arXiv subjects

A. Niang

Publications and source records attributed to A. Niang.

5 recordsLinked to original sources

arXiv2022

Multiphoton ionization of standard optical fibers

Atoms ionization by the simultaneous absorption of multiple photons has found applications in fiber optics, where it leads to unique nonlinear phenomena. To date, studies of the ionization regime have been limited to gas-filled hollow-core fibers. Here, we investigate multiphoton ionization of standard optical fibers, where intense laser pulses ionize the atoms constituting the fiber structure itself, instead of that of the filling gas. We characterize material modifications produced by optical breakdown. Their formation affects laser beam dynamics over hours long temporal scales. The damage features are studied by means of optical microscopy and X-ray microtomography. In the framework of glass photonics, our results pave the way for a novel glass waveguide micromachining technique.

physics.optics↗

arXiv2021

Giving light a new twist with standard optical fibres: rainbow Archimedean spiral emission

We demonstrate a new practical approach for generating multicolour spiral-shaped beams. It makes use of a standard silica optical fibre, combined with a titled input laser beam. The resulting breaking of the fibre axial symmetry leads to the propagation of a helical beam. The associated output far-field has spiral shape, independently of the input laser power value. Whereas, with a high-power near-infrared femtosecond laser, a visible supercontinuum spiral emission is generated. With appropriate control of the input laser coupling conditions, the colours of the spiral spatially self-organize in a rainbow distribution. Our method is independent of the laser source wavelength and polarization. Therefore, standard optical fibres may be used for generating spiral beams in many applications, ranging from communications to optical tweezers and quantum optics.

physics.optics↗

arXiv2020

Multiphoton absorption excited upconversion luminescence in optical fiber

We experimentally demonstrate a novel nonlinear effect in optical fibers: upconversion luminescence generation excited by multiphoton absorption of femtosecond infrared pulses. We directly estimate the average number of photons involved in the up-conversion process, by varying the wavelength of the pump source. We highlight the role of non-bridging oxygen hole centers and oxygen deficient center defects, and directly compare the intensity of side-scattered luminescence with numerical simulations of pulse propagation.

physics.optics↗

arXiv2019

Spatial beam self-cleaning in tapered Yb-doped GRIN multimode fiber with decelerating nonlinearity

We experimentally demonstrate spatial beam self-cleaning in an Yb-doped graded-index multimode fiber taper, both in passive and active configurations. The input laser beam at 1064 nm was injected for propagation from the small to the large core side of the taper, with laser diode pumping in a counterdirectional configuration. The Kerr effect permits to obtain high-beam quality amplification with no accompanying frequency conversions. As a result, our nonlinear taper amplifier may provide an important building block for multimode fiber lasers and amplifiers.

physics.optics↗

arXiv2019

Spatial Beam Self-Cleaning and Supercontinuum Generation with Yb-doped Multimode Graded-Index Fiber Taper Based on Accelerating Self-Imaging and Dissipative Landscape

We experimentally demonstrate spatial beam self-cleaning and supercontinuum generation in a tapered Ytterbium-doped multimode optical fiber with parabolic core refractive index and doping profile when 1064 nm pulsed beams propagate from wider (120 micrometers) into smaller (40 micrometers) diameter. In the passive mode, increasing the input beam peak power above 20 kW leads to a bell-shaped output beam profile. In the active configuration, gain from the pump laser diode permits to combine beam self-cleaning with supercontinuum generation between 520-2600 nm. By taper cut-back, we observed that the dissipative landscape i.e., a non-monotonic variation of the average beam power along the MMF leads to modal transitions of self-cleaned beams along the taper length.

physics.optics↗