Laser-induced parallel structures on multilayer thin films of Ni, Pd, Ti, Ta and W

The interaction of ultrashort laser beam with metal surfaces may induce the generation of periodic structures (LIPSS) with period less than the incoming wavelength, opening wide area of application [1, 2]. The presence of the underneath layer influences the quality of the LIPSS [3] . We have exposed multilayer thin films Ni/Ti, Ni/Pd, W/Ti, Ti/Ta to femtosecond beams of various wavelengths and powers. The interactions have been performed by Mira900 fs laser of Coherent. Detailed surface morphology after irradiation was examined firstly by optical microscopy, and then by scanning electron microscopy (JEOL JSM-7500F, Tokyo, Japan). Two types of structures have been noticed. Their appearance differ in the direction against the polarization direction, in pronounced ablation and in the spatial period, enabling their grouping into LIPSS of higher and lower spatial frequencies. Surface plasmon polariton is seen as the most probable cause of periodic distribution of energy at the surface and consequently to LIPSS.Photonics Workshop (14 ; 2021 ; Kopaonik

Preventing and Reversing Vacuum-Induced Optical Losses in High-Finesse Tantalum (V) Oxide Mirror Coatings

We study the vacuum-induced degradation of high-finesse optical cavities with mirror coatings composed of SiO$_2$-Ta$_{2}$O$_{5}$ dielectric stacks, and present methods to protect these coatings and to recover their initial quality factor. For separate coatings with reflectivities centered at 370 nm and 422 nm, a vacuum-induced continuous increase in optical loss occurs if the surface-layer coating is made of Ta$_{2}$O$_{5}$, while it does not occur if it is made of SiO$_2$. The incurred optical loss can be reversed by filling the vacuum chamber with oxygen at atmospheric pressure, and the recovery rate can be strongly accelerated by continuous laser illumination at 422 nm. Both the degradation and the recovery processes depend strongly on temperature. We find that a 1 nm-thick layer of SiO$_2$ passivating the Ta$_{2}$O$_{5}$ surface layer is sufficient to reduce the degradation rate by more than a factor of 10, strongly supporting surface oxygen depletion as the primary degradation mechanism.Comment: 14 pages, 7 figure

Fast fabrication of large area concave microlens arrays

A single-step process for rapid fabrication of large-area concave microlens arrays using a diode-pumped solid state (DPSS) laser operating at 473 nm is developed. Using tartrazine sensitized gelatin layer treated with tot’hema - mixture of iron (II)-, manganese (II)- and copper(II)gluconate- (denoted short as tSTG) and a direct laser writing device developed in our laboratory, we could produce 10 000 uniform microlens arrays within 30 min. Uniform microlenses with different diameters and depth can be produced by varying the laser power, exposure time and dye concentration

Luminescence properties of Eu3+ activated Y2MoO6 powders calcined at different temperatures

In the last decade, an immense progress has been made in white LEDs, mainly due to the development of red-emitting phosphors. In this paper, we report on the synthesis of Eu3+ activated Y2MoO6 by a self-initiated and self-sustained method. The obtained powder was calcined at various temperatures in the 600–1400 °C range and examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence spectroscopy (PL). The results revealed that all powders are single phase Y2MoO6:Eu3+, with particle size in the nanorange at lower treatment temperatures (600 and 800 °C) and in the microrange at higher calcination temperatures (1000–1400 °C). The obtained powders are promising materials for white light-emitting diodes as they can efficiently absorb energy in 324–425 nm region (near-UV to blue light region) and emit at 611 nm in the red region of the spectrum, while exhibiting high thermal and chemical stability

Luminescence Properties Of Eu3+ Doped Mayenite Under High Pressure

Europium doped mayenite (C12A7) powders of different concentrations (0.5, 1.0, 1.5, and 2.0 at.%) have been synthesized by a modified glycine/nitrate procedure - MGNP). Obtained samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE- SEM), and steady-state photoluminescence spectroscopy. The effect of doping concentration on photoluminescence properties of Eu3+ doped mayenite was studied and discussed. With the increasing of Eu3+ doping concentration, the red-emitting intensity exhibited behavior that increased firstly and then decreased. The optimal Eu3+ ion concentration is found to be 1.5%. High-pressure luminescence was measured in a Betsa high-pressure membrane diamond anvil cell up to 23 GPa

Single- and dual-wavelength laser pulses induced modification in 10x(Al/Ti)/Si multilayer system

The surface morphology of the ablation craters created in the multilayer 10x(Al/Ti)/Si system by nanosecond laser pulses at single- and dual wavelength has been studied experimentally and numerically. A complex multilayer thin film including ten (Al/Ti) bilayers deposited by ion sputtering on Si(1 0 0) substrate to a total thickness of 260 nm were illuminated at different laser irradiance in the range 0.25-3.5 x 10(9)W cm(-2). Single pulse laser irradiation was done at normal incidence in air, with the single wavelength, either at 532 nm or 1064 nm or with both laser light simultaneously in the ratio of 1: 10 for energy per pulse between second harmonic and 1064 nm. Most of the absorbed laser energy was rapidly transformed into heat, producing intensive modifications of composition and morphology on the sample surface. The results show an increase in surface roughness, formation of specific nanostructures, appearance of hydrodynamic features and ablation of surface material with crater formation. Applying a small fraction (10%) of the second harmonic in dual-wavelength pulses, a modification of the 10x(Al/Ti)/Si system by a single laser pulse was reflected in the formation of wider and/or deeper craters. Numerical calculations show that the main physical mechanism in ablation process is normal evaporation without phase explosion. The calculated and experimental results agree relatively well for the whole irradiance range, what makes the model applicable to complex Al/Ti multilayer systems. (C) 2015 Elsevier B.V. All rights reserved

Surface modification of Ti-based nanocomposite multilayer structures by laser beam irradiation

III International School and Conference on Photonics : PHOTONICA2011 : book of abstracts; August 29- September 2, 2011; Belgrad

Inducing LIPSS on multilayer thin metal films by femtosecond laser beam of different orientations

The occurrence of laser-induced periodic surface structures (LIPSS) has been known for a while. Multilayer thin films, like Al/Ti, are suitable for LIPSS formation and attractive for applications—due to their wearing behavior and corrosion resistance; LIPSS generation may improve their properties as well. LIPSS properties depend not only on the material but also on the beam characteristics, like wavelength, polarization and scanning directions, etc. After exposing with NIR femtosecond pulses from Coherent Mira 900 laser system in several beam exposures, we have analyzed the samples of thin metal film systems with Tescan Mira3 SEM and NTegra AFM. The formation of LIPSS is most probably due to the generation of surface plasmon polariton, through the periodic distribution of energy in the interaction zone which lead to thermal processes in layers and interfaces. Two types of LIPSS were generated, which differ in shape, orientation and in ablation pronounced or not. For consecutive interactions in the same direction, LIPSS maintained its orientation, while for orthogonal passes LIPSS with mutually orthogonal orientation were generated. LIPSS period fluctuated between 320 and 380 nm and structures with pronounced ablation have significantly smaller width. Probable mechanism is that for greater accumulated energy pronounced ablation takes place giving LIPSS in the form of trenches or grooves, while for less accumulated energy the buildup of the material—probably due to pronounced oxidation—lead to LIPSS in the form of hills or ridges

Composition and structure of NiAu nanoparticles formed by laser ablation of Ni target in Au colloidal solution

Bimetallic NiAu and complex NiO:Au nanoparticles were formed by laser ablation of Ni target immersed in the colloidal gold solution. Effect of laser parameters (pulse duration, fluences and ablation times) on size and composition of nanoparticles was investigated by ablating the target with two Nd:YAG lasers at 1064 nm, operating with different pulse durations, 150 ps and 20 ns. Stronger ablation of the Ni target and subsequient synthesis of nanoparticles is achieved with picosecond pulses, compared to the nanoparticles production with nanosecond pulses, because the former ablation induces activation of different reactions between species in the colloidal solution. Shape, size and composition of the synthesized nanopraticles were found to correlate with the concentration of Ni species in the colloidal solution. Higher Ni concentration leads to formation of larger NiAu nanoparticles in form of solid solution. Smaller nanoparticles with lower Ni concentration in the colloidal solution were achieved by their synthesis during nanosecond pulses, when the obtained distribution of composition corresponds to the NiO matrix with incorporated golden nanoparticles. The results also demonstrate that the formation of bimetallic NiAu and complex NiO:Au nanoparticles were possible by means of laser ablation in liquids. (C) 2015 Elsevier B.V. All rights reserved