Pulse Frequency Measurement Circuit for Infrared Laser

Frequency measurement circuit based on PIN photodiode was designed to detect laser parameters in real time. The light intensity is decayed by the optical glass fixed in the front of the laser capsule. Photoelectric conversion is achieved by the photodiode. After being processed through the conditioning circuit, the electricity signal is transfered to the microcontroller which calculates the pulse frequency by counting the pulse number in interrupt mode. This system is enable to monitor the state of high-power laser in real time. By testing the whole system, the frequency measurement precision turns out to be less than 0.02%. The sensitivity of this measurement circuit is higher than 0.9V/mW, while the response time is lower than 3ns.