Zhang Qi-Jin

Photoluminescence study of C60 doped polystyrene

We report here a new phenomenon in photoluminescence of C60 doped in polystyrene. Under 488 nm cw laser radiation, the PL intensity of the sample was found to increase with time. With 10 h of irradiation, the PL signal strength increased by 10 times, comparable to that from porous Si. The peak of the PL was found to shift to high frequency as well. More detailed studies showed that such an irreversible change of the sample might be a result of the lowering symmetry of oxidized C60 fullerene in the polystyrene.

Multi-photon-absorption-induced birefringent grating in azobenzene-doped polymethyl methacrylate optical fibres

Birefringent gratings induced by absorbing multi-photons at 532 nm in azobenzene doped polymethyl methacrylate (azo-PMMA) fibres were investigated. The maximum photo-induced birefringence observed from the fibre is about 3.0 × 10−5. The two-photon absorption coefficient β of the azo-PMMA at 532 nm obtained by the Z-scan method is 10.2 cm GW−1, and the birefringence response time of the azobenzene is 10 μs.

Properties of polarized laser-induced birefringent gratings in azobenzene-doped poly(methyl methecrylate) optical fibers

Abstract Birefringent gratings induced by 532 nm polarized laser in an azobenzene-doped polymethyl methacrylate (PMMA) fibers and blocks were investigated. Significant photo-induced birefringence with about 3.0×10−5 has been observed from the fiber. It was found that there is an intensity threshold, which is 0.29 mW/cm 2 at 532 nm. The birefringence decayed gradually when the writing laser turned off. So the dynamic process of the birefringence was studied. Both the rise and the decay processes of the birefringence include an initial “fast” response mode and a subsequent “slow” response mode. Both the fast response and the slow response become faster with increasing irradiating laser intensity. The birefringence was induced by the combination of the nonlinear absorption, linear absorption and thermal effect.

Fluorescence Enhancement of a Polymer Planar Waveguide Doped with Rhodamine B and Ag Nanoparticles

Planar polymer multi-model waveguides doped with Ag nano-particles and rhodamine B are fabricated and investigated by the spectroscopy analysis method as well as the M-line method. Experimental results shown that fluorescence enhancement occurs when excited by a wide band wavelength with Ag nano-particle concentration at a certain level. The maximum enhancement factor in our experiment is obtained to be about 3.8 when excited by 350 nm. Our study may have potential applications in polymers optical elements, such as polymer waveguide lasers and amplifiers.

Polarized Emission of an Eu3+ Doped Azo-Polymer Waveguide

We investigate the polarized emission behaviour of an Eu3+ doped azo-polymer waveguide. Affected by the azobenzene groups in the photoinduced orientation process by the 532 nm linearly polarized laser, the ligands were realigned orderly perpendicular to the direction of the orientation direction. This leads to the polarized absorption and emission of the waveguide in the orientation direction. By an m-line apparatus based on the prism coupling technique, two guided propagation modes were observed in the waveguide, and the refractive index at 650 nm in TE polarizations is 1.7505.

Analysis of Photosensitivity of Copolymer Optical Fibre Preform

The photosensitivity of copolymer optical fibre preform is analysed in comparison with the doped one. The effects of write conditions such as pump power and pump time have been studied. Then, the preform is drawn into single mode polymer optical fibre with core refractive index of 1.499, and core-cladding refractive-index difference of 0.008. Long-period birefringence gratings with period of 120 um are fabricated in the fibre. The duty cycle is 50%, and the refractive index change in the exposed area is about 1×10−3.

Laser Amplification Mechanism in an Nd3+-Doped Polymer Optical Fibre

The Judd-Ofelt theory was applied to optical-absorption transitions in an Nd3+-doped polymer optical fibre to obtain the intensity parameters (Ω2 = 0.83 × 10-20 cm2, Ω4 = 1.64 × 10-20 cm2, Ω6 = 4.04 × 10-20 cm2), the radiative lifetime (371 µs) and the quantum efficiency (0.73) of the 4G5/2 level, from which we found that the transition probability from 4G5/2 to 4I9/2 (Aij = 1995.7 s-1) is higher than others. Thus, in the polymer system, the traditional four-level laser system for Nd3+ was substituted by a three-level system. Furthermore, we have calculated the emission cross section (σije = 2.45×10-21 cm2), and solved the differential equations of the single-pass gain. In comparison with inorganic optical fibres, an increased saturated intensity is observed.

Amplified Spontaneous Emission of Rhodamine B-Doped Step-Index Polymer Optical Fibre

A step-index polymer optical fibre (SI POF) containing rhodamine B in poly (methyl methacrylate) (PMMA) has been fabricated by a perform technique. The rhodamine B content of the doped SI POF is 5 ppm-wt. The spectra of the doped SI POF with different fibre lengths were measured. Amplified spontaneous emission (ASE) at 609 nm of an SI POF in length 40 cm has been observed at ambient temperature by end-pumping with a Nd:YAG laser operated at 532 nm. The threshold of absorbed pump power for the onset of ASE is about 0.003 mJ.

Effects of Laser-Induced Heating on the Photoinduced Birefringence in Azobenzene-Side-Chain Copolymer

The photoinduced birefringence was observed in the polymer poly[2-(4-(4-cyanophenyl) diazenyl phenyloxy) ethoxyl methacrylate] with a cw 532 nm laser. The azobenzene polymer character has been studied under the conditions of various illuminating time and light intensities. By analysing the processes of reorientation, the effect of laser-induced heating has been introduced to the buildup of photoinduced birefringence in azobenzene-side-chain copolymer. The curves for the buildup of birefringence were fitted with a modified function, i.e., biexponential curves and Gaussian curves. The relationship among all the parameters has also been presented. With the modified fitting function, we obtain a better fitting result.

A Simple Model to Describe the Requirement of Realizing All-Optical Poling

All-optical poling (AOP) of a crosslinkable polymer based on hexamethoxymethyl melamine (HMMM) and Disperse red 1 (DR-1) is investigated. It is found that the saturation second harmonic generation (SHG) intensity decreases significantly with the increase of the sample temperature from 33°C to 63°C. From the perspective of energy equilibrium, the main factors of AOP are analysed, and by introducing the classical ideal gas model, a simple inequation is first deduced to describe the requirement of realizing AOP.