6826 research outputs found
Sort by
Creation of metal materials nanoporous structures under the action of laser radiation
Full text linkThe laser radiation exposure for creation ofnanoporous structures in the Cu-Zn alloy wasstudied. Exposure to laser pulse-periodic radiationwith pulse repetition rate up to 5000 Hz makes itpossible to form a nanoporous structure in the nearsurfacelayer. The modes of an increase of the areadepth of such structures formation up to 40...45 μmwere ascertained. The temperature and speed modeswhich provide predominant channel-type nanoporesformation with widths of about 100 nm forming ananoporous net were investigated
UV Picosecond-Laser Induced Bulk Modifications and Luminescence in Single-Crystal Diamond
Full text linkBulk laser-graphitized microstructures have been fabricated in type IIa single-crystal 1.2-mm-thick diamond plates by UV laser irradiation with 10-ps pulses at λ=355 nm wavelength. It is found that the crystallographic-plane-dependent character of structural modifications in the bulk is influenced by the laser wavelength and the direction of the laser beam incidence relative to a given crystallographic direction (<100> or <110>) in the diamond plates. High-order Stokes Raman lasing is observed during UV laser irradiation and bulk modifications of single-crystal diamond. It is shown that the formation of bulk microstructures results in dramatic changes in the behavior of the stimulated Raman scattering in diamond. The formation and migration of the 3H defects (self-interstitial related centers) is also found to take place in the course of bulk microstructuring with UV ps-pulses. Important limitations of the bulk microstructuring caused by high internal stresses in laser-modified regions resulting in ‘uncontrollable’ damage of the diamond single crystals are discussed
Laser Processing of CFRP
Full text linkThe key issue for laser-processing of carbon fiberreinforced plastics (CFRP) is the thermal damage ofboth, the matrix material and the carbon fibres. Thispaper describes the basic mechanisms leading tosuch thermal damage and its implications on thedesign of appropriate laser processing systems
Influence of Submillisecond Er-Laser Pulses on Mechanical Properties of Hard Tooth Tissues
Full text linkIn this paper the influence of pulse duration, pulse repetition rate, pulse number (at single point), and pulse energy of YLF: Er laser radiation with λ=2.84 μm on mechanical properties of human hard tooth tissues was studied. It was found that the multi-pulses action of this laser radiation with pulse energy below hard tooth tissues ablation threshold promotes increase in the microhardness of enamel at 25% and microhardness of dentine at 35%. Such research can open new perspectives in esthetic and preventive dentistry
CARS diagnostics of near-critical fluid in small mesopores
Full text linkDue to the high spacial resolution and theinterference nature, coherent anti-Stokes Ramanscattering (CARS) spectroscopy is well suited forthe diagnostics of composites based on transparentnanoporous hosts. In particular, the adsorption of afluid on the walls of nanopores and the formation ofa condensed phase in their volume leads to obvioustransformation of the CARS spectra. Recently wehave developed a model which describes thebehavior of molecular spectra at isothermalcompression in cylindrical nanopores. Calculationsbased on the model have shown a good agreementwith the experimental results for carbon dioxide innanoporous glass with pores of diameter of severalnanometers. Here we use the developed approach toinvestigate the phase behavior of carbon dioxide inglass nanopores at near-critical temperatures. It hasbeen experimentally shown that condensation innanopores occurs at relatively low pressures atsubcritical and even at supercritical temperatures.The analysis based on the developed model allowsto reveal some qualitative and quantitativecharacterizations of the shift of critical point
Progress in real-time photoacoustic imaging using optical ultrasound detection
Full text linkOptical phase contrast full field detection in combination with a CCD-camera can be used to record acoustic fields. This allows to obtain two-dimensional photoacoustic projection images in real-time. The present work shows an extension of the technique towards full three-dimensional photoacoustic tomography. The reconstruction of the initial three dimensional pressure distribution is a two step process. First of all, projection images of the initial pressure distribution are acquired. This is done by back propagating the observed wave pattern in frequency space. In the second step the inverse Radon transform is applied to the obtained projection dataset to reconstruct the initial three dimensional pressure distribution. An experiment is performed using a phantom sample which mimics the properties of biological samples to show the overall applicability of this technique for real-time photoacoustic imaging
Multi-stage ytterbium fiber-amplifier seeded by a gain-switched laser diode
Full text linkWe demonstrated all-fiber amplification of 11 ps pulses from a gain-switched laser diode at 1064 nm. The diode was driven at a repetition rate of 40 MHz and delivered 13 µW of fiber-coupled average output power. For the low output pulse energy of 325 fJ we have designed a multi-stage core pumped pre-amplifier in order to keep the contribution of undesired amplified spontaneous emission as low as possible. By using a novel time-domain approach for determining the power spectral density ratio (PSD) of signal to noise, we identified the optimal working point for our pre-amplifier. After the pre-amplifier we reduced the 40 MHz repetition rate to 1 MHz using a fiber coupled pulse-picker. The final amplification was done with a cladding pumped Yb-doped large mode area fiber and a subsequent Yb-doped rod-type fiber. With our setup we reached a total gain of 73 dB, resulting in pulse energies of >5.6 µJ and peak powers of >0.5 MW. The average PSD-ratio of signal to noise we determined to be 18/1 at the output of the final amplification stage
Selective Ablation in Cu(In,Ga)Se2 thin-film solar cells – analysis of different process regimes at sub-picosecond to nanosecond pulse duration.
No full textRecent achievements in Cu(In,Ga)Se2 (CIGS) thin film technology allow the industrial production ofhighly efficient solar modules. A large growth of the CIGS-based solar cell production volume can beexpected for the coming years thanks to some favorable properties inherent to this absorber type. A majordrawback of CIGS is the inefficient patterning process. Since CIGS is a particularly difficult material forlaser ablation there is still no industrial all-laser scribing solution available. Manufacturers fall back onmechanical needle scribing for the P2 and P3 scribing process and have to accept substantial broadeningof the electrical interconnects due to unpredictable chipping at the scribe borders. In the present study weexplored a large variety of possible processes for the P1-P3 scribing at different wavelengths and indifferent pulse duration regimes. Beside the direct ablation of CIGS with ultrashort pulses we alsoinvestigated more exotic processes like layer side lift-off variants. The resulting scribes were analyzedusing electron microscopy (EM), laser scanning microscopy (LSM), energy dispersive X-ray spectroscopy(EDX) and electrical conductivity measurements. The most promising processes were selected forproducing functional mini-modules. Multiple optimization cycles allowed us to select the processes withthe best performance in the mini-module
New Circulation System of Laser Gas Mixtures
Full text linkThe electrohydrodynamic flow in air, being formed at issue of ions from plasma of the high-frequency barrier discharge is investigated. It is shown that velocity of a flow is proportional to intensity of electric field between the emitter and a collector of ions. All solid-state pulse generator with voltage of U f = 0-12 kV and pulse repetition rate of f = 10-25 kHz is applied to feed the plasma emitter. It is experimentally established that the increase in high voltage and frequency of the plasma emitter feeding leads to increase velocity of a gas flow. The circulation system with a gas flow rate more than 15 L s–1and velocity more than 1.6 m s–1 was proposed for electric-discharge lasers
Process Developments And Applications Around The Powder In Tube Technique
Full text linkThe purpose of this presentation is to give an overview of techniques available to produce original optical fibers and application dedicated. Some alternative fabrication solutions to the well-know stack and draw technique will be developed, following by the interest to join the stack and draw technique to other ones like Repusil® Technique, Rod in Tube and finally the Powder in Tube methods, first described by the Bell Lab in the seventies and up to date since some years by several groups in the world. Realization of performing optical devices such as light sources or optical sensors can be purposed by this two last original ways
Data sources:
BORIS Portal Bern Open Repository and I...BAF-Online: Proceedings of the Berner Al...HASBonline – Hefte zur Archäologie des M...Informationswissenschaft: Theorie, Metho...Jahrbuch Diakonie SchweizJournal of Eye Movement ResearchJournal of Radiation Oncology Informatic...
BOP SerialsVersants. Revista suiza de literaturas r...BORIS Theses
BOP SerialsVersants. Revista suiza de literaturas r...BORIS ThesesAccess Repository Dashboard
Do you manage BOP Serials? Access insider analytics, issue reports and manage access to outputs from your repository in the CORE Repository Dashboard!