111 can be expressed as:

[0098] (0.10)

[0099] wherein, represents the phase delay of the matrix, and the corresponding Mueller matrix is:

[0100] (0.11)

[0101] represents the diattenuation of the matrix, and the corresponding Mueller matrix is:

[0102] (0.12)

[0103] wherein, , , are different phase delay components of the sample 111, , , are different diattenuation components of the sample 111.

[0104] When the light propagates reversely, the polarization characteristics of the sample 111 remain unchanged, only the coordinate system changes, so the polarization components are reversed. ∆ The depolarizer of the matrix is represented as:

[0105] (0.13)

[0106] wherein, , , are the polarization components of the depolarizer, representing the polarization performance of the depolarizer, a and b are linear depolarization parameters, c is a circular depolarization parameter.

[0107] The depolarization properties of the sample 111 in the forward and reverse directions are the same, and the depolarization parameters do not change. Due to the influence of the coordinate system transformation , The signs of the elements of the Mueller matrix are reversed. Therefore, the Mueller matrix of the back propagation is transformed as:

[0108] (0.14)

[0109] According to the equations (0.8) and (0.14), the vertical bidirectional Mueller matrix measured by the Mueller matrix measuring device can be expressed as:

[0110] (0.15)

[0111] Therefore, the calculation formula of the forward Mueller matrix obtained by the vertical bidirectional Mueller matrix is:

[0112] (0.16)

[0113] Based on the above Mueller matrix measuring device, the present application also proposes a corresponding Mueller matrix calibration method. Since the Mueller matrix measuring device of the embodiment 1 of the present application can be designed with or without the beam expander 104, there are two different calibration methods corresponding thereto, which are as follows:

[0114] Please refer to Figure 2 In an embodiment 2 of the present application, a Mueller matrix calibration method is provided, which is mainly for the measuring device designed without the beam expander 104 in the embodiment 1. When the Mueller matrix measuring device without the beam expander 104 is used to measure the sample 111, the real Mueller matrix of the sample 111 is calibrated by the following method:

[0115] S1: First, the Mueller matrix measuring device without the beam expander 104 is used to measure the sample 111, and the measured Mueller matrix is obtained. The measured Mueller matrix will be affected by the polarized light path error, the bidirectional light path error, and the polarized light path error, wherein the bidirectional light path error is mainly introduced by the first light splitting component 103. Therefore, according to the polarization optics theory, the measured Mueller matrix can be expressed as:

[0116] (0.17)

[0117] wherein is the Mueller matrix of the polarized light path, is the first light splitting component 103 Mueller matrix of the direction of the light beam emitted from the first light splitting component 103 to the sample 111, is the real Mueller matrix of the sample 111, The Mueller matrix of the first light splitting component 103 reflected by the first light splitting component 103 towards the direction of the detection polarized light path is The Mueller matrix of the detection polarized light path.

[0118] According to the above formula, the real Mueller matrix of the sample 111 to be measured can be further constructed as:

[0119] (0.18)

[0120] S2: In order to eliminate the influence of the polarized light path error, the bidirectional light path error, and the detection polarized light path error, a plane mirror 110 is arranged on the light path between the first light splitting component 103 and the sample 111 to be measured, and the Mueller matrix measurement device is used again to measure the Mueller matrix of the light path at this time The Mueller matrix of the light path at this time is which can be expressed as:

[0121] (0.19)

[0122] wherein, is the Mueller matrix of the plane mirror, and are equal.

[0123] S3: The Mueller matrix of the first light splitting component 103 and the Mueller matrix of the polarized light path are measured in advance by other existing methods The measurement process can be measured by traditional equipment or methods such as Mueller matrix ellipsometer. Then and are used to calibrate the real Mueller matrix of the sample 111 to be measured.

[0124] S4: According to the results of S2 and S3, the Mueller matrix error of the sample 111 to be measured reflected back to the light path during the process of the light beam of the sample 111 to be measured being emitted by the plane mirror 110 towards the detection polarized light path (or referred to as the Mueller matrix error of the light path on the back side of the sample 111 to be measured) is derived as:

[0125] (0.20)

[0126] S5: The back side light path error formula (0.20) obtained by S4 is brought into the real Mueller matrix formula (0.18) of the sample 111 to be measured in S1, so as to obtain the real Mueller matrix of the sample to be measured, and the calculation formula is:

[0127] (0.21)

[0128] In formula (0.21), all the matrices have been calibrated, and thus the real measured matrix and the real Mueller matrix of the sample 111 is calculated according to the calibration result .

[0129] Please refer to Figure 3 In an embodiment 3 of the present application, another Mueller matrix calibration method is provided, which is mainly aimed at the measuring device designed in embodiment 1 with the beam expander 104. When the Mueller matrix measuring device with the beam expander 104 is used to measure the Mueller matrix of the sample 111, the real Mueller matrix of the sample 111 is calibrated by the following method:

[0130] a: Similarly, first, the Mueller matrix measuring device with the beam expander 104 is used to measure the sample 111, and the measured Mueller matrix is obtained. At this time, the measured Mueller matrix is different from the data measured in embodiment 2 in numerical value, and both represent the measured Mueller matrix under different conditions. The measured Mueller matrix will be affected by the errors of the polarizing light path, the bidirectional light path, and the analyzing light path, wherein the bidirectional light path error includes not only the part introduced by the first light splitting component 103, but also the error introduced by the beam expander 104. Therefore, according to the theory of polarization optics, the measured Mueller matrix can be expressed as:

[0131] (0.22)

[0132] wherein, is the Mueller matrix of the polarizing light path, is the first light splitting component Mueller matrix of the direction in which the light beam is emitted by the first light splitting component 103 to the sample 111, is the beam expander 104 Mueller matrix of the direction in which the light beam is emitted by the beam expander 104 to the sample 111, i.e. the forward Mueller matrix of the beam expander 104, is the real Mueller matrix of the sample 111, is the first light splitting component 103 reflection Mueller matrix of the direction in which the light beam is emitted by the first light splitting component 103 to the analyzing light path, is the Mueller matrix of the analyzing light path, is the beam expander 104 Mueller matrix of the direction in which the light beam is emitted by the beam expander 104 to the first light splitting component 103, i.e. the reverse Mueller matrix of the beam expander 104.

[0133] b: According to formula (0.22), the bidirectional Mueller matrix of the whole beam expander 104 and sample 111 (i.e. the Mueller matrix of the light path in which the light beam is emitted by the beam expander 104 to the sample 111, reflected by the sample 111, and then emitted again through the beam expander 104) is:

[0134] (0.23)

[0135] c: In order to eliminate the influence of the polarized light path error, the first light splitting component 103, and the polarized light path error, a plane mirror 110 is arranged on the light path between the first light splitting component 103 and the sample 111 to be measured, and the Mueller matrix of the light path is measured again by using the Mueller matrix measuring device to obtain the Mueller matrix at this time , is:

[0136] (0.24)

[0137] d: The Mueller matrix of the first light splitting component 103 and the Mueller matrix of the polarized light path are measured in advance by using other existing methods .The measurement process can be measured by traditional equipment or methods such as Mueller matrix ellipsometer. Then the real Mueller matrix of the sample 111 to be measured is calibrated by using and .

[0138] e: According to the results of steps b and c, it is deduced that the Mueller matrix error of the sample 111 to be measured in the process of the light beam of the sample 111 to be measured being reflected back by the plane mirror 110 and being shot to the polarized light path is:

[0139] (0.25)

[0140] f: The light path error formula (0.25) obtained in step e is brought into the real Mueller matrix formula (0.22) of the sample 111 to be measured in step a, and the real measured Mueller matrix and the error are used to express the Mueller matrix of the whole of the beam expander 104 and the sample 111 to be measured as:

[0141] (0.26)

[0142] g: In order to separately calibrate the Mueller matrix of the beam expander 104, the error introduced by the beam expander 104 is eliminated, as shown in Figure 3 , and the plane mirror 110 also needs to be moved to the light path between the beam expander 104 and the sample 111 to be measured to realize the separation of the beam expander 104 and the sample 111 to be measured. At this time, the Mueller matrix of the light path is measured again by using the Mueller matrix measuring device to obtain the Mueller matrix of the light path at this time is:

[0143] (0.27)

[0144] h: The same as the processing principle of steps a to e, the Mueller matrix of the light path is measured by using The Mueller matrix of the beam expander 104 is calibrated, and the bidirectional Mueller matrix of the beam expander 104 is obtained as follows:

[0145] (0.28)

[0146] According to the calculation formula (0.16) of the Mueller matrix measurement device provided in the foregoing for calculating the unidirectional optical path Mueller matrix from the bidirectional optical path Mueller matrix, the forward transmission Mueller matrix and the reverse transmission Mueller matrix of the beam expander 104 are calculated from the bidirectional Mueller matrix of the beam expander 104, and the separate calibration of the beam expander 104 is completed.

[0147] The forward transmission Mueller matrix and the reverse transmission Mueller matrix of the beam expander 104 are brought into the bidirectional Mueller matrix formula (0.26) of the beam expander 104 and the sample 111 to be measured in step f, and the real Mueller matrix of the sample 111 to be measured is obtained as follows:

[0148] (0.29)

[0149] In formula (0.29), all the matrices have been calibrated, and thus the real Mueller matrix of the sample 111 to be measured can be calculated from the measured matrix and the calibration result.

[0150] In summary, the above only describes preferred embodiments of the present specification, and is not used to limit the protection scope of the present specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present specification shall be included in the protection scope of the present specification.

[0151] The system, device, module or unit illustrated in one or more of the above embodiments can be specifically implemented by a computer chip or entity, or by a product with certain functions. A typical implementation device is a computer. Specifically, the computer may, for example, be a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0152] It is also to be noted that the terms "comprising", "including", and any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises a... " does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the recited element.

[0153] Each of the embodiments in the present specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other. Each of the embodiments focuses on the difference from other embodiments. In particular, for the system embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts can be referred to the part of the method embodiments.

[0154] The above describes specific embodiments of the present specification. Other embodiments are within the scope of the appended claims. In some cases, the acts or steps recited in the claims can be performed in a different order than the order in which the acts or steps are recited in the embodiments and still achieve desirable results. In addition, the processes depicted in the figures do not necessarily require the particular order shown, or sequential order, to achieve the desired results. In certain implementations, multitasking and parallel processing can be advantageous.

Claims

1. A method for scaling the Mueller matrix, characterized in that, include: S1: Obtain the measured Mueller matrix by measuring the sample under test using a Mueller matrix measuring device. The true Mueller matrix of the sample to be tested is constructed as follows: ； in, The Mueller matrix for the polarization path, The Mueller matrix of the first beam splitter is located in the direction from the first beam splitter to the sample under test. The true Mueller matrix of the sample to be tested. The first beam splitter's reflection Mueller matrix is ​​the beam that travels from the first beam splitter towards the polarization analyzer path. The Mueller matrix for the polarization path; The Mueller matrix measurement device includes a light source, a polarizing optical path, and a polarizing optical path, and also includes a bidirectional optical path disposed in the emission direction of the polarizing optical path; the bidirectional optical path includes a first beam splitting component for splitting the polarization-modulated light emitted from the polarizing optical path; The light beam transmitted by the first beam splitter is incident on the sample under test, which is an optical system or a single optical element. An anti-reflective coating is deposited on the rear surface of the last element of the optical system or on the rear surface of the single optical element. The transmitted light beam is reflected by the sample under test back to the first beam splitter, and then reflected again by the first beam splitter into the polarization analyzer path; or, the light beam reflected by the first beam splitter is incident on the sample under test, the reflected light beam is reflected back to the first beam splitter, and then transmitted again by the first beam splitter into the polarization analyzer path; the formula for calculating the unidirectional beam Mueller matrix from the bidirectional beam Mueller matrix is: ； in, The bidirectional optical path Mueller matrix measured by the Mueller matrix measuring device. For unidirectional optical path Mueller matrix, The Mueller matrix of a plane mirror. ; S2: A plane mirror is placed between the first spectroscopic component and the sample to be tested, and the Mueller matrix is ​​measured again using the Mueller matrix measurement device. , for: ； in, The Mueller matrix for a plane mirror; S3: The Mueller matrix of the first spectrometer was measured separately. Muller matrix for polarization path ,use and The true Mueller matrix of the sample to be tested is calibrated. S4: According to and The error of the Mueller matrix during the process of the light beam being directed from the plane mirror to the polarizer path is: ； S5: Using the measured Mueller matrix and error The true Mueller matrix of the sample to be tested is calculated as follows: 。 2. The Mueller matrix calibration method according to claim 1, characterized in that, The light beam enters the optical system in the forward direction and exits from the optical system in the reverse direction; or the light beam enters the individual optical element in the forward direction from the front surface of the individual optical element and exits from the rear surface of the individual optical element in the reverse direction.

3. The Mueller matrix calibration method according to claim 1, characterized in that, The polarizing path includes a polarizer and a rotatable waveplate arranged along the beam transmission direction. The polarizer is used to process the beam provided by the light source into a beam with a specific polarization state, and the waveplate can adjust the beam with the specific polarization state into beams with different polarization states by rotation.

4. The Mueller matrix calibration method according to claim 1, characterized in that, The polarization detection path includes a second beam splitter, a first polarization camera, a second polarization camera, and a quarter-wave plate disposed between the second beam splitter and the first polarization camera.

5. The Mueller matrix calibration method according to claim 1, characterized in that, The beam propagating in the bidirectional optical path is incident perpendicularly on the sample to be tested.

6. A method for scaling the Mueller matrix, characterized in that, include: a: Obtain the measured Mueller matrix by measuring the sample under test using the Mueller matrix measuring device as described in any one of claims 1 to 5, which also includes a beam expander disposed between the first beam splitter and the sample under test. Construct the measured Mueller matrix The expression is: ； in, The Mueller matrix for the polarization path, The Mueller matrix of the first beam splitter is located in the direction from the first beam splitter to the sample under test. The Mueller matrix of the beam expander is the direction in which the beam is directed from the beam expander towards the sample under test, i.e., the forward Mueller matrix of the beam expander. The true Mueller matrix of the sample to be tested. The Mueller matrix representing the reflection of the beam from the first beam splitter in the direction of the polarization analyzer path. To determine the Mueller matrix of the polarization path, The Mueller matrix of the beam expander is the direction in which the beam is directed from the beam expander to the first beam splitter, i.e., the reverse Mueller matrix of the beam expander; The beam expander is used to increase the diameter of the beam directed toward the sample under test; b: The bidirectional Mueller matrix of the beam expander and the sample under test is established as follows: ； c: A plane mirror is placed between the first beam splitter and the beam expander, and the Mueller matrix is ​​measured again using the Mueller matrix measurement device. , for: ； in, The Mueller matrix for a plane mirror; d: The Mueller matrix of the first spectrometer was measured separately. Muller matrix for polarization path ,use and The true Mueller matrix of the sample to be tested is calibrated. e: According to and The error of the Mueller matrix during the process of the light beam being directed from the plane mirror to the polarizer path is: ； f: Using the measured Mueller matrix and error The Mueller matrix of the beam expander and the sample under test as a whole is expressed as: ； g: Move the plane mirror between the beam expander and the sample to be tested, and measure the Mueller matrix again using the Mueller matrix measurement device. , for: ； h: The bidirectional Mueller matrix of the beam expander is established as follows: ； The forward Mueller matrix of the beam expander is obtained by calculating the bidirectional Mueller matrix of the beam expander. and the inverse Mueller matrix ; j: The positive Mueller matrix of the beam expander and the inverse Mueller matrix The two-way Mueller matrix of the beam expander and the sample under test is used to obtain the true Mueller matrix of the sample under test: 。

Images