Vygantas Mizeikis

Nanoparticle Plasmon-Assisted Two-Photon Polymerization Induced by Incoherent Excitation Source

We demonstrate the possibility to achieve optical triggering of photochemical reactions via two-photon absorption using incoherent light sources. This is accomplished by the use of arrays of gold nanoparticles, specially tailored with high precision to obtain high near-field intensity enhancement.

Two-photon lithography of nanorods in SU-8 photoresist

Studies on two-photon lithography in negative SU-8 photoresist demonstrate the possibility of obtaining mechanically stable, stress-free, extended nanorods having lateral sizes of about 30 nm (corresponding to λ/25 resolution). The high resolution achievable with the given combination of materials and fabrication techniques demonstrates its potential for the fabrication of large-scale nanostructures, such as photonic crystals with photonic stop gaps at visible wavelengths.

Ultrafast laser processing of materials: from science to industry

Processing of materials by ultrashort laser pulses has evolved significantly over the last decade and is starting to reveal its scientific, technological and industrial potential. In ultrafast laser manufacturing, optical energy of tightly focused femtosecond or picosecond laser pulses can be delivered to precisely defined positions in the bulk of materials via two-/multi-photon excitation on a timescale much faster than thermal energy exchange between photoexcited electrons and lattice ions. Control of photo-ionization and thermal processes with the highest precision, inducing local photomodification in sub-100-nm-sized regions has been achieved. State-of-the-art ultrashort laser processing techniques exploit high 0.1–1 μm spatial resolution and almost unrestricted three-dimensional structuring capability. Adjustable pulse duration, spatiotemporal chirp, phase front tilt and polarization allow control of photomodification via uniquely wide parameter space. Mature opto-electrical/mechanical technologies have enabled laser processing speeds approaching meters-per-second, leading to a fast lab-to-fab transfer. The key aspects and latest achievements are reviewed with an emphasis on the fundamental relation between spatial resolution and total fabrication throughput. Emerging biomedical applications implementing micrometer feature precision over centimeter-scale scaffolds and photonic wire bonding in telecommunications are highlighted.

Three-dimensional microfabrication of materials by femtosecond lasers for photonics applications

Femtosecond laser fabrication of three-dimensional structures for photonics applications is reviewed. Fabrication of photonic crystal structures by direct laser writing and holographic recording by multiple beam interference techniques are discussed. The physical mechanisms associated with structure formation and postfabrication are described. The advantages and limitations of various femtosecond laser microfabrication techniques for the preparation of photonic crystals and elements of microelectromechanical and micro-optofluidic systems are discussed.

Multiphoton fabrication of periodic structures by multibeam interference of femtosecond pulses

Femtosecond laser pulses are useful for laser microfabrication through multiphoton absorption. However, it is difficult to create interference of femtosecond pulses for the fabrication of periodic structures. In this letter, we report the fabrication of two-dimensional periodic structures by means of multibeam interference of femtosecond pulses. Scanning electron microscopy revealed a rod structure arranged into a square lattice. The possibility of controlling the period of the lattice, rod thickness, and rod shape were demonstrated.

Microcavities in polymeric photonic crystals

We report the fabrication and characteristics of planar microcavities in a log-pile photonic crystal structure formed using light-induced photopolymerization of resin. A planar defect was introduced into the middle of the log-pile structure as a single layer with every second rod missing. The existence of confined cavity states was confirmed experimentally and by numeric simulations. The cavity resonance found at the midgap wavelength λM∼4.0 μm had a quality factor of about 130.

Holographic lithography of periodic two-and three-dimensional microstructures in photoresist SU-8

Micro-fabrication of periodic structures was performed by holographic lithography technique in SU-8 photoresist using a simple and versatile experimental arrangement based on a diffractive beam-splitter. High-fidelity two- and three-dimensional microstructures fabricated with sub-micrometric resolution in large areas of approximately 1 mm diameter. The structures are potentially usable as elements of micro-fluidic systems (e.g., Brownian ratchets), and templates for photonic crystal devices (e.g., mirrors, collimators, superprisms).

Evidence of superdense aluminium synthesized by ultrafast microexplosion

At extreme pressures and temperatures, such as those inside planets and stars, common materials form new dense phases with compacted atomic arrangements and unusual physical properties. The synthesis and study of new phases of matter at pressures above 100 GPa and temperatures above 104 K—warm dense matter—may reveal the functional details of planet and star interiors, and may lead to materials with extraordinary properties. Many phases have been predicted theoretically that may be realized once appropriate formation conditions are found. Here we report the synthesis of a superdense stable phase of body-centred-cubic aluminium, predicted by first-principles theories to exist at pressures above 380 GPa. The superdense Al phase was synthesized in the non-equilibrium conditions of an ultrafast laser-induced microexplosion confined inside sapphire (α-Al2O3). Confined microexplosions offer a strategy to create and recover high-density polymorphs, and a simple method for tabletop study of warm dense matter.

Three-dimensional woodpile photonic crystal templates for the infrared spectral range

High-quality templates of three-dimensional woodpile photonic crystals are fabricated in photoresist SU-8 by use of femtosecond laser lithography. The samples have smooth surfaces, are mechanically stable, and are resistant to degradation under environmental and chemical influences. Fundamental and higher-order photonic stopgaps are identified in the wavelength range 2.0-8.0 microm. These templates can be used for subsequent infiltration by optically active or high-refractive-index materials.

Optical properties of nanoengineered gold blocks.

We report on control over the extinction spectrum of tetragonal gold nanoblocks by changing their lateral aspect ratio. Nanoblocks were patterned on a glass substrate by electron-beam lithography and were 40-400 nm in lateral dimensions and spanned from 1 to 9 in aspect ratio. This allowed us to tune the localized surface plasmon bands from 700 nm to 1.5 microm (longitudinal mode) and from 700 to 550 nm (transverse mode). Unprecedented polarization selectivity of the transverse and longitudinal plasmon bands was achieved via alignment and 3D control of the dimensions of the nanoblocks.