arXiv subjects

Darius Gailevičius

Publications and source records attributed to Darius Gailevičius.

4 recordsLinked to original sources

arXiv2026

Heating of black-Si by microwaves at 2.45 GHz: effect of nano-needle orientation

Silicon, which is highly reflective and has negligible absorption at the microwave 2.45 GHz range, can be heated when it is turned into black-Si with a surface texture of nano-needles made by SF6/O2 plasma etching. Microwave heating of flat Si and of black-Si with vertical and with tilted (oriented) nano-needles was compared under identical conditions in a cylindrical TM010 resonator. Samples were placed horizontally on a 150-micrometer-thick cover glass, which standardized their height and position inside the cavity and allowed a common calibration of the radiation thermometer against a K-type thermocouple. Under a stepwise protocol of only 2-3-4 W of microwave power (60 s per step), black-Si with vertical needles reached ~ 260 C, systematically exceeding flat Si (~ 190 C), while black-Si with oriented needles showed a delayed but abrupt onset of heating at 3 W. In situ monitoring of the cavity resonance revealed a 2-3 MHz downshift of the resonance frequency f for all samples, with the drift consistently appearing once the sample temperature exceeded ~ 120 - 150 C, consistent with thermally activated carrier generation in Si. At a given temperature, each sample loads the cavity at a different f and quality factor Q, indicating an orientation-dependent effective permittivity of the nano-needle array, in line with the strong form birefringence of tilted black-Si. Application potential and challenges in the quantitative temperature and permittivity determination are discussed.

cond-mat.mes-hall↗

arXiv2020

Nanostructured Multilayer Coatings for Spatial Filtering

Spatial filtering is an important mechanism to improve the spatial quality of laser beams. Typically, a confocal arrangement of lenses with a diaphragm in the focal plane is used for intracavity spatial filtering. Such conventional filtering requires access to the far-field domain. In microlasers, however, conventional filtering is impossible due to the lack of space in micro-resonators to access the far-field. Therefore, a novel concept for more compact and efficient spatial filtering is necessary. In this study, we propose and demonstrate a conceptually novel mechanism of spatial filtering in the near-field domain, by a nanostructured multilayer coating - a 2D photonic crystal structure with a periodic index modulation along the longitudinal and transverse direction to the beam propagation. The structure is built on a nano-modulated substrate, to provide the transverse periodicity. The physical vapor deposition is used to provide self-repeating modulation in the longitudinal direction. We experimentally demonstrate a 5 micron thick photonic multilayer structure composed of nanostructured multiple layers of alternating high- and low-index materials providing spatial filtering in the near-infrared frequencies with 2° low angle passband. The proposed photonic structure can be considered as an ideal component for intracavity spatial filtering in microlasers.

physics.optics↗

arXiv2019

Photonic Crystal Spatial Filters Fabricated by Femtosecond Pulsed Bessel Beam

We propose and experimentally demonstrate femtosecond direct laser writing with Bessel beams for the fabrication of photonic crystals with spatial filtering functionality. Such filters are mechanically stable, of small (of order of millimeter) size, do not require direct access to the far-field domain, and therefore are excellent candidates for intracavity spatial filtering applications in mini- and micro-lasers. The technique allows the fabrication of efficient photonic crystal spatial filters in glass, with a narrow angle (~1 degree) nearly 100%-transmission pass-band between broad angle (up to 10 degrees) nearly 0%-transmission angular stop-bands. We show, that this technique can not only significantly shorten the fabrication time, but also allows the fabrication of large-scale defect-free photonic crystal spatial filters with a wide filtering band.

physics.app-ph↗

arXiv2019

Photonic crystal spatial filtering in broad aperture diode laser

Broad aperture semiconductor lasers usually suffer from low spatial quality of the emitted beams. Due to the highly compact character of such lasers the use of a conventional intra-cavity spatial filters is problematic. We demonstrate that extremely compact Photonic Crystal spatial filters, incorporated into the laser resonator, can improve the beam spatial quality, and correspondingly, increase the brightness of the emitted radiation. We report the decrease of the M2 from 47 down to 28 due to Photonic Crystal spatial intra-cavity filtering, and the increase of the brightness by a factor of 1.5, giving a proof of principle of intra-cavity Photonic Crystal spatial filtering in broad area semiconductor lasers.

physics.optics↗