The nonlinear optical (NLO) and optical limiting (OL) properties of three new structures of organic NLO guest–host Poly(N-vinylcarbozole)/disperse orange 3 (PVK/DO3), PVK/disperse orange 13 (PVK/DO13), and PVK/disperse orange 25 (PVK/DO25) as a solution at different concentrations and as a thin-film sample are studied using continuous wave z-scan system at 532 nm. The open-aperture z-scan data of the NLO materials in the solution and thin-film samples displayed two-photon and saturable absorptions, respectively. The PVK/DO13 exhibites the largest and best values of the nonlinearities, such as n2, \beta, (3), compared with those of PVK/DO3 and PVK/DO25. This nonlinearity increases as the concentration increases. The results indicate that these NLO materials are good candidates for optical switching and OL devices.

Red frequency-upconversion fluorescence emission is observed in europium (III) complex with encapsulating polybenzimidazole tripodal ligands, pumped with 930- and 1070-nm picosecond laser pulses. The luminescence of transition 5D0->7F2 (612 nm) is induced by two-photon absorption of hypersensitive transitions 7F0->5D2 (465 nm) and 7F1->5D1 (535 nm). Analysis results suggest that the two-photon excitation strength of these hypersensitive transitions is increased dramatically owing to the C3 symmetry of the coordination field.

The pulse profile influence of excitation light on the two-photon absorption coefficient \beta is theoretically and numerically studied. Based on Gaussian spatial and temporal laser, we obtain an expansion formula of energy transmission. As compared with a plain beam and a pulse beam that is rectangular in time but Gaussian in space, the relative deviations of \beta turn out to be about 214% and 47%, respectively. These differences indicate that a smaller \beta may be obtained than the real one in usual nonlinear transmission. Our result suggests that by taking real pulse profile into account, a more exact \beta can be derived in energy transmission measurement.

A self-organized thin film of a cyanine dye is fabricated by the spin-coating technique and is characterized by ultraviolet-visible spectroscopy, infrared (IR) spectroscopy, small-angle X-ray diffraction, ellipsometer, and atomic force microscopy (AFM). The nonlinear optical properties of the thin films are investigated by degenerate four wave mixing (DFWM) technique. The cyanine dye thin film sample exhibits high optical nonlinearities ('chi(3)=2.55*10^(-12) esu), and the mechanism is analyzed by the exciton coupling theory.

The nonlinear optical properties of a new organic material, N-vinylcarbazole tricarbonyl chromium, are reported. The large two-photon absorption (TPA) coefficient and nonlinear refraction index are measured by an open-aperture Z-scan technique and closed-aperture Z-scan technique, respectively. The sample solution shows excellent optical limiting response.

Two-photon absorption (TPA) cross sections of an organic dye, trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium iodide (abbreviated as ASPI), from 810 to 1100 nm have been measured in two solvents (benzyl alcohol, dimethyl formamide (DMF)) with different polarities. The peak values and positions of ASPI TPA spectra were found to be strongly influenced by the solvents. The maximum molecular TPA cross sections are 26.42*10^(-48) cm4 s/photon at 930 nm (in DMF solution) and 46.81*10^(-48) cm4 s/photon at 960 nm (in benzyl alcohol solution).

The first hyperpolarizabilities ('beta') of four azobenzene derivatives are measured via hyper-Rayleigh scattering (HRS) technique at 1064 nm. These compounds show weak absorbance at 532 nm and neglectable two-photon fluorescence (TPF). Their static first hyperpolarizabilities ('beta0') are estimated by the classical two-level model. The effects of varying the variety and number of the acceptors from chloro to nitro substituents are studied. It is concluded that the first hyperpolarizabilities will be enhanced with increasing polarity or number of the acceptors, attributed to improved transferability of their 'pi'-conjugated electron clouds.

The second-order nonlinear optical characteristics of a novel organic crystal, urea L-malic acid (ULMA), were studied. Both type I and type II phase-matching angles of the biaxial crystal ULMA were calculated, whose loci are in the Hobden class 9. The efficiencies of second harmonic generation (SHG) of ULMA and KDP at a fundamental wavelength of 1064 nm were compared by using the Kurtz powder method. The results showed that the nonlinear coefficient of ULMA is about 1.57 times of that of KDP. High SHG efficiencies were observed over a broad range of the spectrum when ULMA was pumped by outputs generated from an optical parameter oscillator. To our knowledge, it is the first report where continuous SHG at fundamental wavelengths from 1300 to 950 nm with ULMA was achieved.