As an ultrafast laser has recently been developed, this leads to the innovative nanotechnology, the 3-D fabrication of
the two-photon absorbed (TPA) photo-polymerization. The 3-D micro/nano structure by this method has a resolution of
sub-hundred nm which is much smaller than the diffraction limit. Usually the 3-D polymer micro/nano structure by this
method is made by stacking many of a unit polymer structure, so called 'voxel'. The size of the voxel is considered as
the fabrication resolution. The size of a voxel, or the fabricating resolution is determined by several fabricating
conditions such as the laser output power, the exposure time, the N.A. of the focusing lens, the types of polymerizing
material, and the pulse-width. The voxel size due to power, exposure time and NA has been done by many research
groups. Although the pulse-width is a very important condition for two-photon absorption, the study of influence on
fabricating resolution by the pulse-width has not been done before. Therefore we studied the voxel size under the
condition of increasing the pulse-width of the laser. To stretch the pulse-width, a single mode fiber (SMF) has been
used. We demonstrated that the voxel lateral size decreased as pulse-width stretched to several picoseconds.
Arbitrarily complex 3-D polymeric structures with a resolution of under 100 nm are fabricated by two-photon
absorption polymerization (TPAP) by an ultra-short pulsed laser. This method can be applied to many scientific and
engineering fields such as micro/nano-optics, MEMS, microfluidic system, and so on. Many 3-D structures by TPA
fabrication have been made. However the structures made with an acrylate-based prepolymer material have seriously
structural problems, such as shrinkage, collapse, distortion, etc. These problems make the fabrication of a large and fine
3-D structure difficult. Using an epoxy-based material like SU-8, which is widely used in the conventional lithography,
the problems above can be prevented. Although SU-8 is designed for the UV lithography, a two-photon absorbing dye
and proton acid generator can make it a base prepolymer material for the two-photon absorption polymerization. We
studied the size of voxel or the resolution of fabrication from the SU-8 structures under the various fabrication
conditions such as the laser output power and the exposure time. We demonstrated 3-D micro/nano structures with SU-8
and compared them with same structure with SCR-500.
By numerical simulations, it has been shown that a conventional cylindrical rod can be used as a hollow conic beam generator by illuminating a parallel laser beam inclined to the axis of the rod. Half of the conic beam is formed by the reflection at the surface of the cylindrical rod, and the opposite side of the conic beam by its transmission. We discuss the parameters to determine the size of the conic beam and the effect of the dielectric multilayer coating on the intensity distribution of the conic beam. The line beams of the shapes such as circle, ellipse, parabola, or hyperbola can be generated by this hollow conic beam generator, depending on the position and orientation of the observing plane.
Multi-photon absorption phenomena induced by ultra fast laser have been considered for many applications of microfabrications such as metal ablation, glass etching and photopolymerization. Among the applications, the photopolymerization by two-photon absorption (TPA) has been regarded as a new microfabricating method. It is possible to be used in photo mask correcting, diffractive optical element and micro machining. The TPA photopolymerization is made possible to fabricate a complicated three dimensional (3D) micro-structure which the conventional photomask technology has not been able to make. In fact, the shape of the voxel (volume pixel: a unit structure of TPA fabrication) is an important factor which could affect the microfabrication process. In this paper, we have reported that 3D micro-structures were fabricated and the generation of voxel shape was analyzed for various optical conditions.
Multi-photon absorption phenomena induced by ultra fast laser have been considered for many applications of microfabrications such as metal ablation, glass etching and photopolymerization. Among the applications, the photopolymerization by two-photon absorption (TPA) has been regarded as a new microfabricating method. It is possible to be used in photo mask correcting, diffractive optical element and micro machining. The TPA photopolymerization is made possible to fabricate a complicated three dimensional structure which the conventional photomask technology has not been able to make. Furthermore the TPA photopolymerization process applied to a two dimensional structure fabrication may take shorter time than the old process since the absence of etching and deposition processes. Recently we have made a simple 3D structure and applied the technique to PDMS(poly-dimethyl siloxane) molding.
As a femtosecond laser has recently been developed, both of high power and high photon density are easily obtained. The high photon density results in photopolymerization of urethane acrylate resin whose absorption spectrum is shorter than that of the femtosecond laser. The stereo-lithography using the two-photon absorption (TPA) makes micro structures with great resolution. We used this phenomenon to make micron-sized structures with sub-micron resolution. Before fabricating 3-D structures, precise 2-D structures were preceded. The TPA photopolymerization was applied of poly-dimethyl siloxane (PDMS) molding. In this paper, we report the recent progress and application of this technology in our laboratory.
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