The amorphous films show many physical properties which differ from the crystalline state. One of these is the optical transparency photoinduced by light with photon energies higher than optical bandgap. The phenomenon is especially large in amorphous chalcogenide films. However, the changes of optical constants are too small for optoelectronic applications. In this paper we consider structure were the amorphous As<sub>2</sub>S<sub>3</sub> film is placed in a structure which forms a surface plasmon resonance structure. The reflected light is coupled with waveguide modes. The experimental studies show that high nonlinear changes may be achieved for the light intensity of 10- 12 mW when the incident angle is close to resonance. For some film thicknesses the SPR resonance was achieved with prism made from BK7 glass, which is important opportunity for applications.
In this paper we present several numerical simulations of the surface plasmon resonance for Kretschmann type configuration in a metal-chalcogenide waveguide. We assume that the chalcogenide (GaLaS) waveguide layer have finite thickness, whereas the gold film layer and the air cover layer are semi-infinite layers (from an optical point of view). We determined the thickness of the chalcogenide film for which plasmonic resonant coupling of the incident radiation to the waveguide occurs. We calculated the propagation constant for the TE- and TM- modes (both for visible and IR domain), the attenuation coefficient and the electromagnetic field distribution within the waveguide. The obtained results provide the conditions for design an optical memory device 2D based on light-light interaction in plasmonic configuration.
The pulsed laser ablation of aluminium, copper and titanium irradiated with 4.5 ns pulses at 355 nm, 532 nm
and 1064 nm wavelengths is investigated in open air at normal atmospheric conditions. The effect of pulse number,
which is varied in the range of 5 to 50, on ablation rate in these three wavelength regimes is determined. The results
indicate a higher efficiency of the ablation in VIS and UV regimes as compared to IR regime which is characterised
by a very small optical absorbtivity.
The ablation rate is demonstrated to be approximately constant when increasing the pulse number up to a
certain value which strongly depends on the thermal properties of the material. Further increase of pulse number
leads to a progressive decrease of ablation rate. The most pronounced decrease was obtained at 355 nm in aluminium
where the ablation rate corresponding to the 50<sup>th</sup> pulse is about 20% of the ablation rate corresponding to of first
The decay of the ablation rate with the pulse number is attributed to the superposition of two phenomena:
the enhanced attenuation of the laser beam in the plasma plume which is confined within the crater, and the decay of
the effective laser fluence at the target surface due to the gradual increment of the effective irradiated area with pulse
This paper presents an experimental study of the ablation-plasmas and of the craters generated by focusing visible nanosecond laser pulses at normal incidence on a solid target of Er<sup>3+</sup>-doped Ti:LiNbO<sub>3</sub>, in atmospheric air. The laser irradiance was varied in the range of 0.25 to 2.5 TW/cm<sup>2</sup>, which is close to the plume-ignition threshold.
The spatial variation of the neutral Li lines and of the temperature along the axial direction within the plasma plume was evaluated by scanning axially the plume image with a fiber that is coupled at the spectrometer entrance. The results indicate that the intensity of the neutral Li lines increases when increasing the distance from the target's surface. The plasma temperature calculated by accounting for these lines intensities is almost constant (~14000 K) being non-dependent on laser-irradiance and distance from the target.
The spectroscopic study is augmented with an optical microscopy study of the ablated craters in order to
determine the correlation between the ablation rate in multi-pulse regime and the plasma spectrum. The results indicate
that monitoring the plasma spectrum at a fixed position above the target surface the lines intensity decrease with pulse
number, probably due to the confinement of the plume into the deep crater that are drilled in multi-pulse regime.
This paper reports some modelling results concerning a novel Er<sup>3+</sup>:Ti:LiNbO<sub>3</sub> optical waveguide directional
coupler. Based on the mode coupling theory we evaluated the coupling coefficient between the straight and curved waveguides of the directional coupler. Also, using a quasi-two-level model in the small gain approximation and the unsaturated regime in this paper we report some original results concerning the evaluation of the spectral optical gain, spectral noise figure and spectral signal-to-noise ratio in the bent Er<sup>3+</sup>:Ti:LiNbO<sub>3</sub> waveguide of the directional coupler pumped near 1484 nm performed for erfc, Gaussian and constant profile of the Er<sup>3_</sup> ions in LiNbO<sub>3</sub> crystal.
We investigated the process of laser micro-drilling of copper and iron by using nanosecond laser-pulses at 532nm
wavelength in atmospheric air. We analyzed the ablated volume, ablation rate, crater diameter, and craters quality as
functions of laser-fluence and beam-diameter. The fluence was varied between 10 and 6000 J/cm<sup>2</sup> by changing the laserenergy.
The results indicate that the ablated volume increases linearly with fluence, whereas the ablation rate and crater
diameter increase linearly with the fluence's square root. The ablated volume, ablation rate, and crater diameter, increase
with thermal diffusivity of the materials. Additionally, the ablation threshold-fluence is demonstrated to be directly
related to the optical penetration depth.
The ablated volume, ablation rate, and crater diameter were further assessed for beam-diameters in the range of
10-50 microns by translating the targets away from the focal plane while keeping a constant fluence. The results indicate
that the ablated volume increases linearly with beam-diameter, whereas the ablation rate and crater diameter increase
linearly with the inverse of the beam-diameter's square root.
To investigate the craters quality we measured the dimension of the thermally affected zone (TAZ) around the
craters as a function of fluence. At fluences up to 400 J/cm<sup>2</sup>, where strong ionization occurs within the plume, the crater
diameter is <15 microns (comparable with beam diameter) and there is small TAZ around the craters. Further increase of
the fluence leads to a significant increase of TAZ, indicating that the expanding plasma plays a major role in metals
ablation in this fluence domain.