| 摘要 |
PURPOSE:To measure the diameter of light beam with good accuracy, by extracting the intensity level of the light beam when light beam power is zero on the basis of the change quantity of the light beam power and the change quantity of light beam max. quantity. CONSTITUTION:The power of the output of the beam source of an optical head 14 is detected by a power direction circuit 16 and the detection data is sent to CPU 17. The image of light beam 13 is picked up to obtain an image signal 20 which is, in turn, converted to a digital signal to be stored in a frame memory circuit 22. A peak value detection circuit 23 detects the max. intensity value of light beam from the data of the circuit 22 by the order of CPU 17. Subsequently, the power of the light beam 13 is changed by a laser power controlling circuit 26 and, thereafter, an image signal is stored in the circuit 22 in the same way as mentioned above and the max. intensity of the light beam 13 is detected by the circuit 23. Next, the change quantity of the max. intensity values before and after change is calculated and, from the power change quantity of the light beam 13 preliminarily detected, luminous intensity when the light beam power stored in the circuit 22 is zero is obtained. Next, the obtained luminous intensity value is subjected to the comparing operation with the data stored in the circuit 22 to obtain the diameter 12 of the light beam. |
