Ultra-precision machining is an effective approach to achieve high dimension accuracy and surface finish required in optical and laser components. An extensive study using a two-axis diamond turning machine is conduct...Ultra-precision machining is an effective approach to achieve high dimension accuracy and surface finish required in optical and laser components. An extensive study using a two-axis diamond turning machine is conducted to machine the reflector arrays used for laser diode beam shaping. To position the workpiece precisely, theoretical analysis is made so that the dimensional accuracy can be achieved. Investigations into machining burr reduction are carried out. With the process developed, reflectors with optical surface finish of 8 nm in Ra and minimized burr size of less than 0.5 μm have been achieved.展开更多
In this paper, a micro water dissolution machining （MWDM） principle is proposed for machining potassium dihydrogen phosphate （KDP） crystal using water-in-oil micro-emulsion as an abrasive-free polishing fluid. In ...In this paper, a micro water dissolution machining （MWDM） principle is proposed for machining potassium dihydrogen phosphate （KDP） crystal using water-in-oil micro-emulsion as an abrasive-free polishing fluid. In addition, two instances of the application of this principle to ultra-precision machining of KDP crystals are presented. Computer-controlled optical surfacing （CCOS） and diamond wire cutting （DWC） process were carried out according to the MWDM principle. In the case of the CCOS technology, it is found that the micro-waviness was removed completely by following the MWDM principle. The surface undulation decreased from 40 nm to less than 10 nm, and the surface root-mean-square （rms） roughness obviously reduced from 8.147 to 2.660 nm. In the case of the DWC process, the surface rms roughness reduced from 8.012 to 2.391 gm, and the cutting efficiency was improved. These results indicate that the MWDM principle can efficiently improve the machining quality of KDP optical crystal and has a great potential to machine water-soluble materials.展开更多
A potassium dihydrogen phosphate(KDP) optical crystal was machined to an ultra-precision surface with water-in-oil(W/O) micro emulsion polishing fluid. The micro water dissolution principle utilized in the machining p...A potassium dihydrogen phosphate(KDP) optical crystal was machined to an ultra-precision surface with water-in-oil(W/O) micro emulsion polishing fluid. The micro water dissolution principle utilized in the machining process is discussed, its planarization mechanism is illustrated, and an ultra-precision polished surface with 2.205 nm RMS roughness is obtained. However, a substantial quantity of residual contamination remained on the polished surface after machining. This can seriously impact the optical performance of the crystal, and so it must be removed. Fourier transform infrared(FTIR) spectroscopy was used to conduct an investigation into the composition of the surface residue, and the results showed that the residue was comprised of organic chemicals with hydrocarbon chains and aromatic ether, i.e., mostly the polishing fluid. The cleaning method and the principle on which the KDP ultra precision surface investigation is based are discussed in detail, and the cleaning experiments with selected KDP-compatible organic solvents were then performed. FTIR transmittance spectra measurement and microscopic observations were employed to assess the effects of the cleaning process on the surface of the KDP crystal. The results showed that toluene cleaning achieved the most desirable results. This cleaning method produced a surface roughness of 1.826 nm RMS, which allows the KDP crystal to be applied to subsequent engineering applications.展开更多
This paper studies wavelet estimations for supersmooth density functions with additive noises. We first show lower bounds of Lprisk(1 p < ∞) with both moderately and severely ill-posed noises. Then a Shannon wavel...This paper studies wavelet estimations for supersmooth density functions with additive noises. We first show lower bounds of Lprisk(1 p < ∞) with both moderately and severely ill-posed noises. Then a Shannon wavelet estimator provides optimal or nearly-optimal estimations over Lprisks for p 2, and a nearly-optimal result for 1 < p < 2 under both noises. In the nearly-optimal cases, the ratios of upper and lower bounds are determined. When p = 1, we give a nearly-optimal estimation with moderately ill-posed noise by using the Meyer wavelet. Finally, the practical estimators are considered. Our results are motivated by the work of Pensky and Vidakovic(1999), Butucea and Tsybakov(2008), Comte et al.(2006), Lacour(2006) and Lounici and Nickl(2011).展开更多
文摘Ultra-precision machining is an effective approach to achieve high dimension accuracy and surface finish required in optical and laser components. An extensive study using a two-axis diamond turning machine is conducted to machine the reflector arrays used for laser diode beam shaping. To position the workpiece precisely, theoretical analysis is made so that the dimensional accuracy can be achieved. Investigations into machining burr reduction are carried out. With the process developed, reflectors with optical surface finish of 8 nm in Ra and minimized burr size of less than 0.5 μm have been achieved.
基金supported by the National Natural Science Foundation of China(Grant No.51135002)Science Fund for Creative Research Groups(Grant No.51321004)
文摘In this paper, a micro water dissolution machining （MWDM） principle is proposed for machining potassium dihydrogen phosphate （KDP） crystal using water-in-oil micro-emulsion as an abrasive-free polishing fluid. In addition, two instances of the application of this principle to ultra-precision machining of KDP crystals are presented. Computer-controlled optical surfacing （CCOS） and diamond wire cutting （DWC） process were carried out according to the MWDM principle. In the case of the CCOS technology, it is found that the micro-waviness was removed completely by following the MWDM principle. The surface undulation decreased from 40 nm to less than 10 nm, and the surface root-mean-square （rms） roughness obviously reduced from 8.147 to 2.660 nm. In the case of the DWC process, the surface rms roughness reduced from 8.012 to 2.391 gm, and the cutting efficiency was improved. These results indicate that the MWDM principle can efficiently improve the machining quality of KDP optical crystal and has a great potential to machine water-soluble materials.
基金supported by the National Natural Science Foundation of China(Grant No.51135002)the Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.51321004)
文摘A potassium dihydrogen phosphate(KDP) optical crystal was machined to an ultra-precision surface with water-in-oil(W/O) micro emulsion polishing fluid. The micro water dissolution principle utilized in the machining process is discussed, its planarization mechanism is illustrated, and an ultra-precision polished surface with 2.205 nm RMS roughness is obtained. However, a substantial quantity of residual contamination remained on the polished surface after machining. This can seriously impact the optical performance of the crystal, and so it must be removed. Fourier transform infrared(FTIR) spectroscopy was used to conduct an investigation into the composition of the surface residue, and the results showed that the residue was comprised of organic chemicals with hydrocarbon chains and aromatic ether, i.e., mostly the polishing fluid. The cleaning method and the principle on which the KDP ultra precision surface investigation is based are discussed in detail, and the cleaning experiments with selected KDP-compatible organic solvents were then performed. FTIR transmittance spectra measurement and microscopic observations were employed to assess the effects of the cleaning process on the surface of the KDP crystal. The results showed that toluene cleaning achieved the most desirable results. This cleaning method produced a surface roughness of 1.826 nm RMS, which allows the KDP crystal to be applied to subsequent engineering applications.
基金supported by National Natural Science Foundation of China (Grant Nos. 11526150, 11601383 and 11271038)
文摘This paper studies wavelet estimations for supersmooth density functions with additive noises. We first show lower bounds of Lprisk(1 p < ∞) with both moderately and severely ill-posed noises. Then a Shannon wavelet estimator provides optimal or nearly-optimal estimations over Lprisks for p 2, and a nearly-optimal result for 1 < p < 2 under both noises. In the nearly-optimal cases, the ratios of upper and lower bounds are determined. When p = 1, we give a nearly-optimal estimation with moderately ill-posed noise by using the Meyer wavelet. Finally, the practical estimators are considered. Our results are motivated by the work of Pensky and Vidakovic(1999), Butucea and Tsybakov(2008), Comte et al.(2006), Lacour(2006) and Lounici and Nickl(2011).
