Extremely large nonresonant second-order nonlinear optical response in crystals of the stilbazolium salt DAPSH

We report on the extremely large nonresonant quadratic optical nonlinearity of the stilbazolium salt trans-4'-(dimethylamino)-N-phenyl-4-stilbazolium hexafluorophosphate (DAPSH). The phenyl-pyridinium chromophores in DAPSH crystals grown from acetone solution pack with a highly aligned polar order, resulting in a very large birefringence, Δn = 1.17±0.06 at λ = 0.83 μm and Δn = 0.83±0.04 at λ = 1.55 μm. More importantly, this leads to an extremely large diagonal quadratic susceptibility with the nonlinear optical coefficient for second-harmonic generation reaching up to d111 = 290±40 pm/V at 1.907 mu;m fundamental wavelength, which presents a considerable improvement with respect to the presently best material trans-4′-(dimethylamino)-N-methyl-4-stilbazolium tosyate (DAST) with d111 = 210±55 pm/V at λ = 1.907μm. The result is in agreement with the preferential packing of the chromophores and the previous studies demonstrating higher microscopic nonlinearity of the chromophores in DAPSH compared to that of DAST. © 2008 Optical Society of America.