Stokes parameter correction method suitable for high-energy laser polarization detection

Abstract

The invention 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 for overcoming the defect that a polarization parameter measurement error is caused by changing the polarization state of incident laser when a light splitting optical system is used for attenuating laser energy. According to the Stokes parameter correction method suitable for the high-energy laser polarization detection, the Stokes parameter of the laser is extracted by calibrating the polarization transmittance of the light splitting optical system and combining Fourier analysis, and then the Stokes parameter is corrected by using the polarization transmittance, so that the polarization error introduced by the light splitting optical system is further eliminated, and the accuracy of the Stokes parameter correction is improved. And the corrected polarization parameter is closer to the real state of the laser.

Description

Technical Field

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

[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, advanced manufacturing, etc., the precise detection of high-energy lasers is of great significance to the reliability of research and the quality of manufacturing. Polarization among 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 during the interaction between light and matter. For example, changes in the 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 detector measurement range, a spectroscopic optical system must be used to attenuate the laser energy. The schematic diagram of the existing high-energy laser polarization detection system is shown in Figure 1 As shown, the laser is emitted from a high-energy laser light source 01, passes through a spectroscopic optical system 02 for energy attenuation, and finally enters a polarizer 03 for detection; the spectroscopic optical system 02 includes a plurality of spectroscopes 021 for splitting and attenuating the laser beam; the polarizer 03 includes a quarter-wave plate, an analyzer, and a detector. However, the spectroscopic optical system 02 will change the polarization state of the original incident high-energy laser while attenuating the energy, which may lead to errors in the measurement of polarization parameters. Especially in experiments or industrial applications involving high-precision requirements, this error will directly affect the accurate evaluation of the interaction between the laser and the material. Summary of the invention

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

[0005] In order to solve the deficiencies of the above-mentioned prior art, the present invention provides the following technical solutions:

[0006] A Stokes parameter correction method suitable for high-energy laser polarization detection is special in that it includes the following steps:

[0007] Step 1: The laser is output from the laser calibration light source, and the laser is polarized by the polarizer and then input into the spectroscopic optical system. The power of the laser before and after passing through the spectroscopic optical system is measured by a power meter, and the transmittance k of the P polarized light is calculated. p , S polarized light transmittance k s and the unpolarized light transmittance k u, and then get the normalized P polarized light transmittance k pn , Normalized S-polarized light transmittance k sn , normalized unpolarized light transmittance k un ;

[0008] Step 2, the laser is input into the polarizer after passing through the spectroscopic optical system, and the polarization state of the laser is continuously changed by rotating the quarter wave plate in the polarizer, so that the detector receives the optical power signal with periodic changes, and the optical power signal P (mortise) is expressed as Stokes parameters (S0, S1, S2, S3); mortise is the 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 intensity difference between horizontal and vertical polarized light, S2 represents the intensity difference between +45° and -45° polarized light, and S3 represents the intensity difference between left-handed circular polarization and right-handed circular polarization;

[0009] Step 3: Periodically sample the mortar to obtain the optical power signals of N sampling points; and perform Fourier analysis on the optical power signal P(θ n ) to calculate and obtain the Stokes parameters (S0, S1, S2, S3) of the laser after passing through the spectroscopic optical system;

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

[0011] 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 6 are corrected to obtain the corrected Stokes parameters (S 0c , S 1c , S 2c , S 3c ) to complete the Stokes parameter correction.

[0012] Furthermore, the step 2 is specifically as follows:

[0013] The laser is input into the polarizer after passing through the spectroscopic optical system. The transmission axis of the analyzer 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, so that the detector receives a periodically changing optical power signal, and the optical power signal P (mortise) is expressed as Stokes parameters (S0, S1, S2, S3):

[0014]

[0015] In the formula, B=S3,

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

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

[0018]

[0019] Step 3.2: Use Fourier analysis to analyze the optical power signal P(θ n ) to calculate and get the expressions of parameters A, B, C, and D:

[0020]

[0021]

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

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

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

[0025] Step 4.1: Calculate the polarization intensity S of the laser after passing through the spectroscopic optical system according to the Stokes parameters (S0, S1, S2, S3) obtained in step 3. p And the degree of polarization P:

[0026]

[0027] Step 4.2: Calculate the electric field amplitude E of the horizontal component of the polarized light based on the degree of polarization P and parameter S1. x , the electric field amplitude E in the vertical component direction of polarized light y :

[0028]

[0029] 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 (S 0c , S 1c , S 2c , S 3c ):

[0030]

[0031] Complete the Stokes parameter correction.

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

[0033] Step 1.1: The laser calibration light source outputs laser light, and the laser is polarized by the polarizer to output P polarized light to the spectroscopic optical system. The power of the laser before and after passing through the spectroscopic 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 by the polarizer and outputs S-polarized light to the spectroscopic optical system. Use a power meter to measure the power of the laser before and after passing through the spectroscopic optical system, and calculate the transmittance k of the S-polarized light. s ;

[0035] Step 1.3: According to the transmittance k of P polarized light p , S polarized light transmittance k s , calculate the unpolarized light transmittance k 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 present invention has the following beneficial effects:

[0038] (1) The present invention provides a Stokes parameter correction method suitable for high-energy laser polarization detection. The method calibrates the polarization transmittance (including P polarization, S polarization and non-polarized light transmittance) of the spectroscopic optical system and extracts the Stokes parameters of the laser in combination with Fourier analysis. The polarization transmittance is then used to correct the Stokes parameters, thereby further eliminating the polarization error introduced by the spectroscopic optical system, so that the corrected polarization parameters are closer to the actual state of the laser.

[0039] (2) The present invention can effectively compensate for the measurement error caused by the spectroscopic optical system through the calculation and application of normalized transmittance, and ensure that the deviation in the calibration process is minimized.

[0040] (3) In the process of Stokes parameter correction, the present invention can accurately correct the transmittance of different polarization components by combining the normalized transmittance of P-polarized light, S-polarized light and non-polarized light, and can ensure that the corrected Stokes parameters truly reflect the original polarization state of the laser, thereby providing high-precision polarization data support for subsequent applications (such as laser processing and optical experiments). BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic diagram of an existing high energy laser polarization detection system;

[0042] Figure 1 The reference numerals are explained as follows: 01 - high energy laser light source; 02 - spectroscopic optical system, 021 - spectroscope; 03 - polarizer.

[0043] Figure 2 It is a schematic diagram of measuring the power of the laser before passing through the spectroscopic optical system and the power of the laser after passing through the spectroscopic optical system by the first power meter and the second power meter in step 1 of an embodiment of a Stokes parameter correction method suitable for high-energy laser polarization detection of the present invention;

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

[0045] The reference numerals are as follows: 1- laser calibration light source; 2- polarizer; 31- first power meter, 32- second power meter; 4- spectroscopic optical system, 41- spectroscope;

[0046] 5-quarter wave plate; 6-polarizer; 7-detector. DETAILED DESCRIPTION

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

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

[0049] Step 1: The laser calibration light source 1 outputs laser light, which is polarized by the polarizer 2 and then input into the spectroscopic optical system 4. The spectroscopic optical system 4 includes a plurality of spectroscopes 41 ( Figure 2 Only two beam splitters 41 are drawn as examples) to split and attenuate the laser beam; the power meter is used to measure the power of the laser before and after passing through the beam splitting optical system 4, and the transmittance k of the P polarized light is calculated. p , S polarized light transmittance k s and the unpolarized light transmittance k u , and then get the normalized P polarized light transmittance k pn, Normalized S-polarized light transmittance k sn , normalized unpolarized light transmittance k un ;

[0050] The details are as follows:

[0051] Step 1.1, the laser calibration light source 1 outputs laser, and the laser is polarized by the polarizer 2 and outputs P polarized light to the spectroscopic optical system 4, and the power of the laser before passing through the spectroscopic optical system 4 is measured by the first power meter 31 and the second power meter 32 respectively ( Figure 2 A), after passing through the spectroscopic optical system 4, the power ( Figure 2 B), calculate the transmittance k of P polarized light p ;

[0052] Step 1.2, adjust the transmission axis direction of the polarizer 2, the laser is polarized by the polarizer 2 and outputs S polarized light to the spectroscopic optical system 4, and the power of the laser before passing through the spectroscopic optical system 4 is measured by the first power meter 31 and the second power meter 32 respectively ( Figure 2 A), after passing through the spectroscopic optical system 4, the power ( Figure 2 B), calculate the S polarized light transmittance k s ;

[0053] Step 1.3: Calculate the unpolarized light transmittance k according to 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: Reference Figure 3 , define the xyz coordinate system, the z-axis represents the propagation direction of the laser, the x-axis is used to define the horizontal component of the polarized light, and the y-axis is used to define the vertical component of the polarized light; the laser passes through the spectroscopic optical system 4 and is input into the polarizer. According to the polarization light modulation method of rotating the quarter-wave plate 5, the transmission axis of the analyzer 6 is adjusted to be parallel to the x-axis. 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 (mortar) is expressed as Stokes parameters (S0, S1, S2, S3):

[0056]

[0057] In the formula, B=S3, S0 represents the total light intensity, S1 represents the intensity difference between horizontal and vertical polarized light, S2 represents the intensity difference between +45° and -45° polarized light, and S3 represents the intensity difference between left-handed circular polarization and right-handed circular polarization.

[0058] Step 3: Periodically sample the mortar to obtain the optical power signals of N sampling points; and perform Fourier analysis on the optical power signal P(θ n ) is calculated to obtain the Stokes parameter of the laser after passing through the spectroscopic optical system 4;

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

[0060] The optical power signal P(θ n ) is:

[0061]

[0062] Step 3.2: Use Fourier analysis to analyze the optical power signal P(θ n ) to calculate and get the expressions of parameters A, B, C, and D:

[0063]

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

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

[0066] Step 4: Combine the normalized P polarized light transmittance k obtained in step 1.4 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 (S 0c , S 1c , S 2c , S 3c ), complete the Stokes parameter correction;

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

[0068]

[0069]

[0070] Step 4.2: Calculate the electric field amplitude E in the x-axis direction based on the polarization degree P and parameter S1 x , the electric field amplitude E in the y-axis direction y :

[0071]

[0072] Step 4.3: Combine the normalized P polarized light transmittance k obtained in step 1.4 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 (S 0c , S 1c , S 2c , S 3c ):

[0073]

[0074] Complete the Stokes parameter correction.

Claims

1. A Stokes parameter correction method suitable for high-energy laser polarization detection, characterized in that: The steps include: Step 1: The laser calibration light source (1) outputs laser light, and the laser light is polarized by the polarizer (2) and then input into the spectroscopic optical system (4). The power of the laser light before and after passing through the spectroscopic optical system (4) is measured by a power meter, and the transmittance k of the P polarized light is calculated. p , S polarized light transmittance k s and the unpolarized light transmittance k u , and then get the normalized P polarized light transmittance k pn , Normalized S-polarized light transmittance k sn , normalized unpolarized light transmittance k un ; Step 2, the laser light passes through the spectroscopic optical system (4) and is input into the polarizer. The polarization state of the laser light is continuously changed by rotating the quarter wave plate (5) in the polarizer, so that the detector (7) receives a periodically changing optical power signal, and the optical power signal P (θ) is expressed as a Stokes parameter (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 intensity difference between the horizontal and vertical polarized light, S2 represents the intensity difference between the +45° and -45° polarized light, and S3 represents the intensity difference between the left-handed circularly polarized light and the right-handed circularly polarized light; Step 3: Periodically sample θ to obtain the optical power signals of N sampling points; and perform Fourier analysis on the optical power signal P(θ n ) to calculate and obtain the Stokes parameters (S0, S1, S2, S3) of the laser after passing through the spectroscopic optical system (4); N is an even number and N≥16, and 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 6 are corrected to obtain the corrected Stokes parameters (S 0c , S 1c , S 2c , S 3c ) to complete the Stokes parameter correction.

2. According to the Stokes parameter correction method suitable for high-energy laser polarization detection according to claim 1, the step 2 is specifically: The laser is input into the polarizer after passing through the spectroscopic optical system (4). The light 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 () is expressed as Stokes parameters (S0, S1, S2, S3): In the formula, B=S3, 3. According to the Stokes parameter correction method suitable for high-energy laser polarization detection according to claim 2, the step 3 is specifically as follows: Step 3.1, periodically sample the mortar to obtain the optical power signals of N sampling points; the optical power signal P(θ n ) is: Step 3.2: Use Fourier analysis to analyze the optical power signal P(θ n ) to calculate and get the expressions of parameters A, B, C, and D: Step 3.3: Calculate the Stokes parameters (S0, S1, S2, S3) of the laser after passing through the spectroscopic optical system (4): S0=A-C, S1=2C, S2=2D, S3=B.

4. According to the Stokes parameter correction method suitable for high-energy laser polarization detection according to claim 3, the step 4 is specifically: Step 4.1: Calculate the polarization intensity S of the laser after passing through the spectroscopic optical system (4) according to the Stokes parameters (S0, S1, S2, S3) obtained in step 3. p And the degree of polarization P: Step 4.2: Calculate the electric field amplitude E of the horizontal component of the polarized light based on the degree of polarization P and parameter S1. x , the electric field amplitude E in the vertical component direction of polarized light 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 (S 0c , S 1c , S 2c , S 3c ): Complete the Stokes parameter correction.

5. According to a Stokes parameter correction method suitable for high-energy laser polarization detection according to any one of claims 1 to 4, the step 1 is specifically as follows: Step 1.1, the laser calibration light source (1) outputs laser light, the laser is polarized by the polarizer (2) and outputs P polarized light to the spectroscopic optical system (4), the power of the laser before passing through the spectroscopic optical system (4) and the power of the laser after passing through the spectroscopic optical system (4) are measured by a power meter, and the transmittance k of the P polarized light is calculated. p ; Step 1.2, adjust the transmission axis direction of the polarizer (2) so that the laser is polarized by the polarizer (2) and outputs S-polarized light to the spectroscopic optical system (4), and use a power meter to measure the power of the laser before and after passing through the spectroscopic optical system (4), and calculate the S-polarized light transmittance k s ; Step 1.3: According to the transmittance k of P polarized light p , S polarized light transmittance k s , calculate the unpolarized light transmittance k 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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