ACCURACY DEPENDING ON SCANNING ANGLE IN DYNAMIC SPOT SIZE MEASUREMENTMETHOD FOR AN OPTICAL DISK-DRIVE

The spot size has been measured by chopping the beam spot with a knife edge on an optical disk Tangential and radial spot sizes are measured with different two angled knife edges: theta(1)-edge and theta(2)-edg e. In this paper, the errors in the measurement of spot sizes caused b y the error in the scanning angle and the scanning velocity are descri bed. The result of the theoretical analysis gives the best combination s of the scanning angles which are theta(1) = 0 degrees, theta(2) = +/ -45 degrees with the radial direction. For example, if the angle error of theta(1) and theta(2) obtained experimentally 0.64 degrees, then t he calculated error of the radial spot size is 2.2%. The analyzed erro r shows a good agreement with the experimental results. It was analyti cally observed that the influence of the scanning velocity error on th e error of the measured spot sizes can be practically ignored using th is method.