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

Recent advances in ultrafast laser processing of transparent materials

Interaction of intense ulrashort light pulses with transparent materials reveal new interesting properties and phenomena. Recent demonstrations of 3D nanoripple formation, self-assembled form birefringency and ultrafast laser calligraphy are reviewed

Ultrashort laser modification of transparent materials: synergy of excitation/relaxation kinetics, thermodynamics and mechanics

Ultrafast laser modification of transparent materials is an important technique enabling production of 3D photonic structures whose practical applications are rapidly widening. The physics behind laser-induced modifications is extremely rich and involves a variety of consecutive processes initiated by radiation absorption during the laser pulse and extending to millisecond timescales when the final structure becomes "frozen" in the material matrix. The quality of the final structures depends of the synergetic action of excitation of confined electron plasma, its relaxation with drawing matter into different thermodynamic states from soft heating to extreme conditions, generation of GPa pressures resulting in shock-induced material deformations, re-forming of covalent bonds upon photo-excitation of the material network. In this report, we will review the physical processes responsible for various forms of laser-induced modification in wide-bandgap materials, including volume nanograting formation. We will present the modeling results obtained on the basis of the Maxwell’s equations supplemented with equations describing the dynamics of the laser-induced electron plasma on the example of silica glass for typical experimental conditions. The temperature and associated stress levels are mapped in the laser energy absorption zone which may be foreseen at the end of electron - glass matrix relaxation, enabling to make conclusions on the routes of glass modification. Finally, the energy balance is considered, matching the free electron density and temperature with several threshold values (melting, plastic deformation, material failure with void formation, sublimation)

Polarization diffraction grating produced by femtosecond laser nanostructuring in glass

We demonstrate polarization sensitive diffractive optical element fabrication by femtosecond direct writing in the bulk of silica glass. Modulation of the anisotropic properties is produced by controlling light-induced self-assembled nano-gratings

Efficient conversion to radial polarization in the two-micron band using a continuously space-variant half-waveplate

We demonstrate efficient conversion of a linearly-polarized Gaussian beam to a radially-polarised doughnut beam in the two-micron band using a continuously space-variant half-waveplate created by femtosecond writing of subwavelength gratings. The low scattering loss (<0.07) of this device indicates that it would be suitable for use with high power lasers

New phenomena in interaction of intense ultrashort light pulses with transparent materials: from 3D self-assembled nanostructures to quill writing and nonreciprocal photosensitivity

Interaction of intense ulrashort light pulses with transparent materials reveal new ultrafast phenomena. Recent demonstrations of 3D nanoripple formation, ultrafast laser calligraphy and nonreciprocal photosensitivity are reviewed

Glass fibre poling and applications

Recent developments in the application of poled optical fibers to second harmonic generation and electrooptic light modulation are reviewed

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

High power radially-polarized Yb-doped fiber laser

A simple technique for directly generating a radially-polarized output beam from an ytterbium-doped fiber laser using an intracavity spatially-variant waveplate is reported. The laser yielded 32W of output with a corresponding slope efficiency of 65.8% in a radially-polarised beam with beam propagation factor ~2.1 and polarization purity >95%

Femtosecond laser nanostructuring of transparent materials: from bulk to fiber lasers

Progress in high power ultra-short pulse lasers has opened new frontiers in the physics of light-matter interactions and laser material processing. Recently there has been considerable interest in the application of femtosecond lasers to writing inside transparent materials and in particular to fabrication of three-dimensional microstructures