A method for suppressing pre-pulses induced by undetermined stray light in multi-pass amplification systems

Abstract

The present invention discloses a method for suppressing pre-pulses induced by non-determined stray light in a multi-pass amplification system, including: S1, building a test platform for the multi-pass amplification system and setting component defects; S2, analyzing the influencing parameters of different component defects that excite non-determined stray light induced pre-pulses; S3, based on the results of the influencing parameter analysis, controlling the defects that excite non-determined stray light induced pre-pulses in the multi-pass amplification system to achieve pre-pulse suppression. The present invention determines the law of converting stray light into pre-pulses by analyzing factors such as defect position, size, wavelength of incident light, and stray light amplification factor, and obtains optical components and optical paths that are easy to form pre-pulses. Impurities and defects on these components should be promptly removed and focused on, and a guiding rule reference is proposed for the production and processing technology of components of a multi-pass amplification system of high-energy lasers and the precision of laser system construction.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-power laser systems, and particularly relates to a method for suppressing pre-pulses induced by non-deterministic stray light in a multi-pass amplification system. Background Art

[0002] Volume damage defects on a certain component in a high-power laser system will excite non-deterministic stray light and transmit in the system. This process passes through an optical path different from the expected result of the main optical path, ultimately leading to serious consequences: First, it causes secondary damage to this component or other optical components; Second, the stray light is part of the energy of the main optical path, which will cause the main optical path to fail to reach the expected amplification factor, resulting in a decrease in the signal-to-noise ratio of the system; Finally, since the non-deterministic stray light will also undergo amplification by the gain medium, a pre-pulse is formed to reach the energy threshold for breaking through the target material and output in advance of the main optical path. Such negative results will damage the target material, affect the use of the high-energy laser system, and reduce the beam quality and energy of the output laser.

[0003] Therefore, it is very important to study the transmission law and energy amplification law of non-deterministic stray light, which will affect the investigation of dangerous situations based on the treatment of the scattering source, as well as the research on control methods based on the excitation transmission law, and ultimately affect the development of bottleneck problems such as defects in the laser system.

[0004] Current research cannot effectively solve the problems of non-deterministic stray light and pre-pulses, and there are also problems with the volume damage defect theory, stray light modulation mechanism, and imperfect characteristics of stray light transmission and amplification in the source treatment method, so that it is impossible to judge the position of volume damage defects and the classification results of dangerous situations in the multi-pass amplification stage of the high-energy laser system. Summary of the Invention

[0005] Aiming at the above deficiencies in the prior art, the method for suppressing pre-pulses induced by non-deterministic stray light in a multi-pass amplification system provided by the present invention solves the problem that the existing method cannot solve the pre-pulses induced by non-deterministic stray light, so that it is impossible to judge the position of volume damage defects and the classification of dangerous situations in the multi-pass amplification stage of the high-energy laser system.

[0006] To achieve the above invention purpose, the technical solution adopted by the present invention is: A method for suppressing pre-pulses induced by non-deterministic stray light in a multi-pass amplification system, comprising the following steps:

[0007] S1. Build a test platform for the multi-pass amplification system and set component defects;

[0008] S2. Analyze the influence parameters of non-deterministic stray light induced pre-pulses excited by different component defects;

[0009] Among them, the influence parameter analysis includes defect position screening for exciting stray light, stray light transmission angle screening, analysis of the energy transmission amplification law of stray light, and signal-to-noise ratio analysis of stray light;

[0010] S3. Based on the results of the influence parameter analysis, control the defects that induce prepulses by exciting non-deterministic stray light in the multi-pass amplification system to achieve prepulse suppression.

[0011] Furthermore, the test platform of the multi-pass amplification system in step S1 includes a laser, a first lens, a first mirror, a second mirror, a reverse device, a first filter plate, a second lens, a first flat glass, a second flat glass, a third mirror, a fourth mirror, a third lens, a second filter plate, a fourth lens, a third flat glass, a fourth flat glass, and a cavity mirror arranged in sequence;

[0012] The test platform of the multi-pass amplification system also includes a first amplified neodymium glass and a second amplified neodymium glass, and their single-pass amplification times are 6 times and 8 times respectively;

[0013] The first filter plate is arranged on the focal spectrum plane of the first lens and the second lens, and the second filter plate is arranged on the focal spectrum plane of the second lens and the third lens; wherein, the first filter plate is used to control the output beam, and the second filter plate is used to modulate the beam;

[0014] The optical path of the multi-pass amplification system includes the first to fourth optical paths. Among them, the first optical path is the main optical path and is conjugate to the third optical path, the second optical path is conjugate to the fourth optical path, and each optical path corresponds to the aperture of the first and second filter plates with the corresponding number of optical paths;

[0015] In step S1, defects with different positions and sizes are randomly set inside the first to fourth lenses and the first to fourth flat glasses.

[0016] Furthermore, in step S2, the method for screening the defect positions where stray light occurs is as follows:

[0017] Track the spot of the output beam of the multi-pass amplification system on the detector to obtain the spot tracking schematic diagrams corresponding to the first to fourth lenses and the first to fourth flat glasses and each optical path; the spot tracking schematic diagrams characterize the dangerous situation of the induced prepulse where the excited non-deterministic stray light satisfies the stray light spatial transmission law and can output from the apertures of the first and second filter plates 4;

[0018] Analyze the dangerous situation of the prepulse in the spot tracking schematic diagram to obtain the induced prepulse danger distribution map characterizing the lens / flat plate element and its optical path defect positions.

[0019] Further, in the step S2, the screening of the stray light transmission angle means: screening the transmission angle range (δ min , δ max ) of the non-deterministic stray light inducing the prepulse that can pass through the 4-aperture on the first and second filter plates in the multi-pass amplification system, where δ min is the minimum deviation angle of the stray light transmission, and δ max is the maximum deviation angle of the stray light transmission;

[0020] Among them, the stray light transmission deviation angle δ is:

[0021] δ = arcsin(nsint 0 )

[0022] Among them, t 0 is the incident angle when the actual light passes through the lens surface, and n is the refractive index of the lens;

[0023] When the defect position exciting the stray light and the stray light are on the same side of the optical axis, the value of t 0 is t 01 :

[0024]

[0025] When the defect position exciting the stray light and the stray light are on both sides of the optical axis, the value of t 0 is t 02 ;

[0026]

[0027] In the formula, l is the distance that the scattered light passes through the lens at a certain scattering angle, r is the curvature radius of the rear surface of the micro-lens, h is the distance from the defect to the optical axis of the lens, and θ is the actual scattering angle, that is, the angle between the scattered light beam and the main light beam.

[0028] Further, the method for determining the actual scattering angle θ is:

[0029] When the scattered light propagates together with the main optical path at a small angle, that is, when the main optical path and the stray light pass through the same aperture:

[0030]

[0031] When the scattered light is output from the aperture on the opposite side of the main optical path:

[0032]

[0033] When the scattered light is output from the aperture on the same side of the main optical path:

[0034]

[0035] Wherein, L is the distance between the defect center and the center of the first filter plate, a is the diameter of each aperture, t is the actual distance from the aperture center to the first filter plate, and θ 1 is the limit angle range within which scattered light can pass through an adjacent aperture when the actual main optical path beam passes through a certain aperture,

[0036] Furthermore, in the step S2, analyzing the energy transmission and amplification law of stray light means: analyzing the energy transmission and amplification law of stray light when non-deterministic stray light in the multi-pass amplification system can induce pre-pulses and make them transmit in the multi-pass amplification system;

[0037] Among them, during the transmission and amplification process, the stray light energy J is:

[0038]

[0039] Wherein, J 0 is the seed light injection energy, is the light intensity calculation formula of complex Mie scattering under multi-particle modulation, and E 1 is the amplification factor generated during the transmission process before the main optical path scatters, and E 3 represents the amplification factor of the stray light beam that does not transmit along the original expected direction after scattering through the gain medium;

[0040] Among them, E 1 and E 3 are respectively:

[0041]

[0042]

[0043] Wherein, h is the final amplification times that the main optical path corresponding to E 1 passes through, i is the iteration times that the main optical path passes through the neodymium glass before scattering, l is the iteration times that the stray light passes through the neodymium glass alone after scattering, m is the final amplification times that the scattered light passes through alone after scattering, d is the actual thickness of the neodymium glass, φ is the incident angle between the main optical path and the neodymium glass component, α is the incident angle between the scattering optical path and the neodymium glass, and g i is the gain coefficient before the (i + 1)-th amplification, and g l is the gain coefficient before the (l + 1)-th amplification, and g 0 is the small-signal gain coefficient, J i is the light intensity energy value before the (i + 1)-th amplification, J l is the light intensity energy value before the (l + 1)-th gain, and J s is the saturation light intensity energy value.

[0044] Furthermore, in step S3, the signal-to-noise ratio analysis of stray light refers to: calculating the signal-to-noise ratio of each non-deterministic stray light according to the transmission amplification law and its energy value when the non-deterministic stray light induces a pre-pulse, and analyzing the law of how the signal-to-noise ratio changes with the defect parameters;

[0045] Among them, the calculation formula for the signal-to-noise ratio SNR of stray light is:

[0046]

[0047] In the formula, I main is the final energy after the main optical path is amplified four times, and I pre is the final energy of the pre-pulse output in advance when passing through the first filter plate.

[0048] Furthermore, step S3 is specifically:

[0049] Based on the analysis results of the influencing parameters, draw a characterization diagram for suppressing the source of non-deterministic stray light, and perform defect control according to the defect positions shown in the diagram.

[0050] Furthermore, in the characterization diagram for suppressing the source of non-deterministic stray light, mark the positions of the components corresponding to the induced pre-pulse, the positions of the four-pass light spots on the components, and the dangerous positions of the optical path;

[0051] Among them, for the positions of the four-pass light spots on the components, different identifiers are used to characterize the dangerous situations of the induced pre-pulse, including safe situations, dangerous situations of pre-pulse output that meet the spatial distribution adjustment, and dangerous situations of pre-pulse output that meet both the spatial distribution and the energy transmission amplification law;

[0052] For the optical path positions on the components, the quadrant control method is used to characterize the more dangerous / safe quadrants of the induced pre-pulse.

[0053] The beneficial effects of the present invention are as follows: According to the present invention, impurities and defects randomly distributed in the multi-pass amplification system of high-energy lasers will excite non-deterministic stray light, which will form a pre-pulse in the system during transmission and amplification, damage the target, and reduce the signal-to-noise ratio of the system; by analyzing factors such as defect positions, sizes, incident light wavelengths, and stray light amplification multiples, the law of stray light turning into a pre-pulse is determined, and the optical components and optical paths that are prone to form pre-pulses are obtained. Impurities and defects on these components should be removed and controlled in a timely manner, providing a guiding law reference for the production and processing technology of the components of the multi-pass amplification system of high-energy lasers and the precision of the laser system construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a flowchart of a method for suppressing pre-pulses induced by non-deterministic stray light in a multi-pass amplification system provided by the present invention.

[0055] Figure 2 Structural diagram of the multi-pass amplification system provided by the present invention.

[0056] Figure 3 Diagram showing the influence results of different lens elements and defects on different optical paths on the output beam provided by the present invention.

[0057] Figure 4 Diagram showing the influence results of different flat elements and defects on different optical paths on the output beam provided by the present invention.

[0058] Figure 5 Hazard distribution diagram of single defect distribution provided by the present invention.

[0059] Figure 6 Geometric model diagram of the spatial distribution of stray light provided by the present invention; (a) Stray light modulation model diagram of lens flat; (b) Stray light transmission and filtering angle model diagram.

[0060] Figure 7 Diagram of amplified information of stray light energy in different situations provided by the present invention.

[0061] Figure 8 Diagram of the amplification law of stray light provided by the present invention.

[0062] Figure 9 Diagram of signal-to-noise ratio analysis of six dangerous situations of pulse generation provided by the present invention.

[0063] Figure 10 Diagram for suppressing the characterization of the source of stray light provided by the present invention. Detailed implementation manners

[0064] The following describes the detailed implementation manners of the present invention to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed implementation manners. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions made using the concept of the present invention are within the scope of protection.

[0065] A method for suppressing pre-pulses induced by non-deterministic stray light in a multi-pass amplification system, as Figure 1 shown, includes the following steps:

[0066] S1. Build a test platform for the multi-pass amplification system and set component defects;

[0067] S2. Analyze the influence parameters of non-deterministic stray light-induced pre-pulses excited by different component defects;

[0068] Among them, the influence parameter analysis includes defect position screening for exciting stray light, stray light transmission angle screening, analysis of the energy transmission amplification law of stray light, and signal-to-noise ratio analysis of stray light;

[0069] S3. Based on the results of the influence parameter analysis, control the defects that induce prepulses by exciting non-deterministic stray light in the multi-pass amplification system to achieve prepulse suppression.

[0070] In step S1 of the embodiment of the present invention, the light beam of the multi-pass amplification system structure has the characteristics of multi-path transmission and single-path multiple amplification. Based on the theory of bulk damage exciting stray light and the main optical path transmission law, an experimental platform of the multi-pass amplification system as shown in Figure 2 is constructed, which includes a laser, a first lens, a first mirror, a second mirror, a reverse device, a first filter plate, a second lens, a first flat glass, a second flat glass, a third mirror, a fourth mirror, a third lens, a second filter plate, a fourth lens, a third flat glass, a fourth flat glass, and a cavity mirror arranged in sequence;

[0071] The test platform of the multi-pass amplification system in this embodiment also includes a first amplified neodymium glass and a second amplified neodymium glass, and their single-pass amplification times are 6 times and 8 times respectively, with a total amplification of 14 times; due to its complex structure, it cannot be represented by a single element, so it is only represented by text in Figure 2 and not drawn with elements.

[0072] The first filter plate in this embodiment is arranged on the focal spectrum plane of the first lens and the second lens, and the second filter plate is arranged on the focal spectrum plane of the second lens and the third lens, which is convenient for filtering light and used to retain the main optical path; among them, the first filter plate is used to control the output light beam, and the second filter plate is used to modulate the light beam, and filter within each optical path to strengthen the light transmission in the main optical path direction.

[0073] The optical path of the multi-pass amplification system in this embodiment includes the first to fourth optical paths. Among them, the first optical path is the main optical path and is conjugate to the third optical path, the second optical path is conjugate to the fourth optical path, and each optical path corresponds to passing through the apertures of the first and second filter plates with the corresponding number of optical paths. Specifically, in the system structure diagram shown in Figure 2 , the first-pass main optical path of the first pass is laser light source → mirror 1 → mirror 2 → mirror 3 → mirror 4 → cavity mirror; the first-pass main optical path of the second pass is cavity mirror → mirror 4 → mirror 3 → reverse device; the first-pass main optical path of the third pass is reverse device → mirror 3 → mirror 4 → cavity mirror; the first-pass main optical path of the fourth pass is cavity mirror → mirror 4 → mirror 3 → output.

[0074] In this embodiment, according to the structure of the multi-pass amplification system simulated by ZEMAX software, the components with volume damage are lenses or flat glass. Therefore, in step S1 of this embodiment, defects with different positions and sizes are randomly set inside the first to fourth lenses and the first to fourth flat glass.

[0075] In step S2 of the embodiment of the present invention, the method for screening the defect positions where stray light occurs is as follows:

[0076] Track the spot of the output beam of the multi-pass amplification system on the detector to obtain the spot tracking schematic diagrams corresponding to each optical path of the first to fourth lenses and the first to fourth flat glass; the spot tracking schematic diagrams characterize the induced pre-pulse dangerous situations where the excited non-deterministic stray light satisfies the stray light spatial transmission law and can output from the apertures of the first and second filter plates 4.

[0077] Analyze the pre-pulse dangerous situations in the spot tracking schematic diagrams to obtain the induced pre-pulse danger distribution diagrams characterizing the lens / flat plate elements and their optical path defect positions.

[0078] Specifically, based on randomly given component defects, taking the tracking of the spot of the output beam on the detector by the method of tracking through ZEMAX software as an example, the final results when there are volume damage defects on the four lenses are as Figure 3 shown, and the final results when there are volume damage defects on the four flat glass are as Figure 4 shown. In each picture of Figure 3 and Figure 4 , the aperture in the upper right corner is the output aperture, and the white spot in the picture is the tracking spot of the stray light. When the white spot passes through the aperture in the upper right corner, it will be recognized as a dangerous situation.

[0079] We can obtain the dangerous situations of the scattered light transmission excited by single defects in the multi-pass amplification system through Figure 3 and Figure 4 , which include: all lens elements in the first optical path, the second and third light-incident flat plates; all lens elements in the second optical path and the third and fourth light-incident flat plate elements; the second lens in the third optical path, the second and fourth light-incident flat plates. When there are defects in multiple components in the system, it is the superposition result of the scattered light transmission excited by single defects, and the spatial distribution of the stray light generated in the case of multiple defects will be more complex and dangerous.

[0080] According to the dangerous situations given in the figure, the main dangerous optical paths of the four lenses are the first and second optical paths, and the lens element with more dangerous outputs in multiple optical paths is lens 4. The main dangerous optical paths of the four flat glass are the first, second, and third optical paths, and the main dangerous components are flat plate 2, flat plate 3, and flat plate 4. After sorting, the induced pre-pulse danger distribution diagram of single defects as shown in Figure 5 is obtained.

[0081] In step S2 of the embodiment of the present invention, the process of screening the stray light transmission angle is as follows:

[0082] Construct a geometric model diagram of the spatial distribution of stray light as shown in Figure 6 . According to Figure 6 (a), in addition to the stray light with a scattering angle caused by the bulk damage of the lens element, the lens element also has a secondary modulation function of converging the stray light. Therefore, the scattering angle of the stray light will be reduced, resulting in more stray light transmitting along the main optical path, thereby suppressing the prepulse. For the flat glass element, there is only the stray light distribution caused by the internal bulk damage without the secondary modulation effect. Therefore, the stray light excited by the internal defects of the flat glass element is more easily filtered out during the transmission process, while the excitation transmission of the lens element is not easily filtered out.

[0083] In the model diagram of the propagation principle of stray light excited by internal bulk damage of the lens and flat elements as shown in Figure 6 (a), the actual modulation methods of the lens and the flat element are shown by solid lines, while the dotted lines are the beam propagation paths without modulation. The beam transmission path without the secondary modulation of the lens is roughly equivalent to the modulation method of the defects in the flat element. Among them, the maximum deviation angle of the stray light transmission is δ max , and the minimum deviation angle is δ min . For the lens element, it is relatively complex. Therefore, we give the geometric relationship derivation diagrams for the corresponding two cases, which are respectively located on both sides of the schematic diagram of the lens and the flat in Figure 6 (a); they are respectively the relationship diagrams of the defect and the stray light to be considered on the same side and on the opposite side of the optical axis. In Figure 6 (b), the maximum transmission angle range of the stray light generated by a certain defect that can pass through the aperture on each output filter plate is given.

[0084] Based on this, the screening of the stray light transmission angle in this embodiment refers to: screening the transmission angle range (δ min , δ max ) of the non-deterministic stray light that induces the prepulse and can pass through the apertures on the first and second filter plates in the multi-pass amplification system. δ min is the minimum deviation angle of the stray light transmission, and δ max is the maximum deviation angle of the stray light transmission;

[0085] Among them, the stray light transmission deviation angle δ is:

[0086] δ = arcsin(nsint 0 )

[0087] Among them, t 0 is the incident angle when the actual light ray passes through the lens surface, and n is the refractive index of the lens;

[0088] When the defect position that excites stray light and the stray light are on the same side of the optical axis, t 0 takes the value of t 01 :

[0089]

[0090] When the defect position that excites stray light and the stray light are on both sides of the optical axis, t 0 takes the value of t 02 ;

[0091]

[0092] In the formula, l is the distance that the scattered light passes through the lens at a certain scattering angle, r is the radius of curvature of the rear surface of the microlens, h is the distance from the defect to the optical axis of the lens, and θ is the actual scattering angle, that is, the angle between the scattered light beam and the main light beam.

[0093] Specifically, when the defect position that excites stray light and the stray light are on the same side of the optical axis, t 0 takes the value of t 01 The derivation process is as follows:

[0094] When the defect and the stray light are on the same side of the optical axis, the geometric relationship between physical quantities can be obtained from the left derivation diagram of Figure 6 (a). The red dotted line with an arrow represents the traveling direction of the main optical path, and the red solid line is the actual propagation direction of the stray light. According to the trigonometric function relationship in the vector triangle ABC, we have:

[0095]

[0096]

[0097] When the defect position that excites stray light and the stray light are on both sides of the optical axis, t 0 takes the value of t 02 The derivation process is as follows:

[0098] When the defect and the stray light are on different sides of the optical axis, the secondary modulation situation of the lens and the relationship between various physical quantities can be obtained from the right derivation diagram in Figure 6 (a), and thus the relational expression of t 02 can be obtained:

[0099]

[0100]

[0101] Based on Figure 6 the analysis, the method for determining the actual scattering angle θ is:

[0102] When the scattered light propagates along with the main optical path at a small angle, that is, when the main optical path and the stray light pass through the same aperture:

[0103]

[0104] When the scattered light is output from the aperture on the opposite side of the main optical path:

[0105]

[0106] When the scattered light is output from the aperture on the same side of the main optical path:

[0107]

[0108] In the formula, L is the distance between the defect center and the center of the first filter plate, a is the diameter of each aperture, t is the actual distance from the aperture center to the first filter plate, and θ 1 is the limit angle range within which the scattered light can pass through the adjacent aperture when the actual main optical path beam passes through a certain aperture.

[0109] Based on the above analysis process of the stray light transmission angle, the following rules are obtained: For the lens element, the stray light generated by internal modulation can be secondarily modulated to reduce the divergence angle of the scattered light. The stray light angle near the optical axis is reduced less, and there is a minimum value of the offset angle; while the stray light angle far from the optical axis is reduced more, and there is a maximum offset value here.

[0110] In step S2 of the embodiment of the present invention, for the formation of the pre-pulse, in addition to satisfying that the spatial characteristics of the scattered light are output from aperture 4 of the filter plate, it is also necessary to satisfy the energy amplification law; the energy amplification law is that the stray light reaches the pre-pulse condition of the breakdown target damage threshold after a certain amplification. There are mainly two ways for the stray light energy to meet the pre-pulse requirements: One is that after being scattered by the main optical path, it breaks away from the main optical path and is transmitted and amplified alone, and meets the condition of early output; the other is that after the main optical path is amplified many times, it finally encounters a volume damage defect, and the small-angle scattered light energy accompanying the main optical path is relatively high and reaches the pre-pulse energy threshold.

[0111] Therefore, in step S2 of the embodiment of the present invention, analyzing the energy transmission and amplification law of the stray light means analyzing the energy transmission and amplification law of the stray light when the non-deterministic stray light in the multi-pass amplification system can induce a pre-pulse and transmit it in the multi-pass amplification system.

[0112] Regardless of the way of stray light amplification, the beam needs to go through multiple gains to achieve breakdown of the target. The difference between the two ways lies in when the main optical path encounters the volume damage defect. The scattered light in the first pass often only satisfies the spatial distribution and does not meet the angular condition, thus unable to form a prepulse to damage the target material. It can be obtained that the magnification that the stray light generated by volume damage defects at different optical path numbers and different component positions can be amplified corresponding to the optical path that can be output from aperture 4 can be determined by Figure 7 given. A magnification exceeding 50 indicates that the magnification energy multiple that can damage the SiO 2 target material is satisfied, and the magnifications enclosed by the square box satisfy both the energy amplification law and the spatial distribution characteristics, that is, the case where it can be output from aperture 4 of the output filter plate ahead of the main optical path, which is the most dangerous situation for the generation and transmission of prepulses in the system.

[0113] Based on Figure 7 the content, during the transmission and amplification process, the stray light energy J is:

[0114]

[0115] In the formula, J 0 is the seed light injection energy, is the light intensity calculation formula of complex Mie scattering under multi-particle modulation, E 2 is the magnification generated during the transmission process before the main optical path scatters, and E 3 represents the magnification of the stray light beam that does not propagate along the original expected direction after scattering after passing through the gain medium;

[0116] Among them, the S 1 y is the complex amplitude distribution function of the light field, which is a function of θ and , and its specific expression is:

[0117]

[0118] E 1 and E 3 are respectively:

[0119]

[0120]

[0121] In the formula, h is E 1The final magnification factor passed by the corresponding main optical path, i is the number of iterations of the main optical path passing through the neodymium glass before scattering occurs, l is the number of iterations of the stray light passing through the neodymium glass alone after scattering occurs, m is the final magnification factor of the scattered light passing through the neodymium glass alone after scattering occurs, d is the actual thickness of the neodymium glass, φ is the incident angle between the main optical path and the neodymium glass component, α is the incident angle between the scattering optical path and the neodymium glass, g i is the gain coefficient before the (i + 1)-th magnification, g l is the gain coefficient before the (l + 1)-th magnification, and g 0 is the small-signal gain coefficient, J i is the light intensity energy value before the (i + 1)-th magnification, J l is the light intensity energy value before the (l + 1)-th gain, J s is the saturation light intensity energy value.

[0122] Based on the foregoing formulas and theoretical analysis, taking Figure 3 as an example of setting component defects, the stray light magnification law diagram shown in Figure 8 is obtained. In this case, the damage defect is located on the first-pass optical path of the flat component 3. The main optical path has been magnified 22 times, while the stray light has experienced 6 magnifications alone. The injection energy of the incident seed light is 1 mJ, and it can be normally transmitted in the system. The scattering situations at scattering angles of 5 degrees and 10 degrees are calculated respectively, as shown in Figure 8 .

[0123] In step S3 of the embodiment of the present invention, the signal-to-noise ratio analysis of the stray light refers to: calculating the signal-to-noise ratio of each non-deterministic stray light according to the transmission magnification law and its energy value when the non-deterministic stray light induces a pre-pulse, and analyzing the law of the change of the signal-to-noise ratio with the defect parameters;

[0124] Among them, the calculation formula for the signal-to-noise ratio SNR of the stray light is:

[0125]

[0126] In the formula, I main is the final energy after the main optical path passes through four-pass magnification, I pre is the final energy of the pre-pulse output in advance when passing through the first filter plate; this formula links the main optical path magnification and the stray light magnification together, and perfectly expresses the influence of the pre-pulse on the signal-to-noise ratio of the system.

[0127] Taking the foregoing defect setting as an example, Figure 9The signal-to-noise ratio curves of the system in dangerous situations and the influence laws of parameters are characterized in detail. It is found that the system signal-to-noise ratio curves affected by the backscattering of components 3, 4, and 7 are lower than other curves. Therefore, the pre-pulse situation caused by them is more serious. The most dangerous situation is the third-pass light scattering of component 8, where the corresponding stray light has more components that can output from the aperture 4 of the output filter plate and has higher backscattering energy. The relatively safe situations are the forward scattering of components 3, 4, and 7 and the defect situation on component 6.

[0128] Step S3 of the embodiment of the present invention is specifically as follows:

[0129] Based on the analysis results of the influence parameters, a characterization diagram for suppressing the sources of uncertain stray light is drawn, and defect control is carried out according to the defect positions shown in the diagram.

[0130] Specifically, in the characterization diagram for suppressing the sources of uncertain stray light, the positions of components corresponding to induced pre-pulses, the positions of four-pass light spots on the components, and the dangerous positions of the optical paths are all marked;

[0131] Among them, for the positions of four-pass light spots on the components, different identifiers are used to characterize the dangerous situations of induced pre-pulses, including safe situations, pre-pulse output dangerous situations that meet the spatial distribution adjustment, and pre-pulse output dangerous situations that meet both the spatial distribution and the energy transmission amplification law; for the optical path positions on the components, the quadrant control method is used to characterize the more dangerous / safe quadrants of induced pre-pulses.

[0132] Based on the foregoing defect settings as an example, the following is obtained Figure 10 The characterization diagram for suppressing the sources of uncertain stray light as shown. Among them, the dangerous positions of four-pass light spots on the components corresponding to the dangerous situations of induced pre-pulses are marked by dots, indicating the dangerous situations that meet both the spatial distribution and the energy amplification law. Such a defect control method will greatly narrow the output control range of stray light and pre-pulses, thereby greatly reducing the workload of operators and achieving the effect of fast and accurate control.

[0133] In the present invention, specific embodiments are used to elaborate on the principles and implementation manners of the present invention. The descriptions of the above embodiments are only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

[0134] Those of ordinary skill in the art will realize that the embodiments described herein are provided to assist the reader in understanding the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations that do not depart from the essence of the present invention based on these technical revelations disclosed in the present invention, and these deformations and combinations are still within the scope of protection of the present invention.

Claims

1. A method for suppressing pre-pulses induced by undetermined stray light in a multi-pass amplification system, characterized in that: The following steps are involved: S1. Build a test platform for the multi-pass amplification system and set component defects; S2. Analyze the influencing parameters of pre-pulses induced by non-deterministic stray light induced by defects in different components; Among them, the influencing parameter analysis includes the screening of defect positions that excite stray light, the screening of stray light transmission angles, the analysis of the energy transmission amplification law of stray light, and the analysis of the signal-to-noise ratio of stray light; The method for screening defect locations where stray light occurs is: The spot of the output light beam of the multi-pass amplification system on the detector is tracked to obtain a spot tracking schematic diagram corresponding to each optical path of the first to fourth lenses and the first to fourth flat glass; the spot tracking schematic diagram represents the induced pre-pulse danger situation that the excited uncertain stray light satisfies the stray light spatial transmission law and can be output from the first and second filter plates 4 apertures; Analyze the pre-pulse hazard situation in the spot tracking schematic diagram to obtain the induced pre-pulse hazard distribution diagram that characterizes the lens / plate element and its optical path defect position; S3. Based on the results of the influencing parameter analysis, the defects of the pre-pulse induced by the non-determined stray light in the multi-pass amplification system are controlled to achieve pre-pulse suppression.

2. The method for suppressing pre-pulses induced by undetermined stray light in a multi-pass amplification system according to claim 1, characterized in that: The test platform of the multi-pass amplification system in step S1 includes a laser, a first lens, a first reflector, a second reflector, a reverse device, a first filter plate, a second lens, a first flat glass, a second flat glass, a third reflector, a fourth reflector, a third lens, a second filter plate, a fourth lens, a third flat glass, a fourth flat glass and a cavity mirror, which are arranged in sequence; The test platform of the multi-pass amplification system also includes a first amplification neodymium glass and a second amplification neodymium glass, and the single-pass amplification times of the glass are 6 and 8 respectively; The first filter plate is arranged on the focal spectrum plane of the first lens and the second lens, and the second filter plate is arranged on the focal spectrum plane of the second lens and the third lens; wherein the first filter plate is used to control the output light beam, and the second filter plate is used to modulate the light beam; The optical path of the multi-pass amplification system includes first to fourth optical paths, wherein the first optical path is a main optical path and is conjugate with the third optical path, the second optical path is conjugate with the fourth optical path, and each optical path corresponds to an aperture with a corresponding number of optical paths passing through the first and second filter plates; In the step S1, defects of different positions and sizes are randomly arranged inside the first to fourth lenses and the first to fourth flat glasses.

3. The method for suppressing pre-pulses induced by undetermined stray light in a multi-pass amplification system according to claim 2, characterized in that: In step S2, the stray light transmission angle screening refers to screening the transmission angle range of the non-determined stray light induced by the pre-pulse through the four apertures on the first and second filter plates in the multi-pass amplification system. , is the minimum deviation angle of stray light transmission, is the maximum deviation angle of stray light transmission; Among them, the stray light transmission deviation angle for: in, The incident angle of the actual light when it passes through the lens surface, n is the refractive index of the lens; When the defect that excites the stray light is on the same side of the optical axis as the stray light, The value is : When the defect position that excites the stray light and the stray light are located on both sides of the optical axis, The value is ; In the formula, is the distance that the scattered light passes through the lens at a certain scattering angle, The radius of curvature of the rear surface of the microlens, is the distance between the defect and the optical axis of the lens, is the actual scattering angle, that is, the angle between the scattered beam and the main beam.

4. The method for suppressing pre-pulses induced by undetermined stray light in a multi-pass amplification system according to claim 3, characterized in that: The actual scattering angle The method to determine is: When the scattered light propagates along with the main light path at a small angle, that is, when the main light path and the stray light pass through the same aperture: When scattered light is output from the aperture on the opposite side of the main optical path: When the scattered light is output from the aperture on the same side of the main light path: In the formula, is the distance between the defect center and the center of the first filter plate, For the diameter of each aperture, is the actual distance from the aperture center to the first filter plate, When the actual main light path beam passes through a certain aperture, the limited angular range of the scattered light that can pass through the adjacent aperture, .

5. The method for suppressing pre-pulses induced by undetermined stray light in a multi-pass amplification system according to claim 2, characterized in that: In the step S2, analyzing the energy transmission and amplification law of stray light refers to: analyzing the transmission and amplification law of stray light energy when the uncertain stray light can induce a pre-pulse in the multi-pass amplification system and transmit it in the multi-pass amplification system; Among them, during the transmission amplification process, the stray light energy J for: In the formula, Infuse energy into the seed light, is the calculation formula for the light intensity of complex Mie scattering under multi-particle modulation, E 1 is the magnification generated during the transmission process before scattering occurs in the main light path. It indicates the amplification factor of the stray light beam that is not transmitted in the original expected direction after scattering after passing through the gain medium; in, and They are: In the formula, for The final number of magnifications that the corresponding main light path passes through, is the number of iterations of the main light path passing through the neodymium glass before scattering occurs, l is the number of iterations that the stray light passes through the neodymium glass alone after scattering. is the final magnification number that the scattered light passes through after scattering occurs. is the actual thickness of the neodymium glass, is the incident angle between the main light path and the neodymium glass element, is the incident angle between the scattered light path and the neodymium glass, For the i +1 gain factor before amplification, For the l +1 gain factor before amplification, and , , g 0 is the small signal gain coefficient, For the i +1 light intensity energy value before amplification, For the l +1 light intensity energy value before gain, J s is the saturation light intensity energy value.

6. The method for suppressing pre-pulses induced by undetermined stray light in a multi-pass amplification system according to claim 5, characterized in that: In step S3, the signal-to-noise ratio analysis of stray light refers to: calculating the signal-to-noise ratio of each uncertain stray light according to the transmission amplification law and energy value when the uncertain stray light induces the pre-pulse, and analyzing the law of the signal-to-noise ratio changing with the defect parameter; Among them, the signal-to-noise ratio of stray light The calculation formula is: In the formula, is the final energy of the main light path after four-pass amplification. It is the final energy of the pre-pulse output in advance when passing through the first filter plate.

7. The method for suppressing pre-pulses induced by undetermined stray light in a multi-pass amplification system according to claim 1, characterized in that: The step S3 is specifically as follows: Based on the results of the influencing parameter analysis, a characterization diagram of the suppression of the root causes of uncertain stray light is drawn, and defect control is performed according to the defect positions shown in the diagram.

8. The method for suppressing pre-pulses induced by undetermined stray light in a multi-pass amplification system according to claim 7, characterized in that: In the non-determined stray light source suppression characterization diagram, the component position corresponding to the induced pre-pulse, the four-path spot position on the component and the optical path danger position are all marked; Among them, the dangerous situation of induced pre-pulse is characterized by different identifiers for the four-pass spot position on the element, including the safe situation, the dangerous situation of pre-pulse output that satisfies the spatial distribution regulation, and the dangerous situation of pre-pulse output that satisfies both the spatial distribution and the energy transmission amplification law; The more dangerous / safer quadrant of the induced pre-pulse is characterized by the quadrant control method for the optical path position on the element.

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