Laser polishing and laser shape correction of optical glass

Abstract

Mechanical polishing of glass is a time consuming process especially for lenses deviating from spherical surface such as aspheres. With laser polishing, the processing time can be significantly reduced and the wear of hard tooling can be avoided. Using laser radiation for polishing, a thin surface layer of the glass is heated up just below evaporation temperature due to the interaction of glass material and laser radiation. With increasing temperature, the reduced viscosity in the surface layer leads to the reduction of the roughness due to the surface tension. Hence, a contactless polishing method can be realized nearly without any loss of material or need of polishing agent. In this paper, results for laser polishing of fused silica, BK7, and S-TIH6 are presented with area rates up to 5 cm2/s. However, the results show that the achieved roughness with laser polishing is strongly influenced by the thermal properties of the type of glass. During laser polishing, the glass material is relocated at the surface, thus no shape errors can be corrected. To reduce the residual waviness and shape errors after laser polishing, the authors investigated a further laser-based process step (laser beam figuring, LBF) which ablates material for a shape correction. Ablation depths <5 nm allow a high precision laser ablation for selective processing. For both processes, a CO2 laser is used

Electrolytic Plasma Polishing of Pipe Inner Surfaces

“…Mechanical polishing processes include grinding and honing where surface roughness in the µm range is achieved. Willenborg [10,11], Gora [12] and Bordatchev [13] described the laser polishing process in detail. In this process, a thin surface layer is melted.…”

Application of surface analysis in study on removal mechanism and abrasive selection during fused silica chemical mechanical polishing

“…Fused silica possesses very low thermal conductivity, excellent heat resistance, high deformation temperature and softening temperature, low dielectric constant, and optical transmittance in the extremely wide spectrum ranging from ultraviolet to infrared, making it very important in modern industrial and high‐tech fields. However, problems arising from fused silica processing, such as low surface quality, limit its applications in optical elements . In general, two main factors that influence postprocessing surface quality are surface damage produced as a result of mechanical action and residue of abrasives on the polished surface caused by adsorption or embedding.…”

“…Cormont et al employ carbon dioxide laser to eliminate scratches on large polished fused silica optics. According to Weingarten et al, surface quality as well as shape errors is improved by laser polishing. Except for flat fused silica, Weingarten et al succeed in developing microfluidic channel polishing in fused silica.…”

Numerical and Experimental Investigation of Morphological Modification on Fused Silica Using CO2 Laser Ablation

“…Laser processing is an effective and attractive method for surface modification of various materials, including surface texturing of semiconductors [1,2], corrosion prevention in biocompatible metals [3,4], and surface polishing of optical glass [5,6]. Employing CO 2 laser melting in a non-evaporative regime has enabled us to obtain surfaces of optical glass with a roughness smaller than 0.1 nm at a rapid processing rate of up to 5 cm 2 /s [5]. In the process, mass transportation and surface reshaping are predominantly driven by viscous and thermal capillary forces [7].…”