Stray light management system and method for high power compact terminal optical system

Abstract

This invention belongs to the field of optical systems for high-power laser devices, and discloses a stray light control system and method for high-power compact terminal optical systems. The system includes a crystal, a focusing lens, an optical plate element, and an absorber box. The light source passes sequentially through the crystal and the focusing lens before reaching and being reflected by the optical plate element. This invention proposes optimized design methods for higher-order and first-order stray light, and an optimized beam trap design for high-throughput first-order stray light. This trap confines the high-throughput first-order stray light within the beam trap, achieving a significant improvement in system cleanliness from ISO 5 to ISO 3, making it particularly suitable for stray light control in high-power compact terminal optical systems.

Description

Technical Field

[0001] This invention belongs to the field of optical systems for high-power laser devices, and specifically relates to a method for stray light control in a high-power compact terminal optical system based on optimized terminal optical system and stray light management device parameters. Background Technology

[0002] The Final Optics Assembly (FOA) is the final stage of a high-power laser device, bearing the highest laser energy. It consists of expensive transmissive optical elements such as frequency-doubling crystals, focusing lenses, and vacuum windows, playing crucial roles in harmonic conversion, beam focusing, vacuum isolation, and debris shielding. When high-energy laser light passes through the FOA, each surface of every transmissive optical element retains residual reflected light (stray light). When the flux of stray light on the final optical elements and structural components is strong, it can introduce hundreds of thousands of contamination particles into the optical terminal system, reducing the lifespan of the final optical elements and limiting the output energy of the laser device. Therefore, preventing stray light from deteriorating the system's clean environment and effectively managing stray light are critical issues in the design of high-power laser device FOAs, improving the lifespan of optical elements and system output energy, and ensuring the safe operation of the laser device.

[0003] The National Ignition Facility (NIF) in the United States comprises 192 Field of Air (FOA) channels, arranged in a compact configuration within an atmosphere chamber environment, resulting in dense and complex stray light distribution. The NIF's engineering design was completed over nine years, beginning in 1994. The first integration verification on the Beamlet resulted in severe damage to optical components, leading to the FOA being designed as a micro-volume clean environment within the atmosphere chamber. A second integration verification of the FOA was conducted in 2006, which still revealed numerous problems. The overall system finalization was completed in 2007, and the FOA engineering design was completed in 2009. However, even as late as 2017, reports of terminal contamination and severe damage to optical components due to stray light were still being published. The Shenguang series of domestic devices also features a compact FOA arrangement, having undergone continuous design and optimization. The Shenguang II upgraded device incorporated comprehensive stray light control design from the outset, but as late as 2008, the Shenguang II upgraded device underwent another round of optimization design for the FOA to address the destructive effects of stray light on optical components. The Shenguang III prototype device failed to absorb stray light, resulting in stray light incident on the inner wall of the terminal, contaminating the FOA system and significantly reducing the lifespan of optical components. Therefore, the complex stray light distribution in compact FOAs and the contamination caused by stray light have a significant impact on the lifespan of terminal optical components and the improvement of laser device output capabilities, making it a key focus and challenge in current research.

[0004] Compact Fundamental Air Arrays (FOAs) experience numerous and complex stray light interactions due to the small distance between the octave band and the focusing section. Higher-order stray light (reflected twice or more) has lower flux, requiring careful attention to prevent its focal point from directly impacting components and structures. Controlling this primarily involves optimizing the orientation of the vacuum window and shielding. First-order stray light (reflected only once) has high flux, necessitating specialized absorber design. Controlling this mainly focuses on the distance between the fundamental frequency window and the focusing lens, as well as the design of the absorber itself.

[0005] To confine stray light within the beam trap while avoiding contamination of the terminal system by the absorbing glass (AB5 material). Summary of the Invention

[0006] To address the problems mentioned above in the background art, the present invention aims to provide a stray light control method for high-power compact terminal optical systems, which confines stray light in a beam trap while avoiding contamination of the terminal system by the absorbing glass (AB5 material).

[0007] The technical solution adopted in this invention is as follows:

[0008] A stray light control system for a high-power compact terminal optical system, the system comprising eight terminal optical elements arranged longitudinally within a compact distance, concentrated in two modules: a frequency conversion module and a focusing and sampling module.

[0009] Furthermore, the frequency conversion module consists of an isolation window 1, a second harmonic crystal (2), a third harmonic crystal (3), and a polarization smoothing crystal 4. It is located close to the transmission mirror and mainly performs functions such as atmosphere isolation, harmonic conversion, and polarization smoothing. Structurally, it is independently supported.

[0010] Furthermore, the focusing sampling module consists of a focusing lens 5, a vacuum window 6, a primary shielding plate 7, and a secondary shielding plate 8. Located near the vacuum target chamber, it primarily performs functions such as beam focusing, harmonic separation, measurement sampling, vacuum sealing, and debris shielding.

[0011] Furthermore, the stray light control system of the compact terminal optical system first theoretically analyzes the optical characteristics of stray light and establishes a stray light analysis model.

[0012] Furthermore, the stray light control system of the compact terminal optical system includes two types: high-order stray light control and first-order stray light control.

[0013] Furthermore, in order to ensure that high-order stray light stays away from components and structures, the setting parameters between each component in the aforementioned high-order stray light control method must meet the following conditions:

[0014] d1+d2+d3≤f / 6, 3d1≤f / 6

[0015] 3d1+2d2≥f / 6, 2d1+d2≤f3

[0016] 3(d1+d2+d3)≥f / 6,2d1+3d2+3d3≥f / 6 (1)

[0017] Wherein: the focal length of the focusing lens is f, and the distances between the focusing lens and the vacuum window, the vacuum window and the main shield, and the main shield and the secondary shield are d1, d2 and d3, respectively.

[0018] Therefore, the optimal numerical solution for the spacing between optical elements behind the focusing lens is:

[0019]

[0020] Furthermore, the high-order stray light control method, based on parameter settings, employs self-developed software to analyze the second- and third-order stray light focus distributions of the terminal.

[0021] Furthermore, in order to ensure that the focal point of the first-order stray light of the focusing lens is located between the polarization-smoothing crystal and the focusing lens, the setting parameters of each component in the first-order stray light control method must meet the following conditions:

[0022]

[0023] Wherein, the distances between the focusing lens and the polarization smoothing crystal, and between the fundamental frequency window and the polarization smoothing crystal are d4 and d5, respectively.

[0024] Furthermore, the first-order stray light control method is designed with the following principles in mind:

[0025] S1. Optimize the angles of the vacuum window, main shield, and secondary shield to ensure that first-order stray light does not act on the optical elements and frame in the focusing sampling module, while the stray light is in the same position for easy management;

[0026] S2. Add a fused silica element in front of each AB5 glass to ensure that damage to the AB5 glass does not contaminate the terminal system;

[0027] S3. By using a combination of "AB5 glass and quartz glass" in pairs, stray light is absorbed back and forth to ensure that stray light does not escape from the beam trap.

[0028] Furthermore, the first-order stray light control method employs a thin-edge hollow design for the focusing lens to ensure that stray light is controllable at the focusing lens.

[0029] Furthermore, the AB5 glass is placed at the point where the stray light beam diameter is largest, which is offset from the main optical path.

[0030] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0031] 1. The stray light control method for high-power compact terminal optical systems provided by this invention achieves a significant improvement in system cleanliness from ISO 5 to ISO 3.

[0032] 2. The stray light control method for high-power compact terminal optical systems provided by the present invention confines stray light in beam traps while avoiding absorption glass contamination of the terminal system.

[0033] 3. The stray light control method for high-power compact terminal optical systems provided by this invention offers a systematic solution for stray light control and environmental quality improvement in compact FOA systems. Attached Figure Description

[0034] The present invention will be described by way of example and with reference to the accompanying drawings, wherein:

[0035] Figure 1 This is a schematic diagram of a compact FOA stray light control system provided in an embodiment of the present invention;

[0036] Figure 2 This is a high-order stray light design model diagram provided in an embodiment of the present invention;

[0037] Figure 3 This is a diagram showing the high-order stray light control results provided in an embodiment of the present invention;

[0038] Figure 4 This is a diagram of the first-order stray light design model of the focusing lens provided in an embodiment of the present invention;

[0039] Figure 5 This is a diagram showing the first-order stray light control result of the focusing lens provided in an embodiment of the present invention;

[0040] Figure 6 This is a design drawing of the hollowed-out structure of the focusing lens provided in an embodiment of the present invention;

[0041] Figure 7 This is a design drawing of the beam trap provided in an embodiment of the present invention;

[0042] In the diagram: 1-Isolation window, 2-Second harmonic crystal, 3-Third harmonic crystal, 4-Polarization smoothing crystal, 5-Focusing lens, 6-Vacuum window, 7-Main shield, 8-Second shield, 9-Lens cutout, 10-Lens clip, 11-Focusing lens body, 12-Stray light focal point, 13-Combination of fused silica and AB5 glass, 14-Stray light, T-Focal plane. Detailed Implementation

[0043] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application.

[0044] Example 1

[0045] like Figure 1 As shown, this embodiment is a stray light control system, comprising eight terminal optical elements arranged longitudinally within a compact distance, concentrated in two modules: a frequency conversion module and a focusing and sampling module. The frequency conversion module consists of an isolation window 1, a second-harmonic crystal 2, a third-harmonic crystal 3, and a polarization smoothing crystal 4. Located near the transmission mirror, it primarily performs functions such as atmosphere isolation, harmonic conversion, and polarization smoothing, and is structurally independently supported. The focusing and sampling module consists of a focusing lens 5, a vacuum window 6, a primary shielding plate 7, and a secondary shielding plate 8. Located near the vacuum target chamber, it primarily performs functions such as beam focusing, harmonic separation, measurement sampling, vacuum sealing, and debris shielding.

[0046] like Figure 2 The diagram shows a high-order stray light design model. To ensure that high-order stray lights are kept away from components and structural parts, the parameter settings between each component must meet the following conditions:

[0047] d1+d2+d3≤f / 6, 3d1≤f / 6

[0048] 3d1+2d2≥f / 6, 2d1+d2≤f / 3

[0049] 3(d1+d2+d3)≥f / 6,2d1+3d2+3d3≥f / 6 (1)

[0050] Wherein: the focal length of the focusing lens is f, and the distances between the focusing lens and the vacuum window, the vacuum window and the main shield, and the main shield and the secondary shield are d1, d2 and d3, respectively.

[0051] Therefore, the optimal numerical solution for the spacing between optical elements behind the focusing lens is:

[0052]

[0053] Figure 3 The high-order stray light control results are shown in the image. The main steps involve using the self-developed software Ghost to analyze the focal distribution of second- and third-order stray lights at the terminal. Ghost first discretizes each incident ray, and then, for each reflecting surface in the system, uses the reflection theorem to analyze the reflection of each discrete ray after passing through multiple reflecting surfaces. It also displays all fluxes greater than 0.1 J / cm² in the system. 2The beam focus is determined, and then the path of the stray light focus is deduced and displayed based on the searched focus.

[0054] Example 2

[0055] This embodiment provides a design concept for a system to control first-order stray light. Figure 4 The diagram shows the design model for the first-order stray light of the focusing lens. To ensure that the focal point of the first-order stray light of the focusing lens is located between the polarization-smoothing crystal and the focusing lens, the parameter settings of each component must meet the following conditions:

[0056]

[0057] Wherein, the distances between the focusing lens and the polarization smoothing crystal, and between the fundamental frequency window and the polarization smoothing crystal are d4 and d5, respectively.

[0058] The design concept for first-order stray light control is as follows:

[0059] 1. Optimize the angles of the vacuum window, main shield, and secondary shield to ensure that first-order stray light does not act on the optical elements and frame in the focusing sampling module, while keeping the stray light in the same position for easy management;

[0060] 2. Add a fused silica element in front of each AB5 glass to ensure that damage to the AB5 glass does not contaminate the terminal system;

[0061] 3. By using a combination of "AB5 glass and quartz glass" in pairs, stray light is absorbed back and forth, ensuring that stray light does not escape from the beam trap.

[0062] Figure 5 The first-order stray light control effect diagram of the focusing lens is shown in Equation 4, considering an input energy of 4000J and a beam aperture of 360mm. The flux estimate at the fundamental frequency window is shown in Equation 7, and the flux estimate at the polarization smoothing crystal is shown in Equation 7.

[0063]

[0064]

[0065] Among these considerations, after the device has been running for a period of time, the transmittance of the components decreases and the reflectance increases, with the worst-case reflectance being 2%. Therefore, [the following is a possible interpretation based on the context:] Figure 5 As can be seen from Equations 4 and 5, the focal point of the first-order stray light of the focusing lens is located between the frequency conversion module and the focusing sampling module, far away from the optical elements and structural components. The first-order stray light does not act on the structural components, and the flux of stray light at the optical elements is acceptable. The first-order stray light control of the focusing lens is effective.

[0066] In both of the above embodiments, the focusing lens adopts a hollow structure design, the specific structure of which is as follows: Figure 6As shown, Figure 6 This is a design drawing of a focusing lens with a hollowed-out structure. The focusing lens includes a focusing lens body 11, a lens hollowed-out portion 9, and a lens clamp 10. The lens hollowed-out portion 9 is obtained by hollowing out the thin edge of the focusing lens body 11. The lens clamp 9 clamps the focusing lens body 11 on three sides to ensure that stray light does not hit the wedge lens structure after passing through, and does not contaminate the final optical system.

[0067] Figure 7 The design of the beam trap involves several steps. First, to avoid damage and contamination of the terminal system caused by using only absorbing glass, a fused silica glass is added in front of each absorbing glass, forming a glass assembly. Second, the core of the beam trap is to control the first-order stray light reflected from the vacuum window, primary shield, and secondary shield. The key design element is to utilize a pair of pose-optimized glass assemblies to repeatedly absorb and process the stray light, forming a beam trap that ensures the first-order stray light does not escape from this glass-based trap.

[0068] The stray light control scheme of the present invention is simple and easy to implement, and ingeniously designed, making it particularly suitable for stray light control in high-power compact terminal optical systems.

[0069] All features disclosed in this specification, or steps in all methods or processes disclosed herein, may be combined in any way, except for mutually exclusive features and / or steps.

[0070] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0071] This invention is not limited to the specific embodiments described above. The invention extends to any new feature or combination disclosed in this specification, as well as any new method or process step or combination disclosed herein.

Claims

1. A method for controlling stray light in a stray light control system for a high-power compact terminal optical system, characterized in that, The system comprises eight optical elements arranged longitudinally within a compact distance. These optical elements are concentrated in two modules: a frequency conversion module and a focusing and sampling module. The frequency conversion module consists of several different crystals installed side by side, positioned at the front end of the focusing sampling module closer to the transmission reflector. As light passes through the frequency conversion module, it achieves the functions of atmosphere isolation, harmonic conversion, and polarization smoothing. The focusing sampling module is located near the vacuum target chamber. The light passes through the frequency conversion module to reach the focusing sampling module, realizing the functions of beam focusing, harmonic separation, measurement sampling, vacuum sealing, and debris shielding. The control method is used to confine stray light within a beam trap. When using this method to control higher-order stray light, in order to ensure that the higher-order stray light stays away from components and structures, the setting parameters between each component must meet the following conditions: （1） Where f is the focal length of the focusing lens, and d1, d2 and d3 are the distances between the focusing lens and the vacuum window, the vacuum window and the main shielding plate, and the main shielding plate and the secondary shielding plate, respectively. The optimized numerical solution for the spacing between optical elements behind the focusing lens is: （2）。 2. A method for controlling stray light in a stray light control system for a high-power compact terminal optical system, characterized in that, The system comprises eight optical elements arranged longitudinally within a compact distance. These optical elements are concentrated in two modules: a frequency conversion module and a focusing and sampling module. The frequency conversion module consists of several different crystals installed side by side, positioned at the front end of the focusing sampling module closer to the transmission reflector. As light passes through the frequency conversion module, it achieves the functions of atmosphere isolation, harmonic conversion, and polarization smoothing. The focusing sampling module is located near the vacuum target chamber. The light passes through the frequency conversion module to reach the focusing sampling module, realizing the functions of beam focusing, harmonic separation, measurement sampling, vacuum sealing, and debris shielding. The control method is used to confine stray light within a beam trap. When this method is used to control first-order stray light, in order to ensure that the focal point of the first-order stray light of the focusing lens is located between the polarization smoothing crystal and the focusing lens, the setting parameters of each component must meet the following conditions: （3） Where d4 and d5 are the distances between the focusing lens and the polarization smoothing crystal, and between the fundamental frequency window and the polarization smoothing crystal, respectively.

3. A method for controlling stray light in a high-power compact terminal optical system as described in claim 1 or 2, characterized in that, The frequency conversion module includes an isolation window (1), a second harmonic crystal (2), a third harmonic crystal (3), and a polarization smoothing crystal (4) arranged side by side.

4. The stray light control method for a high-power compact terminal optical system as described in claim 3, characterized in that, The focusing sampling module includes a focusing lens (5), a vacuum window (6), a main shield (7) and a secondary shield (8); after the light is refracted by the focusing lens (5), it passes through the vacuum window (6), the main shield (7) and the secondary shield (8) arranged side by side.

5. The stray light control system for a high-power compact terminal optical system as described in claim 4, characterized in that, The focusing lens (5) adopts a thin-edge hollow design to ensure that stray light is controllable at the focusing lens.

6. The stray light control method for a high-power compact terminal optical system as described in claim 4, characterized in that, The optical element uses AB5 stray light absorbing glass, and a fused silica element is added in front of the stray light absorbing glass; AB5 glass is placed at the point where the stray light beam diameter is largest, which is away from the main optical path.

7. The method for controlling stray light in a stray light control system for a high-power compact terminal optical system as described in claim 2, characterized in that, The control design process of the aforementioned control method includes the following steps: S1. Optimize the angles of the vacuum window, main shield, and secondary shield to ensure that first-order stray light does not act on the optical elements and frame in the focusing sampling module, while the stray light is in the same position for easy management; S2. Add a fused silica element in front of each stray light absorbing glass to ensure that damage to the AB5 glass does not contaminate the terminal system; S3. A combination design of paired AB5 glass and fused quartz elements is used as a beam trap to absorb stray light back and forth, ensuring that stray light does not escape from the beam trap.

8. The first-order stray light control method as described in claim 7, characterized in that, AB5 glass is placed at the point where the stray beam diameter is largest, which is offset from the main optical path.

Images