要求准备、通顺。
Introduction
Recently, optical disks ave played an important role as a recording medium with both large storage and removability. Optical disk technology has now been established in barious data-storage fields, such as computer memories and digital audio-bideo disks. Their substrates are commonly made of plastic resin, for example, polycarbonate, polyollefine, or acrylicresin, because plastic resin has mass productivity and shock resistance better than those of glasss. However, because of the limited mechanical strength of the plastics, the substrates tend to be topographi-cally deformed by various factors,i.e.,structural, en-vironmental influences. The plastic disks undergo shape changes, especially during the manufacturing process, which consists of injection molding, reflective film coating, protective resin coating, and a bonding process. Mechanical parameters, i.e., tilt, run-out, and so on, originate mainly in the topographical deformation. In optical disks the disk tilt and the runout induce tracking difficulties. That is, the topographical conditions of disks seriously influence both writing and reading processes of electronic signals. More importantly, a DVD disk, which becomes a principal mediu in the optical disks, consists of two thin substrates, which are 0.6 mm thick, bonded with an adhesive resin. Use of the thin substrate provides an advantage in reducing aberration and in increasing the tolerance for the disk tilt. But the 0.6-mm substrate is mechanically weaker than a usual 1.2-mm substrate. Therefore, complicated dishing and distortion, which appear in the thin substrate, also influence the mechaniacal parameters. The topographical change of a final product with time also worsens the mechanical properties. Consequently, lifetime as a storage device becomes short. For a grasp of the dynamics and improvements of the properties of optical disks, it is necessary to obtain the whole surface topography rather than to reace each mechanical parameter. Thus it is of great concern to map the whole contour with good response, sensitivity, and resolution. However, there have been few experimental studies of disk deformation. Here we employ alaser-interfering contour mapping and measure the whole deformation of optical disks.
The principle of the method is as follows: The method employs a transmission grating plate placed over a sample surface at a small distance h. According to diffraction theorym an incident light wave is divided into both reflected and transmitted diffraction waves at the grating plate.
Where is the angle of an incident light with respect to normal to the grating plane, is the wavelength of incident light, g is a grating constant, and m denotes the diffraction order. The light passing through a grating reflected at a sample surface and optically interferes with diffracted light reflected at the grating plate.