Instituto de Óptica “Daza de Valdés”

Versatile femtosecond laser interference patterning applied to high-precision nanostructuring of silicon

Versatile femtosecond laser interference patterning applied to high-precision nanostructuring of silicon

Laser Processing Group (LPG)

  • A novel femtosecond laser technique improves silicon nanostructuring capabilities with a commercial laser.

  • The achieved laser interference patterns enable the fabrication of periodic surface structures with sizes up to 120 nm.

Madrid / August 9, 2024

A team of researchers from the Laser Processing Group at IO-CSIC has published a scientific article in the journal Optics & Laser Technology in which they present an innovative nanostructuring technique based on the interference of a commercial amplified femtosecond laser. The scientists were able to improve on previous work by manufacturing gratings with tunable periods of up to 650 nm and amorphous silicon dots with feature sizes of up to 120 nm. This versatile technique has the potential for direct application in industrial processes for manufacturing high-precision materials.

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In recent decades, nanostructuring of materials using ultrafast lasers has emerged as a promising field of research. These lasers heat the treated material less and achieve smaller and sharper resolution sizes compared to nanosecond lasers.

In this work, the research team has carried out an innovative study on silicon nanostructuring using interference from a commercial femtosecond amplified laser. The technique employed is based on direct laser interference patterning (DLIP), which enables the fabrication of high-precision periodic surface structures in a single pass. This approach exhibits exceptional versatility and significant potential for rapid and precise fabrication of metasurfaces in a wide range of materials, opening up new opportunities in nanoscale manufacturing and promising substantial impact in diverse fields such as photonics, biology, medicine, microfluidics and others.

Diagram of the different devices through which a red laser beam passes and examples of the lines it causes in the material
Experimental setup for fs-DLIP nanostructuring together with experimentally recorded intensity distributions at the sample plane, shown in false color: (a) Normalized intensity distribution for a single diffraction grating (Ronchi ruling) with period G = 50 μm and a 20x Mag. microscope objective (MO) (b) enlarged region of (a), (c) two crossed diffraction gratings with G = 50 μm, (d) single diffraction grating with G = 100 μm.
The acronyms of the components of the setup are: aperture (A), half-wave plate (λ/2), quarter-wave plate (λ/4), polarizing beam splitter (PBS), focusing lens (FL), microscope objective (MO), tube lens (TL).
To carry out this study, the team of researchers used a commercially available Ti:Sa femtosecond amplified laser with a wavelength of 800 nm, a pulse duration of 120 fs, and a repetition rate of 1 kHz. Using commercial diffractive optical elements and standard optical components, the laser nanostructuring experiment was designed to enable the fabrication of periodic lines with tunable periods up to 650 nm. Furthermore, millimeter-sized diffraction gratings were fabricated using multi-pulse irradiation at processing speeds of up to 0.5 mm/s. Using the same femtosecond laser nanostructuring techniques, the researchers also demonstrated their capabilities by creating amorphous dots in silicon with feature sizes of up to 120 nm. Laser fluence and stripe width were used to achieve complex nanostructures, revealing the presence of various matter reorganization processes in the molten phase. These results highlight the versatility and precision of the technique used, paving the way for future studies related to single-pulse laser treatment and providing new opportunities in understanding the mechanisms of formation of complex surface structures in various materials.

What is direct laser interference pattern?

The direct laser interference pattern (DLIP) technique is a technique that allows the fabrication of periodic nanoscale structures in a wide variety of materials and in large areas. This technique achieves that the laser with which the material is irradiated is periodically modulated by secondary beams so that instead of at a point the laser attacks the material forming a pattern in a single pass.

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