Ultraviolet Laser Beam Research Articles

Laser-induced electrical property patterning of Ag nanowire transparent electrode

We here introduce a laser-driven method to pattern Ag nanowire (AgNW) transparent electrode without material removal. Our approach is to block the current flow in selected areas by cutting nanowires, which is fundamentally based on the Rayleigh instability. AgNW film spin-coated onto a glass substrate was selectively irradiated using a nanosecond-pulsed ultraviolet laser beam. This made it possible to fabricate a patterned structure consisting of spatially separated conducting and insulating regions. The feasibility of this electrical property patterning was demonstrated with white light emitting diodes attached to the fabricated pattern.

Laser-direct process of Cu nano-ink to coat highly conductive and adhesive metallization patterns on plastic substrate

We here present a simple, low-cost laser-direct process to fabricate conductive Cu patterns on plastic substrate. A Cu nano-ink was synthesized using Cu formate as a precursor. The Cu ink spin-coated on a polyimide substrate was selectively sintered using a pulsed ultraviolet laser beam. The unexposed regions of the coated ink could be removed by rinsing the whole film in the dispersion agent of the synthesized ink, which revealed a conductive Cu pattern. This allowed sintering and patterning to be simultaneously accomplished, with a minimum line width of ~20μm available. The fabricated pattern remained strongly adhesive to the substrate and exhibited only a slight increase in resistance even after 1000 bending cycles to a radius of curvature of 4.8mm.

Interference ablation of nanogratings with different duty cycles on gold films

Nanogratings with different duty cycles are directly written on gold films using interference ablation. After exposing the gold film to the interference pattern of ultraviolet laser beams, gold film in the bright fringes will be melted and ablated, whereas much weaker ablation occurs in the dark fringes. The duty cycle of gold nanogratings can be controlled by adjusting the pulse energy and the exposure times, which can be explained by the temperature rise and cumulative effect of the laser–metal interactions. These results introduce additional parameters for the fine fabrication of metal nanogratings based on interference ablation at a large scale and low cost.

Evidence of liquid phase during laser-induced periodic surface structures formation induced by accumulative ultraviolet picosecond laser beam

Laser-induced periodic surface structures (LIPSS) were formed on Cu/Si or Cu/glass thin films using Nd:YAG laser beam (40 ps, 10 Hz, and 30 mJ/cm2). The study of ablation threshold is always achieved over melting when the variation of the number of pulses increases from 1 to 1000. But the incubation effect is leading to reduce the threshold of melting as increasing the number of laser pulse. Also, real time reflectivity signals exhibit typical behavior to stress the formation of a liquid phase during the laser-processing regime and helps to determine the threshold of soft ablation. Atomic Force Microscopy (AFM) analyses have shown the topology of the micro-crater containing regular spikes with different height. Transmission Electron Microscopy (TEM) allows finally to show three distinguished zones in the close region of isolated protrusions. The central zone is a typical crystallized area of few nanometers surrounded by a mixed poly-crystalline and amorphous area. Finally, in the region far from the protrusion zone, Cu film shows an amorphous structure. The real time reflectivity, AFM, and HR-TEM analyses evidence the formation of a liquid phase during the LIPSS formation in the picosecond regime.

Chlorpromazine transformation by exposure to ultraviolet laser beams in droplet and bulk

Multiple drug resistance requires a flexible approach to find medicines able to overcome it. One method could be the exposure of existing medicines to ultraviolet laser beams to generate photoproducts that are efficient against bacteria and/or malignant tumors. This can be done in droplets or bulk volumes. In the present work are reported results about the interaction of 266nm and 355nm pulsed laser radiation with microdroplets and bulk containing solutions of 10mg/ml Chlorpromazine Hydrochloride (CPZ) in ultrapure water. The irradiation effects on CPZ solution at larger time intervals (more than 30min) are similar in terms of generated photoproducts if the two ultraviolet wavelengths are utilized. The understanding of the CPZ parent compound transformation may be better evidenced, as shown in this paper, if studies at shorter than 30minute exposure times are made coupled with properly chosen volumes to irradiate. We show that at exposure to a 355nm laser beam faster molecular modifications of CPZ in ultrapure water solution are produced than at irradiation with 266nm, for both microdroplet and bulk volume samples. These effects are evidenced by thin layer chromatography technique and laser induced fluorescence measurements.

Radiophotoluminescence light scope for high-dose dosimetry

A radiophotoluminescence (RPL) light scope is a remote-sensing technique for measuring in situ the radiation dose in an RPL detector placed at a distance. The RPL light scope is mainly composed of an ultraviolet (UV) pulse laser, telescopic lenses, a photomultiplier tube, and camera modules. In a performance test, some RPL detectors were placed at distances up to 30 m and were illuminated with a pulsed UV laser beam. The photoluminescence responses of the RPL detectors were analyzed using this scope. Their radiation doses were determined from the amplitude of the given component of the photoluminescence responses. The RPL readout could be repeated without fading, and its amplitude exhibited good linearity at a dose ranging from 0.1 to 60 Gy. Furthermore, a two-dimensional distribution of radiation dose was obtained by laser scanning on an RPL detector. It was confirmed that the RPL light scope was a useful remote-sensing tool for high-dose dosimetry.

Investigation the interaction between the pulsed ultraviolet laser beams and PEDOT:PSS/graphene composite films

This research aims to investigate the interaction between pulsed ultraviolet (UV) laser beams and transparent PEDOT:PSS/graphene composite films. The laser ablated microstructure on film surfaces provides the electrical isolation and prevents the electrical contact from each location for the projected capacitive touch screen. Before the laser processing, the surface roughness, microhardness, spectrum and cross-sectional view of PEDOT:PSS/graphene composite film were measured by an atomic force microscope, a nanoindenter, a spectrometer and a scanning electron microscope, respectively. The focused UV laser beam was irradiated along line patterns with an overlapping rate of 60% and the applied laser fluences much over the ablation thresholds of 1.27J/cm2 to 3.82J/cm2. The surface morphology, three-dimensional topography, and cross-sectional profile of isolated lines and electrode structures after laser microstructuring were measured by a confocal laser scanning microscope. By increasing the laser fluence from 1.27J/cm2 to 3.82J/cm2, the ablated line widths and depths increased from 12.17±0.24μm to 21±0.37μm and from 190±9nm to 227±15nm, respectively. Moreover, the ablated lines of microstructuring electrodes had a clear and regular ablated edge quality.

Inscription of long period gratings using an ultraviolet laser beam in the diffusion-doped microstructured polymer optical fiber.

We show that diffusion of azobenzene from the solution in methanol into a cladding of a polymer fiber facilitates fabrication of long period gratings by the use of a He-Cd focused laser beam. We have measured a diffusion rate into PMMA cladding of the microstructured fibers annealed in advance at different temperatures and showed that the diffusion rate is strongly affected by temperature treatment of the fiber. We have also investigated an impact of the azobenzene diffusion on fiber spectral loss and cladding surface quality. Furthermore, we have examined a temporal stability of the fabricated long period gratings and their response to temperature and tensile strain.

Laser capture microdissection: from its principle to applications in research on neurodegeneration.

History and the principle of laser capture microdissection (LCM): LCM, also known as laser microdissection and pressure catapulting, is one of the most powerful and useful techniques in various research areas where isolation of heterogeneous cell population is required. The first use of laser as a cell operation method, was originated in early 1920s (Gilbrich-Wille, 2013), and it became widely used as a microsurgical tool in early 1960s. In the need of extremely small tissue isolation, laser beam of LCM has been modified and developed over several decades from Ultraviolet (UV) laser beam to high-energy nitrogen, infrared and carbon dioxide lasers (Gilbrich-Wille, 2013). Due to the development of its hardware, which combines a laser unit and a microscope, tissue preparation technique also has improved from manual preparation to histological sections in 1980s and this has brought numerous advantages in biochemistry and molecular biology research (Gilbrich-Wille, 2013).

Facile Template Free Synthesis and Tunable RGB Luminescent Properties of Ln3+-Doped Yttrium Oxide Nanospheres

Well-dispersed and uniform Y2O3:Ln3+ (Ln3+ = Eu3+/Tb3+/Yb3+/Er3+/Tm3+) nanospheres have been successfully prepared at 180°C via a facile hydrothermal route without any template, followed by a subsequent calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and cathodoluminescence (CL) spectra as well as kinetic decay were employed to characterize the samples. It was found that the hydrothermal precursor could act as a template to obtain the corresponding oxide Y2O3 which inherited the original morphology of the hydrothermal precursor. The TEM and SEM images indicate that the samples consist of separated spheres with a mean diameter of about 260 nm. Under the excitation of ultraviolet (UV) light, 980-nm laser, and low-voltage electron beams, the Y2O3:Ln3+ phosphors all exhibited bright red, green and blue emissions, respectively, which were easily observed by naked eyes. The corresponding luminescent mechanism had been discussed. Due to the excellent PL (including up-conversion and down-conversion) and CL properties, multicolor tunable luminescence, ideal spherical shape, and cheap Y2O3 host, the as-prepared phosphors can potentially be used as fluorescent lamps, up-conversion fluorescent labels, and field emission display devices.

Enhanced surface coverage and conductivity of Cu complex ink-coated films by laser sintering

We here show that highly conductive copper films are obtainable from Cu complex ink by laser sintering. The synthesized Cu formate ink was spin-coated onto polyimide substrate and the coated films were scanned by an ultraviolet laser beam at 355nm. During the sintering process, N2 gas was blown into the irradiated area to prevent oxidation. Unlike the typical thermal process, laser sintering resulted in tightly packed, dense structures. This made it possible to produce highly conducting thin films with uniform thickness. A minimum resistivity of 1.92×10−5Ωcm was obtained.

Two photon laser spectroscopy of antiprotonic helium atoms at CERN’s AD

The ASACUSA collaboration of CERN has carried out two-photon laser spectroscopy of antiprotonic helium atoms using counter-propagating ultraviolet laser beams. This excited some non-linear transitions of the antiproton at the wavelengths λ = 139.8–197.0 nm, in a way that reduced the thermal Doppler broadening of the observed resonances. The resulting narrow spectral lines allowed the measurement of three transition frequencies with fractional precisions of 2.3–5 parts in 109. By comparing these values with three-body QED calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23). We briefly review these results.

Evolution of Oxygen Deficiency Center on Fused Silica Surface Irradiated by Ultraviolet Laser and Posttreatment

Evolution of oxygen deficiency centers (ODCs) on a fused silica surface irradiated using a 355 nm ultraviolet (UV) laser beam in both vacuum and atmospheric conditions was quantitatively studied using photoluminescence and X-ray photoelectron spectroscopy. When the fusedsilica surface was exposed to the UV laser in vacuum, the laser damage threshold was decreased whereas the concentration of the ODCs was increased. For the fuse silica operated under the high power lasers, creation of ODCs on their surface resulted from the UV laser irradiation, and this is more severe in a high vacuum. The laser fluence and/or laser intensity have significant effects on the increase of the ODCs concentration. The ODCs can be effectively repaired using postoxygen plasma treatment and UV laser irradiation in an excessive oxygen environment. Results also demonstrated that the “gain” and “loss” of oxygen at the silica surface is a reversible and dynamic process.

Laser molecular beam epitaxy of ZnO thin films and heterostructures

We report on the growth of epitaxial ZnO thin films and ZnO-based heterostructures on sapphire substrates by laser molecular beam epitaxy (MBE). We first discuss some recent developments in laser-MBE such as flexible ultraviolet laser beam optics, infrared laser heating systems or the use of atomic oxygen and nitrogen sources, and describe the technical realization of our advanced laser-MBE system. Then we describe the optimization of the deposition parameters for ZnO films such as laser fluence and substrate temperature and the use of buffer layers. The detailed structural characterization by x-ray analysis and transmission electron microscopy shows that epitaxial ZnO thin films with high structural quality can be achieved, as demonstrated by a small out-of-plane and in-plane mosaic spread as well as the absence of rotational domains. We also demonstrate the heteroepitaxial growth of ZnO-based multilayers as a prerequisite for spin transport experiments and the realization of spintronic devices. As an example, we show that TiN/Co/ZnO/Ni/Au multilayer stacks can be grown on (0 0 0 1)-oriented sapphire with good structural quality of all layers and well defined in-plane epitaxial relations.

An efficient all-solid-state doubly resonant continuous-wave ultraviolet laser at 284 nm

We report for the first time coherent ultraviolet radiation at 284 nm by intracavity sum-frequency generation of a 607 nm Pr:YLF laser and a 532 nm frequency doubling Nd:YVO4 laser. The ultraviolet laser is obtained by using double resonator, type-I critical phase matching CsLiB6O10 (CLBO) crystal sum-frequency mixing. With a total pump power of 18.8 W (3.1 W pump power for the 607 nm Pr:YLF laser and 15.7 W pump power for the 532 nm Nd:YVO4 frequency doubling laser), a TEM00 mode ultraviolet laser beam at 284 nm of 242 mW is obtained. The power stability is better than 3.4% and laser beam quality M2 factors are 1.13 and 1.22 in the horizontal and vertical dimensions respectively.

Nanoscale tensile stress approach for the direct writing of plasmonic nanostructures

One- and two-dimensional plasmonic nanostructures can be fabricated using nanoscale tensile stress. A polymer layer, coated with a thin metal film, is exposed to an interference pattern produced by ultraviolet laser beams. Crosslinking is induced between the polymeric molecules located within the bright fringes. This process not only increases the refractive index but also reduces the polymer layer thickness. Corrugations occur on the continuous thin metal film due to the nanoscale stress in the polymer layer. Thus, a periodic nanostructure of area 3 × 3 mm and depth 50 nm is created both in the polymer and metal films with excellent homogeneity and reproducibility. This method enables direct writing of a large-area plasmonic nanostructure at low cost which can be used in the design of optoelectronic devices and sensors.

Direct writing of ferroelectric domains on strontium barium niobate crystals using focused ultraviolet laser light

We report ferroelectric domain inversion in strontium barium niobate (SBN) single crystals by irradiating the surface locally with a strongly focused ultraviolet (UV) laser beam. The generated domains are investigated using piezoresponse force microscopy. We propose a simple model that allows predicting the domain width as a function of the irradiation intensity, which indeed applies for both SBN and LiNbO3. Evidently, though fundamentally different, the domain structure of both SBN and LiNbO3 can be engineered through similar UV irradiation.

Investigation of the ablation of fluorine-doped tin oxide thin films by square top-hat ultraviolet laser beams

This paper presents a square top-hat beam shaper in an ultraviolet (UV) laser processing system for electrode patterning and investigates the interaction between square laser beams and fluorine-doped tin oxide (FTO) thin films deposited on glass substrates. The various patterning parameters to ablate the FTO films used in this experiment are included laser fluences, pulse repetition frequencies, and feeding rates of a motorized platform. The laser pulse repetition frequency and the feeding rate of the motorized platform were used to calculate the overlapping rate of laser spot and to determine the patterning quality. The line width and depth, edge quality, three-dimensional topography, and electrical conductivity properties of the patterned FTO films were measured and analyzed using a confocal laser scanning microscope and a four-point probe instrument. Experimental results indicated that the ablated line width and depth increased with increasing laser fluence. After electrode patterning with laser fluence of 2.07J/cm2 and 80% overlapping rate, no damages were observed in the patterned lines on the glass substrate. Moreover, the patterned line paths were narrow, smooth, clear, and flat in response to uniform laser energy distribution interacted in FTO films. The measured values of sheet resistance ranged from 109.7±3.8Ω/□ to 139.3±4.9Ω/□ at 2.07J/cm2 to 9.37J/cm2 laser fluences, respectively. The proposed process can reduce the fabrication steps and improve the removal efficiency of transparent conductive oxide materials and no waste etching chemical solution is produced.

Dynamic model of thermal reaction of biological tissues to laser-induced fluorescence and photodynamic therapy

The aim of this work was to evaluate the temperature fields and the dynamics of heat conduction into the skin tissue under several laser irradiation conditions with both a pulsed ultraviolet (UV) laser (λ=337 nm) and a continuous-wave (cw) visible laser beam (λ=632.8 nm) using Monte Carlo modeling. Finite-element methodology was used for heat transfer simulation. The analysis of the results showed that heat is not localized on the surface, but is collected inside the tissue in lower skin layers. The simulation was made with the pulsed UV laser beam (used as excitation source in laser-induced fluorescence) and the cw visible laser (used in photodynamic therapy treatments), in order to study the possible thermal effects.

A laser probe 40 Ar/ 39 Ar investigation of poikilitic shergottite NWA 4797: implications for the timing of shock metamorphism

Abstract Spatially resolved argon isotope measurements have been performed on neutron-irradiated samples of NW Africa (NWA) 4797. Shock heating of NWA 4797 completely melted and vesiculated precursor igneous plagioclase, which cooled to an assemblage of plagioclase crystals with interstitial glasses of variable composition (Ca/K ratios). Using a focused ultraviolet laser beam, is has been possible to distinguish between argon isotopic signatures from groundmass minerals (igneous olivine + pyroxene), plagioclase and a shock vein. This study focuses on the potential for this meteorite to shed light on shock ages of shergottites. Apparent 40 Ar/ 39 Ar ages of groundmass minerals show that there are large amounts of excess argon in this phase, yielding a wide range of calculated ages from 690 ± 30 Ma to several apparent ages older than 4.5 Ga. A traverse of laser-probe extractions across the 1 mm-diameter shock vein in NWA 4797 yielded apparent 40 Ar/ 39 Ar ages younger than the groundmass. A signature of the Martian atmosphere, identified by 40 Ar/ 36 Ar ratios of 1600–1900, was not found in the NWA 4797 shock vein. This is distinct from other shergottites where the products of shock melting contain a nearly pure sample of Martian atmosphere. We attribute this to a distinct formation mechanism, and hence gas-trapping mechanism, of the NWA 4797 shock vein. We undertook 44 analyses of plagioclase areas identified by SEM analysis. Ages ranged from 45 ± 27 to 3771 ± 109 Ma and yield an average age of 375 ± 77 Ma, considerably younger than ages obtained in this study from either the groundmass or the shock vein. A plot of age v. 37 Ar/ 39 Ar for plagioclase showed a continuum of ages from the oldest to youngest ages measured. Older ages are correlated with higher Ca/K ratios of plagioclase, indicating contamination from groundmass minerals rich in excess argon. The youngest ages correlate to plagioclase extractions with the lowest Ca/K ratios, interpreted to have crystallized from a nearly pure plagioclase melt with contributions from a K-rich mesostasis. We see no evidence for multiple shock events in NWA 4797. Rather, we favour the interpretation that the cosmic-ray exposure (CRE) age of 3.0±0.5 Ma, obtained on NWA 4797 in this study using cosmogenic 38 Ar, approximates the timing of shock melting in this meteorite. Supplementary material: Laser probe argon isotopic data for NWA 4797 obtained in this study are available at http://www.geolsoc.org.uk/SUP18602 .