A method and system for detecting polarization characteristics of a target in a terahertz wave band

Abstract

The application discloses a terahertz wave band target polarization characteristic detection method and system, and belongs to the technical field of terahertz polarization imaging and target detection. The method comprises the following steps: constructing a terahertz wave polarization function model based on a Jones matrix and target characteristics of terahertz waves; determining a terahertz wave band target polarization result; and determining terahertz wave band target polarization characteristics by using the terahertz wave polarization function model and the target polarization result. The application can identify the polarization characteristics of a target under the condition that the polarization characteristics of the target are unknown.

Description

Technical Field

[0001] This invention relates to the field of terahertz polarization imaging and target detection technology, and more specifically to a method and system for detecting the polarization characteristics of targets in the terahertz band. Background Technology

[0002] Polarization is one of the three major characteristics of light. The transmitted light after polarized light interacts with a target contains polarization information determined by the target's own characteristics. This polarization information differs from the spectrum, intensity, and phase information we usually detect. Different objects or different states of the same object may produce different polarization states. By using this polarization information, we can accurately and clearly obtain relevant information about the detected target.

[0003] Currently, terahertz band target polarization identification technology is receiving increasing attention and has wide applications in multiple fields.

[0004] However, the common method for describing fully polarized light is the polarization elliptic table method (elliptically polarized light, linearly polarized light, and circularly polarized light), while the polarization characteristics of targets in the terahertz band are mostly expressed as partially polarized light, which cannot be expressed by the above three mathematical forms.

[0005] Furthermore, most polarization models are currently based on the infrared band, while there are very few theoretical models for terahertz polarization, resulting in a lack of characterization methods for the polarization characteristics of targets in the terahertz band. Summary of the Invention

[0006] In view of this, in order to at least partially solve the above-mentioned technical problems, the present invention provides a method and system for detecting the polarization characteristics of a target in the terahertz band. Based mainly on the target characteristics of terahertz waves and the Jones matrix, a terahertz polarization function model of the target is constructed, thereby realizing the detection, identification and characterization of the polarization characteristics of the target.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] First, a method for detecting the polarization characteristics of a target in the terahertz band, comprising:

[0009] A terahertz wave polarization function model is constructed based on the Jones matrix and the target characteristics of terahertz waves.

[0010] Determine the polarization characteristics of the target in the terahertz band;

[0011] The polarization characteristics of the target in the terahertz band are characterized using the terahertz wave polarization function model and the target polarization characteristic results.

[0012] Optionally, the steps for constructing a terahertz wave polarization function model include:

[0013] Based on the target characteristics of terahertz waves, a terahertz wave function is constructed;

[0014] Jones matrix representation for determining arbitrary polarization characteristics;

[0015] A terahertz wave polarization function model is constructed based on the Jones matrix representation of the terahertz wave function and the polarization characteristics.

[0016] Optionally, the expression for the terahertz wave polarization function model is:

[0017]

[0018] In the formula, U obj This represents the target polarization result in the terahertz band; θ represents E. J The angle between (δ,θ) and the X-axis, E J (δ,θ) is the Jones matrix of the polarization result, exp[i(kz-ωt)] is the propagation characteristic of the terahertz band target along the Z-axis, k is the wave propagation constant, ω is the time angular frequency, t is time, and δ is the phase difference.

[0019] Optionally, the terahertz band target polarization result can be determined according to the following steps:

[0020] S1. Place the target in front of the polarizer, rotate the polarizer, and determine whether there is an extinction position; if there is, it is a linear polarization state; if not, proceed to step S2.

[0021] S2. Place the polarizer at the position with the maximum transmitted light intensity, and place a quarter-wave plate in front of the polarizer so that the optical axis is parallel to the direction of the maximum transmitted light intensity of the polarizer. Rotate the polarizer. Determine whether there is an extinction position. If there is, it is an elliptically polarized state. If not, proceed to step S3.

[0022] S3. Determine whether the polarizer is in its original position when the light intensity is at its maximum; if so, it is in a partially linearly polarized state, otherwise it is in a partially elliptical polarized state.

[0023] Second, a terahertz band target polarization characteristic detection system, comprising,

[0024] The target polarization result identification module is used to identify and determine the target polarization result in the terahertz band.

[0025] The target polarization characteristic determination module stores a terahertz wave polarization function model, which is used to determine the target polarization characteristics in the terahertz band based on the terahertz wave polarization function model and the target polarization result.

[0026] Optionally, the target polarization result recognition module recognizes the target polarization result according to the following steps:

[0027] S1. Place the target in front of the polarizer, rotate the polarizer, and determine whether there is an extinction position; if there is, it is a linear polarization state; if not, proceed to step S2.

[0028] S2. Place the polarizer at the position with the maximum transmitted light intensity, and place a quarter-wave plate in front of the polarizer so that the optical axis is parallel to the direction of the maximum transmitted light intensity of the polarizer. Rotate the polarizer. Determine whether there is an extinction position. If there is, it is an elliptically polarized state. If not, proceed to step S3.

[0029] S3. Determine whether the polarizer is in its original position when the light intensity is at its maximum; if so, it is in a partially linearly polarized state, otherwise it is in a partially elliptical polarized state.

[0030] Optionally, the expression for the terahertz wave polarization function model is:

[0031]

[0032] In the formula, U obj This represents the target polarization result in the terahertz band; θ represents E. J The angle between (δ,θ) and the X-axis, E J (δ,θ) is the Jones matrix of the polarization result, exp[i(kz-ωt)] is the propagation characteristic of the terahertz band target along the Z-axis, k is the wave propagation constant, ω is the time angular frequency, t is time, and δ is the phase difference.

[0033] As can be seen from the above technical solution, the present invention discloses a method and system for detecting the polarization characteristics of targets in the terahertz band, which has the following technical advantages compared with the prior art:

[0034] The terahertz wave polarization function model in this invention has polarization characteristics that propagate in any direction, which can effectively characterize the polarization characteristics of targets in the terahertz band. At the same time, this invention provides a method for identifying the polarization results of targets in the terahertz band, which can accurately describe the polarization results of targets in the terahertz band.

[0035] The detection method provided by this invention can accurately identify and determine the polarization characteristics of a target when the polarization characteristics of the target in the terahertz band are unknown.

[0036] Furthermore, this invention has broad applicability; that is, based on the mathematical expression of terahertz waves and the Jones matrix, the polarization characteristics of targets can be characterized and targets can be identified in existing terahertz target identification and detection systems. This is of great significance in the exploration of the terahertz band. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0038] Figure 1 This is a flowchart of the terahertz band target polarization characteristic detection method of the present invention;

[0039] Figure 2 Flowchart for determining the target polarization result in the terahertz band of this invention;

[0040] Figure 3-4 This is a schematic diagram showing the positions of the target, polarizer, and quarter-wave plate during the process of determining the target polarization result in the terahertz band of this invention.

[0041] Figure 5 This is a block diagram of the terahertz band target polarization characteristic detection system of the present invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Polarization imaging technology extends the detection of light radiation from intensity and spectrum to the polarization vector domain. The polarization state of a target's reflection and radiation is closely related to its surface state and inherent physicochemical properties; different types of targets possess different polarization characteristics. Terahertz polarization target identification utilizes polarization information in the terahertz band to identify target objects or samples. Research in this field involves analyzing the target's response to terahertz polarized waves to determine the target's properties, shape, and composition. Therefore, terahertz polarization imaging detection is currently one of the important methods for target detection and identification.

[0044] To overcome the current bottlenecks in the field of target polarization characteristic detection, this invention discloses a method and system for detecting the polarization characteristics of targets in the terahertz band, such as... Figure 1 As shown, the specific steps include the following:

[0045] A terahertz wave polarization function model is constructed based on the Jones matrix and the target characteristics of terahertz waves.

[0046] Determine the target polarization results in the terahertz band;

[0047] Using the terahertz wave polarization function model and the target polarization results, the target polarization characteristics in the terahertz band are determined.

[0048] In this invention, the establishment of a terahertz target polarization physical model is an important method for achieving target detection and identification, which can realize a mathematical description of the polarization characteristics of targets in the terahertz band.

[0049] In the scheme of this invention, the target polarization result in the terahertz band is first determined, such as... Figure 2 As shown, the steps to determine this are as follows:

[0050] S1. Place the target in front of the polarizer, rotate the polarizer, and determine whether there is an extinction position; if there is, it is a linear polarization state; if not, proceed to step S2.

[0051] S2. Place the polarizer at the position with the maximum transmitted light intensity, and place a quarter-wave plate in front of the polarizer so that the optical axis is parallel to the direction of the maximum transmitted light intensity of the polarizer. Rotate the polarizer. Determine whether there is an extinction position. If there is, it is an elliptically polarized state. If not, proceed to step S3.

[0052] S3. Determine whether the polarizer is in its original position when the light intensity is at its maximum; if so, it is in a partially linearly polarized state, otherwise it is in a partially elliptical polarized state.

[0053] In this embodiment, the target is placed in front of the polarizer, the polarizer is rotated, and observation is performed. Figure 3 As shown, if there is an extinction position, the terahertz polarization characteristic of the target is a linear polarization state δ = mπ (m = 0, ±1, ±2, ...); if there is no extinction position, place the polarizer at the position of maximum transmitted light intensity, place a quarter-wave plate in front of the polarizer so that its optical axis is parallel to the direction of maximum transmitted light intensity of the polarizer, and rotate the polarizer as follows. Figure 4 As shown, if there is an extinction position, the terahertz polarization characteristic of the target is elliptic polarization (2m-1)π < δ < 2mπ or 2mπ < δ < (2m+1)π, (m = 0, ±1, ±2, ...). When the amplitude ratio is 1, the terahertz polarization characteristic of the target is circular polarization. (Special case of elliptically polarized state); if there is no extinction position, and the polarizer is in its original position when the light intensity is at its maximum, then the terahertz polarization characteristic of the target is a partially linearly polarized state; conversely, the terahertz polarization characteristic of the target is a partially elliptically polarized state.

[0054] Furthermore, the steps for constructing a terahertz wave polarization function model include:

[0055] Based on the target characteristics of terahertz waves, a terahertz wave function model for the target propagating in any direction is constructed; the model expression is:

[0056]

[0057] The Jones matrix that determines arbitrary polarization characteristics is represented as:

[0058]

[0059] Based on the Jones matrix representation of the terahertz wave function and the polarization characteristics, a terahertz wave polarization function model is constructed; this model has polarization characteristics that propagate in any direction, and its expression is:

[0060]

[0061] The derivation process is as follows:

[0062]

[0063] In the formula, U obj The target polarization result is in the terahertz band; E J (δ,θ) is the Jones matrix of the polarization result, exp[i(kz-ωt)] is the propagation characteristic of the terahertz band target along the Z-axis, k is the wave propagation constant, ω is the time angular frequency, t is time, and θ is E J The angle between (δ,θ) and the X-axis, E x0 =E0cosθ, E y0 =E0sinθ represents the amplitude of the vibration in the x and y directions, respectively. E represents the initial phase in the x and y directions. x0 E y0 , All are real numbers. This is the normalized Jones vector. To introduce the amplitude ratio of y-vibration and x-vibration, To introduce the phase difference between the y-vibration and the x-vibration.

[0064] Finally, the polarization characteristics of the target in the terahertz band are determined using the terahertz wave polarization function model and the target polarization results.

[0065] In one embodiment, by combining the detection results and using the Jones matrix and the terahertz target polarization model, the polarization characteristics of the terahertz target are obtained. Specific steps include:

[0066] Given the known polarization result, represent the polarization result using a Jones matrix;

[0067] Substitute the Jones matrix into the terahertz wave polarization function model;

[0068] The phase difference δ and target E in the polarization function model of the target terahertz wave are derived. J The angle θ between (δ,θ) and the X-axis;

[0069] Determine the polarization characteristics of the target in the terahertz band.

[0070] In one embodiment, the Jones matrix of the linearly polarized state is: The Jones matrix of the circularly polarized state is The Jones matrix of the elliptic polarization state is

[0071] Taking linear polarization as an example, its Jones matrix is: Substituting into the polarization function model of the target terahertz wave, we get:

[0072]

[0073]

[0074] Solving this equation yields the target's polarization characteristic parameters δ = 0 and θ = ±45°; based on this, the polarization characteristics of the target in the terahertz band are characterized.

[0075] Similarly, when the polarization characteristic category is circular polarization, the obtained parameter results are: γ = 1 (i.e., E) x0 =E y0 ), θ=45°; when the polarization characteristic category is elliptically polarized, the obtained parameter results are γ≠1 (i.e., E) x0 ≠E y0 ),

[0076] This invention can obtain the polarization characteristics of a target without going through a target polarization characteristic identification system.

[0077] Example 2

[0078] This invention provides a terahertz band target polarization characteristic detection system, such as... Figure 5 ,include,

[0079] The target polarization result identification module is used to identify and determine the target polarization result in the terahertz band.

[0080] The target polarization characteristic determination module stores a terahertz wave polarization function model, which is used to determine the target polarization characteristics in the terahertz band based on the terahertz wave polarization function model and the target polarization result.

[0081] The target polarization result recognition module identifies the target polarization result according to the following steps:

[0082] S1. Place the target in front of the polarizer, rotate the polarizer, and determine whether there is an extinction position; if there is, it is a linear polarization state; if not, proceed to step S2.

[0083] S2. Place the polarizer at the position with the maximum transmitted light intensity, and place a quarter-wave plate in front of the polarizer so that the optical axis is parallel to the direction of the maximum transmitted light intensity of the polarizer. Rotate the polarizer. Determine whether there is an extinction position. If there is, it is an elliptically polarized state. If not, proceed to step S3.

[0084] S3. Determine whether the polarizer is in its original position when the light intensity is at its maximum; if so, it is in a partially linearly polarized state, otherwise it is in a partially elliptical polarized state.

[0085] Furthermore, the expression for the terahertz wave polarization function model is:

[0086]

[0087] In the formula, E J (δ,θ) represents the target polarization result in the terahertz band; θ is the E J The angle between (δ,θ) and the X-axis, E J (δ,θ) is the Jones matrix of the polarization result, exp[i(kz-ωt)] is the propagation characteristic of the terahertz band target along the Z-axis, k is the wave propagation constant, ω is the time angular frequency, t is time, and δ is the phase difference.

[0088] This invention has unprecedented application effects and has wide applications in multiple fields, including terahertz imaging, security detection, biomedicine, materials science, communication technology, food safety, and nanotechnology. It also has advantages such as non-invasiveness, high resolution, safety, ability to provide spectral information, multimodal analysis, material identification, non-destructive testing, and precise polarization control.

[0089] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0090] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting the polarization characteristics of a target in the terahertz band, characterized in that, include: A terahertz wave polarization function model is constructed based on the Jones matrix and the target characteristics of terahertz waves; the expression of the terahertz wave polarization function model is as follows: In the formula, The target polarization result in the terahertz band; for The angle with the X-axis, The Jones matrix representing the polarization result. The propagation characteristics of a terahertz band target along the Z-axis. Let be the wave propagation constant. The frequency is the time angular frequency, and t is time. Phase difference; Determine the target polarization results in the terahertz band; Using the terahertz wave polarization function model and the target polarization results, the target polarization characteristics in the terahertz band are determined.

2. The method for detecting the polarization characteristics of a target in the terahertz band according to claim 1, characterized in that, The steps for constructing a terahertz wave polarization function model include: Based on the target characteristics of terahertz waves, a terahertz wave function is constructed; Jones matrix representation for determining arbitrary polarization characteristics; A terahertz wave polarization function model is constructed based on the Jones matrix representation of the terahertz wave function and the polarization characteristics.

3. The method for detecting the polarization characteristics of a target in the terahertz band according to claim 1, characterized in that, The target polarization result in the terahertz band is determined according to the following steps: S1. Place the target in front of the polarizer, rotate the polarizer, and determine whether there is an extinction position; if there is, it is a linear polarization state; if not, proceed to step S2. S2. Place the polarizer at the position with the maximum transmitted light intensity, and place a quarter-wave plate in front of the polarizer so that the optical axis is parallel to the direction of the maximum transmitted light intensity of the polarizer. Rotate the polarizer. Determine whether there is an extinction position. If there is, it is an elliptically polarized state. If not, proceed to step S3. S3. Determine whether the polarizer is in its original position when the light intensity is at its maximum; if so, it is in a partially linearly polarized state, otherwise it is in a partially elliptical polarized state.

4. A terahertz band target polarization characteristic detection system, characterized in that, include, The target polarization result identification module is used to identify and determine the target polarization result in the terahertz band. The target polarization characteristic determination module stores a terahertz wave polarization function model, which is used to determine the target polarization characteristics in the terahertz band based on the terahertz wave polarization function model and the target polarization result; the expression of the terahertz wave polarization function model is: In the formula, The target polarization result in the terahertz band; for The angle with the X-axis, The Jones matrix representing the polarization result. The propagation characteristics of a terahertz band target along the Z-axis. Let be the wave propagation constant. The frequency is the time angular frequency, and t is time. This represents the phase difference.

5. A terahertz band target polarization characteristic detection system according to claim 4, characterized in that, The target polarization result recognition module recognizes the target polarization result according to the following steps: S1. Place the target in front of the polarizer, rotate the polarizer, and determine whether there is an extinction position; if there is, it is a linear polarization state; if not, proceed to step S2. S2. Place the polarizer at the position with the maximum transmitted light intensity, and place a quarter-wave plate in front of the polarizer so that the optical axis is parallel to the direction of the maximum transmitted light intensity of the polarizer. Rotate the polarizer. Determine whether there is an extinction position. If there is, it is an elliptically polarized state. If not, proceed to step S3. S3. Determine whether the polarizer is in its original position when the light intensity is at its maximum; if so, it is in a partially linearly polarized state, otherwise it is in a partially elliptical polarized state.

Images