Figure 4. Transient periodic heating pattern on GaAs induced by S polarised excimer radiation incident at 60°. Ripple spacing is 2.2 um. a) Net permanent change in the first 30 excimer pulses b) Net transient heating pattern during the 31st incident excimer pulses c) Permanent rippling after 35 incident excimer pulses Close inspection of b and c shows that the areas of transient periodic heating on the right hand side of 4b have become well defined permanent ripples in 4c. Figure 5. Transient periodic heating pattern on Ge induced by S polarised light incident at 60. Ripple spacing is 6 μm. a) Net transient heating effect b) Net permanent rippling It can be seen that 3 distinct transiently heated bands are induced. Figure 5b shows that this has produced no permanent rippling. Figure 6. Profile of the transient periodic heating pattern observed in figure 5 a) Profile obtained along the vertical line shown Pixel Grey Level 8 SURFACE TRANSIENT HEATING PROFILE Vertical Pixel Position Figure 6. b) Profile of transient heating where the vertical axis is the intensity (greylevel) of the image and the horizontal axis is position in pixels from the top. Note that a pixel greylevel of 31 corresponds to no change between the initial and transient images that were processed to yield 6a. It is apparent that between the fringes there is no surface heating as the pixel greylevel is 31. MANUSCRIPT NOT RECEIVED SPUTTER ETCHING OF COATING SUBSTRATES K. Yoshida, H. Yoshida, and S. Nakai Osaka University Suita, Osaka, 565 Japan and M. Ohtani Physics & Chemical Technology Dept. 1 Canon Inc. Ohta-ku, Tokyo 146, Japan ABSTRACT Glass substrates for the optical coatings have many contaminations on the surfaces which can not be removed by standard optical cleaning techniques. In this paper, the significant improvement of laser damage threshold due to sputter etching is presented. In order to improve the damage threshold, we have prepared the BK-7 substrate sputter etched with Ar gas pressure of 5 x 10-1 Pa. The damage threshold of the AR coating on the etched surface showed 2 3 times improvement compared with that of un-etched surface at the laser wavelength of 1.06 μm with a 1 ns pulse width. The roughness of the etched surface was almost the same as the polished surface ones. MANUSCRIPT NOT RECEIVED ULTRA-PRECISION GRINDING OF OPTICAL MATERIALS Y. Namba Chubu University 1200 Matsumotocho, Kasugai Aichi 487, Japan ABSTRACT The ultra-precision surface grinder has been developed to get optical surfaces with submicron accuracy on optical glasses. The machine has precise and rigid hydrostatic oil bearings in both spindles for a grinding wheel and table. The grinding wheel spindle is made of zero-thermal expansion glass-ceramics to prevent from thermal deformation of the spindle. The depth of cut is controlled in 0.1 micron by a numerical controller. The machine can grind optical glasses to the degree of conventionally-polished optical surfaces in fugure and surface roughness. |