Holographic lithography combines the techniques of holography and laser-induced polymerization in which a photo-resist is exposed to the interference pattern formed by multiple coherent laser beams. Regions with high intensity are polymerized, while under-exposed regions are washed away in a post-exposure process, leaving behind a 2D/3D polymerized structure. This method is very flexible such that various structures, like SC, FCC and BCC, can be fabricated by controlling the beam configurations, intensities, and polarizations. It can also be extended to aperiodic or quasi-periodic structures using five or more beam configurations. Furthermore, chiral structures are also possible by using circularly polarized beams.
In the Physics Department of HKUST, we have several setups using an argon ion laser at 448nm and a HeCd laser at 325nm. FCC structures and 2D Penrose quasicrystals had been fabricated . We have also obtained interesting results for 3D quasicrystals, woodpiles, and spirals [2-4]. Recently, we have used holographic gelatin plates instead of photoresists to record the interference patterns. The gelatin samples exhibit interesting photonic bandgaps. After doped with fluorescence dyes, the gelatin samples can also lase when excited. We have observed visible range lasing in 3D icosahedral quasicrystals for the first time .
- “Large area two-dimensional mesoscale quasicrystals”, X. Wang, C. Y. Ng, W. Y. Tam, C. T. Chan and P. Sheng, Adv. Materials 15, 1526-1528 (2003).
- “Chiral Microstructures (Spirals) Fabrication by Holographic Lithography”, Yee Kwong Pang, Jeffrey Chi Wai Lee, Hung Fai Lee, Wing Yim Tam*, C. T. Chan, and Ping Sheng, Optics Express 13, 7615-7620 (2005).
- “Realization of Woodpile Structure Using Optical Interference Holography”, Yee Kwong Pang, Jeffrey Chi Wai Lee, Cheuk Ting Ho and Wing Yim Tam*, Optics Express 14, 9113-9119 (2006);http://arxiv.org/ftp/physics/papers/0607/0607147.pdf.
- “Icosahedral Quasicrystals for Visible Wavelength by Optical Interference Holography”, Jun Xu, Rui Ma, Xia Wang and Wing Yim Tam, Optics Express 15, 4287-4295 (2007).
- “Visible Light Lasing From Dye-doped Icosahedral Quasicrystals in Dichromate Gelatin Emulsions”, Mang Hin Kok, Weixin Lu, Wing Yim Tam*, and George K. L. Wong, Optics Express 17, 7275-7284 (2009).