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532-nm-modulated pulse generation based on a time-delay loop and polarization rotation.

A simple and low-cost scheme of generating 532 nm modulated pulses is investigated both theoretically and experimentally. The modulator is an external cavity based on a temporal delay loop and polarization rotation that is realized by two half-wave plates. Propagating in the temporal delay loop multiple times and being outputted partially after each round trip, the intensity of the initial green laser pulse is modulated. By analyzing the polarization of the pulse in each round trip, the pulse train is modeled to simulate the waveform of the modulated pulse. This modulator is coupled with a sub-nanosecond 532-nm-laser source to verify the model of intensity modulation. In the experiment, by rotating the HWPs, modulated pulses with various temporal profiles are obtained. The fundamental modulation frequency is calculated to be 520 MHz, and the frequency of the second harmonic also exceeds 1 GHz. Such a scheme of intensity modulation can be applied in underwater detection and ranging.