Matthieu Lancry

Asymmetric Orientational Writing in glass with femtosecond laser irradiation

We review the question on the origin of the differences observed on various properties when we scan the femtosecond laser beam in an isotropic media (i.e. a glass) in two orientations of a given direction. Publications on refractive index changes, birefringence, nanogratings, stress, bubbles formation and on quill writing effects are analyzed. A new interpretation based on space-charge built from ponderomotive force and stored in the dielectric inducing an asymmetric stress field is proposed.

Broadband anisotropy of femtosecond laser induced nanogratings in fused silica

We demonstrate operation of femtosecond laser imprinted birefringent optical elements from 200 to 2100u2009nm. The absorption losses in the UV can substantially reduced by the post-annealing of the structures. The birefringence is also accompanied with the weak dichroism which is related to the polarization dependent scattering. The transition from the isotropic modification to nanostructures is accompanied by occurrence of ODC(II) defect.

Regenerated femtosecond fibre Bragg gratings

We demonstrate the thermal regeneration of fibre Bragg gratings inscribed by direct writing using a femtosecond, infrared laser into standard SMF-28 and pure silica core fibres. Post-H2 loading was used. The regeneration process is shown to extend the temperature operation of these gratings up to 1200°C. The temperature durability of regenerated 193nm-written gratings in SMF-28 fibre is presented for comparison. The ability to enhance the temperature durability of femtosecond inscribed index changes has significance beyond fibre Bragg gratings; for example, the micromachining of photonic components such as planar waveguides.

Time-resolved plasma measurements in Ge-doped silica exposed to infrared femtosecond laser

Using a time-resolved interferometric technique, we study the laser-induced carrier-trapping dynamics in SiO 2 and Ge-doped SiO 2. The fast trapping of electrons in the band gap is associated with the formation of self-trapped excitons (STE). The STE trapping is doping dependent in SiO 2. The mean trapping time of electrons excited in the conduction band was found to be significantly lower in Ge-doped silica (75 ± 5 fs) when compared to pure silica (155 ± 5 fs). At our concentration level, this indicates that the plasma properties are determined by the presence of easily ionizable states such as the presence of Ge atoms in the glass network. Therefore, we suggest that in Ge-doped silica there exist an additional trapping pathway that leads to a significantly faster excitons trapping and a higher plasma density when compared to undoped silica.

Asymmetric orientational femtosecond laser writing detected in several properties in various glasses

Asymmetric orientational writing is demonstrated clearly in various silica-based glasses. It occurs for a domain of laser parameters and is likely connected to a memory effect coupled to an asymmetry of the beam.

Viscoelastic tuning of fibre Bragg gratings during regeneration

Regenerating at constant temperature under load allows inelastic changes in glass that can be exploited to tune the Bragg wavelength of a filter to any arbitrary spectral position. We have reported < 20nm of tuning of a 1 cm grating with no limit in sight. Further, regenerating under a temperature profile allows complex spectral shaping of the grating profile. As an example, we have reported broadband chirping by more than Δλ < 9 nm over 1 cm using this approach. High temperature viscoelastic tuning therefore offers a simple and powerful low cost way of tuning the properties of fibre Bragg gratings using a single phase mask.

Refractive Index Tensor Mapping In Femtosecond Laser Irradiated Silica

Here, we provide quantitative mapping of refractive index tensor in and around the laser tracks photo-induced by femtosecond laser in silica. We tentatively propose an interpretation based on permanent densification and related photo-elastic stress

Doping Dependence of the Femtosecond Laser Damage Thresholds in Silica Glasses

We observed that the first threshold (i.e. permanent isotropic index change) is not significantly dependent on the doping whereas it is the contrary for the second threshold (i.e. permanent linear birefringence).

Index change mechanism in erbium codoped aluminosilicate glass from 193nm irradiation

The absorption process causing index change in erbium codoped aluminosilicate optical fiber preform plates induced with 193 nm irradiation is determined to be triggered by two-photon excitation. The main contribution to index change is from material densification.