Traditional methods of measuring out-of-squareness of ultra-precision motion stage have many limitations, especially the
errors caused by inaccuracy of standard specimens, such as bare L-square and optical pentaprism. And generally, the
accurate of out-of-squareness measurement is lower than the accurate of interior angles of standard specimens. Based on
the error separation, this paper presents a novel method of out-of-squareness measurement with a polygon artifact. The
angles bounded with the guideways and the edges of polygon artifact are measured, and the out-of-squareness distraction
is achieved by the principle that the sum of internal the angles of a convex polygon artifact is (n-2)π. A out-of-squareness
metrical experiment is carried out on the profilometer by using an optical square brick with the out-of-squareness of
interior angles at about 1140.2 arcsec. The results show that the measurement accuracy of three out-of-squareness of the
profilometer is not affected by the internal angles. The measurementwith the method can be applied to measure the
machine error more accurate and calibrate the out-of-squareness of machine.
Surface and subsurface damage in optical element will greatly decrease the laser induced damage threshold (LIDT) in the intense laser optical system. Processing damage on the workpiece surface can be inevitably caused when the material is removed in brittle or plastic mode. As a non-contact polishing technology, hydrodynamic effect polishing (HEP) shows very good performance on generating an ultra-smooth surface without damage. The material is removed by chemisorption between nanoparticle and workpiece surface in the elastic mode in HEP. The subsurface damage and surface scratches can be effectively removed after the polishing process. Meanwhile ultra-smooth surface with atomic level surface roughness can be achieved. To investigate the improvement of LIDT of optical workpiece, polishing experiment was conducted on a magnetorheological finishing (MRF) silica glass sample. AFM measurement results show that all the MRF directional plastic marks have been removed clearly and the root-mean-square (rms) surface roughness has decreased from 0.673nm to 0.177nm after HEP process. Laser induced damage experiment was conducted with laser pulse of 1064nm wavelength and 10ns time width. Compared with the original state, the LEDT of the silica glass sample polished by HEP has increased from 29.78J/cm2 to 45.47J/cm2. It demonstrates that LIDT of optical element treated by HEP can be greatly improved for ultra low surface roughness and nearly defect-free surface/subsurface.
Single layer piezoelectric driving deformable mirror (Unimorph DM) with large deformation, simple fabrication process and low cost has been widely applied for the adaptive optics system in recent years. In the past, the optimal design of deformable mirror is often used in analytic method, and made much simplified approximation in theory. This results in large error between theoretic and real system. In this paper, the influence laws between the fitting error and the effective aperture, and the spatial distribution are studied by the dynamic–electricity coupling simulation method. The relationship between the displacement and the thickness of the mirror, the diameter and thickness of the electrode and the width of the support ring are discussed. According to these rules, a scheme of optimizing the structure of deformable mirror has been proposed, and the key parameters are designed according to the requirements of the retinal imaging system. In the end, all the fitting errors of former Zernike items 3-30 are less than 0.4 with the rated voltage of 400V.
A kind of formation mechanism of periodic ripple on finished KDP (potassium dihydrogen phosphate) crystal in cutting
process is studied by analyzing the change of equivalent axial stiffness of aerostatic spindle and consequent motion of
spindle shaft caused by fluctuation of supply air pressure. The analysis shows that fluctuation of supply air pressure is
one of the reasons to cause surface ripple. Correlative experiments are taken and validate the analysis. By strictly
controlling air pressure fluctuation, the Peak-to-Valley (PV) value of surface ripple generated by both spiral turning and
face flycutting processes are reduced to less than 5nm.
Differing from the traditional pad polishing, hydrodynamic effect polishing (HEP) is non-contact polishing with the wheel floated on the workpiece. A hydrodynamic lubricated film is established between the wheel and the workpiece when the wheel rotates at a certain speed in HEP. Nanoparticles mixed with deionized water are employed as the polishing slurry, and with action of the dynamic pressure, nanoparticles with high chemisorption due to the high specific surface area can easily reacted with the surface atoms forming a linkage with workpiece surface. The surface atoms are dragged away when nanoparticles are transported to separate by the flow shear stress. The development of grand scale integration put extremely high requirements on the surface quality on the silicon wafer with surface roughness at subnanometer and extremely low surface damage. In our experiment a silicon sample was processed by HEP, and the surface topography before and after polishing was observed by the atomic force microscopy. Experiment results show that plastic pits and bumpy structures on the initial surface have been removed away clearly with the removal depth of 140nm by HEP process. The processed surface roughness has been improved from 0.737nm RMS to 0.175nm RMS(10μm×10μm) and the section profile shows peaks of the process surface are almost at the same height. However, the machining ripples on the wheel surface will duplicate on the silicon surface under the action of the hydrodynamic effect. Fluid dynamic simulation demonstrated that the coarse surface on the wheel has greatly influence on the distribution of shear stress and dynamic pressure on the workpiece surface.
A material removal mechanism of ceria particles with different sizes in a glass polishing process was investigated in detail. Contrast polishing experiments were carried out using ceria slurries with two kinds of particle sizes and different amounts of hydrogen peroxide (H 2 O 2 ) added in the slurries. The Ce 3+ ions on the surface of the ceria particles were gradually oxidized to Ce 4+ with increased H 2 O 2 concentration. It was found that the material removal rate (MRR) decreased sharply with an increasing concentration of H 2 O 2 . There was no material removal when the concentration reached 2.0% for nanoparticle slurry. Nevertheless, the application of microparticles made the MRR decrease to a constant value when excessive H 2 O 2 was added. By comparison, we conclude that the material is removed by chemical reaction for ceria nanoparticles, while chemical reaction and mechanical abrasion simultaneously take place for ceria particles with sizes at scale of micrometers in the glass polishing process. It is clearly demonstrated from the experimental results that Ce 3+ instead of Ce 4+ ions play an important role in chemically reacting with the glass surface. An ultrasmooth surface with root-square-mean roughness of 0.272 nm was obtained after being polished by ceria nanoparticles.
This article [Opt. Eng.. 52, (4 ), 043401 (2013)] was originally published on 15 April 2013 with an error on page 6, Sec. 4, paragraph 2. The first sentence “Figure 8 shows the AFM image of surface microstructure images of 10×10 μm on the silica glass surface…” has been corrected to read “Figure 8 shows the AFM image of surface microstructure images of 5×5 μm on the silica glass surface…”
Nanoparticle jet polishing (NJP) is presented as a posttreatment to remove magnetorheological finishing (MRF) marks. In the NJP process the material is removed by chemical impact reaction, and the material removal rate of convex part is larger than that of the concave part. Smoothing thus can progress automatically in the NJP process. In the experiment, a silica glass sample polished by MRF was polished by NJP. Experiment results showed the MRF marks were removed clearly. The uniform polishing process shows that the NJP process can remove the MRF marks without destroying the original surface figure. The surface root-mean-square roughness is improved from 0.72 to 0.41 nm. power spectral density analysis indicates the surface quality is improved, and the experimental result validates effective removal of MRF marks by NJP.
Potassium dihydrogen phosphate (KDP) crystals, which are widely used in high-power laser systems, are required to be free of defects on fabricated subsurfaces. The depth of subsurface defects (SSD) of KDP crystals is significantly influenced by the parameters used in the single point diamond turning technique. In this paper, based on the deliquescent magnetorheological finishing technique, the SSD of KDP crystals is observed and the depths under various cutting parameters are detected and discussed. The results indicate that no SSD is generated under small parameters and with the increase of cutting parameters, SSD appears and the depth rises almost linearly. Although the ascending trends of SSD depths caused by cutting depth and feed rate are much alike, the two parameters make different contributions. Taking the same material removal efficiency as a criterion, a large cutting depth generates shallower SSD depth than a large feed rate. Based on the experiment results, an optimized cutting procedure is obtained to generate defect-free surfaces.
Proc. SPIE. 8418, 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Smart Structures, Micro- and Nano-Optical Devices, and Systems
Micro V-groove array is a critical fundamental component of optical fiber array for optical communication system of next generation. The accuracy of micro V-groove directly determines the precision of optical fiber array. The test precision of the image method and the light intensity search method can't satisfy the test requirements including micro V-groove pitch and depth currently. A new stylus measurement method is presented for the ultra-precision testing of micro V-groove array. Stylus profilometer is used to travel over the surface of micro V-groove, the measurement data points are fitted by cubic spline curve. The center of optical fiber circle in the V-groove is calculated according to the theory of equidistant line. The least square theory is used to qualify the error of core pitch and depth combined with theoretical analysis of measurement accuracy in the error theory. The impact of deviation error in the workpiece clamping is analyzed, and a differential method is presented to eliminate the deviation error. The experimental result indicates that the new measurement method can accurately detect the precision of micro V-groove array.
Off-axis conic aspheric mirrors are crucial components in some optical systems, such as three-mirror-anastigmatic
telescopes (TMA). However, because of the swing limitation of lathe, off-axis aspheric mirrors are not easy to fabricate
using a general-purpose diamond turning machine. This research demonstrates slow tool servo diamond turning process
which allows fabricating off-axis conic aspheric mirrors on-axis. The figure error caused by tool centering error was
studied on. An off-axis parabolic mirror was fabricated and actual machining data are discussed. The result proved that
proposed approach is capable of fabricating copper off-axis parabolic mirror of 46mm diameter to a form accuracy of
0.736μm in PV error value.