△ Huachuang Hongdu Highly Reliable Solid Lasers

With the rapid development of laser technology,solid-state lasers with their high power,high efficiency, long life and other advantages have played an important role in industrial processing,medical and cosmetic,military and national defense.However,with the increasing complexity and stringency of application scenarios,the reliability requirements of lasers are becoming more and more stringent.As the ” heart ” of the laser,the reliability of the optical system directly determines the overall performance and life of the laser.

This article is the first of the optical reliability series in the “high reliability” column.Due to its detailed content,it will be published in two parts.This is the first part,we will focus on optical design,selection of optical components and optimization of solid-state laser manufacturing process,to reveal how to build a solid foundation of laser optical reliability from the source of design and manufacturing.

01 Optical Scheme Design and Optical Component Selection

Optical scheme design and optical component selection are the first steps to ensure the optical reliability of lasers.

Optical Scheme Design

① Analog optical path transmission

• During the optical design stage,the optical path can be simulated by optical simulation software to ensure the mode matching degree of the beam and the change of the fundamental mode volume of the laser transmission process.The layout of the optical elements can be accurately evaluated by simulation.

For example,in resonance cavity design,by adjusting the mirror curvature and cavity length and optimizing the pattern matching parameters,the probability of higher-order mold production can be significantly reduced,thereby improving the stability and monomode nature of laser output.

② Predicting the effect of thermal lensing

• In addition,the optical scheme needs to be combined with the thermal-optical coupling analysis to predict the thermal lens effect of the laser.In the simulation model,the heat conduction equation is introduced to simulate the thermal distribution of laser crystal and gain medium,and the dynamic effect of temperature gradient on the spot size and focusing performance is evaluated.

For example,for high-power solid lasers,thermal deformation can be effectively suppressed by optimizing the cooling system layout to ensure that spot sizes remain stable over long periods of operation.

③ Simulate different work conditions

• The optical design should also take into account the influence of environmental adaptability and mechanical vibration.The stability of the optical path is simulated by simulation software to verify the precision of the optical elements and the rigidity of the structure.

For example,in portable lasers,the lightweight and highly rigid bracket design reduces the interference of external vibrations on spot positioning and improves the reliability of the laser in dynamic environments.

△ Optical Simulation Examples

Ultimately,through the combination of multiphysics field simulation and experimental verification,the optical solution can be optimized to ensure that lasers can maintain high performance output in complex application scenarios.

Optometry Selection

① Pick quality materials

• The selection of optical components should give priority to materials with high optical quality , low coefficient of thermal expansion and good mechanical stability.

For example,when selecting a laser crystal,it should be ensured that it has high purity and a uniform dispersion distribution to reduce the effect of thermal lensing effects and thermal stress on laser performance.

② Consider the conditions of use

• The selection of optical components should fully consider their working environment and use conditions.

For example,for high-power lasers, optical components with high reflectivity/high transmission rates on the surface should be chosen to reduce the loss of light energy and improve the utilization of light energy.A multilayer membrane system design is used to increase the threshold value of the optical components against laser damage and extend their service life.

△Laser Crystals and Highly Damaging Laser Lenses

02 Optimization of Solid Laser Manufacturing Process

Optimization of the solid laser manufacturing process is a key part of improving the optical reliability of lasers,including the processing of optical components,semi-finished product production, laser debugging process and cleanliness control.

Optical Component Processing

Ensure the quality and precision of the machining

• In the processing of optical components,it is necessary to strictly control the processing accuracy and surface quality to reduce optical defects and reduce the loss of light energy.

For example,advanced polishing techniques and equipment should be used in the polishing process of optical components to ensure that the surface roughness of outstanding components reaches nanoscale to improve their optical performance and service life.

Semi-finished Product Making

① Control of mechanical stress

• In the production of semi-finished products,the mechanical stress of mechanical parts and optical components should be controlled to avoid deformation of optical components,interface separation or film damage caused by assembly stress or thermal expansion mismatch.

For example,in the assembly of laser lenses and heat frame components,a low stress adhesive process is required.Furthermore,finite element analysis simulations and tests validate the stress distribution under the heat cycle,optimize the thickness of the bonding layer to match the thermal expansion coefficient of the material,thereby reducing the interface shear stress caused by temperature change.At the same time, the structural stability of the semi-finished product is verified through environmental adaptation testing to ensure that there is no stress accumulation caused by performance degradation in long-term use.

② Upgrade the welding process

• The welding process of laser crystal is very important for the thermal stability of solid-state laser,which needs to realize the seamless combination of crystal and heat sink through precision welding technology to avoid the optical spot distortion caused by high thermal lens effect.

For example, in the welding of laser crystals and copper heat sink, flakes can be used to fill the welding process, effectively improving the thermal conductivity and reducing the residual stress of the welding.

• In addition,the welding process needs to be optimized in conjunction with the heat sink design.

For high-power laser crystals, for example, a microchannel cooling structure can be designed whereby the cooling tube is integrated with the crystal base through a welding process, making the cooling liquid directly contact the back of the crystal. At the same time, the temperature distribution of the welding interface is simulated through finite element thermal analysis, optimizing the thickness of the solder layer and avoiding the concentration of thermal stress due to thermal expansion mismatch.

△ Output Stability of High-power Lasers Based on Huachuang Hongdu’s High Reliability Semi-finished Products

Experiments show that the laser crystal with precision welding technology can improve its heat dissipation performance by 40%,The output power stability is improved to ± 0.2%,It provides a key guarantee for the long-term reliable operation of high-power lasers.

Laser Tuning Process

① Reduce component position errors

• The assembly process of solid-state lasers should ensure the collimation and positioning accuracy of the optical elements.

For example,high-precision assembly jigs and adjustment structures ensure that relative positional errors between optical components are controlled within microns,thereby improving laser beam quality and stability.

② Reduction of mechanical stress on components

△ Huachuang Hongdu Highly Reliable Solid Laser Tuning

• At the same time,in the assembly process,excessive adhesives and fasteners should be avoided,and the specifications and tightening torques of the connecting screws should be determined to reduce the mechanical stress of the optical elements.The determination of the tightening torque needs to be combined with the yield strength of the material and the friction coefficient of the contact surface,Through the experiment of torque-angle curve,after the temperature cycle and vibration test,the power fluctuation and optical path offset of the re-measured solid-state laser are verified,and the appropriate torque corresponding to different devices is finally selected.

Cleanliness Control

In the manufacturing process of solid-state lasers,one of the key links is to strictly control the cleanliness of optical components,semi-finished components and laser cavity.Throughout the assembly and commissioning phase,it is essential to ensure that the laser and all its components are kept in a constant temperature and humidity,dust-free environment.Specific measures include:

① Dustless Storage Process

• Optical components and semi-finished products should be stored in nitrogen cabinets in clean rooms , and the environmental parameters should be constant temperature and humidity,in order to avoid thermal deformation of components caused by temperature fluctuations or moisture absorption caused by coating changes.

② Clean assembly debugging

• The processing,assembly and debugging of optical components,need to be carried out in a clean room with a cleanliness of 1000 or higher,and the concentration of particulate matter in the air and the ambient temperature and humidity are precisely controlled by high-efficiency filters.

For example,in the process of laser crystal assembly and bonding of lenses,A second cleansing table needs to be used in the cleanroom to isolate the operating area,prevent the particles brought by people or equipment from contaminating the bonding interface,and monitor the environmental parameters in real time through a temperature and humidity sensor to ensure that the bonding process is not disturbed by the environment.In the laser debugging process, the risk of human pollution is reduced through the operation of anti-static workstations and dustless gloves specifically designed for the cleanroom.

△ Huachuang Hongdu Highly Reliable Solid Laser 1000-Grade Production Workshop

The high reliability of solid lasers is no accident.It derives from precision optical design and simulation, and becomes a rigorous manufacturing process that covers many dimensions of machining, assembly,clean control and more. From the two cornerstones of the design and process discussed above, we are able to shape lasers’ outstanding optical stability and long life from the source.

In the next section,we will continue to explore how high-reliability lasers can maintain stable and reliable operation in a variety of harsh application scenarios by improving environmental adaptability and building intelligent maintenance monitoring strategies.Stay tuned.

Trailer for the series

This paper opens the “High Reliability” series of in-depth analyses of optical reliability.In the next section, we will focus on environmental adaptation improvement and maintenance monitoring strategies.Stay tuned!

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