441 research outputs found
Electric-field thermally poled optical fibres for quasi-phase-matched second harmonic generation
We report on quasi-phase-matched frequency doubling to the blue in electric-field poled optical fibres. An increase of a factor of ~10 in the conversion efficiency in comparison with the previous results is obtained. Our experiments show that the structure of the induced nonlinear grating is not uniform, both longitudinally and transversely. For this reason the value of the effective nonlinear coefficient is still far from the optimum expected from the measured value, through Maker's oscillation, for a uniformly poled fibre
Frequency doubling in Ga:La:S optical glass with microcrystals
Second harmonic generation in gallium-lanthanum-sulphide (Ga:La:S) and GeS2+Ga:La:S glasses is investigated. It is shown that microcrystals of Ga:La:S and of alpha-phase of gallium-sulphide (alpha-Ga2S3), whose presence in the glass matrix is revealed by x-ray diffraction analysis, are responsible for the frequency doubling process
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
Intensities of Combination IR Bands as an Indication of the Concerted Mechanism of Proton Transfer from Acidic Hydroxyl Groups in Zeolites to Ethylene Hydrogen-Bonded by Protons
IR Extinction Coefficients as a Measure of Chemical Activation of Hydrocarbons via Polarization
Visible luminescence from hydrogenated amorphous silicon modified by femtosecond laser radiation
Visible luminescence is observed from the composite of SiO2 with embedded silicon nanocrystallites produced by femtosecond laser irradiation of hydrogenated amorphous silicon (a-Si:H) film in air. The photoluminescence originates from the defect states at the interface between silicon crystallites and SiO2 matrix. The method could be used for fabrication of luminescent layers to increase energy conversion of a-Si:H solar cells
Towards practical second-harmonic generation in optical glass fibres
Recent advances in silica fibres exhibiting second-order optical nonlinearities as a result of both self-induced and thermal poling processes are reported. Efficient second-harmonic generation in silica fibre subjected to a strong electrostatic field via internal electrodes was observed. Spatial periodic modulation of the applied electric field, responsible for the second-harmonic signal, arises from the interaction of the intense light at fundamental and doubled frequencies with glass, which has its inversion symmetry broken by the applied field. The process could represent the first evidence of coherent photoconductivity in glass - conductivity being dependent on the relative phase of the light fields at different frequencies. Moreover, D-shaped silica fibres have been periodically poled at elevated temperature by applying high voltage via a patterned electrode fabricated an the planar surface and high quality quasi-phase-matching structures have been created. Efficient frequency doubling of picosecond pulses to the blue in periodically poled fibre was demonstrated
Parametric fluorescence in periodically poled silica fibres
We report the observation of quasiphase matched parametric fluorescence from a periodically poled silica fiber. A pair-photon production rate of more than 100 MHz around 1532 nm was achieved in second-order nonlinear gratings for 300 mW of pump power at 766 nm. These results are very promising for the realization of reliable all-fiber single-photon sources for quantum cryptography systems and metrology applications
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