Nowadays nanophotonics is one of the most exciting fields of research in modern optical technologies. For nanophotonics the basic idea is to modify light as an electromagnetic wave at a size level, which is usually smaller than the base length of the light itself, or in other words, its wavelength. As of now, creating subwavelength structures is the cornerstone of modern photonics where structures can manipulate the effective optical properties of materials. Unfortunately, the main snag facing nanophotonics is the high fabrication costs and low throughput of top-down fabrication methods coupled by the lack of reproducibility and uniformity of bottom-up fabrication methods. Fortunately, a glimmer of hope has been found in the adoption of femtosecond lasers that can alter the optical, electrical, and mechanical properties of materials.
To be precise, the formation of laser-induced periodic surface structures (LIPSSs) promises large-area, single-step, maskless fabrication of surface structures. A careful and thorough review of existing literature reveals that 2D LIPSSs lack uniformity and periodicity. Further, rigorous perusal of published studies show that multi-pulsed femtosecond laser fabrication differs from traditional laser interference lithography which can create 2D structures due to multi-beam interference.
The fabrication of subwavelength two-dimensional structures on metals is of paramount importance to modern nanophotonics. Therefore, harmonization of various techniques to better existing approaches would be highly commendable. In this context, a group of researchers from the Changchun Institute of Optics, Fine Mechanics and Physics at Chinese Academy of Sciences: Dr. Sohail Jalil, Yuhao Lei, Wanlin He, and lead by Professor Jianjun Yang in collaboration with Professor Chunlei Guo at University of Rochester developed a new method to fabricate 2D conic structures on nickel surfaces using a single beam with three temporally delayed pulses. Their work is currently published in the research journal, Optics Letters.
In brief, the research team studied the effect of triple, temporally delayed, femtosecond laser pulses on the formation of 2D LIPSSs on a nickel (Ni) surface. As a matter of fact, the three pulses were mutually orthogonal and were temporally delayed using two separate delay lines. Furthermore, by varying the delay time between the pulses, the researchers were able to find the optimal conditions for creating large-area, uniform 2D conic structures with subwavelength periodicities and features.
The authors reported that by controlling the delay between the three pulses, they were able to control the effect of each pulse in creating laser induced periodic surface structures which enabled the control of the 2D structure features, namely, the period and structure dimensions. In fact, they further explained their results based on the surface plasmon polariton-femtosecond laser interference model.
In summary, the study demonstrated the 2D periodic surface structures could be produced on large areas using three temporally delayed pulsed beams. Remarkably, the researchers were able to show that by using a triple-pulsed beam, one could gain control over the different structural parameters owing to the fact that it allows for additional degrees of freedom. Overall, the proposed new technique can be used on harder metals, such as: tungsten carbide, to create molds that can be used on polymers to create anti-reflection moth eye structures.
Sohail A. Jalil, Jianjun Yang, Mohamed Elkabbash, Yuhao Lei, Wanlin He, Chunlei Guo. Formation of uniform two-dimensional subwavelength structures by delayed triple femtosecond laser pulse irradiation. Volume 44, Number 9 / 2019 / Optics Letters.Go To Optics Letters