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Photoluminescence (PL) of Gd-doped silica in the ultraviolet (UV) is investigated. The strong emission detected at 314 nm is assigned to the 6P7/2 to 8S7/2 transition under excitation of 6DJ, 6IJ, and 6PJ energy levels of the Gd3+. After glass densified by rapid thermal treatment (RTT), significant enhanced luminescence and decreased loss covering the UV band are observed.
Weakly-fused optical fibre couplers can be simplified as a system of two optical fibre tapers, which are often called nanofibers when having sub-micron diameters. While conventional optical fibre couplers exhibit a wide spectral region of modal interference where two modes provide a continuous oscillatory behaviour associated to the large difference between phase constants of interfering supermodes...
A scheme for directly exciting the radially-polarized TM01 mode in a fiber laser is reported. Preliminary results for cladding-pumped ytterbium-doped and thulium-doped fiber lasers are discussed along with prospects for scaling to high power levels.
We demonstrate direct-write laser nanostructuring of semiconductor thin-films and transparent dielectrics resulting in space-variant anisotropic materials. The continuous phase profile of nearly any optical component can be achieved solely by the means of geometric phase.
High order gratings using phase mask technique are investigated theoretically and experimentally. The results shows that even a small amount of the zeroth-order component in the diffraction distribution would have substantial effects on high order gratings. It provides a useful basis for producing different gratings towards short wavelength application using one single phase mask.
Orbital angular momentum (OAM) beam generation has been investigated using all-fibre and free space configurations. In the first approach, the composite fused coupler is based on a single mode fibre (SMF) and an air-core fibre. The second approach exploits geometrical phase introduced by nanostructuring of silica glass. Both approaches are demonstrated to achieve power coupling efficiencies in excess...
We demonstrate femto- and picosecond laser assisted nanostructuring of hydrogenated amorphous silicon (a-Si:H). The laser-induced periodic sub-wavelength structures exhibit the dichroism and giant form birefringence giving extra dimensions to the polarization sensitive image recording.
We demonstrate space variant polarization and phase converters imprinted by femtosecond laser nanostructuring in hydrogenated amorphous silicon thin film. Giant birefringence of imprinted structures allows fabrication of microoptic element arrays.
Polarization spatio-temporal coupling reveals new degree of freedom in ultrafast laser material processing. Control of modification in fused silica is demonstrated with the use of prism compressors and polarization azimuth of ultrashort pulse laser beam.
Femtosecond laser assisted crystallization is used to produce nanocrystalline silicon from hydrogenated amorphous silicon. Changes in structural, optical, electrical and photoelectric properties of laser modified amorphous silicon were investigated. Laser treated films were characterized using atomic force microscopy, Raman spectroscopy, constant photocurrent method and current measurements. Crystalline...
We demonstrate a method of optical vortices generation with continuous orbital angular momentum control. The beam generated with an S-waveplate is used as an optical spanner where the rotation speed of trapped particles can be controlled.
We demonstrate maskless, single-step fabrication of micro-waveplate array by femtosecond direct writing in the bulk of silica glass. The waveplate array enables instant measurement of the distribution of the Stokes vectors in the visible spectrum.
Surface texturing with 30 nm resolution is demonstrated by KOH wet etching and ultrafast laser nanostructuring of silica. An increase of three times in retardance is achieved leading to the fabrication of dichroic glass-metal patterns.
Directly written structure created on the surface of silicon by the single pulse femtosecond laser irradiation are observed to function as microreflector. The smooth surface of the structure is a result of molten material flow.
Sub-wavelength ridge structures are observed on silicon surface after irradiation with two femtosecond pulses. Cat's-eye-shaped structures are aligned perpendicular to polarization of the second pulse and can be used for polarization-sensitive recording.
For several decades, hydrogenated amorphous silicon (a-Si:H) has been playing a significant role in the world's production of photovoltaic modules. In this work, we investigate different types of modifications induced by a femtosecond laser in a-Si:H thin films. We demonstrate that several distinctive modification regimes with peculiar optical properties can be obtained in a narrow range of the laser...
Recently, strong longitudinal electric fields have raised great interest in the laser fabrication, microscopy and optical data storage [1]. Here we demonstrate high quality cylindrically polarized annular beam produced by ultrafast laser written spatially variant polarization converter. We observed that nanogratings cannot be formed by strong longitudinal electric fields, created by a ring-shaped...
The interaction of femtosecond laser pulses with transparent media has been a focus of research due to its unique properties. It has been established that above a certain threshold, self-assembled nanogratings in silica glass can be induced [1]. Although the mechanism that triggers the nanostructure is still unclear, a theory has been introduced involving the mechanism of nanogratings formation based...
Under certain conditions, femtosecond lasers can be used to introduce self-organized nanogratings in the bulk of fused silica. Here, we report that the nanogratings orientation influences the induced stress distribution around laser affected zones.
The correlation between 3/2 harmonic generation and self-assembled nanostructuring during ultrafast laser writing in glass was observed with an unexpected enhancement of harmonic generation for elliptically polarized light.
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