409 research outputs found
Effect of poling conditions on second harmonic generation in fused silica
A systematic study of the effects of poling time and applied voltage on second harmonic generation (SHG) in thermally poled silica glass reveals that the SH signal is proportional to the square of the applied voltage, and that the speed of the poling process is inversely proportional to the applied voltage. Prior treatment of the samples is found to affect the poling process, and the optimum poling conditions are observed to depend on the poling atmosphere. The mechanism of thermal poling is discussed in the light of these new results
Threshold Laws for the Break-up of Atomic Particles into Several Charged Fragments
The processes with three or more charged particles in the final state exhibit
particular threshold behavior, as inferred by the famous Wannier law for (2e +
ion) system. We formulate a general solution which determines the threshold
behavior of the cross section for multiple fragmentation. Applications to
several systems of particular importance with three, four and five leptons
(electrons and positrons) in the field of charged core; and two pairs of
identical particles with opposite charges are presented. New threshold
exponents for these systems are predicted, while some previously suggested
threshold laws are revised.Comment: 40 pages, Revtex, scheduled for the July issue of Phys.Rev.A (1998
Theoretical study of ionization of an alkali atom adsorbed on a metal surface by laser assisted subfemtosecond pulse
The first numerical simulation of the process of ionization of an atom
adsorbed on a metal surface by the subfemtosecond pulse is presented. The
streaking scheme is considered, when a weak sub-femtosecond pulse comes
together with a strong IR pulse with a variable delay between them. The problem
is analyzed with numerical solving the non-stationary Schroedinger equation in
the cylindrical coordinate. The results obtained are compared with ones in the
gas phase. We show that the surface influences the DDCS, but the observation of
this influence, beside the trivial polarization shift of the energy of the
initial state, requires a quite high experimental resolution
Efficient conversion to radial polarization in the two-micron band using a continuously space-variant half-waveplate
We demonstrate efficient conversion of a linearly-polarized Gaussian beam to a radially-polarised doughnut beam in the two-micron band using a continuously space-variant half-waveplate created by femtosecond writing of subwavelength gratings. The low scattering loss (<0.07) of this device indicates that it would be suitable for use with high power lasers
Ultrafast Laser Nanostructured ITO Acts as Liquid Crystal Alignment Layer and Higher Transparency Electrode
Electrodes with higher transparency that can also align liquid crystals (LCs)
are of high importance for improved costs and energy consumption of LC
displays. Here we demonstrate for the first time alignment of liquid crystals
on femtosecond laser nanostructured indium tin oxide (ITO) coated glass
exhibiting also higher transparency due to the less interface reflections. The
nano paterns were created by fs laser directlly on ITO films without any
additional spin coating materials or lithography procces. Nine regions of
laser-induced nanostructures were fabricated with different alignment
orientations and various pulse energy levels on top of the ITO. The device
interfacial anchoring energy was found to be comparable to the anchoring energy
of nematic LC on photosensitive polymers. The device exhibits contrast of 30:1
and relaxation time of 330ms expected for thick LC devices. The measured
transparency of the LC device with two ITO nanograting substrates is 10% higher
than the uniform ITO film based LC devices. The alignment methodology presented
here paves the way for improved LC displays and new structured LC photonic
devices
Self-assembled nanostructuring of a-Si:H films with ultrashort light pulses
For several decades, hydrogenated amorphous silicon (a-Si:H) has been playing a significant role in the world's production of photovoltaic modules. In this work, we investigate different types of modifications induced by a femtosecond laser in a-Si:H thin films. We demonstrate that several distinctive modification regimes with peculiar optical properties can be obtained in a narrow range of the laser pulse energies
SnO<sub>2</sub> nanoparticles in silica: nanosized tools for femtosecond-laser machining of refractive index patterns
We show that SnO2 nanoclusters in silica interact with ultrashort infrared laser pulses focused inside the material generating a hydrostatic compression and photoelastic response of the surrounding glass. This effect, together with the laser-induced nanocluster amorphization, gives rise to positive or negative refractive-index changes, up to 10–2, depending on the beam-power density. This result points out a wide tuning of the refractive index patterns obtainable in silica-based optical technology
Beyond conventional 3D ultrafast laser material processing
Material processing with ultrafast lasers has attracted considerable interest due to a wide range of applications from laser surgery and integrated optics to optical data storage, 3D micro- and nano-structuring [1,2]. A decade ago it has been discovered that under certain irradiation conditions ordered sub-wavelength structures with features smaller than 20 nm can be formed in the volume of silica glass [3]. The effect of nanograting formation has attracted considerable interest with proposals of applications ranging from nanofluidics [4,5] to polarization control devices [6]
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