Fig. 1. Experimental setup of non-speak to microsphere femtosecond laser irradiation and the fabricated nano-structures. Credit: Compuscript Ltd
In present decades, the improvement of nano-fabrication technologies is driven by the want to boost the density of components and efficiency, which requires greater accuracy in material processing and the capability of manufacturing in an atmospheric atmosphere. Compared to other sophisticated processing options, ultrafast laser processing has been recognized as 1 of the most extensively applied tools for micro/nano-structuring.
Getting mentioned that, the essential challenge of ultrafast laser processing to make specifically smaller sized attributes is the optical diffraction limit. The heat impacted zone by suggests of these approaches is nonetheless substantially larger than the nano-structures, which mostly exhibit >300 nm melting zone.
Employing a dielectric microsphere as a close to-field lens for super-resolution nano-imaging and nano-fabrication has attracted terrific evaluation interest. The optical phenomenon identified as photonic nano-jet can contribute to laser beam focusing to overcome the diffraction limit. To boost the microsphere ultrafast laser processing throughput, the self-assembly approach and micro-lens arrays lithography have been designed to fabricate surface patterns at a swiftly speed and low expense.
In addition to nano-hole structures achieved by speak to mode, the microsphere femtosecond laser fabrication can also recognize arbitrary structures on sample surfaces in non-speak to mode. By lifting the microsphere to type a gap involving the sample and the microsphere, the functioning distance can be elevated to quite a few micrometers.
This strategy leads to the microsphere functioning in far field. In this case, the function size of surface structures can only be decreased to ~300 nm by the 405 nm lamp, 512 nm, and 800 nm femtosecond laser irradiation, which is nonetheless far from the optical diffraction limit. As a result, how to attain a wonderful balance involving the functioning distance and function size is a vital concern for microsphere assisted laser fabrication.
To overcome these troubles, the evaluation group of Prof. Minghui Hong from Xiamen University and the National University of Singapore, and Prof. Tun Cao from Dalian University of Technologies jointly reported an ultrafast laser processing technologies mainly primarily based on non-speak to microspheres, realizing Opto-Electronic Advances.
In non-speak to mode, the microsphere is placed on a specially created holder, and the nano-structures can be obtained by flexibly controlling of microsphere in x-y-z scanning. In this case, the distance involving the microsphere and the sample is in the order of microns. By suggests of the femtosecond laser irradiation of microsphere, this new technologies enables the greater speed machining of finer function nano-structures in non-speak to mode in quite a few circumstances.
Fig. two. Formation mechanism of microsphere assisted femtosecond laser irradiation. Credit: Compuscript Ltd
The researchers also analyzed and explained the forming mechanism of these nanostructures. By theoretical calculation, the focused spot size of the incident laser passing by suggests of the 50 µm microsphere is only ~678 nm. Due to the nonlinear effects of ultrafast laser, which consists of two-photon absorption and top threshold effect, the function of nano-structures can be decreased down to sub-50 nm. For that explanation, the surface nano-structures are attributed to the co-effect of the microsphere focusing, the two-photon absorption, and the top threshold effect of the ultrafast laser irradiation.
This approach delivers a new notion for ultrafine laser surface nano-machining, and its machining efficiency and machining freedom are anticipated to be added optimized and enhanced by suggests of microsphere array and microsphere engineering.
Zhenyuan Lin et al, Microsphere femtosecond laser sub-50 nm structuring in far field by suggests of non-linear absorption, Opto-Electronic Advances (2023). DOI: ten.29026/oea.2023.230029
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