Zhenqian Wei

Photoinduced anisotropy and polarization holography in azobenzene side-chain polymer

Abstract Photoinduced anisotropy and polarization holographic recording have been studied in an amorphous tripolymer containing azo-side groups. It is shown that diverse mechanisms should be invoked to explain the experimental results. The polymer possesses a large value of photoinduced birefringence (Δ n =7.8×10 −3 ). A reversible polarization hologram with high efficiency (19.3%) has been recorded with a CW 532 nm laser at relatively low light intensity in the thin polymer film.

Photoinduced birefringence and reversible optical storage in liquid-crystalline azobenzene side-chain polymers

A liquid crystal with an azobenzene moiety as a photoactive mesogenic unit is investigated in photoinduced birefringence. Measurements reveal that it possesses large magnitude of photoinduced birefringence (Δn∼10−2) and the characteristic of long-term optical storage. The resulting polarization information can be erased either by heating the sample to a temperature much higher than the glass transition temperature, or by optical method with a circularly polarized light. The mechanism of long-term optical storage is discussed in this letter.

Low-power phase conjugation in push–pull azobenzene compounds

Push-pull azobenzene compounds were synthesized by the diazocoupling reaction, and low-power phase conjugation of azobenzene-compound-doped poly(methyl methacrylate) films was studied with a He-Ne laser at 632.8 nm. It is shown that this kind of polymer has appreciable third-order optical nonlinearity, with a chi((3)) of approximately 10(-4) esu in the tail of absorption.

Phase conjugation in methyl orange doped polyvinyl alcohol film by DFWM based on excited state absorption

The kinetic process of degenerate four-wave mixing (DFWM) based on excited state absorption is studied for the first time. A four-level model of two singlet states and two triplet states was used to explain the DFWM. The lower triplet state could be significantly populated through intersystem crossing between an excited singlet state and the triplet state, therefore the degenerate four-wave mixing based on triplet-triplet absorption was achieved. The phase conjugation signal in the DFWM process was modulated by the preexciting intensity. A typical experiment was performed, in which methyl orange doped in polyvinyl alcohol film was used as the experimental sample, an argon ion laser at 514.5 nm was used as the preexciting field, and a HeNe laser at 632.8 nm was used as the DFWM source. The experimental and calculated results were in good agreement.

Photorefractive effect in an inorganic nanoparticle polymer-doped system

In this paper, photorefractive (PR) effect of polymer doped inorganic nanoparticles is reported. In the photorefractive polymer material system, Cu2S nanoparticles were used as photo-sensitizer, N-polyvinylcarbazole (PVK) was used as carrier transport agent, and EPNAC molecules were used as electro-optical molecules. Two beam coupling in this kind of composite was studied. The experimental results prove that this kind of inorganic nanoparticles can be used as photosensitizer in polymer PR materials.

IMAGE STORAGE BASED ON PHOTOINDUCED ALIGNMENT IN AZOBENZENE LIQUID-CRYSTALLINE FILMS

Image storage based on photoinduced alignment in azobenzene liquid-crystalline films is reported. Measurements reveal that the liquid-crystalline film possesses large photoinduced birefringence (Δn similar 10-2) and permanent optical storage characteristics. The photoinduced alignment process is used for storing images. It is clearly demonstrated that the alignment of the azo chromophores as well as the stored image can be controlled by choosing the appropriate polarization of the irradiating light.

Photoinduced anisotropy and high-efficiency optical storage in azobenzene side-chain polymer

An amorphous tripolymer containing azo-side groups has been investigated in photoinduced anisotropy and polarization holographic recording. Measurements reveal that the effect of photobleaching process should be taken into account in explaining the experimental result using the mechanism of angular hoe burning or the angular redistribution of molecules in the azobenzene side-chain polymer film and that the polymer possesses large magnitude of photoinduced birefringence. A reversible polarization hologram with high efficiency is recorded with a CW 532 nm laser in this thin film at relatively low light intensity.

Study of degenerate four-wave mixing based on excited state absorption in methyl orange/polyvinyl alcohol polymer film

Abstract In this paper, the kinetic processes of degenerate four-wave mixing (DFWM), based on excited-state absorption, was studied for the first time and explained with a four-level model. The lower triplet state was significantly populated through intersystem crossing from an excited singlet state and degenerate four-wave mixing based on triplet-triplet absorption was achieved. Experimental results from methyl orange doped in polyvinyl alcohol film were in good agreement with calculations.