The fluid field knocks out the light field for laser-


image: (ab) SEM images showing side and top views of cracked structures obtained by fs-LAL of Si at 700 mW laser power, 15 μm scan interval and 1 mm/s scan speed . (c) Structure of a macropore. (d) Magnified CLIPSS morphology in (c). (e, f) Twin CLIPSS in a macropore. (g,h) SEM images of grooves obtained by 50mW-fs-LAL. High contrast applied to (g) allows the macropores in the valleys of the grooves to be seen more clearly. (i/k, j/l) Enlarged images of green and blue rectangles in (g) and (h), respectively. The direction of laser polarization is shown in (b, l). (i, j, k) and (l) normal CLIPSS and LIPSS, respectively. (m) Velocity vector of a fluid vortex formed in a hole structure upon impact of superimposed high-velocity horizontal and vertical flows of fluids.
to see Continued

Credit: OAE

In a new publication by Advances in optoelectronics; DO I 10.29026/oea.2021.210066researchers from Shanghai Jiao Tong University, China, Sun Yat-sen University, China and RIKEN Center for Advanced Photonics, Japan discuss liquid vortices and fluxes induced by laser ablation femtosecond in liquid formation governing the circular and intersecting LIPSS.

Since the discovery of laser-induced periodic surface structures (LIPSS) in 1965, one-step formation of LIPSS has been considered one of the distinct advantages of laser micro/nanofabrication over 50 years. LIPSS can be formed in various materials including metals, semiconductors, ceramics, dielectrics and polymers with relevant applications in optics, optoelectronics, electrochemistry, biology and other fields. LIPSS can be categorized into Low Spatial Frequency LIPSS (LSFL), High Spatial Frequency LIPSS (HSFL), Ultra-High Spatial Frequency LIPSS (UHSFL), and Supra Wavelength Periodic Surface Structure (SWPSS) by function of their periods with respect to the wavelength of the laser. UHSFL is defined as the periodic structure with a period less than 100 nm; HSFL, ~100 nm at less than 1/2 the laser wavelength; LSFL, greater than 1/2 at the same dimension of the laser wavelength, while the period of SWPSS is greater than the laser wavelength. For a linearly polarized laser, the direction of LIPSS is typically perpendicular to the polarization direction of the laser. LIPSS’s orientation control presents different rainbow colors from the same viewing angle, enabling the use of color printing for anti-counterfeiting applications. Other types of LIPSS including triangular, rhombic, arc and circular LIPSS have also been produced using nonlinearly polarized light, such as circular or vortex polarized light.

Article reference: Zhang DS, Li XZ, Fu Y, Yao QH, Li ZG et al. Vortex and liquid flows induced by femtosecond laser ablation in a liquid governing the formation of circular and intersecting LIPSS. Opto-Electron Adv 5, 210066 (2022). do I: 10.29026/oea.2021.210066

Key words: Circular LIPSS / Criss-Cross LIPSS / Liquid Laser Ablation / Water Femtosecond Laser Ablation / Liquid Vortex / Vortex Detachment

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The research groups of Associate Professor Dongshi Zhang, Professor Zhuguo Li of Shanghai Jiao Tong University, Professor Qinghe Yao of Sun Yat-sen University and Professor Koji Sugioka of RIKEN Center for Advanced Photonics demonstrate that in ablating with a linearly polarized femtosecond laser in water, the complex fluid dynamics associated with fluid vortex generation can break the light field boundary to regulate LIPSS orientations, leading to the formation of irregular circular LIPSS ( CLIPPS) and intersecting LIPSS (CCLIPSS). A theoretical simulation was carried out to verify the fluid scenes, which strongly supports the experimental observations. This article not only breaks the traditional cognition, but also displays a new way for fluid-based LIPSS manipulation by introducing new CLIPPS/CCLIPSS structures and proposes the fluid field-based training mechanism, which is of great importance to enrich the diversity of LIPSS and accurately interpret the formation mechanism of LIPSS.

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Advances in optoelectronics (OEA) is a high-impact, open-access, peer-reviewed SCI monthly journal with an impact factor of 9.682 (Journals Citation Reports for IF 2020). Since its launch in March 2018, OEA has been indexed in SCI, EI, DOAJ, Scopus, CA and ICI databases over time and has expanded its editorial board to 36 members from 17 countries and regions (average h-index of 49).

The journal is published by the Institute of Optics and Electronics of the Chinese Academy of Sciences, aiming to provide a platform for researchers, scholars, professionals, practitioners and students to impart and share knowledge under the form of high quality empirical and theoretical research papers covering the topics of optics, photonics and optoelectronics.

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