The current study presents a detailed theoretical analysis on the performance of aerostatic journal bearings. The dimensionless Reynolds equation is derived and discretized by the finite difference method. An iterative procedure is adopted to get the air film pressure distribution. The bearing characteristics such as load capacity, stiffness and air flow rate under various bearing operating and geometric parameters are investigated. The numerical results show that the journal rotation plays an important role on the bearing characteristics, and the rotating speeds must be taken into consideration. The proposed method provides a valuable approach for analyzing the performance of aerostatic journal bearings, and can be used for the bearing optimizing design.
The laser induced damage to optics has been an issue of paramount importance in laser research community. The low damage threshold of fused silica surfaces predominantly restricts the development of high power and high energy systems. This paper is aimed at improving the surface damage threshold of fused silica substrates by researching the effect of mechanical and chemical defects on laser damage: cracks/scratches and metallic impurities. The cracks were found to close, at least in part, after thermal processing and the damage threshold of the indented region was little affected by the thermal processing. In contrast, the cracks were enlarged after chemical etching and the damage threshold was improved slightly. Concerning scratches, the damage threshold can be recovered significantly after different HF-based etching. The metallic contamination can be removed by HF-based etching and acid leaching. The etched surface shows that the damage threshold increased first to ~30J/cm2 and then decreased with etching time while the damage threshold stabilized at ~30J/cm2 for leaching >45min. The surface roughness may degrade after etching, from <1nm to 3~5nm RMS, but that is ~1nm after leaching. The leaching may be a potential method for dissolving metallic contaminants on the glass surface in order to get a smooth surface with high damage resistance.
Fused silica is widely used in high-power laser systems because of its good optical performance
and mechanical properties. However, laser damage initiation and growth induced by 355 nm laser illumination
in optical elements have become a bottleneck in the development of high energy laser system. In order to
improve the laser-induced damage threshold (LIDT), the fused silica optics were treated by two types of
HF-based etchants: 1.7%wt. HF acid and buffer oxide etchant (BOE: the mixture of 0.4%wt. HF and 12%wt.
NH4F), respectively, for varied etching time. Damage testing shows that both the etchants increase the damage
threshold at a certain depth of material removal, but further removal of material lowers the LIDT markedly.
The etching rates of both etchants keep steady in our processing procedure, ~58 μg/min and ~85 μg/min,
respectively. The micro-surface roughness (RMS and PV) increases as etching time extends. The hardness (H)
and Young’s modulus (E) of the fused silica etched for diverse time, measured by nano-indenter, show no
solid evidence that LIDT can be related to hardness or Young’s modulus.
The purpose of this paper is to study the effect of the inner pressure to the tool influence function (TIF) for polishing using a semi-rigid (SR) bonnet tool. The simulation model of a Semi-rigid (SR) bonnet polishing tool polishing BK7 is demonstrated and the pressure distribution data under different inflated-pressures in the contact area has been extracted. It’s observed that the inflated-pressure has few effects to the polishing pressure, and their shapes are also Gaussian-like. Hence, we made a hypothesis that the effect of inflated-pressure to the TIF is rather small. To verify this hypothesis, a group of experiments to generate TIFs under different inflated-pressure are conducted, and the hypothesis has been proved to be correct through comparing these TIFs.
Ultrasonic vibration assisted machining with harder abrasives than the material to be machined can improve the quality
of machined surface and manufacturing efficiency. Therefore, we integrated ultrasonic vibration (UV) into a recently
developed technique chemo-mechanical bound-abrasive polishing in anticipation of further increasing the material
removal rate (MRR) and/or surface roughness. The preliminary results indicate that ultrasonic vibration assisted
chemo-mechanical bound-abrasive polishing can lead to increased material removal rate of manufactured optics while
leaving the surface roughness comparable to conventional chemo-mechanical bound-abrasive polishing. The great MRR
is attributed to the superiority of UV-assisted chemo-mechanical bound-abrasive polishing in discharging resultant swarf
The paper summarizes the recent progress on the optical materials and components for the high power laser system in
China. The amplifier material, Nd glass, has been developed with continuous melt. Non-linear crystals, KDP/DKDP,
have been grown with rapid and traditional growth method. Fused silica and K9 glass has been achieved high quality.
Some potential materials for next generation high power laser system are also evinced in this summary.
A simple method which can be used to map mid-spatial scale surface irregularities with high signal noise ratio is described. Two major sources of errors are analyzed and removed. One is the contributions of small-scale irregularities of the reference surface, which are subtracted by shifting the test surface laterally by a distance. The other is the spurious response of CCD, which is removed by interpolation function. The presented method is verified by simulations and experiments. It shows that it can measure mid-spatial scale surface irregularities exactly and smaller scale surface irregularities can be obtained by making measurement for a series of the lateral shifting values corresponding to one-half of the pixel space on CCD.
Ultra-precision machining for optical lens is a key subject in the field of modern optics machining, the focus of which is the higher demands for profile precision and surface roughness. As a kind of deterministic machining, the single point diamond turning lathe is widely used in the optical field, thus higher stabilization for the turning lathe is required with small amplitude of vibrations in a broad frequency-domain. The single point diamond turning lathe now boast its various forms both at home and abroad, and the vertical flying cutting milling style is an important branch. This kind of lathe is characterized with low guide rail velocity and main errors of this part are the alignment error of guide rail, the disturbance evolved by driving components, and the low velocity crawl. Such errors are presented as low-frequency profile error on the workpiece surface, and often relate to the guide rail velocity. The rotate speed of the spindle is higher comparatively, and the system is composed as a vibration element with mass, air-rigidity, air-damping and the periodicity impact vibration. As a result, this vibration can copy to the work piece by the tool nose in machining process, so we must manage to reduce the vibration for high machining precision. This paper is to deduce the proper dynamic parameter for reducing the spindle vibration and optimize the spindle structure via dynamic calculation for the diamond turning lathes used and bring forward the reformative idea for the lathes.
Because of the demand for better performance in optical systems, there's a continuing effort to find more efficient ways of producing large optics. FOERC's involvement in developing new techniques for the fabrication of large optical components has resulted in the AOMTIL (Advanced Optical Manufacturing Technology Integrated Line). The purpose of the AOMTIL is to demonstrate the novel manufacturing process and technology for large optics in modern optical system. The progress of AOMTIL is presented in the paper. There are mainly four parts in AOMTIL as follows, the ultra-precision grinding, deterministic figuring or polishing, perfect surface conditioning and precision optical metrology. The preliminary results of the AOMTIL show the possibility to yield more than 20 pieces large optical components per month and the advantages in achieving high accuracy. Optical flats larger than 500mm in diameter have been produced with flatness better than λ/10 peak to valley.
A novel manufacturing method that is different from the traditional method for off-axis parabola is described. Generally, the figure error between the best-fit sphere and the parabola is many microns. It cannot be measured by high-precision interferometer and traditional hand finishing is not efficient. An advanced technology is introduced and the desired off-axis parabola is produced directly from the best-fit sphere. In this paper, magnetorheological finishing (MRF) technology is employed. The character of polishing spot, the material removal rate and the major manufacturing parameters are described. Fabrication parameters are optimized and the problems of fabricating off-axis parabola in practice are also discussed. A 150 mm diameter part was produced in a period of time in the experimentation with new deterministic polishing method. The final results show that the manufacturing ratio is more obviously improved than the traditional manufacturing method. It is a valid means to fabricate off-axis parabola with high efficiency and high-accuracy.
In this paper, the laser damage of transmissive optics used in high power Nd:YAG laser was studied in details by use of Nd:YAG damage testing system, the damage experiment was taken by 1-on-1 damage measurement method, and the damage morphology was observed by 200X Normaski microscope. The wavelength of laser is 1064nm and the duration of pulse is 10ns. Experiment result shows that the damage morphology of transmissive optics such as AR coatings and polarizer has same damage shape-pinhole, which is notable different from that of HR coatings. The pinhole is about round with diameter 10-50um, separated on the damage area of coatings and deep to the surface and sub-surface of the substrate. Specially, the damage pinhole exhibits on the rear surface of AR coatings and on the front surface of the polarizer respectively. On certain range of the laser energy density, the density improvement don't increase the size of the pinhole, just only increases the amounts of the pinhole. We think the pinhole is mainly induced by standing wave electrical field formed by laser and the defects near the both surface of the substrate.
In this paper, an experimental instrument for large-scale optics grinding is introduced, which is a three-axis CNC precision grinding machine. After resolving several essential technological problems (grinder dressing and dynamic balancing, positioning of large-scale optics and profile measurement) in precision grinding of large-scale optics, many experiments are carried on the workpiece of 330mm square K9 optics by applying the experimental instrument. Typical process values in grinding flat and spherical optics include: X-axis feed rate is 15-200mm/min, grinding depth 2-30μm, 1400-2000 rpm spindle speed for grinder and workpiece spindle speed of 40-150 rpm. The grinders are 250mm diameter resin bond with 8-10μm to 80-90μm diamond abrasives, used in rough or finish grinding. Experiment results are presented. The PV surface form of flat and spherical optics is 3-4μm, 4-5μm respectively.
A 500-mm-aperture wavelength-tuning phase-shifting interferometer has been developed in FOERC applied to the measurement of large optics. The optical and mechanical design and the calibration technique of the phase shifter are described in detail. Test results show that Peak-to-Valley value smaller than 63nm of interference cavity is achieved.
A 100-mm-aperture high lateral resolution interferometer has been developed in Fine Optical Engineering Research Center (FOERC), which is applied to the measurement of spatial frequencies of up to 2.5 lines/mm over a 100mm field of view. The system transfer function of the interferometer is greater than 60% at near half the Nyquist frequency. To demonstrate the performance of this high lateral resolution interferometer, theoretical errors of the system are thoroughly analyzed and the design implementation is carefully studied, such as light source, wave front slope, tolerance analysis, CCD sample and so on.
The goal of this 4" phase shifting Fizeau interferometer design is to measure the small scale deformations of the optical surface down to 0.1 millimeter in 100 millimeter diameter. In this paper, the factors of affecting the wavefront information testing in medium and high frequencies are analyzed. The general description of the 4" high spatial resolution interferometer is provided and the design of the major optical components in the interferometer is described. Finally, the interferograms of such kind of high spatial resolution interferometer producing are showed, and the last result is analyzed.
A 500-mm-aperture wavelength-tuning phase-shifting interferometer has been developed in FOERC applied to the measurement of large optics. Also it can switches to a smaller 130-mm-aperture. We describes in detail the optical and mechanical design as well as calibration technique of phase shifter and phase-shifting algorithm design. A Zygo 4 inch standard reflective flat is used to evaluate the accuracy and repeatability of our wavelength-tuning phase-shifting system.