Abstract
The transmission efficiency of photoelectrons emitted from CsI photocathodes operated in Ar-CH4 and Xe-CH4 mixtures is experimentally investigated and compared to Monte Carlo simulation results: the ratio between the number of photoelectrons collected in the gas media and in vacuum is determined as a function of the pressure-reduced electric field E/p at the photocathode surface, for irradiation with the VUV photons from an Hg(Ar) lamp. The addition of a small percentage of CH4 to At and Xe results in a significant increase of the photoelectron transmission, in particular for electric fields below E/p similar to 1 V cm(-1) Torr(-1). Below E/p similar to 0.5 V cm(-1) Torr(-1) the transmission efficiency f in Ar-CH4 Mixtures reaches values higher than in pure CH4, going through a maximum in the range of 10-30% CH4. The addition of 5% and 20% CH4 to Xe increases f by a factor of about 2 and 3, respectively, when compared to pure Xe.

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Abstract
The study of the strain and temperature characteristics of a sensing head based on a four-hole suspended-core fibre in a Sagnac interferometric configuration is reported. It is shown that, for the case of using an uncoated suspended-core fibre, a relatively large strain sensitivity is obtained (similar or equal to 1.94 pm/mu epsilon), while the temperature sensitivity is small (similar or equal to 0.29 pm/degrees C), pointing to a temperature-independent strain sensor. When the fibre is coated, the strain sensitivity remains essentially the same, while the temperature sensitivity becomes much larger and with a value that changes with the localisation of the temperature variation range.

Abstract
In this work, a curvature sensor based on a highly birefringent (Hi-Bi) photonic crystal fibre loop mirror is presented. For this purpose, a novel Hi-Bi photonic crystal fibre was designed and fabricated. Half of the microstructured region of the photonic crystal fibre was composed by holes with large diameter, while the other half contained holes with small diameter. Due to this geometry, the fibre core was shifted from the centre and high birefringence appears in the optical fibre. The Hi-Bi photonic crystal fibre loop mirror was demonstrated as a curvature sensor. The curvature was applied for three different fibre directions for the range of 0.6 - 5 metres(-1). The configuration was also characterized for temperature and longitudinal strain, showing insensitivity for these two physical parameters.

Abstract
We report on the use of a frequency-reflectometry domain technique for referencing optical intensity sensors located between two fibre Bragg gratings. The experiment combines the concept of frequency modulated continuous wave with the spectrally selective mirror proper-ties of fibre Bragg gratings to interrogate with referencing properties intensity based sensors. Multiplexing two of these sensors using this technique in a parallel topology system was also experimentally demonstrated. Due to the use of different fibre lengths (delay lines), signals from the fibre Bragg gratings located at different positions in an array are separated in the frequency-domain.