Jintang Huang

Tunable surface texturing by polarization-controlled three-beam interference

For the fabrication of periodic microstructures, a high-precision and highly efficient polarization-controlled three-beam interference technology (PoTBI) has been developed. With the theory of superposition of multiple laser beams, simulations on the influence of polarization upon the intensity distribution in the overlapped area have been carried out. By controlling the polarization of the interfering beams, various intensity patterns can be obtained. An optical setup for PoTBI has been realized and used to generate microstructures in polyimide foil. Micro cavities, micro bumps, eye-like cavities and rectangular columns of hexagonal symmetry and one-dimensional lines are produced. Compared with other multi-beam interference technologies, different surface textures of hexagonal symmetry with the same periodicity can be obtained only by changing the polarization status of the interfering beams without changing the geometrical interference setup. Thus, PoTBI provides a simply tunable texturing technology with a wide range of applications in surface structuring.

Optically controllable polarized luminescence from azopolymer films doped with a lanthanide complex

Two azopolymers (DACENO2 and DACEOCH3) with a special structure were designed and synthesized. The azopolymer films doped with the lanthanide complex Eu(TTA)3Phen were prepared by a casting method with a mixed solution of the azopolymer and lanthanide complex. UV-vis spectra show that the absorption peaks of the predesigned azopolymers DACENO2 and DACEOCH3 are separated from that of Eu(TTA)3Phen. Under this circumstance, the photo-induced anisotropy of the films could not be destroyed by excitation and emission during fluorescence measurements. Polarized luminescence of both oriented films was observed with polarization ratios of 3.0 for the DACENO2–Eu(TTA)3Phen film and 2.7 for the DACEOCH3–Eu(TTA)3Phen film at 613 nm, respectively. The luminescent properties of the film were found to be affected by the chemical structure of the azopolymer, the extent of the photo-induced alignment and the angle between the orientated direction of the film and the direction of the polarizer. All the results from this work revealed that the polarized luminescence from the azopolymer film doped with a lanthanide complex can be controlled by the extent of photo-induced alignment.

Block copolymer supramolecular assemblies hierarchically structured by three-beam interference laser ablation

We report the fabrication of hierarchical structures by combining bottom-up self-assembly of block copolymer supramolecular assemblies with top-down three-beam interference laser ablation methods. To fabricate the shorter length scale in the hierarchical structures, we use supramolecular assemblies (SMAs) of azobenzene compounds hydrogen bonded with poly(vinyl pyridine) blocks of polystyrene-block-poly(vinyl pyridine) block copolymers. The SMAs form phase separation nanostructures by solvent vapor annealing. The longer length scale of the hierarchical structures is fabricated by three-beam interference laser ablation on the phase separated nanostructures of the SMAs. The ablation process is induced by single laser shots with 35 ns pulse duration. Tuning of both length scales is feasible by changing the interference conditions and chemical composition of the SMAs, which enables efficient and straightforward fabrication of hierarchical photonic structures.

All-optical fabrication of ellipsoidal caps on azobenzene functional polymers.

We have fabricated an azobenzene (azo) polymer microellipsoidal cap array of hexagonal symmetry with high-power laser ablation and subsequent single-beam-induced mass migration. High-power interference with polarization-controlled triple beams is utilized to inscribe a circular bump array directly on the surface of the azo polymer film. The produced circular cap array is exposed to the linearly polarized beam, and the caps are stretched along the polarization direction of the irradiating beam. A model of gradient force emerged by the interaction of the polarized beam and azo polymer is constructed to explain the mechanism of such polarization-induced microscale shape deformation.

Optical manipulable polymer optical fiber Bragg gratings with azopolymer as core material

Polymer optical fiber (POF) with a core of azopolymer has been fabricated. Based on the photoinduced birefringence of azopolymer materials, a mechanism for writing POF gratings is presented. After writing in azopolymer optical fiber (APOF) by two beams of mutually orthogonal polarizations, a birefringence grating was formed, and then the gratings could be erased almost totally for a short time by the circularly polarized beam at the same wavelength. By manipulating the APOF gratings, the transmittance through APOF at 632.8nm can be adjustable as revealed by the transmittance change during write-erase-write procedure.

Light driving force for surface patterning on azobenzene-containing polymers

In this paper, we investigated the effect of light driving force induced surface deformation on azobenzene-containing polymers. The surface deformation is attributed to light-induced mass migration inside the polymers. Circular cap arrays are firstly fabricated by high power laser ablation via polarization controlled three-beam interference. The circular caps are subsequently exposed to polarization controlled two-beam interfering field. The results illuminate that when the interfering laser beams are both set to P polarization, the circular caps are deformed. While the laser beams are of other interfering modes like (S, S) and (+45° , -45°), the caps are seldom deformed. The circular caps are also exposed to single intensity-homogeneous linearly polarized laser beam. The deformation of the caps keeps the same direction as the irradiating polarization. A model based on the focusing effect of the circular caps is addressed to explain the origin of the light driving force for mass migration in azopolymers. The all-optical approach for the production of deformed caps can be used to generate aspherical lens, which may be applied to many domains.