| Micro-machining (micro-fabrication technology) which originated in the semiconductor manufacturing process, usually refers to the production method in the micron range of processing scale. In the research field of MEMS, it can be the generally name of micron, submicron and nanometer micro-processing. Micro-machining technology includes a variety of modern special processing, high-energy beam processing, and other processing methods. Traditional micro-machining technology which use single-photon-induced polymerization, has been systematically study and become a complete set of high-precision machining processWith the development of laser technology ,in particular the ultra-fast pulsed laser technology, new type of two-photon absorption femto-second laser-induced polymerization of the three-dimensional micro-machining combined with three-dimensional optical molding technology came forth quickly, and has aroused widespread attention within the scope of scientific research workers in the whole worldFemto-second laser-induced two-photon excitation three-dimensional micro-machining has a very good application in 3-D high-density information storage technology , the nano-femtosecond near-field processing with Nano-resolution capability, production of Embossed metal surface structure .And it showed great potential a particularly in Photonic Integration device (photonic crystal, micro-waveguide arrays, etc.) processing.Two-photon absorption which is an important nonlinear optical phenomena, belong to three order nonlinear optical effect. Compared to continuous laser pulse and Long pulse laser pulse, the interact between Ultra fast femtosecond pulses and materials reveals essential changes. Instantaneous excited light intensity in Gw magnitude, which can be realized in a very low average output power by the focus of femto-second laser pulses, can induce a significant material nonlinear photochemical reaction.Femto-second laser induced Two-photon polymerization means fabricating three-dimensional polymer integrated micro-optical systems in a polymer bulk with laser in precise control of dimension and spatial locations using two-photon initiated photo polymerization to change the character of the fabricated position .Two-photon 3D micro fabrication has its unique technological characters, like fabrication ability of true 3D microstructures, sub-micron resolution power. It becomes more and more important in MEMS research areaTake advantage of the fact that the two-photon absorption (TPA) probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order A3. This characteristic of two-photon processes has made TPA-based photo-polymerization an effective tool for processing structures with high spatial resolutionFemto-second laser which used long-wavelength light, has great penetration power, and has a truly three-dimensional processing capacity. Two-photon 3-D micro-nano fabrication is a fine machining precision processing technology, with sub-micron spatial resolution capability, small thermal effects; low energy threshold, processing method of confectioning in one time. Two-photon 3-D micro-nano fabrication has no harsh terms for processing environment.Its processing system is simple, stable, easy to maintain. The method has enormous appeal and potential applications.For two-photon free radical photo-polymerization, the polymerization rate and photo-initiation threshold is closely related to the absorption behavior of the initiator at the excitation wavelength( generally twice its single-photon absorption wavelength).Although 3D micro fabrication has been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, the TPA cross sections a of these initiators are typically very small, and as a result ,they exhibit low two-photon sensitivity. At present, effective initiators are still rare because the photo polymerization mechanism and relationships of structure/property for the initiator remained unclear. Some approaches to improve the photosensitivity of photo initiator molecules that have been reported are based on the idea of increasing their TPA cross-sections. Go deep into the study of existing UV photoresist material of the two-photon Machinable, develop the new kind of material with a large cross section of two-photon absorption, composite materials and functional materials to widen range of the two-photon Machinable materialAs a new type of laser based lithography technology, femto-second laser two-photon 3D micro fabrication has its unique technological characters, like fabrication ability of true 3D microstructures, sub-micron resolution power. It becomes more and more important in MEMS research area. This characteristic of two-photon processes has made TPA-based photo-polymerization an effective tool for processing photonic devices, micro machines, zero-threshold lasers and integrated optical waveguides in three dimensions with high spatial resolution.The types and quantities of Two-photon absorption material are still quite limited. The main objective of this field is to find a new material of strong two-photon absorption (that is, large two-photon absorption cross section)Recently, ab initio calculations have been carried out for increased dimensionality of the charge-transfer networks, showing that the TPA cross sections of multi-branched molecules can be strongly enhanced compared with the one-branched counterparts. Experimental measurements have also confirmed this conclusion.In this thesis, DBASDMB molecule with good absorption and initiator properties was selected to be initiator. All compounds synthesized have been characterized by 1H NMR spectra, spectra. By measuring the absorption, transmission spectrum, the emission spectrum and two-photon fluorescence spectrometry its linear and nonlinear optical properties were studied.Some three dimensional structures were created by two-photon polymerization of an EA oligomer using these initiators. The film of the mixture of initiator and oligomer with a weight ratio of 4-5 %(a little dichloromethane was added to make a solution of initiator and oligomer) was prepared by spin-coating onto glass plates. a pulse duration of 200fs and repetition rate of 76MHZ,mode-locked Ti:sapphire laser was used for two-photon microfabircation. The corresponding lasing source was tightly focused via an objective lens(x60,NA=1.25),and the focal point was focused on the sample film on the xy-step monitorized stage controlled by computer. The pulse energy before being focused by the objective lens was about 6mw, the polymerized solid skeleton was obtained and was observed through a polarization microscope... |
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