Single crystal silicon mirrors were widely used in high-energy laser system, and the surface accuracy/quality seriously restricted the output of laser system. So, how to improve the manufacturing level of single crystal silicon mirrors was particularly important, especially the polishing level. This work focus ed on the manufacturing requirements of high-load-capacity single crystal silicon mirrors and conducted a detailed study on the evolution of surface accuracy, roughness and absorption in IBF process. For IBF technique, the incident electron voltage was set to 750 eV and the beam incident angle was set to zero degree. The optical surface profile data was obtained through sub-aperture stitching method. After IBF process, the surface accuracy PV of the single crystal silicon cylindrical mirror converged from the initial 469.280 nm to 101.173 nm, and the roughness RMS diminished from 0.626 nm to 0.506 nm, the surface accuracy and quality had been significantly improved. The weak absorption of the optical surface was detected by weak-absorption platform, and absorption results of the mirror increased to a certain extent, from the initial 0.473 ppm to 0.536. The results showed that IBF technique could effectively improve the surface accuracy/quality of single crystal silicon mirror, which was of great significance to improve the performance of high-energy laser system.
Fused silica, as an excellent optical material, was widely used in the fabrication of laser optics applied in short-pulse/high-power laser systems. Fused silica containing structural defects was easy to be destroyed under laser irradiation. Deeply understanding the impact of different structural defects on the damage characteristics was of great significance for improving the laser damage threshold of fused silica optics. This work focused on structural defects including Oxygen Deficiency Center (ODC), Non-Bridging Oxygen Hole Center (NBOHC), E’ center, Peroxy Linkage (POL), Peroxy Radical (PDR), and elaborated on its formation laws in detail. The changes of damage characteristics and optical property of fused silica with different structural defects were calculated by first principle method. Taking E’ center defect as example, the band gap of defective silica was 3.1242 eV while that of β silica was 5.61 eV, which meant that electrons were more likely to cross the band gap under laser irradiation, led to electron avalanche and induced laser damage. Meanwhile, the optical properties of fused silica with different structural defects also showed significant difference. The reflectivity of β silica was 0.045, while that of silica with E’ center defects was 0.0715. Under 355nm laser irradiation, the absorption of β silica was 0 cm-1 while that of E’ center defects was 16600 cm-1, the absorptivity increased significantly. The change of optical properties also increased the probability of laser damage. In this work, certain support could be provided for the laser-damage theory of fused silica, and the relevant results could also provide important reference for suppression of structural defects.
The main factor affecting the laser damage resistance of optical components is the damage precursor introduced in the manufacturing process. Some studies have shown that the ideal intrinsic matrix of fused quartz has a laser radiation damage threshold of up to 100J/cm2, but the manufactured optical components are far below this index. Therefore, effectively inhibiting or even eliminating the damage precursor is the key to improve the anti-laser damage performance of optical components. Abrasive Water Jet Polishing (AWJP) technology mainly removes materials through the collision and shear between abrasive particles and the workpiece surface, which has the characteristics of non-damage and non-contact processing. However, due to the small size of Tool Influence Function (TIF) and low efficiency, it is still challenging to achieve widespread application. In this paper, we analyzed the flow field characteristics near the workpiece surface when different nozzle tilt angles were used for processing under two different machining methods: maintaining the jet length unchanged and maintaining the standoff distance unchanged and corrected the pressure distribution. It was found that the changes in pressure distribution and shear stress distribution in the impact zone under different nozzle tilt angle conditions will result in a change in the width of the Gaussian-shaped TIF obtained after nozzle rotation machining. In addition, under the condition of the same nozzle tilt angle, the TIF of Gaussian shape with larger size can be obtained by using the processing method that keeps the standoff distance constant.
The high-power laser system imposes stringent demands on the complete spatial frequency range, particularly the mid-spatial frequency errors of its optical elements. The presence of mid-spatial frequency errors significantly compromises the optical performance of the system. To mitigate the mid-spatial frequency waviness error in high-power laser elements following magnetorheological polishing, this study utilized a proprietary rotatable magnetorheological polishing apparatus. The aim was to simulate the impact magnetorheological polishing on the surface's mid-spatial frequency waviness errors in the absence of rotation, as well as to evaluate the effectiveness of random rotation angles in suppressing the surface's mid-spatial frequency waviness errors. Ultimately, the fused quartz element was simulated and modified. The simulation results demonstrate that utilizing the rotatable magnetorheological polishing equipment with a rotating magnetorheological polishing head effectively suppresses the low-spatial frequency surface accuracy, resulting in reduced mid-spatial frequency waviness on the processed element's surface. The RMS of surface errors decreases from 11.142 nm to 0.765 nm, eliminating noticeable mid-spatial frequency waviness errors and completely eradicating the characteristic peak in the Power Spectral Density (PSD) curve. Consequently, the surface accuracy of the element is significantly enhanced. Therefore, by adjusting the rotational angle of the magnetorheological polishing head, it is possible to effectively suppress mid-spatial frequency waviness errors on the element's surface and achieve deterministic shaping, thereby meeting the manufacturing requirements for high-power laser elements.
We propose a novel design of two-dimensional geometrical waveguide combiner, which integrates the vertical pupil expansion area and horizontal pupil expansion area into one planar waveguide. Different from previous solutions, the proposed design allows larger FOV and easier pupil matching with compact structure. The relationship between maximum vertical FOV and slanted angle of partially reflective mirror array, the exit pupil matching method for vertical and horizontal FOV are discussed. Then the optimization process of the waveguide structure to obtain a large FOV and uniform illuminance is showed, and the simulation shows that the method is solid. The FOV of the designed waveguide combiner is 𝑉FOV × 𝐻FOV 33° × 49.5° and diagonal FOV 57.4°, and the thickness of the waveguide is 1.7𝑚𝑚.
Single crystal silicon carbide (SiC), the third-generation semiconductor material, has many advantages, such as wide band gap, low thermal expansion coefficient and high thermal conductivity, etc. It has a wide application space in the field of electronic equipment. Its surface quality has great influence on the performance of electronic devices. Therefore, the ultrasmooth polishing of single crystal silicon carbide is very important. At present, the main problems of single crystal silicon carbide processing are poor surface quality and low removal efficiency. In this paper, the ultra-smooth and efficient polishing of single crystal silicon carbide materials is the main research goal. The polishing experiment is carried out by using a uniaxial polishing machine, and the computer-controlled optical shaping (CCOS) immersion polishing is introduced. To achieve super smooth and efficient polishing of single crystal silicon carbide, the corresponding polishing fluid was prepared by Fenton reaction for chemical mechanical polishing (CMP), and KMnO4 polishing fluid was also used for CMP. A series of experiments were carried out by setting different process parameters. The effects of pH value of Fenton fluid, catalyst concentration, type of polishing pad on polishing efficiency and surface roughness were studied, and the influence rules on polishing effect were summarized, so as to seek the optimal process parameters and realize ultrasmooth and low defect polishing of single crystal silicon carbide by combination.
In order to solve the problem that the extra removal layer and the motion characteristics of the machine tool are difficult to meet the processing requirements of ion beam figuring, an ion beam figuring method based on new controllable ion source is proposed. By changing the working parameters of the ion optical system, the timing and duration of ion beam extraction are controlled in real time. The influence law of the machine tool motion acceleration in the process is analyzed theoretically, and then a new ion beam figuring method is proposed for the lack of dynamic performance. By adjusting the working parameters of the ion source developed by ourselves, the pulse duty ratio is continuously adjustable from 0 to 100% , and the pulse frequency is continuously adjustable from 1 to 1000 Hz. The sample is Φ100 mm monocrystalline silicon plane mirror. Firstly, the long-time stability of the new ion source was verified by line- scanning experiments, and then the error of 14.5 mm wavelength was etched with the axis of motion at a constant speed. The results show that the technology can make up for the lack of motion acceleration and avoid the extra removal layer, and have a wide range of potential applications in high precision quality adjustment, special surface treatment and so on. It is expected to promote the progress of ultra-precision machining technology.
Monocrystalline silicon reflectors are widely used in infrared high energy laser systems. In order to ensure the system to achieve high precision and high stability of beam transmission, the reflector needs to have a good laser load capacity for high power density laser under long time irradiation. However, the evaluation of reflector laser load capacity is influenced by multiple factors, which is difficult to be decoupled one by one, and the multiple index systems are not perfect. In this paper, multi-modal characterization methods such as reflectivity, fluorescence detection and surface roughness detection are proposed to establish the influence model of multiple influencing factors on the laser load capacity of monocrystalline silicon reflector. Through quantitative analysis of these defects with specific types and different properties, the surface cleanliness and integrity of the monocrystalline silicon reflector were analyzed from different angles, and the influence trend of each influencing factor on the laser load capacity of the element was obtained. In this paper, a relatively completed characterization system of monocrystalline silicon and the influence model of the laser load capacity of the monocrystalline silicon reflector have been established effectively. The influencing factors of the laser load capacity on the surface of the monocrystalline silicon reflector are evaluated effectively, which lays a foundation for the efficient acquisition of the monocrystalline silicon reflector with high load capacity.
The fused silica optics are important functional ultraviolet optical elements in the high-power laser system. Contamination plays an extremely important role in laser-induced damage, which will affect the laser damage threshold of the components to varying degrees, and finally affects the output flux of high-power laser system. An organic solvent needs to be used to wipe the optical surface before applying it, and this process will introduce organic pollution. In addition, different optical films and organic solvents have different effects on the laser damage threshold of fused silica, which need to be studied further. In this work, the photo-thermal weak absorption platform was used to test the photothermal weak absorption of three samples before and after the organic solvent treatment. The first sample was tested on the surface of the fused silica substrate; the surface of the second sample was coated with aluminum oxide; and the surface of the third sample was coated with hafnium oxide. The results show that the use of ethanol can increase the photo-thermal weak absorption of the substrate by 29.6%; the photo-thermal weak absorption signal of the fused silica element coated with aluminum oxide is reduced by 20% after the surface is wiped with ethanol; the fused silica element with hafnium oxide coated on the surface reduces the photo-thermal weak absorption signal by 33%. The experimental results verify the feasibility of using ethanol to wipe fused silica components.
The rapid development of high-power optical system and free electron laser put higher request forward the reflectivity performance of monocrystalline silicon optical materials. In this paper, the surface characteristics of monocrystalline silicon elements before and after ion beam figuring are tested. Firstly, the photothermal absorption was measured at the infrared band of 1064 nm, which shows that the absorption amplitude of the processed region is higher than the other. Then, the power spectral density function(PSD) was used to compare the surface roughness in different frequency bands. And surface reflectivity of the processed infrared band is improved by 5% measured by spectrophotometer. The experimental results show that after ion beam figuring, the hydrolyzed layer of monocrystalline silicon optical element is exposed, and the absolute reflectivity and photothermal absorption performance are improved, which can improve the performance of optical element in high power laser system.
To realize the rapid repairing of surface damage of fused silica optics, a method combining magnetorheological and Computer controlled optical surface (CCOS) was proposed to quickly remove small size damage points on the surface of damaged fused silica optics. In this paper, the size and number of damage points on the surface of fused silica optics are analyzed. Meanwhile, the surface of the fused silica optics is evenly removed by the magnetorheological technology, and the change rule of damage points on the surface of fused silica optics is analyzed. After that, CCOS smoothing technology is used to restore the surface quality of the optics. The experimental results show that the combined technology can effectively remove the small size damage points on the surface of fused silica optics and maintain the surface quality of the optics, achieving a good repair effect.
High-precision cylindrical surfaces are widely utilized in X ray telescope systems, laser systems, synchrotron radiation systems, etc. These systems put forward strict requirements on surface figure errors of cylindrical surfaces. As a supporting technique for fabrication, interferometric null test method for measuring cylindrical surfaces usually requires a Computer Generated-Hologram (CGH) as null. However, Limited by the aperture and F/number of CGHs for cylinders, large convex cylindrical surfaces with small R/number (ratio of the radius of curvature to the aperture) cannot be tested in a single measurement.Subaperture stitching along both axial direction and sagittal direction is required to acquire the full aperture surface figure map. a convex cylindrical mirror with R/3 and 350mm aperture was tested adopting our subaperture stitching test system for cylindrical surfaces. The key challenges are presented here including, subaperture stitching platform, subaperture algorithm, subaperture lattice, and the system alignment.
For avoiding the defect of introducing contamination for doped phosphate glass in conventional polishing technology, this paper proposes the machining method of Ion Beam Figuring(IBF). Material removal mechanism is also presented from a microscopic view. Surface roughness was analyzed by changing the incidence angle of normally and 20°. The results show that both surface roughness RMS are increased a little, and the PSD(power spectral density) of surface roughness RMS is shown, too.
With the expansion of military master and the adjustment of military scale structure, new requirements have been put forward for talent cultivation, especially for the high-level applied talents cultivation. Talents with different specifications, types and levels must be cultivated in the education process. Therefore, the master cultivation mode needs to be explored and improved. This paper systematically studies the classification standards, training scheme, graduation standards in the classification cultivation mode for master majoring in precision optical engineering, as well as the feasibility and implementation suggestions of the classification cultivation for master in military academy. By means of field investigations, collection and arrangement of network resources, questionnaire survey of characteristic samples, and combining with data resources of master, the sample database is established by collecting relevant data including professional types, training scheme, dissertation quality, professional development prospects and post applicability to output talents. The results indicate that the quality of graduate training can be effectively improved by the classifying training mode of “academic” and “applied”. The classified cultivation can not only satisfy the reform and development trend of military academy and the diversified demands of modern war for military talents, but also provide reference for high-level innovative military talents cultivation.
Single crystal silicon is a chemically active semiconductor material with good processing characteristics. With the development of technology, the role of single crystal silicon components in the field of ICF is becoming more and more important. Restricted by traditional processing method and MRF, damage precursors such as scratches and impurities still remain on the surface after processing. That may influence the performance of the elements. In this paper, we study the effect on the surface by two chemical etching methods and the influence on the damage precursors of nano jet polishing. We used HF solution/HNO3 and KOH/ isopropanol to etch the surface of the element. When the etching depth comes to 0.2 μm, pits and scratches could be easily found on the surface. After the etching process, the element was processed by nano jet polishing and the roughness decreased from 1.264nm to 0.986nm.We used nano jet polishing method to process the element polished by MRF in order to research the evolution of comet-tail scratch. The In-situ tracking method was also applied in this study. After the polishing process, the W-D (width to depth ratio) increased from 30.51 to 45.84. The scratch was deactivated and the PTA (photothermal absorption) decreased from 1.5413nA to 1.3500nA. The Ce impurities were also removed. Its concentration decreased from 0.1162mg/L to 0.0005mg/L and the PTA of the element decreased from 0.3044nA to 0.0652nA. From the research, we can easily know that the subsurface damage exposed after the etching process. That may lay the foundation of the nondestructive processing of single crystal silicon. After nano jet polishing process, the quality of the element became better. The roughness and concentration of Ce impurities decreased. The damage precursors were deactivated and the PTA decreased. In a word, chemical etching could expose the surface damage of single crystal silicon and nano jet polishing can improve the laser damage resistance.
The combination process of Magnetorheological finishing (MRF) and Computer controlled optical surfacing(CCOS) are adopted to overcome the drawback of traditional polishing method in final finishing of single-crystal silicon and the deterioration of the surface roughness of single-crystal silicon by Magnetorheological finishing. In order to meet the requirements of single-crystal silicon by magnetorheological finishing, a new magnetorheological finishing fluid is prepared and orthogonal process parameters experiments are designed to optimize the magnetorheological finishing parameters. Through the uniform finishing experiment of MRF and CCOS, the processing sequence conditions of the combined process are obtained. A single-crystal silicon mirror with diameter of 100 mm is finished with several iterations of MRF and CCOS, the surface roughness Ra reaches 0.7 nm which verified the prepared magnetorheological finishing fluid and the optimized parameters satisfied the Finishing requirements of the single-crystal silicon surface. The results prove that the combination of MRF and CCOS process has unique advantages in the final finishing of single-crystal silicon.
This article introduces the modification of single crystal silicon cylindrical mirror that combined immersed CCOS polishing with IBF polishing. In the processing of smoothing and modifying, the quality of the mirror’s surface has been further improved. In this experiment, we optimize the CCOS polishing process and improve the traditional CCOS polishing apparatus to polish the single crystal silicon convex cylindrical mirror. During the CCOS polishing process, the parameter were set as follows: pressure 0.4kPa, speed 25 r/min, polishing liquid concentration 4.5% (pH 10), polishing time 20 min. After polishing by CCOS, IBF is used on its heels. The parameter were set as follows: energy 1000-1200eV (Ar+ ion beam with low energy), incident angle of ion beam 90°, polishing time 30 min. The immersed CCOS polishing process and IBF polishing process iterated repeatedly until the surface quality of the single crystal silicon convex cylindrical mirror meets the requirement. After the polishing process, the sub aperture stitching method and Zygo interferometer are used to detect the surface. The PV value of the single crystal silicon convex cylindrical mirror is 0.265 lambda, the roughness is 0.679nm the residual Zernike is 70.5 nm after testing. The errors over the whole frequency band were significantly reduced. It could be seen from the above that the single crystal silicon convex cylindrical mirror had high accuracy and better profile on the surface after polishing process. The error over the whole frequency band also converged obviously. Therefore, the method that had been described in this paper could be used for the surface modification of single crystal silicon cylindrical mirror.
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