Periodic structures fabricated by nanosecond laser four-beam interference ablation

Abstract

Periodic micro/nano-structure has been playing an important role in microelectronics, microfluidics, micro/nano-optics. There are many technologies that have been proposed for structure manufacture, for example, photolithography, electron beam etching technique, nanoimprint technology. Although these technologies have their advantages, it is troubled by template production, corrosion solution and material choices. Multi-beam interference is one of the common technologies for fabrication of periodic structures as sacrificial layer. It is widely used for its easy setup, quick, and low cost capacities. Laser processing has the advantages of direct writing by light-absorbing under high energy density of pulsed laser of low costs, high quality, fine precision, non-flat three dimensional fabrication ability in transparent medium. Herein, based on principle of interference lithography especially four-beam interference and laser ablation, we proposed one step method of fabrication of large-area mocro/nano-structures by multiple beam laser interference ablation technology. As we all know, light intensity would be redistributed and represent periodic strong and weak variation. Quanta-Ray Nd:YAG Laser of wavelength 355 nm, repetition of 10 Hz and pulse duration of 10 ns was used for laser interference ablation with maximum power 1100 mW and diameter of 10 mm. Area under high light intensity above the threshold will be ablated and removed, while area under low light intensity below the threshold will be left. Thus with this periodic intensity distribution in multiple beam interference and the ablation mechanism, two-dimensional periodic structures in large area can be fabricated maskless on zinc sulfide (ZnS) surface in one step. Additionally, the experiment is in normal atmosphere and donnot need vacuum, which makes it easy and low cost. Structure with period of 3 μm at incident angle of 4.8° was chosen for example to investigate the transition of structure type, as well as the morphology evolution with exposure time in detail. While the incident angle of any beam is slightly changed, the two-dimensional distribution will break into two types, both of which have its own distribution. At the same time, these two types are distributed periodically. In our experiment, periodic holes and pillars were fabricated repeatedly on ZnS surface in the interference ablated area with a larger period about 74 μm. Periodic holes were of period 3 μm while pillars were of period 3 μm 1 / 2 . Distribution directions of pillars were 45° titled with that of holes. Further, the phenomenon of phase shift was studied by adjusting the incident angle of one beam in theory, which explained the experiment results well. At last, according to our study in recent years, the opportunity and challenge of multiple-beam interference ablation technology was discussed in this article. We are believed this interference ablation technology will be taking an important role in hard material processing, two dimensional periodic and quasi-periodic structure fabrication, OLED, solar cells and many more potential micro and nanotechnology regions.