07_非線性光學實驗.pdf

Second Harmonic Generation in a KTP Crystal Experimental brief In this experiment, we are going to investigate the properties of the critically phase-matched second harmonic generation (SHG) in a KTP (KTiOPO ) crystal when 4 pumped by a 1.064µm passively Q-switched laser. We will first learn to use the type II phase matching method to find out the best phase-matching angle set (θ, ϕ) in KTP’s crystal coordinate for the 1.064µm pumped SHG in this crystal. Under this condition, we are able to measure the conversion efficiencies of the crystal as a function of the crystal angle and temperature, and therefore to deduce the effective nonlinear coefficient of the crystal. In the meanwhile, we will also obtain the information for characterizing the angular and temperature bandwidths of the crystal. Introduction and Principle Second harmonic generation was the first experimentally demonstrated nonlinear optical phenomenon after the invention of the laser sources because it is the most efficient one among all nonlinear frequency conversion processes. Since all materials are dispersive, it is the birefringence of a material that makes the possibility of achieving phase matching in a nonlinear frequency conversion process including the SHG. There are two types of birefringence crystals, uniaxial and biaxial crystals. A uniaxial crystal like LiNbO3 has the optic axis along the z-axis and is characterized by the index symmetry of revolution with its principle axes. The phase-matching condition of frequency mixing waves in such a crystal will be easier to be analyzed than a biaxial crystal. For biaxi