Advances in Nano-finishing of Optical Glasses and Glass Ceramics

It has been a challenge to finish optical glass surface due to their hard and brittle nature. Moreover tight tolerances of surface figure and finish make polishing a more critical operation. This work reports the results of an experimental study performed for full aperture polishing of BK7 optical glass. Flat samples of BK7 glass are polished using optical pitch polisher and cerium oxide slurry. Taguchi’s L9 orthogonal array is used for design of experiments. Abrasive concentration, pressure and overarm speed are taken as variable process parameters. Polishing is performed for duration of 120 minutes for each combination of parameters. Material removal is measured using the precision weighing balance. Surface roughness was measured using Form Talysurf PGI 120 profiler. Abrasive slurry concentration is observed to be one of the most significant parameters in optical polishing process. It affects material removal rate as well as surface roughness. Pressure applied at workpiece-polisher interface affects material removal rate but variation of pressure is not found to affect surface roughness significantly. Relative motion at workpiece-polisher interface is also observed to be significant in defining final polishing outputs.

Applied Optics, 2015

BK7 is an optical glass extensively used in lens manufacturing. In this work, magnetic abrasive finishing (MAF) method was utilized for finishing of this hard-to-machine material and the effect of various process parameters on surface roughness was investigated using response surface methodology. The best surface roughness value achieved was 23 nm. Among various finishing parameters, the abrasive size was found to be the most significant parameter followed by machining gap, magnetic particles size, rotational speed, and percentage weight of binding agent. Also, the mechanisms of material removal were studied by using atomic force microscopy (AFM). The AFM observations revealed that both microcutting and microfracture mechanisms might exist during MAF of brittle materials depending on the finishing conditions.

Precision Engineering, 2015

With the advance of contemporary technology, high precision surface finishing techniques for optical glasses are of great concern and developing to meet the requirements of the effective industrialized processes. Not only the used tools but also process parameters have great influence on the surface roughness improvements. In this paper, surface roughness improvement of Zerodur optical glass using an innovative rotary abrasive fluid multi-jet polishing process has been presented. For the same purpose, a tool for executing ultra precision polishing was designed and manufactured. Taguchi's experimental approach, an L 18 orthogonal array was employed to obtain the optimal process parameters. ANOVA analysis has also been carried out to determine the significant factors. It was observed that about a 98.33% improvement on surface roughness from (R a) 0.360 m to (R a) 0.006 m has been achieved. The experimental results show that a surface finished achieved can satisfy the requirements for optical-quality surface (R a < 12 nm). In addition, the influence of significant factors on surface roughness improvement has been discussed in this study.

Optical Engineering, 1998

Rapid generation of large area polished optical surfaces by high-power CO 2 laser irradiation is shown. Results focus on glasses with high expansion coefficients (␣у10 Ϫ5 /°C) conventionally used in the optical industry. The technique involves active beam integration to obtain an intensity irradiation profile with a good uniformity over large spot sizes and is applied to preheated glass samples with initial rms roughness up to 500 nm. To find out the conditions for successful and reliable use of the proposed laser polishing method, the laser-driven heating process was monitored by means of the surface and depth temperature distributions. Whereas the former was determined in situ from the IR radiation emitted by the glass surface, the latter was obtained by comparison of the IR radiation emitted by the bulk sample with a theoretical model. Laser polishing of 5000 mm 2 glass surfaces is reported and processes involved in the modification of the surface texture of the irradiated samples are described and discussed. © 1998 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(98)04101-4] Subject terms: high power CO 2 laser application; rapid generation of polished glass surface; in-process temperature measurements; laser beam integration.

Transactions of Nonferrous Metals Society of China, 2009

This study is focused on the application of an effective fabrication method combining electrolytic in-process dressing(ELID) grinding and magnetic assisted polishing(MAP) to nano-precision mirror surface grinding on the optics glass-ceramic named Zerodure that is commonly used in precision optics components. The results show the variation of surface roughness after MAP processes utilizing Fe+CeO 2 , Fe+CeO 2 +diamond paste and Fe+diamond paste are applied to ELID ground surfaces. The MAP surface roughnesses for ELID ground surface roughnesses(R a ) of 52.1, 39.8 and 51.1 nm using #1200 grinding wheel are improved to 6.1, 4.6 and 1.9 nm, respectively. The surface roughness of MAP process using Fe+CeO 2 +diamond paste is superior to that using other processes. Moreover, it takes less than 10 min to conduct the MAP processes. The combined method suggested effectively reduces the working time to get the required surface qualities.

IOP conference series, 2012

The use of powders in metallic oxides as means of grinding and polishing of the optical glass components have seen recently a large application in optical industry. In fact, cerium oxide abrasive is more used in the optical glass polishing. It is used as grains abrasive in suspension or fixed abrasive (pellets); these pellets are manufactured from a mixture made of cerium oxide abrasive and a organic binder. The cerium oxide used in the experiments is made by (Logitech USA) of 99 % purity, the average grain size of the particle is 300 nm, the density being 6,74 g /cm 3 and the specific surface is 3,3042 m 2 /g. In this study, we are interested in the surfaces quality of the optical glass borosilicate crown (BK7) polished by particles in cerium oxide bounded by epoxy. The surfaces of the optical glass treated are characterized by the roughness, the flatness by using the microscope Zygo and the SEM.

Proceedings of SPIE, 1996

Rapid generation of large area polished optical surfaces by high-power CO 2 laser irradiation is shown. Results focus on glasses with high expansion coefficients (␣у10 Ϫ5 /°C) conventionally used in the optical industry. The technique involves active beam integration to obtain an intensity irradiation profile with a good uniformity over large spot sizes and is applied to preheated glass samples with initial rms roughness up to 500 nm. To find out the conditions for successful and reliable use of the proposed laser polishing method, the laser-driven heating process was monitored by means of the surface and depth temperature distributions. Whereas the former was determined in situ from the IR radiation emitted by the glass surface, the latter was obtained by comparison of the IR radiation emitted by the bulk sample with a theoretical model. Laser polishing of 5000 mm 2 glass surfaces is reported and processes involved in the modification of the surface texture of the irradiated samples are described and discussed. © 1998 Society of Photo-Optical Instru- mentation Engineers. [S0091-3286(98)04101-4] Subject terms: high power CO 2 laser application; rapid generation of polished glass surface; in-process temperature measurements; laser beam integration.

The aim of advanced optical fabrication is to produce highly accurate optical surface with better reproducibility. It demands a good control and systematic understanding of the process and its parameters. Optical polishing process defines the final surface figure and finish of the component. Controlled amount of finishing forces and material removal rate are necessary for polishing of brittle materials. However, the conventional or full aperture polishing process still depends on the operator’s skills to achieve the desired surface figure and finish. The process may be well optimized at individual manufacturing setups but there appears to be a little prediction about polishing outputs. Thus, it is essential to study the fundamental mechanisms of material removal during polishing in order to achieve the accurate prediction of process outputs. This paper reviews the work carried out in the area of full aperture optical polishing.

Key Engineering Materials, 2013

In the paper a new surface refining technology which uses nano-particles to improve the soda -lime -silica glass surfaces is presented. The SEM-EDS (Energy Dispersive X-ray Spectrometry) analysis was carried out to determine modification of the glass surface. A very thin modification layer was observed on the glass surface. The surface modification leads to an improvement of physical and chemical properties of the investigated glass.

Applied Optics, 1994

It is shown that optical surfaces traditionally ground in conventional glasses with high coefficients of thermal expansion may be polished by irradiation with a space-and time-controlled uniform CO 2 laser beam. Comparisons of a theoretical simulation model of the laser-driven heating process with the experimental results allow us to determine the conditions for successful and reliable use of this technique. The technique can be applied indiscriminately to preheated samples made of different glasses, with any topography, and, of any size in a limited range that depends only on the available laser power.