Photoinduced phase-matched second-harmonic generation in azodye-doped polymer films

Phase-matched second-harmonic generation (SHG) in azodye-doped polymethylmethacrylate films was demonstrated using the nonresonant optical poling technique. During the seeding process, samples were irradiated simultaneously by coherent superposition of the fundamental and the second-harmonic light of a femtosecond laser. Optical poling experiments were performed at three wavelengths of 1500, 1320, and 1300 nm, respectively. The quadratic dependence of SHG on the film thickness showed that a χ(2)grating that satisfied the phase-matching condition for SHG was optically induced in the polymer films. The SHG conversion efficiency of a 105 μm thick film was estimated to be about 2%. A relaxation retardation effect of the photoinduced χ(2) was also observed in the thick films

Carbohydrate-protein interactions characterized by dual polarization hybrid plasmonic waveguide

Optical biosensors present good performance for the affinity analysis of a molecular binding event. However, most of those excited with single optical mode are “blind” to the conformational change of bound molecules. We theoretically demonstrate a dual polarization hybrid plasmonic (DPHP) waveguide with nano-slots. By addressing the structure with dual polarizations, the optogeometrical properties (density and thickness) of protein layers have been determined without ambiguity. Differences in the hybrid mode dispersion between the transverse electric (TE) and transverse magnetic (TM) modes allow to separately determine the thickness and the density at all stages during the molecular interaction. In addition, nano-slots can be equated with an effective optical capacitance resulting in a strong field confinement; thereby, subtle changes in the ambient medium can be sensed. A proof of concept is conducted by analyzing the conformational change of HepV, a recombinant fragment of collagen V, during complicated molecular interaction. Integrated with adlayer thickness and density, we can conclude that a thick sparse layer formed after heparin capture and a thin dense layer arising from HepV bound. Accordingly, HepV undergoing conformational change has been traced and verified as molecular interaction occurs

Phase-matched second-harmonic generation in bulk azodye-doped polymers by all-optical poling

We demonstrate phase-matched second-harmonic generation (SHG) in bulk azodye-doped polymethylmethacrylate using an all-optical poling technique. During the seeding process, samples were irradiated simultaneously by coherent superposition of the fundamental and the second-harmonic light of a nanosecond laser. The measurements for the dependence of SHG on the sample thickness show that the SHG signals increase with the increase in thickness of the samples, indicating that a χ(2)grating that satisfies the phase-matching condition for SHG could be optically induced in the polymer samples

Luminescence of black silicon fabricated by high-repetition rate femtosecond laser pulses

We studied the photoluminescence (PL) from black silicon that was fabricated using an 800 nm, 250 kHz femtosecond laser in air. By changing the scan velocity and the fluence of the femtosecond laser, the formation of the PL band between the orange (600 nm) and red bands (near 680 nm) could be controlled. The red band PL from the photoinduced microstructures on the black silicon was observed even without annealing due to the thermal accumulation of high-repetition rate femtosecond laser pulses. The orange band PL was easily quenched under 532 nm cw laser irradiation, whereas the red band PL was more stable; this can be attributed to "defect luminescence" and "quantum confinement", respectively