arXiv subjects

Michalis Stavrou

Publications and source records attributed to Michalis Stavrou.

3 recordsLinked to original sources

arXiv2026

High-Repetition-Rate Projection Multiphoton Lithography for Large-Area Sub-Micron 3D Printing

High-resolution lithographic techniques are often limited by low volumetric throughput, since there is no universal and scalable manufacturing process that can produce 3D metasurfaces. In this work, we demonstrate a high-speed holographic 3D printing platform based on spatiotemporal beam shaping, exceeding the repetition rate while keeping the resolution high. The system integrates a femtosecond laser source with a spectral pulse compressor and a beam shaper to project uniform, axially confined light fields to project patterns directly on the advanced photoresists using a Digital Micromirror Device DMD. We investigate the process window for rapid polymerization, optimizing the photoinitiator choice to eliminate thermal crosstalk at high repetition rates. Using this setup, we achieve a production throughput of more than a million voxels per second with sub-micron resolution below 400 nm. The system's reliability is validated through the fabrication of large-area woodpile-like lattices and uniform micropillar arrays, establishing a workflow for scalable manufacturing of micro-optical components.

physics.optics↗

arXiv2024

Emerging Ta$_{4}$C$_{3}$ and Mo$_{2}$Ti$_{2}$C$_{3}$ MXene Nanosheets for Ultrafast Photonics

Ultrafast nonlinear optical (NLO) response, fast carrier recovery, broadband absorption, and resistance to radiation and heat make 2D materials promising for photonic technologies. However, low electronic conductivity and carrier concentration limit the performance of semiconducting or semimetallic materials. This work investigates the ultrafast NLO properties and carrier dynamics of Ta$_{4}$C$_{3}$T$_{x}$ and out-of-plane ordered Mo$_{2}$Ti$_{2}$C$_{3}$T$_{x}$ MXenes using Z-scan and pump-probe optical Kerr effect techniques under visible and infrared femtosecond laser pulses. Their NLO response surpasses all previously studied MXenes and most other 2D nanomaterials, attaining exceptionally high third-order susceptibility (\c{hi}(3)) values on the order of 10^{-13} esu. Mo$_{2}$Ti$_{2}$C$_{3}$T$_{x}$ exhibits the strongest NLO response under both excitation regimes, attributed to charge transfer between Mo and Ti layers in the MXene structure. Under visible excitation, the studied MXenes display pronounced saturable absorption, while under infrared excitation, they exhibit strong reverse saturable absorption, resulting in efficient optical limiting. Additionally, pump-probe experiments identify two distinct relaxation processes: a fast one on the sub-picosecond timescale and a slower one a few picoseconds after photoexcitation. Our results indicate that these MXenes are among the strongest NLO materials. They show their great potential for advanced photonic and optoelectronic applications in laser technologies, optical protection, telecommunications, and optical/quantum computing.

physics.optics↗

arXiv2023

Crystalline Phase Effects on the Nonlinear Optical Response of MoS2 and WS2 Nanosheets

In the present work, some MoS2 and WS2 nanosheets were prepared and characterized. Depending on the preparation procedures, trigonal prismatic (2H) or octahedral (1T) coordination of the metal atoms were obtained, exhibiting metallic (1T) or semiconducting (2H) character. Both MoS2 and WS2 nanosheets were found exhibiting large nonlinear optical (NLO) response, strongly dependent on their metallic (1T) or semiconducting (2H) character. So, the semiconducting character 2H-MoS2 and 2H-WS2 exhibit positive nonlinear absorption and strong self-focusing, while their metallic character counterparts exhibit strong negative nonlinear absorption and important self-defocusing. In addition, the semiconducting MoS2 and WS2 were found exhibiting important and very broadband optical limiting action extended from 450 to 1750 nm. So, by selecting the crystalline phase of the nanosheets, i.e., their semiconduction/metallic character, their NLO response can be greatly modulated. The results of the present work demonstrate unambiguously that the control of the crystalline phase of MoS2 and WS2 provides an efficient strategy for 2D nanostructures with custom made NLO properties for specific optoelectronic and photonic applications.

cond-mat.mtrl-sci↗