| 摘要 |
PURPOSE:To keep an exposure power in a fixed value and to attain stable exposure by detecting the intensity of a laser beam incident in an objective lens and controlling a laser output of a laser beam generating means in response to the detection level. CONSTITUTION:A laser beam transmitted through a reflection mirror 12 is made incident on a photodetector 13 to supply an output signal in response to the intensity to a control circuit 11. The circuit 11 compares an output signal level of the detector 13 with a prescribed reference level and decreases the laser beam intensity of a laser oscillator 1 gradually when the signal level is larger and decreases the laser beam intensity when the signal level is smaller. Thus, the intensity of the laser beam made incident on an objective lens 6 is made constant and the exposure power is controlled constant. Thus, even when the laser beam intensity is changed due to the temperature or the humidity of optical components, the exposure power is controlled in a fixed value and stable exposure is attained. |
