External optical cavity locked by laser frequency

With the peak-seeking servo-controlled technology based on a residual error, an external optical cavity can keep in resonance with the frequency of Ti-sapphire laser in the experiment. The servo loop uses a piezoelectric transducer (PZT) as a modulator, which modulates the intensity of the transmitted light passing through the cavity. The servo signal is obtained from the lock-in amplifier, then it is amplified by a high voltage amplifier, which adjusts the length of the cavity according to the laser frequency. In this approach, the resonant frequency of the cavity can be locked to the laser frequency for a long time as the laser operates in a fixed frequency and the relative fluctuation of output power from the cavity is lower than 2%. When the frequency of the laser scans, the cavity is also capable to follow the variation of laser frequency automatically in an uninterrupted range of 2 GHz.