Diode-pumped Q-switched laser is controlled using fluorescence feedback

In conventional active Q-switching, triggering the output pulse is done by electronic control with a pulse generator at a preset pulse-repetition frequency. The cavity's Q is switched by dead reckoning from the pulse generator without examination of the true state of population inversion of the pumped medium. Stable laser performance requires a stable pump laser and stabilized cavity conditions.

According to researchers at the Photonics Research Group at Nanyang Technological University in Singapore, an alternative electronic control method could remove the uncertainty in the actual inversion level at the onset of Q-switching. Their technique incorporates an active optical-feedback loop based on the monitoring of fluorescence intensity outside the laser cavity of an acousto-optic Q-switched Nd:YVO4 (vanadate) laser. With this method, they can select the level of fluorescence intensity that triggers the Q-switch. When the initial inversion level indicated by the detected fluorescence reaches that predetermined value, Q-switching is initiated. Researchers can then vary the reproducibility of the output-pulse peak power and pulsewidth and reduce the shot-to-shot variations of both parameters. Contact Wenjie Xie at [email protected].