arXiv subjects

Darius Gailevicius

Publications and source records attributed to Darius Gailevicius.

9 recordsLinked to original sources

arXiv2026

Writing with Near-Field: towards Atomic Resolution in Material Processing

Direct laser writing with ultra-short pulses is the most flexible route to two- and three-dimensional (2D/3D) material modification, yet its resolution is judged against the optical diffraction limit. This review argues the opposite: the finest, most reproducible modifications come not from shortening the wavelength but from localising the absorber. Through the threshold effect and a transient epsilon-near-zero (ENZ) state - the dielectric-to-metal (Die-Met) state of the excited solid - the deposited energy is confined to a dipole-like nano-seed whose near-field intensity falls as r^-6 (ideal point dipole). The localisation is thus set by the seed size, not the focal wavelength, and the final feature is shaped by the material response: post-pulse heat flow, cavitation and quenching. We show that polarisation controls the anisotropy of deposition: the quasi-static near-field and interface boundary conditions select the writing direction and the modification orientation, down to a single defect. We survey energy-deposition mechanisms from 100 nm to the single-nanometer scale and link them to working engineering: stitch-free large-area patterning and record aspect-ratio (10^3-10^4) dicing and wafering of transparent crystals. Finally, we conjecture guided volumetric deposition, in which laser-inscribed lossy nano-seeds act as antennas that let cavity microwaves anneal the modified nano-volumes from within, as a 2.45 GHz oven heats food through water-dipole absorption. Throughout, atomic resolution is used in a quantum-confined sense and denotes a direction of travel: 10-20 nm features are demonstrated, while deterministic single-defect and single-bond modification remain goals. The thesis is that ultrafast direct write beats diffraction-limited intuition because the material itself forms a transient nanoscale absorber whose near-field and boundary conditions govern energy deposition.

physics.optics↗

arXiv2026

Direct Production of Ultra-High Radioisotopic Pure $^{64}$Cu from Natural Zinc Metal via D-D Fusion Narrowband Fast Neutron Source Irradiation

Copper-64 radiopharmaceuticals have seen limited clinical deployment primarily due to the high cost of the isotopically enriched $^{64}$Ni metal required for its production. In this work we demonstrate that ultra-high radioisotopic pure $^{64}$Cu can be directly produced in a no-carrier-added-form from natural zinc metal through irradiation with D-D fusion narrowband fast neutron sources. A highly controlled D-D fusion narrowband fast neutron source at the ELI-ALPS Laser Facility was deployed to irradiate encapsulated 99.995\% pure natural zinc for 1 hour. Time-resolved gamma-ray spectroscopy of the irradiated sample over 72 hours was deployed to assess copper radioisotope activity. $^{64}$Cu was the only copper radioisotope detected within the irradiated sample, with a minimum and Minimum Detection Activity (MDA) threshold-corrected $^{64}$Cu radioisotopic purity of 99.62\% and 99.97\% respectively. Our result illustrates that highly controlled D-D fusion narrowband fast neutron sources have the potential to reduce the raw material production costs for $^{64}$Cu radiopharmaceuticals on the order of 2000 times. Cheaper $^{64}$Cu radiopharmaceuticals will increase their use in clinical practice, and, in-turn, increase outcomes for cancer patients receiving radionuclide therapy.

physics.med-ph↗

arXiv2025

Ablation of black-Si by (Gauss-)Bessel femtosecond laser beams

Laser machining and modification of black-Si (b-Si) by femtosecond laser Gaussian (G-) and Gauss-Bessel (GB-) beams are compared at a wavelength of 1030 nm. The GB-beam was generated using a diffractive axicon lens and 10x demagnification optics. It was found that modification of b-Si well below (a factor 50x) the single pulse ablation fluence of 0.2 J/cm2 was possible, corresponding to ablation/melting of nano-needles. The width of modification was almost independent of pulse energy/fluence and had a width of 1/e2-intensity profile at the melting regime. For the GB-beam, the smallest width of laser modification at 0.2 J/cm2 threshold (at the center core) was close to the FWHM of the core of the GB-beam. The aspect ratio of the ablated groove on the surface of b-Si made by GB-beam was twice as large - up to 8 - compared to that achievable with G-beam, and it was at a lower fluence of 4 J/cm2 (50x reduction). Reflectivity of two-side nanotextured b-Si on plasma-thinned 70-micrometers thick Si was strongly reduced in the near-IR range, reaching transmittance >95% at 1.7-2.1 micrometres wavelengths.

physics.optics↗

arXiv2024

3D Free-Form Optical Lens -- Miniaturised Fibre Couplers for Astrophotonics

In astronomy, multi-object spectrographs employ fibre positioning robots to couple the light from multiple astronomy sources (stars or galaxies) into multiple multi-mode fibres, which are distributed across the focal plane of the telescope. These fibres transport the celestial light to the entrance slit of a spectrograph (or bank of spectrographs) for analysis. For any multi-object system mm-scale opto-mechanical solutions are required to couple the telescope light efficiently into the fibre. We demonstrate a unique micro-optics solution to replace current optical fibre couplers. Specifically, we target technology on board the Keck telescope's FOBOS - Fibre-Optic Broadband Optical Spectrograph - which operates at UV to IR spectral ranges. For spectrally broad UV-IR band operation we use glass and crystals: fused silica, crystalline quartz (transparency 0.16 - 2 micrometers), sapphire Al2O3 (0.2 - 5 micrometers), CaF2 (0.2-7 micrometers), and BaF2 (0.2-10 micrometers). The miniaturised micro-coupler is monolithic, with the entire light path contained within glass or crystal, seamlessly extending to the fibre entrance, which is laser-machined and precisely aligned with the optical axis.

astro-ph.IM↗

arXiv2024

Light Trapping by Non-Hermitian Thin Films

One of the exceptional features of non-Hermitian systems is the unidirectional wave interactions. Simultaneous modulation of the real and the imaginary part of the interaction potentials (of the refractive index and the gain/loss in the case of optical systems) can result in unequal coupling coefficients between the fields of different parts of the system. The unidirectional coupling can also be arranged not only between the internal fields of the system but also between internal fields and external radiation. At a particular (exceptional) point the situation can be achieved, that the external radiation is efficiently coupled into the system, but the internal radiation cannot escape backwards. In this way, the incident radiation can be trapped inside the non-Hermitian system and, eventually, can be efficiently absorbed there. We realize this idea in non-Hermitically modulated thin films. The modulation consists of a Hermitian part - the periodic corrugation of the surfaces of a thin film, and a non-Hermitian part - the modulation of losses along the film. We prove numerically and demonstrate experimentally that the incident radiation, coupled with such a non-Hermitian thin film, is unidirectionally trapped into a planar mode of the film, does not escape from the film (or escape weakly due to experimental imperfections), and is efficiently absorbed there.

physics.optics↗

arXiv2024

Interferometric microscale measurement of refractive index at VIS and IR wavelengths

Determination of refractive index of micro-disks of a calcinated ($1100^\circ$C in air) photo-resist SZ2080$^\mathrm{TM}$ was carried out using transmission and reflection spectroscopy. Interference fringes at specific wavenumbers/wavelengths were selected for determination of the optical thickness, hence, the refractive index when the thickness of micro-disks was measured by scanning electron microscopy (SEM). Refractive index of disks of $\sim 6\pm 1~μ$m thickness were determined at visible and IR (2.5-13~$μ$m) spectral ranges and where $2.2\pm 0.2$ at visible and IR wavelengths. Peculiarities of optical characterisation of micro-optical structures are discussed in view of possible uncertainties in the definition of geometric parameters, shape and mass density redistribution.

physics.optics↗

arXiv2022

Extremely Narrow, Sharp-Peaked Resonances at the Edge of the Continuum

We report a critical narrowing of resonances of a driven potential well, when their eigenfrequencies approach the edge of the continuum. The resonances also obtain unusual sharp-peak shapes at the continuum boundary. The situation can be realized for the electromagnetic wave propagating across the dielectric thin films with a periodically modulated interface(s). We show the general phenomenon semi-analytically on a simplified model of a driven quantum potential well, also by rigorous numerical analysis of Maxwell equations for the wave propagation across the thin film with a modulated interface(s). We justify the phenomenon experimentally, by the measurements of light reflection from the dielectric thin film deposited on a periodically modulated surface. The narrow and sharp-peak resonances can be used for an efficient narrow-band frequency- and spatial filtering of light.

physics.optics↗

arXiv2020

Tilted black-Si: ~0.45 form-birefringence from sub-wavelength needles

The self-organised conical needles produced by plasma etching of silicon (Si), known as black silicon (b-Si), create a form-birefringent surface texture when etching of Si orientated at angles of $θ_i < 50 - 70^\circ$ (angle between the Si surface and vertical plasma E-field). The height of the needles in the form-birefringent region following 15~min etching was $d\sim 200$ nm and had a 100 $μ$m width of the optical retardance/birefringence, characterised using polariscopy. The height of the b-Si needles corresponds closely to the skin-depth of Si $\simλ/4$ for the visible spectral range. Reflection-type polariscope with a voltage-controlled liquid-crystal retarder is proposed to directly measure the retardance $Δn\times d/λ\approx 0.15$ of the region with tilted b-Si needles. The quantified form birefringence of $Δn = - 0.45$ over $λ= 400-700$~nm spectral window was obtained. Such high values of $Δn$ at visible wavelengths can only be observed in the most birefringence calcite or barium borate as well as in liquid crystals. The replication of b-Si into Ni-shim with high fidelity was also demonstrated and can be used for imprinting of the b-Si nanopattern into other materials.

physics.app-ph↗

arXiv2016

Nanoscale precision of 3D polymerisation via polarisation control

A systematic analysis of polarization effects in a direct write femtosecond laser 3D lithography is presented. It is newly shown that coupling between linear polarization of the writing light electric field and temperature gradient can be used to fine-tune feature sizes in structuring of photoresists at a nanoscale. The vectorial Debye focusing is used to simulate polarization effects and a controlled variation up to 20% in the linewidth is shown experimentally for the identical axial extent of the polymerised features. The revealed mechanisms are relevant for a wide range of phenomena of light-matter interaction at tight focusing in laser-tweezers and in plasmonic or dielectric sub-wavelength focusing where strong light intensity and thermal gradients coexist.

physics.optics↗