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Fig. 1. Experimental setup of non-make contact with 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 overall performance, which needs higher accuracy in material processing and the capability of manufacturing in an atmospheric atmosphere. Compared to other sophisticated processing procedures, ultrafast laser processing has been recognized as 1 of the most extensively utilized tools for micro/nano-structuring.

Nonetheless, the crucial challenge of ultrafast laser processing to create incredibly little capabilities is the optical diffraction limit. The heat impacted zone by means of these tactics is nonetheless a great deal bigger than the nano-structures, which mainly 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 excellent 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 price.

In addition to nano-hole structures accomplished by make contact with mode, the microsphere femtosecond laser fabrication can also recognize arbitrary structures on sample surfaces in non-make contact with mode. By lifting the microsphere to kind a gap amongst the sample and the microsphere, the operating distance can be enhanced to numerous micrometers.

This technique 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 realize a superior balance amongst the operating distance and function size is a essential challenge for microsphere assisted laser fabrication.

To overcome these challenges, 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-make contact with microspheres, realizing Opto-Electronic Advances.

In non-make contact with mode, the microsphere is placed on a specially made holder, and the nano-structures can be obtained by flexibly controlling of microsphere in x-y-z scanning. In this case, the distance amongst 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-make contact with mode in several situations.

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 means of the 50 µm microsphere is only ~678 nm. Due to the nonlinear effects of ultrafast laser, which includes two-photon absorption and top rated threshold impact, the function of nano-structures can be lowered down to sub-50 nm. For that reason, 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 concept for ultrafine laser surface nano-machining, and its machining efficiency and machining freedom are anticipated to be additional optimized and enhanced by means of microsphere array and microsphere engineering.

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

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