Third harmonic generation of Nd:YAG laser light in periodically poled LiNbO3 waveguide

Third harmonic generation (THG) is one of the most attractive techniques for producing short-wavelength coherent light. THG is yielded by a third-order nonlinear process, but it is difficult to achieve efficient THG because the third-order nonlinear optical coefficient is usually small. A TH wave can also be obtained by using two second-order nonlinear processes in series, and high efficiency can be expected because second-order nonlinear processes are usually more efficient than third-order nonlinear processes. In this method, a pump wave is once converted into a second harmonic (SH) wave, and then converted into a TH wave by frequency-mixing of the pump wave and the generated SH wave. Previous works used two bulk crystals and a birefringent phase-matching method for such second-order nonlinear processes [1]. Recently, efficient second-order nonlinear processes have been demonstrated by using a waveguide structure and ferroelectric-domain-inverted grating for quasi-phase-matching (QPM) in second harmonic generation (SHG) devices [2-8] and sum-frequency generation (SFG) devices [9]. We have proposed the application of such techniques to the generation of a TH wave [10]. In this paper, we demonstrate THG of a Nd:YAG laser light with cascading QPM-SHG and QPM-SFG in LiNbO3 waveguide.