1,720,965 research outputs found
Extraordinary stability of femtosecond direct written structures
No full textWe report novel results on the stability of femtosecond direct written structures: a silica sample previously irradiated with ultrashort pulses was annealed at increasing temperatures till 1400° C where it crystallized. Our results show that the birefringent direct written structures are stable till a temperature close to the glass transition of silica. After annealing at a temperature as high as 1100° C the form birefringence of the structures is still present, proving that the nature of the laser induced anisotropy is related to a structural change
Waveguide fabrication in bismuthate glasses using femtosecond laser pulses
No full textFemtosecond direct written waveguides in bismuthate glasses are reported. This is the first demonstration of direct written guiding channels in bismuthate glass which show an index of refractive change as high as 3 x 10-3
Symmetric waveguides written in Er<sup>3+</sup>-doped Bi<sub>2</sub>O<sub>3</sub>-based glass using femtosecond laser pulses
No full textSingle-mode channel waveguides are fabricated in Er-based glass using femtosecond laser pulses at 800nm. A waveguide with circular transverse profile is demonstrated without using any beam shaping technique
Extraordinary stability of anisotropic femtosecond direct-written structures embedded in silica glass
No full textIn this letter we report the different response to temperature displayed by isotropic femtosecond written structures (type I_fs), and anisotropic ones (type II_fs), which are characterized by the presence of a self-assembled sub-wavelength periodic structure within the irradiated volume. We observe that the anisotropic structures display an extraordinary annealing behavior, namely, their photo induced change in refractive index increases with the annealing temperature. We explain our experimental results with a theoretical model
Form birefringence and negative index change created by femtosecond direct writing in transparent materials
No full textAlthough femtosecond lasers have proved to be of great utility for micromachining within bulk transparent materials, little is known about the fundamental physics that drive the process. Depending on the laser intensity delivered to the sample, any of three types of feature can be written into the glass. We observed that in the intermediate regime there is a correlation among the negative sign of the effective index change, the presence of anisotropic reflection, and birefringence. We propose a model that can explain all three principal characteristics. Results show that the local index change can be as high as 10-1
Birefringent Fresnel zone plates in silica fabricated by femtosecond laser machining
No full textWe demonstrate maskless, single-step fabrication of strongly birefringent Fresnel zone plates by focusing of femtosecond laser pulses deep within silica substrates. The process allows us to produce alternate zone rings directly by inducing a local refractive-index modification of the order of n~10-2 . The embedded zone plates shown in this Letter exhibit efficiencies that vary by as much as a factor of ~6 for orthogonal polarizations. Focal lengths of primary and secondary foci are shown to compare well with theory
Femtosecond direct writing of embedded photonic structures
No full textIn the last few years, femtosecond lasers have proven to be of great utility for micromachining within the bulk of transparent materials and this processing technique has attracted much attention due to its simplicity compared to lithographic methods and its ability to write in three-dimensions. When an intense femtosecond laser pulse is tightly focused into transparent material, high-order non-linear absorption allows the energy to be deposited predominantly within the focal volume producing a local permanent refractive index modification
Self-assembled periodic sub-wavelength structures by femtosecond laser direct writing
No full textSelf-assembled, sub-wavelength periodic structures are induced in fused silica by a tightly focused, linearly polarized, femtosecond laser beam. Two different types of periodic structures, the main one with period (λE) in the direction of the laser beam polarization and the second with period (λk) in the direction of the light propagation, are identified from the cross-sectional images of the modified regions using scanning electron microscopy. We demonstrate the spatial coherence of these nanogratings in the plane perpendicular to the beam propagation direction. The range of effective pulse energy which could produce nanogratings narrows when the pulse repetition rate of writing laser increases. The period λE is proportional to the wavelength of the writing laser and period λk in the head of the modified region remains approximately the wavelength of light in fused silica
Breaking symmetry in glass by femtosecond laser irradiation
No full textIt is observed that writing by femtosecond laser from left to right can be different from writing in the opposite direction. Structures with broken mirror symmetry in chalcogenide glass are discovered. Chiral patterns are demonstrated
Characterisation of nanoscale structures observed in femtosecond laser micromachining
No full textWe present a quantitative analysis of self-arranged sub-wavelength structures created by femtosecond laser micromachining in silica. From the spatial correlation we calculate the periods of the structures versus laser energy and wavelength, and translation speed
- …
