23 research outputs found
Effects of nonorthogonality in the time-dependent current through tunnel junctions
A theoretical technique which allows to include contributions from
non-orthogonality of the electron states in the leads connected to a tunneling
junction is derived. The theory is applied to a single barrier tunneling
structure and a simple expression for the time-dependent tunneling current is
derived showing explicit dependence of the overlap. The overlap proves to be
necessary for a better quantitative description of the tunneling current, and
our theory reproduces experimental results substantially better compared to
standard approaches.Comment: 4 pages, 1 table, 1 figur
Critical Properties of Condensation of Field-Induced Triplet Quasiparticles
A review on the field-induced magnetic ordering is given, together with some
results of a quantum Monte Carlo simulation focused on the critical behevior
near the quantum critical point.Comment: Proceedings of SPQS, Sendai, 200
Highly efficient relief diffraction gratings inscribed on a chalcogenide bulk glass by a femtosecond laser
Direct laser writing has been already demonstrated for the fabrication of under surface "buried" 3D mid-IR waveguides in chalcogenide glasses by employing a large photo-induced refractive index change in the features formed in the path of the focused beam from a short pulse laser. In this paper, we report on direct laser writing of relief diffraction gratings with periods of 6, 14 and 24 μm into the surface of Ge Ga Sb S chalcogenide glass by using a 800 nm Ti:saphire femtosecond pulse laser. The first order diffraction efficiency of the fabricated gratings was over 60 % at 650 nm. We have also fabricated a "composite" grating composed of three relief diffraction gratings inscribed in the same position, but with a mutual tilt. Composite grating provided complex multidirectional diffraction of the light in the accordance with geometrical arrangement and grating period of all the gratings inscribed. The fabrication was implemented on a computer controlled stage employing surface-to-beam alignment, laser power and raster pattern control. Pulse energies of 1.5, 3.0 and 4.5 μJ were used, resulting in channel widths of around 4, 5 and 6 μm, respectively, and depths up to 1.7 μm. We propose practical applications including surface relief diffraction micro-gratings at the ends of multimode chalcogenide optical waveguides or on the surfaces of bare core optical fibers used for chemical sensing. © 2012 SPIE
Direct laser writing of relief diffraction gratings into a bulk chalcogenide glass
We inscribed relief diffraction gratings with periods of 6, 14, and 24 μm into the surface of Ge15Ga3Sb12S70 bulk glass by the material's ablation using a femtosecond λ = 800 nm Ti:sapphire pulsed laser. The laser writing was done with sample implemented on a computer-controlled stage employing surface-to-beam alignment, laser power, and raster pattern control. Pulse energies of 1.5, 3.0, and 4.5 μJ were focused on spot diameter of 1.5 μm, resulting in channel widths, measured on the surface, of around 4, 5, and 6 μm and depths up to 1.7 μm. The first-order diffraction efficiency of the fabricated gratings was up to 10% at 650 nm. We have also fabricated a "composite" grating combining the three relief diffraction gratings inscribed in the same position, but with a mutual tilt. The composite grating provides complex multidirectional diffraction of the light in accordance with geometrical arrangement and grating period of all the gratings inscribed. We propose practical applications of femtosecond pulsed-laser surface patterning, for example, surface-relief diffraction microgratings integrated at the ends of multimode mid-IR chalcogenide optical waveguides or on the surfaces of bare core chalcogenide glass optical fibers used for chemical sensing. © 2012 Optical Society of America
Direct laser writing of relief diffraction gratings into a bulk chalcogenide glass
We inscribed relief diffraction gratings with periods of 6, 14, and 24 μm into the surface of Ge15Ga3Sb12S70 bulk
glass by the material’s ablation using a femtosecond λ � 800 nm Ti:sapphire pulsed laser. The laser writing was
done with sample implemented on a computer-controlled stage employing surface-to-beam alignment, laser
power, and raster pattern control. Pulse energies of 1.5, 3.0, and 4.5 μJ were focused on spot diameter of
1.5 μm, resulting in channel widths, measured on the surface, of around 4, 5, and 6 μm and depths up to
1.7 μm. The first-order diffraction efficiency of the fabricated gratings was up to 10% at λ � 650 nm. We have also
fabricated a “composite” grating combining the three relief diffraction gratings inscribed in the same position, but
with a mutual tilt. The composite grating provides complex multidirectional diffraction of the light in accordance
with geometrical arrangement and grating period of all the gratings inscribed. We propose practical applications of
femtosecond pulsed-laser surface patterning, for example, surface-relief diffraction microgratings integrated at the
ends of multimode mid-IR chalcogenide optical waveguides or on the surfaces of bare core chalcogenide glass
optical fibers used for chemical sensing