A stokes parameter correction method suitable for high-energy laser polarization detection

Abstract

The present application relates to a Stokes parameter correction method, in particular to a Stokes parameter correction method suitable for high-energy laser polarization detection, which is used to solve the problem that the polarization state of incident laser is changed when the energy of laser is attenuated by using a light splitting optical system, thereby causing the polarization parameter measurement error. The Stokes parameter correction method suitable for high-energy laser polarization detection calibrates the polarization transmittance of the light splitting optical system, extracts the Stokes parameter of the laser by combining Fourier analysis, and then corrects the Stokes parameter by using the polarization transmittance, thereby further eliminating the polarization error introduced by the light splitting optical system, so that the corrected polarization parameter is closer to the real state of the laser.

Description

TECHNICAL FIELD

[0001] The application relates to a Stokes parameter correction method, in particular to a Stokes parameter correction method suitable for high-energy laser polarization detection. BACKGROUND

[0002] High-energy laser technology has been widely used in the fields of nuclear physics, laser processing, etc. Especially in the fields of scientific research and advanced manufacturing, the accurate detection of high-energy laser is of great significance to the reliability of research and the quality of manufacturing. Polarization in laser parameters is a key detection parameter, which describes the oscillation path of the electric (magnetic) field vector of light and can reveal many characteristics that cannot be directly observed in the process of light and matter interaction. For example, the change of polarization state may indicate the absorption, reflection or scattering characteristics of the material to the laser.

[0003] In the detection of high-energy laser parameters, due to the limitation of the measurement range of the detector, it is necessary to use a light splitting optical system to attenuate the laser energy. The schematic diagram of the existing high-energy laser polarization detection system is shown in Figure 1 , the laser is emitted from a high-energy laser light source 01, attenuated by a light splitting optical system 02, and finally detected by a polarimeter 03; the light splitting optical system 02 includes a plurality of light splitters 021 for splitting and attenuating the laser beam; the polarimeter 03 includes a quarter-wave plate, a polarizer and a detector. However, the light splitting optical system 02 will change the polarization state of the original incident high-energy laser while attenuating the energy, which may cause polarization parameter measurement error. Especially in experiments or industrial applications involving high-precision requirements, such error will directly affect the accurate evaluation of the interaction between laser and material. SUMMARY

[0004] The purpose of the present application is to solve the problem that the use of a light splitting optical system to attenuate the laser energy will change the polarization state of the incident laser, thereby causing polarization parameter measurement error, and to provide a Stokes parameter correction method suitable for high-energy laser polarization detection.

[0005] In order to solve the above-mentioned problems existing in the prior art, the present application provides the following technical solutions:

[0006] A Stokes parameter correction method suitable for high-energy laser polarization detection, characterized in that it comprises the following steps:

[0007] Step 1: outputting laser from a laser calibration light source, inputting the laser into a light splitting optical system after the laser is polarized by a polarizer, measuring the power of the laser before and after passing through the light splitting optical system by a power meter, and calculating the P-polarized light transmittance k p , the S-polarized light transmittance k s and the non-polarized light transmittance k u, and further obtaining normalized P-polarized light transmittance k pn , normalized S-polarized light transmittance k sn , and normalized non-polarized light transmittance k un .

[0008] Step 2, the laser passes through the optical system and is input into the polarimeter, the polarization state of the laser is continuously changed by rotating the quarter-wave plate in the polarimeter, the detector receives a periodically changing optical power signal, and the optical power signal P(θ) is expressed as Stokes parameters (S0, S1, S2, S3); θ is the included angle between the fast axis of the quarter-wave plate and the horizontal component of the polarized light; S0 represents the total light intensity, S1 represents the difference between the horizontal and vertical polarized light intensities, S2 represents the difference between the +45° and -45° polarized light intensities, and S3 represents the difference between the left circularly polarized and right circularly polarized light intensities;

[0009] Step 3, periodically sampling θ to obtain the optical power signal of N sampling points; the optical power signal P(θ n ) of the nth sampling point is calculated by Fourier analysis to obtain the Stokes parameters (S0, S1, S2, S3) of the laser after passing through the optical system;

[0010] N is an even number and N≥16, the sampling interval is 360° / N; n=1, 2,..., N;

[0011] Step 4, combining the normalized P-polarized light transmittance k pn , the normalized S-polarized light transmittance k sn , and the normalized non-polarized light transmittance k un obtained in step 1, the Stokes parameters (S0, S1, S2, S3) obtained in step 6 are corrected to obtain corrected Stokes parameters (S 0c , S 1c , S 2c , S 3c ), and the correction of the Stokes parameters is completed.

[0012] Further, the step 2 is specifically:

[0013] The laser passes through the optical system and is input into the polarimeter, the light transmission axis of the polarimeter is adjusted to be parallel to the horizontal component of the polarized light, the polarization state of the laser is continuously changed by rotating the quarter-wave plate, the detector receives a periodically changing optical power signal, and the optical power signal P(θ) is expressed as Stokes parameters (S0, S1, S2, S3):

[0014]

[0015] In the formula, B=S3,

[0016] Further, the step 3 is specifically as follows:

[0017] Step 3.1, periodically sampling θ to obtain optical power signals of N sampling points; wherein the optical power signal P(θ n ) of the nth sampling point is:

[0018]

[0019] Step 3.2, calculating the optical power signal P(θ n ) by Fourier analysis method to obtain the expression of parameters A, B, C, D:

[0020]

[0021]

[0022] Step 3.3, calculating the Stokes parameters (S0, S1, S2, S3) of the laser after passing through the optical splitting system:

[0023] S0=A-C, S1=2C, S2=2D, S3=B.

[0024] Further, the step 4 is specifically as follows:

[0025] Step 4.1, calculating the polarized light intensity S p and the degree of polarization P of the laser after passing through the optical splitting system according to the Stokes parameters (S0, S1, S2, S3) obtained in step 3:

[0026]

[0027] Step 4.2, calculating the horizontal component direction electric field amplitude E x and the vertical component direction electric field amplitude E y of the polarized light according to the degree of polarization P and the parameter S1:

[0028]

[0029] Step 4.3, combining the normalized P-polarized light transmittance k pn , the normalized S-polarized light transmittance k sn , and the normalized non-polarized light transmittance k un obtained in step 1 to correct the Stokes parameters (S0, S1, S2, S3) obtained in step 3 to obtain the corrected Stokes parameters (S 0c , S 1c , S 2c , S 3c ):

[0030]

[0031] Complete the Stokes parameter calibration.

[0032] Furthermore, step 1 is specifically as follows:

[0033] Step 1.1: The laser is output from the laser calibration source. The laser is polarized by a polarizer to output P-polarized light to the beam splitting optical system. The power of the laser before and after passing through the beam splitting optical system is measured by a power meter, and the transmittance k of the P-polarized light is calculated. p ;

[0034] Step 1.2: Adjust the transmission axis direction of the polarizer so that the laser is polarized and output as S-polarized light to the beam splitter. Measure the power of the laser before and after passing through the beam splitter using a power meter, and calculate the S-polarized light transmittance k. s ;

[0035] Step 1.3: Based on the transmittance k of P-polarized light p S-polarized light transmittance k s Calculate the transmittance k of unpolarized light. u ;

[0036] Step 1.4: Calculate the normalized p-polarized light transmittance k. pn Normalized S-polarized light transmittance k sn Normalized unpolarized light transmittance k un .

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] (1) The present invention provides a Stokes parameter correction method for high-energy laser polarization detection. By calibrating the polarization transmittance (including P-polarization, S-polarization and unpolarized light transmittance) of the beam splitting optical system and combining it with Fourier analysis to extract the Stokes parameter of the laser, the polarization transmittance is then used to correct the Stokes parameter, thereby further eliminating the polarization error introduced by the beam splitting optical system and making the corrected polarization parameter closer to the true state of the laser.

[0039] (2) By calculating and applying normalized transmittance, this invention can effectively compensate for measurement errors caused by the spectroscopic optical system and ensure that deviations during the correction process are minimized.

[0040] (3) In the Stokes parameter correction process, this invention can accurately correct the transmission of different polarization components by combining the normalized transmittance of P-polarized light, S-polarized light and unpolarized light, and can ensure that the corrected Stokes parameter truly reflects the original polarization state of the laser, thereby providing high-precision polarization data support for subsequent applications (such as laser processing and optical experiments). Attached Figure Description

[0041] Figure 1 This is a schematic diagram of an existing high-energy laser polarization detection system;

[0042] Figure 1 The following are the annotations in the attached figures: 01-High-energy laser source; 02-Spectroscopic optical system; 021-Spectroscope; 03-Polarizer.

[0043] Figure 2 This is a schematic diagram illustrating step 1 of an embodiment of a Stokes parametric correction method for high-energy laser polarization detection according to the present invention, in which the power of the laser before and after passing through the beam splitting optical system is measured by a first power meter and a second power meter.

[0044] Figure 3 This is a schematic diagram of the measurement using the rotating quarter-wave plate polarization modulation method in step 2 of an embodiment of the present invention.

[0045] The reference numerals in the attached figures are explained as follows: 1-Laser calibration light source; 2-Polarizer; 31-First power meter; 32-Second power meter; 4-Spectroscopic optical system; 41-Beam splitter;

[0046] 5 - Quarter-wave plate; 6 - Analyzer; 7 - Detector. Detailed Implementation

[0047] The present invention will be further described below with reference to the accompanying drawings and exemplary embodiments.

[0048] Reference Figure 2 A Stokes parameter correction method suitable for high-energy laser polarization detection includes the following steps:

[0049] Step 1: The laser is output from the laser calibration light source 1, and after being polarized by the polarizer 2, it is input into the beam splitting optical system 4. The beam splitting optical system 4 includes multiple beam splitters 41. Figure 2 Only two beam splitters (41) are shown in the diagram as an example, used to split and attenuate the laser beam; the transmittance k of the P-polarized light is calculated by measuring the power of the laser before and after passing through the beam splitting optical system 4 using a power meter. p S-polarized light transmittance k s Unpolarized light transmittance k u Thus, the normalized P-polarized light transmittance k is obtained. pnNormalized S-polarized light transmittance k sn Normalized unpolarized light transmittance k un ;

[0050] Specifically as follows:

[0051] Step 1.1: The laser is output from the laser calibration light source 1. The laser is polarized by the polarizer 2 and output as P-polarized light to the beam splitting optical system 4. The power of the laser before passing through the beam splitting optical system 4 is measured by the first power meter 31 and the second power meter 32, respectively. Figure 2 At point A), the power after passing through the beam-splitting optical system 4 ( Figure 2 (at point B), calculate the transmittance k of P-polarized light. p ;

[0052] Step 1.2: Adjust the transmission axis direction of polarizer 2. The laser light is polarized by polarizer 2 and outputs S-polarized light to the beam splitting optical system 4. The power of the laser light before passing through the beam splitting optical system 4 is measured by the first power meter 31 and the second power meter 32, respectively. Figure 2 At point A), the power after passing through the beam-splitting optical system 4 ( Figure 2 (at point B), calculate the transmittance k of the S-polarized light. s ;

[0053] Step 1.3: Calculate the unpolarized light transmittance k based on the unpolarized light model. u =(k p +k s ) / 2;

[0054] Step 1.4: Calculate the normalized p-polarized light transmittance k. pn Normalized S-polarized light transmittance k sn Normalized unpolarized light transmittance k un ;

[0055] Step 2, refer to Figure 3 Define an xyz coordinate system, where the z-axis represents the propagation direction of the laser, the x-axis defines the horizontal component of the polarized light, and the y-axis defines the vertical component of the polarized light. After passing through the beam splitting optical system 4, the laser is input to the polarizer. Based on the polarization modulation method using a rotating quarter-wave plate 5, the transmission axis of the analyzer 6 is adjusted to be parallel to the x-axis. By continuously changing the polarization state of the laser through the rotating quarter-wave plate 5, the detector 7 receives a periodically changing optical power signal, and the optical power signal P(S0, S1, S2, S3) is expressed as a Stokes parameter (S0, S1, S2, S3).

[0056]

[0057] In the formula, B = S3, θ is the angle between the fast axis of the quarter-wave plate 5 and the x-axis (horizontal component of the polarized light); S0 represents the total light intensity, S1 represents the difference in intensity of horizontally and vertically polarized light, S2 represents the difference in intensity of +45° and -45° polarized light, S3 represents the difference in intensity of left-handed and right-handed circularly polarized light;

[0058] Step 3, periodically sample θ to obtain the optical power signal of N sampling points; calculate the optical power signal P(θ n ) of the nth sampling point by Fourier analysis method to obtain the Stokes parameters of the laser after passing through the light splitting optical system 4;

[0059] Step 3.1, periodically sample θ to obtain the optical power signal of N sampling points; the sampling number N is even and N≥16, and the sampling interval is 360° / N;

[0060] The optical power signal of the nth sampling point P(θ n ) is:

[0061]

[0062] Step 3.2, calculate the expression of each parameter A, B, C, D by Fourier analysis method on the optical power signal P(θ n );

[0063]

[0064] Step 3.3, calculate the Stokes parameters (S0, S1, S2, S3) of the laser after passing through the light splitting optical system 4 as:

[0065] S0=A-C, S1=2C, S2=2D, S3=B;

[0066] Step 4, combine the normalized P-polarized light transmittance k pn , the normalized S-polarized light transmittance k sn , and the normalized non-polarized light transmittance k un obtained in step 1.4 to correct the Stokes parameters (S0, S1, S2, S3) obtained in step 3 to obtain the corrected Stokes parameters (S 0c , S 1c , S 2c , S 3c ), and complete the correction of the Stokes parameters;

[0067] Step 4.1, calculate the polarized light intensity S p and the degree of polarization P of the laser after passing through the light splitting optical system 4 according to the Stokes parameters (S0, S1, S2, S3) obtained in step 3:

[0068]

[0069]

[0070] Step 4.2, calculate the x-axis direction electric field amplitude E x , y-axis direction electric field amplitude E y :

[0071]

[0072] Step 4.3, combine the normalized P-polarized light transmittance k pn , normalized S-polarized light transmittance k sn , normalized non-polarized light transmittance k un obtained in step 1.4 to correct the Stokes parameters (S0, S1, S2, S3) obtained in step 3 to obtain the corrected Stokes parameters (S 0c , S 1c , S 2c , S 3c ):

[0073]

[0074] Complete the correction of the Stokes parameters.

Claims

1. A Stokes parameter correction method suitable for high-energy laser polarization detection, characterized in that, Includes the following steps: Step 1: The laser output from the laser calibration light source (1) is polarized by the polarizer (2) and then input into the beam splitting optical system (4). The power of the laser before passing through the beam splitting optical system and the power after passing through the beam splitting optical system (4) are measured by the power meter, and the transmittance k of the P-polarized light is calculated. p S-polarized light transmittance k s Unpolarized light transmittance k u Thus, the normalized P-polarized light transmittance k is obtained. pn Normalized S-polarized light transmittance k sn Normalized unpolarized light transmittance k un ; Step 2: After the laser passes through the beam splitting optical system (4), it is input into the polarizer. The polarization state of the laser is continuously changed by the quarter-wave plate (5) in the rotating polarizer, so that the detector (7) receives the periodically changing optical power signal and expresses the optical power signal P(θ) as Stokes parameters (S0, S1, S2, S3); θ is the angle between the fast axis of the quarter-wave plate (5) and the horizontal component of the polarized light; S0 represents the total light intensity, S1 represents the difference in intensity between horizontal and vertical polarized light, S2 represents the difference in intensity between +45° and -45° polarized light, and S3 represents the difference in intensity between left-handed and right-handed circularly polarized light. Step 3: Periodically sample θ to obtain the optical power signal at N sampling points; use Fourier analysis to analyze the optical power signal P(θ) at the nth sampling point. n The Stokes parameters (S0, S1, S2, S3) of the laser after passing through the beam splitting optical system (4) are calculated. N is an even number and N≥16, the sampling interval is 360° / N; n=1,2,...,N; Step 4: Combine the normalized p-polarized light transmittance k obtained in Step 1. pn Normalized S-polarized light transmittance k sn Normalized unpolarized light transmittance k un The Stokes parameters (S0, S1, S2, S3) obtained in step 3 are corrected to obtain the corrected Stokes parameters (S0, S1, S2, S3). 0c S 1c S 2c S 3c ), complete the Stokes parameter calibration.

2. The Stokes parameter correction method for high-energy laser polarization detection according to claim 1, wherein step 2 specifically comprises: After passing through the beam splitting optical system (4), the laser is input into the polarizer. The transmission axis of the analyzer (6) in the polarizer is adjusted to be parallel to the horizontal component of the polarized light. The polarization state of the laser is continuously changed by rotating the quarter-wave plate (5), so that the detector (7) receives the periodically changing optical power signal, and the optical power signal P(θ) is expressed as the Stokes parameter (S0, S1, S2, S3): In the formula, B = S3, 3. The Stokes parameter correction method for high-energy laser polarization detection according to claim 2, wherein step 3 is specifically as follows: Step 3.1: Periodically sample θ to obtain the optical power signal at N sampling points; where the optical power signal at the nth sampling point is P(θ). n The optical power signal is: Step 3.2: Analyze the optical power signal P(θ) using Fourier analysis. n ) Perform calculations to obtain the expressions for parameters A, B, C, and D: Step 3.3: Calculate the Stokes parameters (S0, S1, S2, S3) of the laser after passing through the beam splitting optical system (4): S0=AC, S1=2C, S2=2D, S3=B.

4. The Stokes parameter correction method for high-energy laser polarization detection according to claim 3, wherein step 4 specifically comprises: Step 4.1: Calculate the polarization intensity S of the laser light after passing through the beam splitting optical system (4) based on the Stokes parameters (S0, S1, S2, S3) obtained in Step 3. p And polarization degree P: Step 4.2: Calculate the amplitude of the electric field E in the horizontal component direction of the polarized light based on the degree of polarization P and parameter S1. x The amplitude of the electric field in the perpendicular component direction of polarized light, E y : Step 4.3: Combine the normalized p-polarized light transmittance k obtained in Step 1. pn Normalized S-polarized light transmittance k sn Normalized unpolarized light transmittance k un The Stokes parameters (S0, S1, S2, S3) obtained in step 3 are corrected to obtain the corrected Stokes parameters (S0, S1, S2, S3). 0c S 1c S 2c S 3c ): Complete the Stokes parameter calibration.

5. A Stokes parameter correction method for high-energy laser polarization detection according to any one of claims 1 to 4, wherein step 1 is specifically as follows: Step 1.1: The laser is output from the laser calibration light source (1). The laser is polarized by the polarizer (2) and output as P-polarized light to the beam splitting optical system (4). The power of the laser before passing through the beam splitting optical system (4) and the power after passing through the beam splitting optical system (4) are measured by a power meter. The transmittance k of the P-polarized light is then calculated. p ; Step 1.2: Adjust the transmission axis of the polarizer (2) so that the laser is polarized by the polarizer (2) and outputs S-polarized light to the beam splitting optical system (4). Measure the power of the laser before and after passing through the beam splitting optical system (4) using a power meter, and calculate the S-polarized light transmittance k. s ; Step 1.3: Based on the transmittance k of P-polarized light p S-polarized light transmittance k s Calculate the transmittance k of unpolarized light. u ; Step 1.4: Calculate the normalized p-polarized light transmittance k. pn Normalized S-polarized light transmittance k sn Normalized unpolarized light transmittance k un .

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