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A newly synthesized 1,3,4-oxadiazole derivatives have been studied using a femtosecond Ti:sapphire laser system. The series molecules present strong three-photon absorption and frequency upconversion fluorescence at wavelengths from 1205nm to 1575nm. Furthermore, there is no proportional relationship between three-photon absorption cross sections and the chemical structure transformation from monomer, dimer to trimer. Effective charge-transfer distance by π-conjugation bonds may be the contributing factor. In the experimental design, the far-field intensity distribution of femtosecond laser beam has been taken into account. We give the optimized analytical solution of nonlinear transmission in a three-photon absorption (3PA) process when the incident beam has a Gaussian transverse spatial profile.

Strong second-order nonlinear effect of ZnO nanowires on a silicon wafer are demonstrated by using the hyper-Rayleigh scattering (HRS) measurement. The large nonlinear effect can be attributed to the following two factors: (1) the large total dipole moment caused by high surface defect density and electrostatic potential gradient, (2) coherent effect due to high crystal quality of single nanowire. Moreover, the second-order nonlinear effect is found to become weaker when the chip is put into organic solvent due to modification of surface defect caused by organic molecules. The variation of second-order signal in the solvent indicated the potential applications of ZnO nanowires as a sensor-on-chip (SoC).

An organic dye salt trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium iodide (ASPI) is doped with an electron transport organic molecule tris(8-hydroxyquinoline) aluminium (Alq3) in a host matrix of poly(methylmethacrylate) (PMMA), and the amplified spontaneous emission (ASE) is studied. By efficient Forster energy transfer from Alq3 to ASPI, it is demonstrated that the ASE threshold of ASPI:Alq3:PMMA waveguide (about 11μJ/pulse) is much lower than that of ASPI:PMMA system (about 38μJ/pulse). Meanwhile, the peak position of ASE can be controlled by the effect of film thickness on waveguide modes. We show that the ASE peak position can be tuned over 37nm. These characteristics indicate the ASPI:Alq3 system as a promising gain medium for optical amplifiers and organic semiconductor lasers.

We report the stimulated emission from a dye doped polymer plane waveguide with TiO2 particles. This waveguide consists of a poly (methylmethacrylate) (PMMA) film containing laser dye DCM as a gain medium. The emission spectrum of the film pumped by the Nd:YAG laser is different from the amplified spontaneous emission of the dye-doped film without particles. It is shown that when the excitation intensity reaches the threshold 9.6 ?J, the broad band emission spectrum narrows into multiple separate peaks with central wavelength of 608 nm. The linewidth of the sharp peak is 0.5 nm. According to our analyses, this phenomenon is due to the multiscattering of the disordered TiO2 particles inside the gain polymer film.