<title>Second-order cascaded frequency shifting and signal amplification in organic and inorganic crystals</title>

Abstract

We report wavelength shifting (generation of a pulse at the wavelength 2-AX from a signal at 2,+A2 under the action of a pump at ?) and parametric amplification through a cascaded second order process in a periodically poled lithium niobate crystal and also in an organic crystal N-(4-nitrophenyl)-L-prolinol (NPP). NPP could convert signal pulse (from 1 .16 to 1 . 14 rim) with unit gain under the action of a pump pulse (at 1 .1 5 pm) of peak intensity as low as 9 MW/cm2. In the limit ofnegligible conversion, where the cascading effect can be described through an effective we derive for NPPIx7 2.4 x 1017 rn2/V2 , which is iO2 larger than of conjugated polymers or semiconductors. In a 19 lTflifl long PPLN sample, at ?=l .8 pin and zX as large as 60 nm, we could obtain unit gain with a pump intensity of 6 MW/cm2, while amplification by a factor of 1 0 requires 1 8 MW/cm2. We also present a theoretical comparison between frequency mixing and cascading.