Abstract
Periodically poled lithium niobate (PPLN) attracts enormous interests because of its high efficient nonlinear coefficient and designable phase-matching characteristics. Many labs have demonstrated significant results of efficient and low-pump-threshold nonlinear frequency-conversion based on PPLN. We fabricate a device-quality PPLN for an efficient, high peak-power 1550nm eye-safe laser system. The PPLN crystal is 50-mm-long, 12-mm-wide, 0.5-mm-thick 30-mm-QPM (quasi-phase matching) period. The eye-safe laser system involves optical parametric generation pumped by a flash-lamped Q-switched Nd:YAG laser. We characterize the optical parametric generation (OPG) based on a 50-mm-length 30-mm-period PPLN. According to our experimental results, the deff coefficient is estimated to be 15.71pm/Vm, about 92% of the theoretical value. The conversion efficiency of OPG is about 40%.Due to low damage threshold (~2.7J8/cm2 in a 10-ns pulse at 1064nm) of congruent LiNbO3, a pump area limits the maximum allowed pump energy. A straightforward approach to enhance the energy throughput is increasing the pump aperture. For increasing the pump energy, this thesis presents two optical systems to transform a spherical pump beam to an elliptical beam to increase the pump area. The OPG pumped by an 8:1 elliptical beam based on a 50-mm-length 30-mm-period PPLN has a threshold of 7.12 mJ and produces a 5.2 mJ 1.55 mm OPG signal with 16 mJ 1.064 mm pumping energy. The optical system transforms a spherical pump beam to an elliptical beam and reverses the beam shape to a well circular beam. At the same time, the beam profiles of the pump beam and the signal beams have been inspected during pumping at the lasing threshold and two times the lasing threshold.