May 30, 2023 6:57 am

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Fig. 1. Experimental setup of non-speak to microsphere femtosecond laser irradiation and the fabricated nano-structures. Credit: Compuscript Ltd

In current decades, the improvement of nano-fabrication technologies is driven by the need to have to improve the density of elements and efficiency, which needs higher accuracy in material processing and the capability of manufacturing in an atmospheric atmosphere. Compared to other sophisticated processing solutions, ultrafast laser processing has been recognized as 1 of the most extensively applied tools for micro/nano-structuring.

Nevertheless, the crucial challenge of ultrafast laser processing to generate particularly modest characteristics is the optical diffraction limit. The heat impacted zone by way of these methods is nonetheless significantly bigger than the nano-structures, which largely exhibit &gt300 nm melting zone.

Applying a dielectric microsphere as a close to-field lens for super-resolution nano-imaging and nano-fabrication has attracted fantastic study interest. The optical phenomenon identified as photonic nano-jet can contribute to laser beam focusing to overcome the diffraction limit. To improve the microsphere ultrafast laser processing throughput, the self-assembly technique and micro-lens arrays lithography have been created to fabricate surface patterns at a speedy speed and low expense.

In addition to nano-hole structures accomplished by speak to mode, the microsphere femtosecond laser fabrication can also understand arbitrary structures on sample surfaces in non-speak to mode. By lifting the microsphere to kind a gap in between the sample and the microsphere, the operating distance can be improved to many micrometers.

This approach leads to the microsphere operating in far field. In this case, the function size of surface structures can only be lowered 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 accomplish a great balance in between the operating distance and function size is a very important challenge for microsphere assisted laser fabrication.

To overcome these complications, the study 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 primarily based on non-speak to microspheres, realizing Opto-Electronic Advances.

In non-speak to mode, the microsphere is placed on a specially developed holder, and the nano-structures can be obtained by flexibly controlling of microsphere in x-y-z scanning. In this case, the distance in between the microsphere and the sample is in the order of microns. By means of the femtosecond laser irradiation of microsphere, this new technologies enables the higher speed machining of finer function nano-structures in non-speak to mode in a variety of 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 way of the 50 µm microsphere is only ~678 nm. Due to the nonlinear effects of ultrafast laser, like two-photon absorption and top rated threshold impact, the function of nano-structures can be lowered down to sub-50 nm. As a result, the surface nano-structures are attributed to the co-impact of the microsphere focusing, the two-photon absorption, and the top rated threshold impact of the ultrafast laser irradiation.

This technique delivers a new notion for ultrafine laser surface nano-machining, and its machining efficiency and machining freedom are anticipated to be additional optimized and enhanced by way of microsphere array and microsphere engineering.

Additional data:
Zhenyuan Lin et al, Microsphere femtosecond laser sub-50 nm structuring in far field by way of non-linear absorption, Opto-Electronic Advances (2023). DOI: ten.29026/oea.2023.230029

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Compuscript Ltd