Introducing adaptive optics such as spatial light modulators (SLMs) can help troubleshoot the ‘one-to-one’ test mode of interferometric null surface figure tests for aspheric and free-form surfaces. However, the phase controlling accuracy of methods based on birefringence effects and phase-wrapping is too low for applying SLMs in interferometric surface figure tests. To this end, the flexible phase control method based on computer holography for SLMs is presented. The difference of phase control principle between the computer holography-based method and the birefringence effects and phase-wrapping based method is discussed. Phase control accuracy of the proposed method is about λ/30 (λ=632.8 nm) root-mean-square (RMS) according to the theoretical analysis result. The inherent wavefront error of a SLM HoloeyeTM LC 2012 is significantly nulled to from RMS 0.426λ to RMS 0.015λ, which verifies the high phase controlling accuracy of the proposed method. By troubleshooting the phase control accuracy issue, the presented method is promising for promoting the application of SLMs in interferometric surface figure tests.
Jet polishing plays an important role in ultra-precision machining. In this paper, the effects of slotted and slotless nozzles on micro jet machining are investigated. The pressure distribution and magnitude of the two nozzles on the workpiece were first calculated by finite element simulation software. Then a set of comparative tests were conducted on two single crystals of silicon. The results showed that the pressure distribution of the slotless nozzle was more uniform compared to the slotted nozzle, and the pressure value of the slotless nozzle on the surface of the workpiece was greater. In addition, the slotless nozzle is more capable of improving the surface roughness of the workpiece in the same time.
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.
To further increase the laser-induced damage threshold (LIDT) of calcium fluoride (CaF2), combined technique of chemical mechanical polishing (CMP) and acid etching as a function of removal mechanical defect and impurity contamination was investigated. After CMP process, the surface roughness reduced to Ra 0.68nm, the scratch and subsurface defect were mitigated which rise the LIDT to 8.6 J/cm-2. Due to the acid etching, the surface roughness of CaF2 elements increased to Ra 0.8nm, while the LIDT reached 11 J/cm-2, benefit from the elimination of impurity contamination. The result laser-induced damage test shows that, comparing to mechanical abrasive polishing (MAP), the LIDT increased by 240% after combined technique, it demonstrated that combined technique is an effective way to improve the resistance of laser damage of CaF2.
In order to explore the feasibility of ion beam figuring (IBF) on DKDP crystal, the DKDP crystal machined by single point diamond turning (SPDT) was processed by IBF. This paper investigates the influence of IBF on DKDP crystal. Firstly, the surface quality and the photo-thermal absorption of DKDP crystal were measured respectively after SPDT and IBF. Then,the laser-induced damage threshold (LIDT) of two different processing crystals were tested by R-on-1 method. Finally, the mechanisms that the effect of IBF on LIDT were analyzed and discussed. After processing, the DKDP crystal remained intact. The surface quality satisfied the frequency tripping crystal requirement. However, due to the environmental impact, DKDP crystal had deliquescence, which contribute to decrease the LIDT of DKDP by 27.5%. IBF on DKDP is feasible,it is necessary to control the processing environment to avoid the crystal deliquescence.
The influence of surface defects on high power laser optical elements will cause some harm to the performances of imaging system, including the energy consumption and the damage of film layer. To further increase surface defects on high power laser optical element, on-machine defects measuring system was investigated. Firstly, the selection and design are completed by the working condition analysis of the on-machine defects detection system. By designing on processing algorithms to realize the classification recognition and evaluation of surface defects. The calibration experiment of the scratch was done by using the self-made standard alignment plate. Finally, the detection and evaluation of surface defects of large diameter semi-cylindrical silicon mirror are realized. The calibration results show that the size deviation is less than 4% that meet the precision requirement of the detection of the defects. Through the detection of images the on-machine defects detection system can realize the accurate identification of surface defects.
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