Study On Narrow Linewidth OPOS With Mgo:PPLN Crystals

Comparing with traditional lasers, the optical parametric oscillator can produce tunable signals. More importantly, OPOs extend the range of the output wavelength. For this advantage, there are lots of valuable applications, such as laser spectroscopy, military and medical applications. With the progress of laser technologies and processing technologies of nonlinear optical materials, the performances of OPOs have been greatly improved, including the range of the output wavelength, the conversion efficiency and the application areas. In this paper, we study on the tunable and narrow linwidth OPO using a nanosecond pump laser and a MgO:PPLN crystal with quasi-phase matching (QPM).The pump source is a Nd:YAG laser with wavelength of 1064 nm, pulse duration of 8 ns, repetition rate of 1kHz. The dimension of the PPLN crystal is 3mmx4mmx50mm and the period of the PPLN crystal is 29.78μm. The output signal wavelength of the OPO covers 1483-1527nm. The largest conversion efficiency is 23.1% when the pump power is 1.59w. In this case, the output signal power is 0.367W. When the pump power is 0.8 W, the linewidth of the signal is 0.5nm. With the increase of pump power, the signal linewidth increases to 0.8nm due to the increased gain.We further introduce an optical delay system to make the single pump pulse to be an adjacent double pulses. When the delay time is 8ns, the conversion efficiency reaches the maximum of 30% while the pump power is 3.06 W, and the signal output power is 0.918 W. When the pump power is 5 W, the signal linewidth is 0.6nm. In order to further decrease the signal linewidth, we introduce a FP etalon into the OPO cavity. When the pump power is 1.4 W, the signal linewidth becomes 0.05 nm. When increasing the pump power to 5 W, the signal linewidth increase to 0.2nm. The introduction of the FP etalon decreases the conversion efficiency. With FP etalon inside cavity, the conversion efficiency reaches the maximum of 17% when the pump power is 2.79W and the signal output power is 0.47W.