arXiv subjects

Dan Kapsaskis

Publications and source records attributed to Dan Kapsaskis.

3 recordsLinked to original sources

arXiv2026

Olivine annealed up to 1500 C: changes traced by polarised IR reflectance and magnetization

Spectral analysis at the infrared (IR) spectral range is introduced with assignment of synthetic red-green-blue (RGB) colours defined by adjustable wavelength and bandwidth. The RGB bands were selected at the phase-specific absorbance A or reflectance R bands of olivine and related materials, which can be formed via high temperature annealing (HTA) of natural minerals up to 1500 C. Natural olivines were collected from quarry at volcanic site in Mortlake, Victoria, Australia and spectrally characterised during IR-THz spectroscopy beamtime experiments at Australian Synchrotron. Phase changes in HTA natural olivines were traced by correlation of optical IR 4-polarisation spectroscopy, X-ray energy dispersive spectroscopy and magnetisation. After HTA, olivine samples were magnetized via precipitation of Fe-rich oxides.

physics.geo-ph↗

arXiv2026

Burst-mode fs-laser direct writing for full-thickness oxidation of Ta thin films

Direct fs-laser (1030~nm/200~fs) write of a throughout oxide Ta$_{2}$O$_{5}$ on a 200~nm Ta film was achieved using a combined ps- and ns- burst mode (Burst-in-Burst or BiB) of fs-pulse exposure at a high 0.6~MHz repetition rate. Few micrometers-wide lines were formed at the center of 12~$\mu$m focal spot by controlled oxidation without ablation. The oxidized regions were flat and optically transparent. Wavelength-scale self-organized ripples of oxidized Ta$_{2}$O$_{5}$ sub-1~$\mu$m gratings were recorded by rastering a $1\times 1$~mm$^2$ area. The oxidized ripples with periodic pattern $\sim wavelength$ were aligned with the polarization of the writing beam. Energy deposition in the burst-mode oxidation is discussed by comparing 200~fs and 20~ps BiB-mode writing modes. The presented strategy of self-guided oxidation with heat deposition by BiB fs-laser opens an opportunity for debris-free and annealing-free oxidation on a sub-wavelength scale.

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↗