The High Beam Quality, Eye-safe Unstable Resonator Optical Parametric Oscillation Laser

In this paper, the mechanism of intracavity Optical Parametric Oscillators(IOPO) is used ,which is a single resonator. The pump power is from a Cr4+:YAG Q-switched ((Ce, Nd):YAG laser. And the nonlinear crystal is an X-cut KTP at non-critical typeⅡ phase-matched, which is placed inside a kind of unstable resonator. Now we get a eyesafe unstable cavity IOPO laser .According to the characteristic of the unstable resonator, The ABCD law of matrix methods of Optics and geometrical conjugated imaging method are used to define the transformation as the 1.57μm laser beam transmitting in the unstable resonator. When seeking the solutions of the geometrical self-consistent eigen mode in the unstable resonator, we can get the anser by calculating the ABCD law functions at self-consistent status or geometrical conjugated imaging equation ,Then we get the real curvature radius expression of the unstable resonator in the eigen mode.The virtual confocal OPO resonator and plano-convex resonator are two typical unstable cavity resonators, which has collimation lenses, are two kinds of unstable cavity resonators. When their structural characteristics make the laser beam (spherical wave) real curvature radius become infinity emitted from the unstable resonator,we type them in the Fast Fourier Transform (FFT) digital simulation files and get the beam's far field intensity distribution property. Adding up to results of the experiments: output of virtual confocal OPO laser is: 6mJ energy), 3mrad (divergence angle), 1Hz (repetition requency) , 1Hz (repetition frequency). The output of the plano-convex OPO laser is: 4mJ(energy), 2.8mrad(divergence angle). Now we say that it is feasible to get high beam quality eyesafe laser beams by the unstable resonators.