Second Order Optical Non-Linearity and Phase Matching in 4-Nitro-4′- Methyl benzylidene Aniline (NMBA)

Abstract

Large single crystals (5 × 4 × 1 cm3) of the noncentrosymmetric, monoclinic form of the organic crystal (NMBA) have been prepared by seeded growth from supersaturated solutions. Optically clear volumes permitted the preparation of polished specimens with faces parallel to the (100) and (010) directions. These were examined by the Maker fringe technique. The sections showed no dispersion of the dielectric axes with wavelength in the range 440–630 nm. The χ2 elements d11 and d23 were found to be 4 and 143 respectively relative to quartz d11.

Type II phase matching was observed using 1064 nm light at and near to normal incidence to the (100) plane with an efficiency of ≈10% of that for a 2-(N,N-dimethylamino)-5-nitroacetanilide (DAN) crystal of the same thickness tested under identical conditions. Since the half angle between the molecular dipoles in the monoclinic NMBA crystal is 12°; a far from optimal angle for efficient phase matching, this lower efficiency was expected.