Papers by Keyword: KDP Crystal

Abstract: Potassium Dihydrogen Phosphate (KDP) crystal is widely used in laser frequency multiplications and electro-optical modulators, but its soft-brittle property and thermal sensitive characteristic make it a very difficult-to-machine material. In this paper, an in-house made diamond tool with one tooth is used to face-mill KDP crystal specimens on a high-speed micro CNC machining centre, based on a statistically designed experiment. The morphology and roughness of the milled KDP crystal surfaces are analyzed with respect to the process parameters. It has been found that cutting speed has the largest effect on surface roughness, while axial depth of cut and feed per tooth show a comparable effect on both the Ra and PV roughness measures. From this study, 3 m/s cutting speed, 3 μm axial depth of cut and 1 μm/z feed per tooth are recommended for single point diamond milling of KDP crystal.

Abstract: PID parameters of machine tool for micro-defect mitigation of KDP crystal had been optimized, after which the velocity fluctuation frequency and amplitude variation of motion axis under different spindle speeds were studied. It is evident that the stability and following errors of the system run better under the velocity&acceleration feed forward PID control algorithm and Notch filters. The velocity fluctuation frequency of motion axis varies with spindle speeds significantly when the tool system is stable, while the fluctuation amplitude variation is slightly changed. To be conclude, the optimal working spindle speed is verified to be 4.78×104 rpm based on comparative experiments, at which damage pits can be mitigated by micro-machining successfully with roughness value of 34.4nm.

Abstract: Temperature variation of KDP crystal is an important reason for its cracking. A finite element model was constructed to analyze temperature and thermal stress distribution of KDP crystal during wire saw slicing. The results showed that the highest temperature of the crystal which was located on the sawing kerf remained stable during slicing. The temperature inside the crystal rose slowly at the start of the slicing, and then tended steady with the continued increase of sawing depth. Because of the good cooling condition during the sawing process, the overall rise in temperature was small, and the maximum thermal stress on the sawing kerf was less than the tensile strength of KDP crystal, so temperature variation during slicing had little effect on crystal cracking.

Abstract: Surface micro-defects of large diameter KDP crystal have great influence on its laser damage threshold. The method of micro-mechanical repairing can inhibit growth of the laser damage obviously. The paper adopts Fourier modal method to periodically process Gaussian repaired contour and established the light intensity modulation model of the Gaussian contour inside the crystal. Based on the model, the paper researches the influences on the light intensity inside the crystal made by Gaussian repaired contour with different width. Calculation results show that when the curve depth is fixed, the maximum relative light intensity decreases gradually as the curve width increases. Through experiments of micro-mechanical repairing and laser irradiation, we find that the laser damage threshold of Gaussian repaired contour with 20μm depth and 400μm width is 3ω, 5J/cm². Meanwhile, experimental results verify the theoretical analysis. Keyword: KDP crystal, Gaussian repaired contour, internal intensity modulation, Fourier modal method, surface defect

Abstract: The large diameter-thickness-ratio KDP crystals are the main optical element in Inertial Confinement Fusion (ICF) device to realize the harmonic generation, thus they need to maintain high quality surface figure, and therefore, research on the influence of force environment (including clamping force and gravity) on harmonic loss is quite necessary. In this paper, grinding mount surface topography is simulated by the fractal theory; contact and clamp FEM model is established; four parameters are proposed to present non-uniform clamping force; the mathematical model between crystal mechanical performance and the harmonic loss is established; and finally the impact of clamping force and gravity on the harmonic loss is obtained. The calculation results have guiding significance on the design of clamping force magnitude and configuration and crystal working gesture.

Abstract: The ultra-precision floating motion platform is the key device for equipment detectingand processing optical elements, and this paper mainly studies the floating motion platform used fordetecting the surface detects in KDP crystal. The load capacity of air cushion supporting the floatingmotion platform is studied theoretically and experimentally, and finally the supply pressure of thefour air cushions were optimized under the guidance of its load characteristic curve. The structureparameter of plane flexure hinge, a key part of floating motion platform, is optimized and thesimulation results show that the optimized plane flexure hinge can eliminate the disturbance inZ-direction obviously, which is produced by the two motors. Finally the support position of crystalholder is optimized by means of static and modal analysis; and the set of optimized support way canmake the maximum deformation of the platform reducing by 2μm and make the 1st order naturalfrequency increase from 49.078Hz to 51.787Hz.

Abstract: The influence of tool rake angle, feed rate and back cutting depth on the surface roughness and surface waviness of KDP crystal were studied when processing KDP crystal in the way of horizontal fly cutting. Comparing with the influence laws of vertical single point diamond fly cutting, we analyzed the respective advantages of the two kinds of cutting processing methods and summarized the similarities and differences of the influence rules that cutting parameters on surface quality under the two ways.

Abstract: KDP crystal (Potassium dihydrogen phosphate single crystal) is extremely difficult to obtain flawless surface because of its soft, brittle, and hygroscopic. And a large amount of time has been spend on obtaining flawless surface with ultra-precision machining methods. In order to quickly reduce surface roughness on KDP crystal, a new micro-deliquescence polishing method with fine water mist was proposed, the polishing tool with fine water mist was designed, and the polishing experiment was carried out. The micro-deliquescence polishing with fine water mist can improve the surface quality of KDP crystal quickly, so it is an effective preprocessing before ultra-precision machining.

Abstract: KDP crystals were rapidly grown from point seeds by temperature reduction method. White-beam synchrotron radiation X-ray topography was used to study the growth imperfections in KDP crystals. Strong dislocation bunches originate on the prismatic faces of the seed were found. The producing reason of these dislocation bunches was discussed. Sector boundary between the prismatic sector and pyramid sector caused by the unbalance distribution of trivalent metal ions were also observed and analyzed.

Abstract: Although Single Point Diamond Turning (SPDT) can do pretty well in optical surfacing of large scale KDP crystal, both the surface accuracy and integrity are considerably high; meanwhile as the defects of micro-waveness and stress are inevitable, the laser-induced damage threshold of KDP optical elements after SPDT still cannot be satisfied. Because of the characters of deliquescent and water-soluble, the process of computer controlled Micro-nano deliquescence is attempted to remove the residual micro-waveness on KDP surface after SPDT. Based on the assumption of Preston and the characters of Micro-nano deliquescence, the model of material removal ratio is suggested, the dwell time for ascertained KDP surface is solved, the processing of computer controlled Micro-nano deliquescence is simulated and the processed surface condition on theory is obtained. Besides, the influences of different parameters on the surfacing efficiency and accuracy are analyzed. Finally, three polishing tracks are comparatively analyzed. The simulation results are quite important in guiding the experimental polishing of large scale KDP by computer controlled Micro-nano deliquescence