| 摘要 |
PURPOSE:To hold the quantity of a composite beam constant by comparing the light quantity signal of the composite signal with a reference signal and varying a laser driving current. CONSTITUTION:The quantity of the spot S of the composite beam 45 is detected by a light quantity detector 52 at every time a scan is made once and when the light quantity signal P is inputted to a comparing circuit 51, the circuit 51 compares the signal P with the reference signal Sr which indicates the specific quantity of light and outputs an H or S signal. The L or H signal is inputted to a control circuit D4, which lower the set current of a constant current circuit C4 while receiving the H signal to decrease the light output of a semiconductor laser 14, so that the quantity of the spot S decreases and approximates the specific quantity of light. When the L signal is inputted, the circuit D4 increases the set current of the circuit C4 to increase the light output of the laser 14, so that the quantity of the spot S approximates the specific quantity of light. Consequently, the specific quantity of the spot of the composite beam is maintained.
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