1,721,032 research outputs found
Nonlinear thickness dependence of two-photon absorptance in Al2O3 films
No full textLinear and nonlinear absorptance in Al2O3 films of different optical thicknesses are investigated using an ArF laser calorimeter. While the linear absorptance at 193 nm shows the expected linear increase, nonlinear absorptance increases quadratically with increasing film thickness. Thus, it cannot be described by a constant nonlinear absorption coefficient beta. The experimental findings are explained by a simple phenomenological approach using excited states with a finite interaction length longer than the actual film thickness, a new material constant Gamma is introduced, which describes the nonlinear absorptance behavior correctly
Bragg gratings in planar polydiactylene waveguides and their application in integrated optics
No full textWe present the fabrication of high quality non-uniform Bragg gratings in planar poly(4-BCMU) channel waveguides using an optimized photobleaching set-up and report the optical characterization of the resulting photonic band gap. The suitability of our system to all-optical switching phenomena in different geometries as a result of non-linear wave propagation effects will be shown and discussed. Our results contribute to open up the wide field of device applications in integrated optics based on periodically structured planar polymer waveguides. (C) 2001 Elsevier Science B.V. All rights reserved
A 100 mJ table-top short pulse amplifier for 248 nm using interferometric multiplexing
No full textA polarization multiplexing method (based on Sagnac interferometer's principle) was used in combination with a table-top wide aperture discharge pumped excimer amplifier to amplify femtosecond UV pulses. It is possible to optimize the operational conditions of the device within a wide range of input energies by changing the optical setup, while keeping the signal-to-noise ratio (short pulse - amplified spontaneous emission (ASE) ratio) of the pulses on a reasonably low value. The amplifier was tested for two different front ends. With similar to 40 muJ input energy similar to 50 mJ output energy was obtained in a 3-pass arrangement, and applying a seed pulse carrying an energy of around 2-3 mJ a maximum output energy of 100 mJ was reached in a single subpicosecond beam at 248 nm
New simplified coupling scheme for the delivery of 20 MW Nd : YAG laser pulses by large core optical fibers
No full textThe feasibility of transmitting 20 MW, 5 ns laser pulses from a frequency doubled Nd:YAG laser through a standard 1500 mum multi mode optical fiber is demonstrated. A new coupling scheme employing an optical homogenizer prevents breakdown in air without the use of a vacuum chamber. At the same time a very homogeneous flat top beam profile on the fiber surface is achieved. The new scheme therefore clearly simplifies fiber coupling of high power laser pulses. Experiments on the delivery of more than 20000 pulses with 1 10 mJ mean energy without fiber damage have been performed
F-2-laser ablation patterning of dielectric layers
No full textSpatially defined patterning of multi-layer dielectric optical systems by laser-induced ablation is demonstrated. A 49-layer high-reflectivity mirror for 193-nm light was irradiated with Fz-laser light through the CaF2-substrate to cleanly remove the whole dielectric stack by rear-sided ablation. The 157-nm light is absorbed efficiently by dielectric layers such as SiO2 and Al2O3 that are typically used for ultraviolet (UV) transmission at 193-nm and longer wavelengths. Thus it is possible to ablate highly reflective UV-laser mirrors (HR 193 nm) and to create dielectric masks that withstand high power levels at 193 nm. A single 157-nm pulse with a fluence of less than 500 mJ/cm(2) is sufficient to cleanly ablate the whole layer stack with sharp edges and without debris deposition
Table-top KrF amplifier delivering 270 fs output pulses with over 9 W average power at 300 Hz
No full textApplying the combination of a solid-state Ti:Sa laser system and a newly developed wide-aperture, discharge-pumped KrF amplifier, output pulses with over 9 W average power at 300 Hz have been achieved in a single output beam. The frequency-tripled seed pulses of the Ti:Sa system - delivering approximately 10 muJ energy at 248 nm - were amplified to over 30 mJ using a 3-pass off-axis amplification scheme. The optical set-up has been fitted to the amplifier's parameters, and stored-energy measurements were carried out with different parameters in order to optimize the operational conditions of the device for the highest average power
New simplified coupling scheme for the delivery of 20 MW Nd : YAG laser pulses by large core optical fibers
No full textThe feasibility of transmitting 20 MW, 5 ns laser pulses from a frequency doubled Nd:YAG laser through a standard 1500 mum multi mode optical fiber is demonstrated. A new coupling scheme employing an optical homogenizer prevents breakdown in air without the use of a vacuum chamber. At the same time a very homogeneous flat top beam profile on the fiber surface is achieved. The new scheme therefore clearly simplifies fiber coupling of high power laser pulses. Experiments on the delivery of more than 20000 pulses with 1 10 mJ mean energy without fiber damage have been performed
Resonant double-grating waveguide structures as inverted Fabry-Perot interferometers
No full textA multiple-interference model to describe double-grating waveguide structures is presented. It is based on the multiple-interference model for single-grating waveguide structures previously established by Friesem and co-workers [J. Opt. Soc. Am. A 14, 2985 (1997)]. We show that double grating waveguide structures, in particular, as well as the usual single-grating waveguide structures can be completely described by our model and that explicit dependences of the resonant conditions on the wavelength, the angle, and the polarization of the incident light as well as on system parameters such as refractive indices, layer thickness, grating depths, and grating period can be given. This multiple-interference model elucidates the resonance behavior of single- and double-grating waveguide structures and predicts reflection and transmission resonance bandwidths in analogy to those of the classic Fabry-Perot interferometer. One can explain and understand the periodicity of resonances by interpreting grating waveguide structures as inverted Fabry-Perot interferometers. Comparison with exact numerical calculations and verification by experimental investigations prove the model to be a powerful tool for design purposes and to provide a deep understanding of the observed resonance phenomena. (C) 2004 Optical Society of America
On the competition between electron autodetachment and dissociation of molecular anions.
Full text linkWe treat the competition between autodetachment of electrons and unimolecular dissociation of excited molecular anions as a rigid-/loose-activated complex multichannel reaction system. To start, the temperature and pressure dependences under thermal excitation conditions are represented in terms of falloff curves of separated single-channel processes within the framework of unimolecular reaction kinetics. Channel couplings, caused by collisional energy transfer and “rotational channel switching” due to angular momentum effects, are introduced afterward. The importance of angular momentum considerations is stressed in addition to the usual energy treatment. Non-thermal excitation conditions, such as typical for chemical activation and complex-forming bimolecular reactions, are considered as well. The dynamics of excited SF6− anions serves as the principal example. Other anions such as CF3− and POCl3− are also discussed
Room temperature adsorption of Na on Si(111)-7×7 as studied by resonant optical second harmonic generation
No full textResonantly enhanced optical second harmonic generation at a pump laser energy of 1.17 eV was applied to investigate the Na-adsorption process on the 7 x 7 reconstructed Si(1 1 1) surface at room temperature. The change of second harmonic (SH) intensity as a result of Na deposition at normal incident pump radiation varies significantly from that measured at 45 degrees angle of incidence. The observed difference can be explained in terms of electronic transitions from the rest-atom state to the adatom state of the 7 x 7 reconstructed Sill 1 1) surface as well as of the features of Na growth on the silicon surface. By measuring the SH polarization dependence for different stages of Na deposition, a change of the interface symmetry in both directions, namely, parallel and perpendicular to the (1 1 1) plane, was clearly observed at the very beginning of the adsorption process. (C) 2001 Elsevier Science B.V. All rights reserved
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