The origin of inhibition of high power second harmonic generation in periodically poled lithium niobate crystal

Abstract

This paper investigates the origin of the inhibition of the second harmonic generation (SHG) in a periodically poled lithium niobate (PPLN) crystal by using coupled-mode equations in which both absorption and photorefractive properties of the crystal were taken into account. SHG, using fundamental laser beams with radii of 150, 33, and 25 μm, respectively, were calculated. The calculated results showed that the changes of refractive index difference resulting from the photorefractive effect were ∼300 times smaller than that from absorption-induced heating in SHG using a fundamental laser beam with a radius of 150 μm. However, in SHG using a fundamental laser beam with a radius smaller than 33 μm, the changes of refractive index difference resulting from the photorefractive effect were comparable to those resulting from absorption-induced heating. It revealed that the photorefractive effect is one of the main factors that inhibits the SHG using a fundamental laser beam with a radius smaller than 33 μm at high pump powers.