Abstract
The photoelectron-collection efficiency from photocathodes in noble gases and methane is experimentally investigated. The ratio between the number of transmitted photoelectrons in the gas media and in vacuum is determined as a function of the applied reduced electric field Elp, where p is the gas pressure. Results are presented for He, Ne, Ar, Xe, Kr and CH4.

Abstract
The technique to realize 3D position sensitivity in a two-phase xenon time projection chamber (XeTPC) is described. Results from a prototype detector (XENON3) are presented.

Abstract
The XENON experiment aims at the direct detection of dark matter in the form of WIMPs (Weakly Interacting Massive Particles) via their elastic scattering off Xenon nuclei. With 1 ton of LXe distributed in ten identical modules, the proposed XENON1T experiment will achieve a sensitivity more than a factor of thousand beyond current limits. The detectors are time projection chambers operated in dual (liquid/gas) phase, to detect simultaneously the ionization, through secondary scintillation in the gas, and primary scintillation in the liquid produced by low energy recoils. We review some of the results from the prototype XENON3 detector and briefly discuss about the status of current XENON10 at Gran Sasso Laboratory in Italy.

Abstract
In this work, numerical simulations are performed and the performance comparison of four types of dispersion compensating Raman/EDFA hybrid amplifiers configurations in terms of gain, noise figure and nonlinear effect induced penalty is presented. A numerical simulator is presented for the analysis and design optimization of Raman/EDFA hybrid amplifiers for multi-wavelength operation. This simulator combines a steady-state model of a discrete Raman Amplifier (RA) with a spectrally resolved model for the Erbiurn Doped Fiber Amplifier (EDFA). The numerical simulator allows us to calculate the overall gain, the noise figure (NF), the optical signal-to-noise ratio (OSNR) and the signal and ASE spectrum at the output of a Raman/EDFA hybrid amplifier. We concluded that performance tradeoffs should be considered when an optimum hybrid amplifier configuration for a given fiber optic transmission system is to be decided.

Abstract
Relations between fabrication conditions and optical characteristics of planar waveguides made by proton exchange in benzoic acid are documented in the literature, but reports on the characterization of waveguide fabrication processes, performed in a systematic way, could not be found, resulting in the need to combine data from several authors. Discrepancies among results from different researches are evident, resulting from different experimental methodologies and calibration of equipment. Therefore, aiming at extracting a consistent data set, optical characterization of the refractive index profile was employed to study series of samples. The objective was to develop a methodology for fabrication of proton-exchanged channel waveguides in LiNbO3 operating in the single-mode regime at several wavelengths, with specific characteristics required to optimize integrated devices. To achieve this, it is necessary to obtain the relations between the optical characteristics of the waveguides and their fabrication conditions, and to introduce models of the waveguide formation process. (c) 2007 Society of Photo-Optical Instrumentation Engineers.

Abstract
By measuring intensity distributions of cladding modes and using an optimization technique we show that the perturbation which forms arc-induced gratings in standard fibers is antisymmetric, while the perturbation in boron-germanium codoped fibers is symmetric. © 2006 Optical Society of America.