Non-collinear efficient continuous optical frequency doubling in periodically poled lithium niobate

Phase-matched nonlinear diffraction

“…An interesting case occurs when only the second order nonlinear coefficient is periodically modulated, thereby leading to nonlinear diffraction (NLD): the beam at the fundamental frequency (FF) will remain in its original direction, but its second harmonic (SH) will diffract in specific angles. Whereas the first demonstration of NLD was made by Freund back in 1968 [1], there was a renewed interest in this effect and its applications [2][3][4][5][6] in recent years, due to the wide availability of periodically poled ferroelectric crystals. In the most common scheme used to realize NLD, the FF propagates along the optical axis (i.e., the crystallographic z axis) of a periodically poled crystal.…”

“…These are the main reasons for the low conversion efficiencies reported so far. A different configuration was proposed recently in which light propagates perpendicular to the optical axis [5]. Such a scheme allows for a longer interaction length, but the reported result indicated that the conversion efficiency is still small, since only the transverse phase-matching condition was fulfilled.…”