| 摘要 |
PROBLEM TO BE SOLVED: To provide a photoelectric detector using an avalanche photo diode which operates stably in a region of a large current amplification factor. SOLUTION: By increasing a command voltage applied to an APD voltage setting circuit 2 step by step, a reverse bias voltage applied to an APD 3 is increased step by step, and each time the reverse bias voltage is increased, the current in the APD 3 is measured with a current detecting circuit 4. When a difference between the detected current and a specified value falls within an allowable value, the reverse bias voltage becomes a reference reverse bias voltage. Next, an MPU 1 determines the reverse bias voltage (reference reverse bias voltage) multiplied by a specific ratio as a reverse bias voltage to be used in the measurement, and then applies it to the APD 3 via the APD voltage setting circuit 2. Consequently, even if the characteristics of the APD 3 change, the current amplification factor of the APD 3 is kept constant.
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