Antti Hakola

Self-erasing and rewritable wettability patterns on ZnO thin films

Self-erasing patterns allow a substrate to be patterned multiple times or could store temporary information for secret communications, and are mostly based on photochromic molecules to change the color of the pattern. Herein we demonstrate self-erasing patterns of wettability on thin ZnO films made by atomic layer deposition. Hydrophilic patterns are written using UV light and decay spontaneously, i.e. become hydrophobic, or are erased aided by vacuum conditions or heat. We demonstrate that these patterns can be applied for channels to confine flow of water without physical walls.

Creation of a narrow Bessel-like laser beam using a nematic liquid crystal

We present a simple and efficient method to convert a Gaussian laser beam into a Bessel-like beam with a long and narrow focal line by using a nematic liquid crystal with a high third-order nonlinearity.

Energetic Bessel–Gauss pulses from diode-pumped solid-state lasers

We discuss the generation of Bessel–Gauss pulses directly from a diode-pumped solid-state laser. The laser resonator has a plano–concave configuration with the concave end mirror replaced with a diffractive phase element. As the active material, Nd-doped yttrium lithium fluoride (YLF) and GdVO4 crystals have been used. The pulsed operation is obtained by passively Q-switching the laser using Cr4+:yttrium aluminum garnet (YAG) crystals with different unsaturated transmission coefficients. When guiding the pulses out from the resonator through the laser crystal, 5–10 ns long pulses with energies of 40–50 μJ and peak powers on the order of 10 kW are obtained. Even 70 μJ is possible, but this is achieved at the expense of slightly deteriorated beam quality in the far field.

Substrate-free structures of iron-doped Ni-Mn-Ga thin films prepared by pulsed laser deposition

We discuss the preparation of thin films of ferromagnetic shape-memory Ni-Mn-Ga alloys on NaCl using pulsed laser deposition and present a simple way to release the film from its substrate and to realize free-standing Ni-Mn-Ga structures.

Laser beam shaping using self-focusing in a nematic liquid crystal

A simple and efficient method to convert a Gaussian laser beam into a nearly non-diverging Bessel-like beam or into a thin-walled hollow beam is described. The optical system used for the beam conversion consists of a thin liquid-crystal cell and one or two lenses. At certain parameter values, self-focusing of a Gaussian beam directly results in the formation of a narrow Bessel-like beam, and, if an additional lens is used to collimate the self-focused beam, the collimated beam shows an accurate ring-shaped profile.

Microscopic atom traps on an evanescent-wave mirror

An alternative technique is proposed to create microscopic atom traps loaded with atoms from a gravito-optical surface trap (GOT), which is composed of an evanescent-wave mirror and a vertically aligned hollow laser beam. Our trap design is based on the use of current-carrying transparent conductors and transparent permanent magnets fabricated on the surface of a glass prism in the form of an internal structure of a refractive-index-matched thin dielectric film. The conductors can be fabricated of indium tin oxide (ITO) and the magnets of yttrium iron garnet (YIG). Different kinds of traps may be envisaged: i) spin-independent electro-optical ii) magneto-optical for either high- or low-field seeking atoms, and iii) purely magnetic for atoms in the low-field seeking states. In case iii), the magnetic-field minimum is located far enough from the film surface to make the contribution of the optical field negligible.