Linear and nonlinear optical properties of N-4-nitrophenyl L-prolinol single crystals

N-4-nitrophenyl-(L)-prolinol (NPP), an organic molecular crystal with application in quadratic nonlinear optics, has been characterized in terms of its absorption spectrum and refractive indices. A strong birefringence, with n_χ-n_z as high as 0.78 at 53 2 nm, is reported. All collinear phase-matching (PM) configurations in the principal planes for second harmonic generation (SHG) are subsequently identified; three of them correspond to effective nonlinear coefficients d_eff larger than 50 pm V^-1 for SHG at 1.06 μm, with a factor of merit reaching 834 pm V^-1. The most efficient PM configurations for near infrared SHG are close to normal incidence with respect to the cleavage plane of the crystal, allowing to take full advantage of the main molecular hyper-polarizability coefficient without projection factors. A θ-noncritical configuration at 1.15 μm corresponds to a d_eff value of 70 pm V^-1, which remains, to the best of our knowledge, unsurpassed by other organic as well as inorganic crystals in the same spectral range.