The benefits obtained in terms of costs and applicability by the development of flexible and stretchable electronics, compared to its rigid counterpart, have fostered the quest for flexible photonic technologies and integrated platforms on suitable material systems. By adding mechanical flexibility to photonic structures, novel functionalities would be added to their already broad range of applications. In case of oxides, their typical qualifying properties in terms of transparency, high thermal and chemical resistance could be exploited in suitable material systems. Here it is presented two flexible SiO2/HfO2 1D photonic crystals, fabricated by radio frequency sputtering. As expected, the systems show a strong dependence of the optical features on the light incident angle. Nevertheless, the most interesting result is the experimental evidence that, even after the sample breakage, where the flexible glass shows naked-eye visible cracks, the multilayer structures generally maintain their integrity, resulting to be promising systems for flexible photonic applications thanks to their optical, thermal and mechanical stability.
In this work, we present preliminary results of the fabrication and characterization of 1D Fabry–Perot microcavity realized on Yb3+ activated SiO2-SnO2 glass-ceramic (SiO2-SnO2:Yb3+). A radiofrequency-sputtering/sol-gel hybrid deposition process was developed for the microcavity fabrication. The fabrication included (i) radiofrequency-sputtering (rf-sputtering) of SiO2/HfO2 Bragg reflectors and (ii) sol-gel deposition of the active SiO2-SnO2:Yb3+ defect layer. A good control and enhancement of the spontaneous emission for Yb3+ luminescence sensitized by SnO2 nanocrystals was achieved exploiting microcavity properties. Such results are valuable for development of low-threshold rare-earth-based coherent light sources, pumped by broadband UV diodes.
Integration of photonic systems on deformable substrates has given rise to flexible photonics, a research field that has rapidly emerged in recent years. By adding mechanical flexibility to planar photonic structures, the spectrum of applications gains an incredible expansion. Flexible glassy photonic structures require a careful design and suitable fabrication protocols, in order to keep the optical and spectroscopic properties similar to their traditional rigid counterparts, even under mechanical deformation. Here, a radio frequency (RF) sputtering deposition protocol is developed for fabricating glass-based 1D photonic crystals on ultrathin flexible glass as well as on rigid substrates for comparison. Three different 1D multilayer structures, constituted by SiO2 and HfO2 layers, were first designed and modelled by Transfer Matrix Method to tailor targeted optical features (transmission windows, stopband ranges) and then fabricated by RF-sputtering technique. The structural, morphological, and optical features of the samples were investigated. In particular, the transmission spectra of the glass-based 1D photonic crystals, deposited on both flexible and rigid substrates, were acquired to highlight up to which extent the different nature of the substrates and the mechanical deformations (bending tests on the flexible structures) are not influencing the key spectral properties of the photonic crystals.
For the development of flexible photonic devices, polymeric substrates are of capital importance due to their low cost and mechanical flexibility. However, they are sensitive to the environment’s influence on their durability. To overcome problems of polymeric substrates’ stability, we developed organically modified hybrid silica-titania coated PET (polyethylene terephthalate) films. The focus was put on the determination of the optical properties’ changes in dependence on the synthesis and materials processing parameters. Thanks to the application of the coatings, a protection effect on substrate and improvement in the transparency in comparison to the uncoated heat-treated polymeric material, was obtained.
As already done in electronics, passive and active photonic devices demand integration on flexible substrates for a broad spectrum of application ranging from optical interconnection to sensors for civil infrastructure and environments, to coherent and uncoherent light sources and functionalized coatings for integration on biological tissue. In this communication we will present some recent results concerning the fabrication of novel flexible optical layers by sol-gel and radio frequency sputtering deposition techniques. The perspective is to give a technological way to transform intrinsically rigid or brittle materials into a highly mechanically flexible and optically functional systems
One of the current forefront in the field of photonic are flexible photonic research and development. The desired deliverable is to adjust the mechanical properties of materials to fabricate flexible photonic systems with various applications, e.g. gratings, channel waveguides, solar cells, protective coatings. It is well known that sol-gel metal oxide coatings may find applications as flexible coatings in photonics. Moreover, these materials can be easily functionalized to obtain materials with additional special, desired, properties like easy-to-clean, anti-fingerprint, anti-fogging and others, what is attractive for the potential of future commercialization of flexible photonic materials. In this work, we present the first step of research aimed to obtain silica-based coatings with appropriate adhesion on flexible substrates as poorly wettable surface – polymer PET and Ti-6Al-4V and 316L metallic thin foil as active oxide surface. The use of various types of substrates was aimed at presenting diversity in the possibilities of using the proposed coating materials. Nanoindentation, tensile test and scratch test of the investigated samples were studied. Measuring the mechanical properties of thin oxide films is difficult because it is usually impossible to detach of coating, not destroying its, from substrates. The thickness of coatings can range from a dozen to a few hundred nanometres, so complete methodology to determine a full set of mechanical properties is still lacking. In literature, the surface of samples is measured without a clear indication on coating properties, but on features which are the results of substrate-coating combinations.
We present the radio frequency sputtering fabrication protocols for the fabrication on flexible polymeric substrates of glass-based 1D photonic crystals and erbium activated planar waveguides. Various characterization techniques, such as atomic force microscopy and optical microscopy, are employed to put in evidence the good adhesion of the glass coating on the polymeric substrates. Transmittance measurements are performed on the multilayer structure and indicate that there are no differences between the samples deposited on the polymeric and SiO2 substrates, even after bending. Prism coupling technique is used to measure the optical parameter of the planar waveguide fabricated on flexible substrates. The 4I13/2 → 4I15/2 emission band, detected upon TE0 mode excitation at 514.5 nm, exhibits the spectral shape characteristic of Er3+ ions embedded in a crystalline environment.
Laser plasma sources of soft x-rays and extreme ultraviolet (EUV) developed in our laboratory for application in various areas of technology and science are presented. The sources are based on a laser-irradiated gas puff target approach. The targets formed by pulsed injection of gas under high-pressure are irradiated with nanosecond laser pulses from Nd:YAG lasers. We use commercial lasers generating pulses with time duration from 1ns to 10ns and energies from 0.5J to 10J at 10Hz repetition rate. The gas puff targets are produced using a double valve system equipped with a special nozzle to form a double-stream gas puff target which secures high conversion efficiency without degradation of the nozzle. The use of a gas puff target instead of a solid target makes generation of laser plasmas emitting soft x-rays and EUV possible without target debris production. The sources are equipped with various optical systems, including grazing incidence axisymmetric ellipsoidal mirrors, a “lobster eye” type grazing incidence multi-foil mirror, and an ellipsoidal mirror with Mo/Si multilayer coating, to collect soft x-ray and EUV radiation and form the radiation beams. In this paper new applications of these sources in various fields, including soft x-ray and EUV imaging in nanoscale, EUV radiography and tomography, EUV materials processing and modification of polymer surfaces, EUV photoionization of gases, radiobiology and soft x-ray contact microscopy are reviewed.
In this work soft X-ray (SXR) and extreme ultraviolet (EUV) laser-produced plasma (LPP) sources employing Nd:YAG laser systems of different parameters are presented. First of them is a 10-Hz EUV source, based on a double-stream gaspuff target, irradiated with the 3-ns/0.8J laser pulse. In the second one a 10 ns/10 J/10 Hz laser system is employed and the third one utilizes the laser system with the pulse shorten to approximately 1 ns. Using various gases in the gas puff targets it is possible to obtain intense radiation in different wavelength ranges. This way intense continuous radiation in a wide spectral range as well as quasi-monochromatic radiation was produced. To obtain high EUV or SXR fluence the radiation was focused using three types of grazing incidence collectors and a multilayer Mo/Si collector. First of them is a multfoil gold plated collector consisted of two orthogonal stacks of ellipsoidal mirrors forming a double-focusing device. The second one is the ellipsoidal collector being part of the axisymmetrical ellipsoidal surface. Third of the collectors is composed of two aligned axisymmetrical paraboloidal mirrors optimized for focusing of SXR radiation. The last collector is an off-axis ellipsoidal multilayer Mo/Si mirror allowing for efficient focusing of the radiation in the spectral region centered at λ = 13.5 ± 0.5 nm. In this paper spectra of unaltered EUV or SXR radiation produced in different LPP source configurations together with spectra and fluence values of focused radiation are presented. Specific configurations of the sources were assigned to various applications.
In this work photoionized plasmas were created by irradiation of He, Ne and Ar gases with a focused EUV beam from one of two laser-plasma sources employing Nd:YAG laser systems of different parameters. First of them was a 10-Hz laser-plasma EUV source, based on a double-stream gas-puff target, irradiated with the 3-ns/0.8J laser pulse. EUV radiation in this case was focused using a gold-plated grazing incidence ellipsoidal collector in the wavelength range λ = 9÷70 nm. The most intense emission was in the relatively narrow spectral region centred at λ = 11 ± 1 nm. The second source was based on a 10 ns/10 J/10 Hz laser system. In this case EUV radiation was focused using a gold-plated grazing incidence multifoil collector or a Mo-coated ellipsoidal collector. The most intense emission in this case was in the 5 ÷ 15 nm spectral region. Radiation fluence ranged from 60 mJ/cm2 to 400 mJ/cm2. Different gases were injected into the interaction region, perpendicularly to an optical axis of the irradiation system, using an auxiliary gas puff valve. Irradiation of the gases resulted in ionization and excitation of atoms and ions. Spectra in EUV range were measured using a grazing incidence, flat-field spectrometer (McPherson Model 251), equipped with a 450 lines/mm toroidal grating. In all cases the most intense emission lines were assigned to singly charged ions. The other emission lines belong to atoms or doubly charged ions. The spectra were excited in low density gases of the order of 1 ÷ 10% atmospheric density.
In this work results of investigations concerning ablation and surface modification of polymers and some other solids
using a laser-plasma EUV source are presented. The plasma radiation was produced using a gas puff target and was
focused with a gold-plated grazing incidence ellipsoidal collector. The ablation process was investigated using a
scanning electron microscope (SEM) and a quadrupole mass spectrometer (QMS). The chemical changes were
investigated by X-ray photoelectron spectroscopy (XPS). Different kinds of micro- and nanostructures created in nearsurface
layers of the materials were obtained. Forms of the structures depend on a particular material and the EUV
exposure. In case of some polymers even a single shot was sufficient for creation of the visible changes in surface
morphology. In case of inorganic solids visible changes required usually the exposure with tens or hundreds of EUV
pulses. XPS investigations revealed chemical changes in near surface layers of polymers. Significant differences were
revealed in the XPS spectra acquired for irradiated and not-irradiated polymers. Significant decrease of functional groups
containing oxygen was indicated. Analysis of QMS spectra indicate emission of different kinds of fragments of the
polymer chains including the repeating structural units. In case of some polymers only fragments of the repeating unit
were detected.
Results on micro- and nanoprocessing of organic polymers with extreme ultraviolet (EUV) radiation from a compact
laser plasma EUV source based on a gas puff target are presented in the paper. Processing of polymers is connected with
non-thermal ablation under the influence of energetic EUV photons. The process can be useful for practical applications
as it makes possible to produce structures with sub-micron spatial resolution that is not possible using the thermal
ablation. The new technology will be used for production of photonic microstructures and for modification of polymer
surfaces for biomedical applications.
In the paper a newly developed compact and debris-free laser plasma soft X-ray source is presented. The source is based on the double-stream gas puff target approach. The targets are formed by pulsed injection of high-Z gas (xenon, krypton or argon) into a hollow stream of low-Z gas (helium or hydrogen) using the valve system composed of two electromagnetic valves and equipped with the double-nozzle setup. The outer stream of gas confines the inner stream improving the gas puff target characteristics (higher density of high-Z gas at longer distance from the nozzle output). It causes efficient absorption of laser energy in a plasma and strong soft X-ray production. Additionally, the use of the double-stream gas puff target approach makes possible to avoid degradation of the nozzle by the laser plasma. Spectral characteristics of soft X-ray emission from the source are presented. Applications in X-ray pulsed radiography, microprocessing of polymers by direct soft X-ray photo-etching, and EUV technologies are discussed.
A pulse-train Nd:YAG laser system consisting of repetitively Q-switched Nd:YAG oscillator with Cr4+:YAG saturable absorber, double pass Nd:YAG amplifier and stimulated Brillouin scattering (SBS) pulse compressor has been demonstrated. Number and energy of the laser pulses were controlled by adjusting width and amplitude of the flash lamp pumping pulses. Efficient SBS compression of Nd:YAG laser pulses was obtained using single-cell compressor.
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