Darius Gailevicius

Flat lensing in the visible frequency range by woodpile photonic crystals

We experimentally demonstrate full two-dimensional focalization of light beams at visible frequencies by a three-dimensional woodpile photonic crystal. The focalization (the flat lensing) with focal distances of the order of 50-70 μm is experimentally demonstrated. Experimental results are compared with numerical calculations and interpreted by harmonic expansion studies.

Nanoscale Precision of 3D Polymerization via Polarization Control

NATO SPS-985048 “Nanostructures for Highly Effi cient Infrared Detection” grant is acknowledged. D.G. is grateful for the fi nancial support by “FOKER” (Grant No. MIP-14459) grant from the Research Council of Lithuania.

Optically Clear and Resilient Free-Form µ-Optics 3D-Printed via Ultrafast Laser Lithography

We introduce optically clear and resilient free-form micro-optical components of pure (non-photosensitized) organic-inorganic SZ2080 material made by femtosecond 3D laser lithography (3DLL). This is advantageous for rapid printing of 3D micro-/nano-optics, including their integration directly onto optical fibers. A systematic study of the fabrication peculiarities and quality of resultant structures is performed. Comparison of microlens resiliency to continuous wave (CW) and femtosecond pulsed exposure is determined. Experimental results prove that pure SZ2080 is ∼20 fold more resistant to high irradiance as compared with standard lithographic material (SU8) and can sustain up to 1.91 GW/cm2 intensity. 3DLL is a promising manufacturing approach for high-intensity micro-optics for emerging fields in astro-photonics and atto-second pulse generation. Additionally, pyrolysis is employed to homogeneously shrink structures up to 40% by removing organic SZ2080 constituents. This opens a promising route towards downscaling photonic lattices and the creation of mechanically robust glass-ceramic microstructures.

Spatial filtering by axisymmetric photonic microstructures.

We propose and show experimentally axisymmetric spatial (angular) filtering of two-dimensional light beams by axisymmetric photonic microstructures. Such three-dimensional microstructures (similar to photonic crystals), in gapless configuration, were recorded in bulk of glass, where the refractive index has been point-by-point modulated using tightly focused femtosecond laser pulses. Axisymmetric angular filtering of approximately 25 mrad is demonstrated experimentally.

Photonic Crystal Microchip Laser

Microchip lasers are very efficient, compact and convenient sources of coherent light. However they have a serious disadvantage that, especially in high power operation regimes, the emitted beam structure is relatively bad (with large angular divergence). We show that the intracavity photonic crystals with spatial filtering functionality, can strongly improve the spatial characteristics of the microchip laser. The angular divergence of the emitted beam is strongly reduced, and the radiation brightness is significantly increased due to the intracavity photonic crystal filter.

Chirped axisymmetric photonic microstructures for spatial filtering

Abstract. We explore, theoretically and experimentally, the spatial (angular) filtering of two-dimensional light beams by longitudinally chirped axisymmetric photonic microstructures. The structures comprise a set of planes of concentric rings with the separation between the plates smoothly varying along the propagation direction. Axisymmetric structures were recorded in a bulk of glass, in which the refractive index has been modulated using tightly focused femtosecond laser pulses. We show that the spatial filtering recently shown in nonchirped axisymmetric structures can be substantially improved by the chirp: the angular range of filtering was increased approximately two times. The numerical study reveals that the filtering efficiency can be strongly increased using the longer and larger index contrast axisymmetric photonic structures.

Super-collimation by axisymmetric photonic crystals

We propose and experimentally show the mechanism of beam super-collimation by axisymmetric photonic crystals, specifically by periodic (in propagation direction) structure of layers of concentric rings. The physical mechanism behind the effect is an inverse scattering cascade of diffracted wave components back into on- and near-axis angular field components, resulting in substantial enhancement of intensity of these components. We explore the super-collimation by numerical calculations and prove it experimentally. We demonstrate experimentally the axial field enhancement up to 7 times in terms of field intensity.

Femtosecond pulsed light polarization induced effects in direct laser writing 3D nanolithography

We demonstrate how the coupling between (i) polarization of the writing laser beam, (ii) tight focusing and (iii) heat conduction affects the size, shape and absorption in the laser-affected area and therefore the polymerization process. It is possible to control the sizes of 3D laser-produced structure at the scale of several nanometers. Specifically we were able to tune the aspect ratio of 3D suspended line up to 20% in hybrid SZ2080 resist. The focal spot of tightly focused linearly polarized beam has an elliptical form with the long axis in the field direction. It is shown here that this effect is enhanced by increase in the electronic heat conduction when polarization coincide with temperature gradient along with the absorption. Overlapping of three effects (i- iii) results in the difference of several tens of nanometers between two axes of the focal ellipse. Narrow line appears when polarization and scan direction coincide, while the wide line is produced when these directions are perpendicular to each other. The effect scales with the laser intensity giving a possibility to control the width of the structure on nanometer scale as demonstrated experimentally in this work. These effects are of general nature and can be observed in any laser-matter interaction experiments where plasma produced by using tight focusing of linear-polarized light.

Focussing by a flat woodpile 3D photonic crystal

This paper reports on numerical and experimental observation of a beam focusing behind a flat 3D woodpile PhC. The work demonstrates this idea using paraxial approximation model, as well as using a conventional Finite-Difference Time-Domain (FDTD) method.

Focusing by a flat woodpile 3D photonic crystal

We investigate spatial propagation effect behind the Photonic Crystal under particular dispersion conditions, which lead to a near field focusing. We analyze and experimentally demonstrate full two-dimensional near field focusing of light beams at visible frequencies behind the flat three-dimensional woodpile photonic crystal. Experimental results correspond well with numerical FDTD calculations as well as with the mode expansion studies. The focusing distance of 50 - 70 μm behind the crystal is obtained.