Search results for "laser"
showing 10 items of 3161 documents
Characterisation of cw Nd : YAG laser keyhole dynamics
2001
Abstract The paper concerns laser–matter interaction characterisation. In this work, we use a rapid CCD camera located coaxially to the laser beam and we compare recorded images with those obtained by numerical modelling. Because images are difficult to understand, we compute thermal radiation emitted by a keyhole of fixed geometry and we adjust it trying to approach the camera record. The modelling treats radiative heat transfer within the keyhole and determines the sensor illumination map. By adjusting the geometrical characteristics of the hole, we seek to obtain the image that corresponds as well as possible to the realised experiment. Results are compared with other experimental method…
The influence of laser beam-width and focusing angle about the precision of cutting metallic materials
2005
To realize a high precision cutting operation, we must know the position and pointing of the beam axis- which are defined in accordance with ISO, by the centers of gravity of energy density distributions at different distances from the exit lens of laser. The angle of focalization must be related at least with; material width, beam energy, cutting speed, precision requirements and workpiece destination. Authors have realized experimental set-up for simultaneous measurement of energy density distributions, correlated with the mentioned working parameters. Besides the geometrical details, the authors studied also the influence of different values of beam density, about the zone affected by he…
Fluorescence lifetime spectroscopy: potential for in-vivo estimation of skin fluorophores changes after low power laser treatment
2013
The impact of visible cwlaser irradiation on skin autofluorescence lifetimes was investigated in spectral range from 450 nm to 600 nm. Skin optical provocations were performed during 1 min by 405 nm low power cw laser with power density up to 20 mW/cm 2 . Autofluorescence lifetimes were measured before and immediately after the optical provocation.
Doubly active Q switching and mode locking of an all-fiber laser
2009
Simultaneous and independent active Q switching and active mode locking of an erbium-doped fiber laser is demonstrated using all-fiber modulation techniques. A magnetostrictive rod attached to the output fiber Bragg grating modulates the Q factor of the Fabry-Perot cavity, whereas active mode locking is achieved by amplitude modulation with a Bragg-grating-based acousto-optic device. Fully modulated Q-switched mode-locked trains of optical pulses were obtained for a wide range of pump powers and repetition rates. For a Q-switched repetition rate of 500 Hz and a pump power of 100 mW, the laser generates trains of 12-14 mode-locked pulses of about 1 ns each, within an envelope of 550 ns, an o…
Kinetics of Photorefractive Light Scattering in Stoichiometric LiNbO3Single Crystals Grown from Melt Containing 58.6 Mole% of Li2O
2011
A study of kinetics of photo-refractive light scattering in ostensibly pure stoichiometric LiNbO3 (Li/Nb = 1) single crystal grown from melt containing 58.6 mole% Li2O excited by laser radiation of 0.53 μm is reported. Asymmetry of the distribution of scattered light intensity is revealed and found to be a linear function of the intensity of the exciting radiation in the 35–160 mW range. Due to heating of the crystal, at farther increase of the radiation intensity the distribution of scattered light contracts.
Structural and Optical Homogeneity in Lithium Niobate Crystals of Low Photorefractivity
2015
Comprehensive studies by Raman and photo-induced light scattering complemented by laser conoscopy and electron spectroscopy of structural and optical homogeneity of nominally pure and modified lithium niobate crystals are reported.
Time-resolved photoemission electron microscopy
2009
The excellent time structure of Synchrotron radiation and short-pulse lasers has opened the door to a novel way of time-resolved imaging using PEEM. Periodic or repetitive processes can be studied by stroboscopic illumination with the pulsed photon beam. Since the first experiments in 2003, two fields of applications have been established in several groups. One concerns the investigation of fast magnetisation processes like precessional switching, Gigahertz-eigenmodes of ferromagnetic nanostructures or travelling spin waves in thin films. More recently, femtosecond lasers have been used for imaging of localised surface plasmons in nanoparticles and their temporal behaviour in the femtosecon…
Efficient pulsed 946-nm laser emission from Nd:YAG pumped by a titanium-doped sapphire laser
2008
Efficient pulsed room-temperature laser emission at 946 nm is obtained from a Nd:YAG rod pumped by a Ti-doped sapphire laser in the free-running mode. Three bonded YAG rods of 3-mm diameter with different Nd concentrations and active lengths were tested. A maximum output energy of 83.5 mJ at 3 Hz was obtained with a slope efficiency of 32.3% in an end-pumping configuration.
Radiation-induced defects in antiferroelectric thin films
2003
Abstract Radiation effects on highly oriented antiferroelectric (AFE) PbZrO3 (PZ) films with a thickness of approximately 400 nm are investigated in view of their possible application as a temperature sensitive element in a new bolometer system for fusion devices like ITER. The films were prepared by pulsed laser deposition (PLD). The dielectric constant was measured in the frequency range from 1 to 250 kHz in a stepwise cooling mode (∼2 °C min−1) from 400 °C to room temperature before and after irradiation to a fast neutron fluence of 2×1022 m−2 (E>0.1 MeV). After irradiation, the films were annealed in several steps up to ∼400 °C to remove the radiation-induced defects. The results are di…
Passive interferometric interrogation of a magnetic field sensor using an erbium doped fiber optic laser with magnetostrictive transducer
2015
Abstract An erbium doped (Er3+) fiber optic laser is proposed for magnetic field measurement. A pair of FBGs glued onto a magnetostrictive material (Terfenol-D rod) modulates the laser wavelength operation when subject to a static or a time dependent magnetic field. A passive interferometer is employed to measure the laser wavelength changes due to the applied magnetic field. A data acquisition hardware and a LabVIEW software measure three phase-shifted signals at the output coupler of the interferometer and process them using two distinct demodulation algorithms. Results show that sensitivity to varying magnetic fields can be tuned by introducing a biasing magnetic field. A maximum error o…