R. Drevinskas

Anisotropy of optical, electrical, and photoelectrical properties of amorphous hydrogenated silicon films modified by femtosecond laser irradiation

Two types of independent anisotropic structures have been formed simultaneously in amorphous hydrogenated films by applying a femtosecond laser pulse to them, i.e., a structure with a period of several micrometers to several tens of micrometers and a structure with a period of several hundred nanometers. The formation mechanisms of these strictures are different, which allows us to orient them relative to each other in a desirable way. Both structures independently influence the optical properties of the modified films, which causes the diffraction of transmitted light and making the films polarization-sensitive. The conductivity of the modified films correlates with the mutual orientation of the anisotropic structures, whereas no interrelation between the photoconductivity and optical performance of the modified films has been observed.

Ultrafast laser induced nanostructured ITO for liquid crystal alignment and higher transparency electrodes

Femtosecond laser nanostructured indium tin oxide (ITO) coated glass is shown to act both as a liquid crystal (LC) alignment layer and as an electrode with higher transparency. The nanopatterns of the 120u2009nm period were created using ultrashort laser pulses directly on ITO films without any additional spin coating materials or lithography process. Nine regions of laser-induced nanostructures were fabricated with different alignment orientations and various pulse energy levels on top of the ITO confirming the follow-up of the LC director to the line orientation. The device interfacial anchoring energy was found to be ∼ 1 μ J / m 2, comparable to the anchoring energy of nematic LC on photosensitive polymers. The transparency as an electrode was found to improve due to the better antireflection and lower absorption expected from a nanostructured surface.Femtosecond laser nanostructured indium tin oxide (ITO) coated glass is shown to act both as a liquid crystal (LC) alignment layer and as an electrode with higher transparency. The nanopatterns of the 120u2009nm period were created using ultrashort laser pulses directly on ITO films without any additional spin coating materials or lithography process. Nine regions of laser-induced nanostructures were fabricated with different alignment orientations and various pulse energy levels on top of the ITO confirming the follow-up of the LC director to the line orientation. The device interfacial anchoring energy was found to be ∼ 1 μ J / m 2, comparable to the anchoring energy of nematic LC on photosensitive polymers. The transparency as an electrode was found to improve due to the better antireflection and lower absorption expected from a nanostructured surface.

Solving the puzzle of non-reciprocity in ultrafast laser writing

The nanostructuring of transparent media with ultrashort laser pulses has attracted interest due to its unique applications. However, little is understood with respect to the physical mechanisms responsible for the peculiarities of the dielectrics inscribing with high intensity laser beams. It has been shown that spatio-temporal couplings (STC) inherent to the ultrashort pulses make inscribing sensitive to the writing direction [1, 2] and that anisotropic photosensitivity [3] originates from the pulse front tilt (PFT). More recently, a greater appreciation of STC in focussing has been gained, shedding light on previously unknown parameters of the pulse such as a lighthouse-like wavefront rotation [4] emphasizing the need for a better understanding of the STC effects in light-matter interaction. Nevertheless, understanding of the microscopic processes responsible for the modifications of dielectrics with ultrashort laser pulses and control of the writing process via STC is still lacking. Here we show with control of STC through the use of grating compressors, allows one to control and understand ultrafast phenomena associated with material modification. We reveal unambiguously that PFT gives rise to the non-kreciprocity during femtosecond laser writing in transparent media and induces either an isotropic damage-like structure or a self-assembled nanostructure depending on the writing direction. This phenomenon is known as the “quill-writing effect” (Fig. 1a). A switching of the modification regime is observed when the translation of the beam is in the direction of the tilt, which can be qualitatively described in terms of a first-order phase transition.

Liquid crystal alignment on ultrafast laser nanostructured ITO coated glass

Liquid crystal (LC) devices are widely used as building blocks of many electro-optical systems including linear polarization rotators, dynamical wave plate retarders, and pixilated devices for displays, spatial light modulators, and tunable filters [1]. Precise alignment of the LC molecules is required for high quality components. The anisotropic nature of LC molecules allows them to align on solid surfaces. This can be achieved either due to physicochemical interaction such as photo-alignment on surfaces using polarized blue light or due to the elastic interaction when aligned along nanogrooves created by mechanical rubbing or lithography techniques [2]. Although numerous methods enabling the manufacturing of LC devices have been reported, the technological flexibility and precision remains a problem.

Recent progress in ultrafast laser nanostructuring: from two-plasmon decay to longitudinal field puzzle

Correlation between 3/2 harmonic, two-plasmon decay and ultrafast laser induced nanogratings is observed. Paradoxically, no crystallization of amorphous Si by longitudinal field produced by S-waveplate is observed, despite strongest intensity.