《双光子聚合-微加工的新途径》由会员分享，可在线阅读，更多相关《双光子聚合-微加工的新途径（8页珍藏版）》请在金锄头文库上搜索。
1、T he rapid technical develop- ment of ultrashort laser sys- tems is creating exciting pos- sibilities for very precise local- ization of laser energy in time and space. These achievements have triggered novel laser applications based on nonlinear interaction processes. A promising three-dimensional
2、microfabrication method that has recently attracted consider- able attention is based on two- photon polymerization with ul- trashort laser pulses.1-5When focused into the volume of a photosensitive material (or pho- toresist), the pulses initiate two-photon polymerization via two-photon absorption
3、and sub- sequent polymerization. After illumination of the desired struc- tures inside the photoresist vol- ume and subsequent develop- ment e.g., washing out the nonilluminated regions the polymerized material remains in the prescribed 3-D form. This al- lows fabrication of any com- puter-generated
4、 3-D structure by direct laser “recording” into the volume of a photosensitive material (Figure 1). Because of the threshold be- havior and nonlinear nature of the process, a resolution beyond the diffraction limit can be real- ized by controlling the laser pulse energy and the number of applied pul
5、ses. As a result, the technique provides much better structural resolution and quality than the Reprinted from the October 2006 issue of PHOTONICS SPECTRA Laurin Publishing Worldwide Coverage: Optics, Lasers, Imaging, Fiber Optics, Electro-Optics, Photonic Component Manufacturing Two-Photon Polymeri
6、zation: A New Approach to Micromachining Femtosecond lasers enable microfabrication with resolution beyond the diffraction limit. by Andreas Ostendorf and Boris N. Chichkov, Laser Zentrum Hannover eV Figure 1. These SEM images show a micro-scale dragon (left) and a movable windmill (right) fabricate
7、d by two-photon polymerization in organically modified ceramics. well-known stereolithography method. Three-dimensional micro- structuring of photosensitive ma- terials by two-photon polymer- ization is effective for the fabri- cation of 3-D structures having a resolution of 100 nm or better. For tw
8、o-photon polymerization and 3-D materials processing, computer-controlled positioning systems are combined with a light source that is typically a near-infrared Ti:sapphire fem- tosecond laser oscillator emitting at 800 nm. To benefit from the high res- olution inherent in the two-pho- ton polymeriz
9、ation process, highly accurate positioning sys- tems e.g., piezoelectric stages and/or scanners are re- quired. However, piezoelectric stages have a traveling range of only a few hundred microns in each direction. Alternatively, op- tical scanning systems can be used to move the laser beam, but they
10、 must deflect the writ- ing laser beam through the outer edges of the focusing op- tics, which can cause distor- tions in the outer parts of the image and a subsequent loss of intensity and structural homo- geneity. 3-D microstructuring system To overcome these limitations, Laser Zentrum Hannover eV
11、 has developed an autonomous, mov- able system for the generation of micro- and nanoscale 3-D struc- tures. The system integrates a femtosecond laser, a scanner for fast writing of small-area struc- tures and a motor-driven linear positioning system from Aerotech GmbH that uses air bearings. The las
12、er is a compact Ti:sapphire system from High Q Laser Production GmbH, with 200-mW of average power, an 800-nm wavelength, a pulse duration below 100 fs and a repetition rate of 73 MHz. Figure 2. Front view of the 3-D microstructuring system shows a CAD drawing (top) and a photograph (bottom). Two-Ph
13、oton Polymerization The positioning system, with three axes, provided a traveling range of 10 cm in each direction. Now commercially available, the 3-D system is equipped with a rotational axis that allows curved cylindrical structures to be cre- ated by two-photon polymeriza- tion (Figure 2). For t
14、wo-photon polymerization microstructuring, an X-Y galvo scanner deflected the expanded laser beam through the high-nu- merical-aperture immersion-oil objective, which focused the fem- tosecond pulses into the photo- sensitive material, or resin (Figure 3). The scanner was mounted on the Z-axis of th
15、e large-range X-Y positioning system. The CCD camera enabled real-time process monitoring. The sample was mounted on a 2-D translational stage. By using a scanner and trans- lational stages to move the tiny beam waist three-dimensionally inside the resin, one can write complex 3-D structures. The ac
16、- curacy of the scanner-based writ- ing is 100 nm, while the posi- tioning accuracy over the com- plete travel range is better than 400 nm. Negative- and positive-tone photoresists are the two types of photosensitive materials that can be structured by two-photon polymerization (Figure 4). With negative-tone photoresists, two- photon exposure results in cross- linking of polymer chains, allow- ing the unexposed resist to be washed out. With positive-tone resists, light exposure leads
