A method for measuring the effective spot area of ​​short pulse Gaussian beams in a vacuum environment

Abstract

A method for measuring the effective spot area of ​​a short pulse Gaussian beam in a vacuum environment comprises a pulse laser, a shutter, an energy regulator, a focusing lens, a sampling mirror, a metal target, a sample stage, an energy meter, a computer, and a vacuum chamber. The method is based on the correlation between the damage profile of the metal target and the energy distribution characteristics of the Gaussian beam. By measuring the change of the corresponding area of ​​the damage profile on the metal target (106) with the irradiated laser energy, the effective spot area of ​​the short pulse laser Gaussian beam at the focus position in the vacuum environment is obtained by fitting. The method is simple and feasible, and can accurately measure the effective spot area of ​​a short pulse laser at different incident angles in a vacuum environment.

Description

Technical Field

[0001] The invention relates to the measurement of the effective spot area of ​​a short pulse laser, in particular to a method for measuring the effective spot area of ​​a short pulse Gaussian beam in a vacuum environment. Background Art

[0002] Pulse lasers, especially short-pulse lasers, often produce air breakdown and nonlinear self-focusing effects during transmission in the air due to excessive peak power, so they often need to be transmitted in a vacuum environment. In the short-pulse laser damage threshold test, the short-pulse laser is focused by a lens and irradiated to the surface of the test element at its focal position. The peak power density of the irradiated laser near the focus is very high. In order to avoid air breakdown and nonlinear self-focusing effects, the test element needs to be placed in a vacuum environment. Beam quality analyzers are often used to measure the spot in an air environment, but conventional beam quality analyzers are not suitable for working in a vacuum environment. Therefore, it is very necessary to solve the problem of accurately measuring the effective spot area of ​​a short-pulse Gaussian beam in a vacuum environment, which is of great significance to the short-pulse laser damage threshold test of optical components. Summary of the invention

[0003] In order to overcome the shortcomings of the above-mentioned prior art, the present invention proposes a method for measuring the effective spot area of ​​a short pulse Gaussian beam in a vacuum environment. The method utilizes the strong absorption characteristics of a metal target and is based on the correlation between the damage profile of the metal target and the energy distribution characteristics of the Gaussian beam to accurately measure the effective spot area of ​​a short pulse in a vacuum environment at different incident angles.

[0004] The technical solution of the present invention is as follows:

[0005] S1 builds the measurement optical path:

[0006] S1.1 Place the metal target on the sample stage and place it in a vacuum chamber;

[0007] S1.2 A shutter, an energy regulator and a focusing lens are sequentially placed along the output pulse laser direction of the short pulse laser, and a sampling mirror and a metal target are sequentially placed along the transmission light path direction of the focusing lens, so that the pulse laser irradiates the surface of the metal target, and the surface is located at the focal position of the focusing lens; an energy meter is placed along the reflection light path direction of the focusing lens to measure the energy of the reflected light and transmit it to a computer; the shutter, energy regulator and energy meter are respectively connected to the computer;

[0008] S2 pulse laser irradiates different areas on the metal target surface and records the reading E of the energy meter i :

[0009] S2.1 turns on the short pulse laser to output a pulse laser with a fixed frequency, and the computer controls the shutter to be in a normally open state, so that the pulse laser irradiates a certain area on the surface of the metal target;

[0010] S2.2 The computer controls the energy regulator to gradually adjust the laser energy in the optical path from small to large, while the human eye observes the surface of the metal target:

[0011] When the metal target surface begins to produce visible plasma flash, the reading of the energy meter at this time is recorded as E 0min ;

[0012] When the metal target surface begins to produce a strong plasma flash, the energy meter reading at this time is recorded as E 0max ;

[0013] S2.3 The computer controls the shutter to close and ensures that the vacuum chamber is in a vacuum state;

[0014] S2.4 The computer controls the energy regulator to adjust the laser energy in the optical path so that the reading of the energy meter reaches E 0min ;

[0015] S2.5 moving the sample stage so that the pulsed laser irradiates other areas of the surface of the metal target;

[0016] S2.6 The computer controls the shutter to extract a laser pulse and records the reading of the energy meter at this time as E 0i , where i = 1, 2, 3, ...;

[0017] S2.7 The computer controls the energy regulator to increase the laser energy in the optical path;

[0018] S2.8 Repeat S2.5 to S2.7 until the energy meter reads E. 0i Reach E 0max until;

[0019] S3 calculates the effective spot area A of short pulse Gaussian beam T,eff :

[0020] S3.1 Calculate the energy E of the pulsed laser irradiating different areas on the metal target surface i , the formula is as follows:

[0021] E i =E 0i N

[0022] Where N is the splitting ratio;

[0023] S3.2 Measure the area S of each damage contour using a microscope i ;

[0024] S3.3 Energy E i The area S corresponding to the damage contour i The fitting formula is as follows: the slope of the curve is the effective spot area A of the short pulse Gaussian beam T,eff ;

[0025] S i (E i )=A T,eff *ln(E i )-A T,eff *ln(A T,eff *H c )

[0026] In the formula, H c is the energy density corresponding to the damage contour, which is a fixed value and can be obtained by comparing any damage contour with the energy distribution of its corresponding irradiated Gaussian beam on the metal target surface.

[0027] The laser energy irradiating the metal target is obtained by placing a second energy meter in front of the metal target.

[0028] The technical effects of the present invention are:

[0029] The present invention measures the change of the corresponding area of ​​the damage profile on the metal target with the irradiated laser energy, and fits to obtain the effective spot area of ​​the focus position of the short pulse laser Gaussian beam in a vacuum environment. The method is simple and feasible, and can accurately measure the effective spot area of ​​the target surface under different incident angles of the short pulse laser in a vacuum environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of a device for measuring the effective area of ​​a pulsed laser Gaussian beam in a vacuum environment.

[0031] Figure 2 It is the relationship between the energy of irradiated metal target and the area of ​​damaged region fitted by computer.

[0032] In the figure, 101 is a pulse laser, 102 is a shutter, 103 is an energy regulator, 104 is a focusing lens, 105 is a spectroscope, 106 is a metal target, 107 is a sample stage, 108 is an energy meter, 109 is a computer, and 110 is a vacuum chamber. DETAILED DESCRIPTION

[0033] The present invention is further described below with reference to examples and drawings, but the protection scope of the invention shall not be limited thereto.

[0034] See also Figure 1 . Figure 1It is a schematic diagram of a device for measuring the effective spot area of ​​a short pulse Gaussian beam in a vacuum environment. The relationship between the components is as follows: the pulse laser output by the short pulse laser 101 passes through the shutter 102, the energy regulator 103, the focusing lens 104, and the sampling mirror 105 in sequence, and then enters the vacuum chamber 110 to irradiate the metal target 106; the metal target 106 is located in the vacuum chamber 110 and placed on the sample stage 107, and its front surface is located at the focal position of the focusing lens 104; the energy meter 108 is located in the direction of the reflected light from the front surface of the sampling mirror 105. The computer 109 is connected to the shutter 102, the energy regulator 103, and the energy meter 108, and records the reading of the energy meter 108 in real time.

[0035] See also Figure 2 . Figure 2 It is the relationship between the energy of irradiated metal target and the area of ​​damaged region fitted by computer.

[0036] A method for measuring the effective spot area of ​​a short pulse Gaussian beam in a vacuum environment, by measuring the data of the damage area on a metal target and the irradiated laser energy, and fitting to obtain the effective spot area of ​​the short pulse laser Gaussian beam at the focus position in the vacuum environment. The method is characterized in that the method comprises the following steps:

[0037] ① Turn on the short pulse laser 101 to make it emit light at a fixed frequency;

[0038] ② placing the metal target 106 on the sample stage 107;

[0039] ③ The computer 109 controls the shutter 102 to be in a normally open state, and the computer 109 controls the energy regulator 103 to gradually adjust the laser energy in the optical path from small to large; at the same time, the human eye observes the surface of the metal target 106, and when the surface of the metal target 106 begins to produce visible plasma flash, the reading of the energy meter 108 at this time is recorded as E 0min When a strong plasma flash begins to appear on the surface of the metal target 106, the reading of the energy meter 108 is recorded as E 0max ;

[0040] ④ The computer 109 controls the shutter 102 to close and evacuates the vacuum chamber 110 to a vacuum state;

[0041] ⑤ The computer 109 controls the energy regulator 103 so that the reading of the energy meter 108 reaches E 0min ;

[0042] ⑥ Move the sample stage 107 so that the metal target 106 moves to the unirradiated area;

[0043] ⑦ The computer 109 controls the shutter 102 to extract a laser pulse and records the reading of the energy meter 108 at this time as E 0i (i=1,2,3,…);

[0044] ⑧ The computer 109 controls the energy regulator 103 to increase the energy in the optical path;

[0045] 9. Repeat steps 6 to 9 for no less than 10 times until the reading of the energy meter 108 reaches E. 0max until;

[0046] ⑩ Calculate the energy E irradiated to the metal target 106 at this time i =E 0i N, and use a microscope to measure the area S corresponding to each damage contour i , where N is the splitting ratio, which is numerically equal to the ratio of the laser energy irradiating the metal target 106 to the reading of the energy meter 108 at the same time;

[0047] For any incident angle α, the energy density distribution of the Gaussian beam on the metal target surface is E i is the total energy of the pulsed Gaussian beam, A T,eff is the effective spot area of ​​the target surface, ω x ,ω y They are the peak energy density of the elliptical spot 1 / e 2 Compared with the normal incidence case, the light spot expands in the x-axis direction, while the y-axis remains unchanged.

[0048] (x c ,y c ) represents the position coordinates of the damage contour of the metal target 106. The corresponding damage contour area can be calculated according to the standard ellipse equation and the ellipse area formula. The damage contour area S i Substitute the Gaussian beam energy density distribution H i (x, y), the damage contour area S can be obtained i and irradiation energy E i Relationship: S i (E i )=A T,eff *ln(E i )-A T,eff *ln(A T,eff *H c )(i=1,2,3,…),H cis the energy density at the damage contour, which is a fixed value and can be obtained by comparing any damage contour with the energy distribution of its corresponding irradiated Gaussian beam on the metal target surface;

[0049] The energy E irradiated on the metal target 106 i and the corresponding damage contour area S i Substituting the data into the fitting, the slope of the fitting curve can be obtained as the effective spot area A of the target surface of the short pulse Gaussian beam at any incident angle T,eff .

Claims

1. A method for measuring the effective spot area of ​​a short pulse Gaussian beam in a vacuum environment, characterized in that: The steps include: S1 builds the measurement optical path: S1.1 placing a metal target (106) on a sample stage (107) and placing it in a vacuum chamber (110); S1.2 A shutter (102), an energy regulator (103) and a focusing lens (104) are sequentially placed along the direction of the output pulse laser of the short pulse laser (101); a sampling mirror (105) and a metal target (106) are sequentially placed along the transmission light path of the focusing lens (104), so that the pulse laser irradiates the surface of the metal target (106), and the surface is located at the focal position of the focusing lens (104); an energy meter (108) is placed along the reflection light path of the focusing lens (104) to measure the energy of the reflected light and transmit it to a computer (109); the shutter (102), the energy regulator (103) and the energy meter (108) are respectively connected to the computer (109); S2 pulse laser irradiates different areas on the surface of the metal target (106), and records the reading E of the energy meter (108) i : S2.1 Turn on the short pulse laser (101) to output a pulse laser of a fixed frequency, and the computer (109) controls the shutter (102) to be in a normally open state, so that the pulse laser irradiates a certain area on the surface of the metal target (106); S2.2 The computer (109) controls the energy regulator (103) to gradually adjust the laser energy in the optical path from small to large. At the same time, the human eye observes the surface of the metal target (106): When visible plasma flash begins to appear on the surface of the metal target (106), the reading of the energy meter (108) is recorded as E 0min ; When a strong plasma flash begins to be generated on the surface of the metal target (106), the reading of the energy meter (108) is recorded as E 0max ; S2.3 The computer (109) controls the shutter (102) to close and ensures that the vacuum chamber (110) is in a vacuum state; S2.4 The computer (109) controls the energy regulator (103) to adjust the laser energy in the optical path so that the reading of the energy meter (108) reaches E 0min ; S2.5 moving the sample stage (107) so that the pulsed laser irradiates other areas of the surface of the metal target (106); S2.6 The computer (109) controls the shutter (102) to extract a laser pulse and records the reading of the energy meter (108) at this time as E 0i , where i = 1, 2, 3, ...; S2.7 The computer (109) controls the energy regulator (103) to increase the laser energy in the optical path; S2.8 Repeat S2.5 to S2.7 until the energy meter (108) shows the reading E. 0i Reach E 0max until; S3 calculates the effective spot area A of short pulse Gaussian beam T,eff : S3.1 Calculate the energy E of different areas of the metal target (106) irradiated by the pulsed laser i , the formula is as follows: AND i =And 0i N Where N is the splitting ratio; S3.2 Measure the area S of each damage contour using a microscope i ; S3.3 Energy E i The area S corresponding to the damage contour i The fitting formula is as follows: the slope of the curve is the effective spot area A of the short pulse Gaussian beam T,eff ; S i (HAVE BEEN i )=A T,eff *ln(E i )-A T,eff *ln(A T,eff *H c ) In the formula, H c is the energy density corresponding to the damage contour, which is obtained by comparing any damage contour with the energy distribution of its corresponding irradiated Gaussian beam on the metal target surface.

2. The method for measuring the effective spot area of ​​a short pulse Gaussian beam in a vacuum environment according to claim 1, characterized in that: The splitting ratio N is the ratio of the laser energy irradiating the metal target (106) to the reading of the energy meter (108) at the same time.

3. The method for measuring the effective spot area of ​​a short pulse Gaussian beam in a vacuum environment according to claim 2, characterized in that: The laser energy irradiating the metal target (106) is obtained by placing a second energy meter in front of the metal target (106).

Images