1,721,072 research outputs found
Pulsed laser deposition of optical films: a route for the development of holographic memories and waveguide lasers
No full textFabrication of reflective volume gratings in pulsed-laser-deposition Ti:sapphire waveguides with UV femtosecond-laser pulses
No full textHighly reflective volume Bragg gratings (R~80%) were written in Ti:sapphire planar and channel waveguides fabricated via pulsed-laser deposition (PLD) by exposure to UV (266 nm) femtosecond laser irradiation through suitable phase masks. Large photo-induced refractive index modulations of up to ~1×10-2 ions were observed, which were completely reversible at temperatures of ∼100°C. The dependence of the refractive index modulation on intensity suggests that the mechanism for grating inscription is an one-photon absorption process. Generation of gratings may result from a charge transfer process between the Ti3+ and Ti4+ ions and/or transient localized structural re-arrangements
Dielectric binary oxide films as waveguide laser media: a review
No full textSapphire (α-Al are excellent laser hosts due to their very good thermomechanical properties, broad transparency range and ease of doping with active ions. This article reviews recent research towards the realization of active optical films and the demonstration of gain and laser operation in the waveguides produced from these materials. Compound structures in which laser operation has been demonstrated are highlighted together with the applied fabrication techniques, and details of the laser performance are presented
Encoding of volume gratings in pulsed-laser-deposited Ti:sapphire waveguides by femtosecond UV laser irradiation and a phase mask
No full textTi:sapphire is a widely used laser material with broad tunability (650-1100 nm), which makes it suitable for the development of short pulse and broadly tunable lasers. Development of Ti:sapphire channel waveguide lasers has recently attracted attention and various techniques such as pulsed laser deposition (PLD) [1], and proton implantation [2] have been used for their realization. The cavity of these lasers was formed by attaching thin dielectric mirrors at the end-faces of the waveguides. However, this approach induces instabilities in the laser operation due to etalon effects between the mirrors and the substrate, and imposes limitations on the integrability of the device. A route to improve both performance and scale of integration would be to substitute the cavity optics by grating structures incorporated in the waveguides. Here, we report on the fabrication of Bragg gratings within crystalline Ti:sapphire layers grown on sapphire substrates by PLD. Encoding was performed by focusing the third harmonic output from a femtosecond Ti:sapphire laser (266 nm, 110 fs, 1 kHz 170 µJ pulse energy) with a 75 mm cylindrical lens through a silica phase mask optimized for use at 266 nm with a period of 1077 nm and a residual zero order intensity of less than 1%. Recording of gratings was monitored with a He-Ne laser at lambda=633 nm by illuminating the sample from the top of its surface and measuring its diffraction efficiency. A diffraction efficiency value of 19% was obtained for a film with a thickness of 5 µm. This would equate to a diffraction efficiency of approximately 50 % for an equivalent 10 µm thick film. The recorded gratings were stable for annealing temperatures up to ~70°C. Since generation of gratings was not observed in commercial bulk Ti:sapphire crystals, we speculate that formation in PLD-grown films may result from refractive index modulation due to structural rearrangements at defect sites such as F color centers (oxygen vacancies occupied by one electron) that are present in the deposited layers. Such rearrangements would lead to the formation of metastable states in the film. The thermal stability of gratings depends on the barrier height that separates the metastable from the initial state. The focus of current work is on the further investigation of the recording mechanism as well as on the incorporation of Bragg thick gratings into Ti:sapphire channel waveguides and results will be reported
Reflective (R=80%) volume gratings in Ti:sapphire waveguides fabricated by femtosecond UV-laser pulses
No full textMicrostructured optical fibres for gas sensing: design fabrication and post-fab processing
No full textAir/silica Microstructured Optical Fibers (MOFs) offer new prospects for fiber based sensor devices. In this paper, two topics of particular significance for gas sensing using air guiding Photonic Bandgap Fibers (PBGFs) are discussed. First, we address the issue of controlling the modal properties of PBGFs and demonstrate a single mode, polarization maintaining air guiding PBGF. Secondly, we present recent improvements of a femtosecond laser machining technique for fabricating fluidic channels in PBGFs, which allowed us to achieve cells with multiple side access channels and low additional loss
UV photosensitivity in a Ta<sub>2</sub>O<sub>5</sub> rib waveguide Mach-Zehnder interferometer
No full textThe ultraviolet (UV) photosensitivity of Ta2O5 measured in a rib waveguide Mach-Zehnder interferometer (MZI) is reported. With a cumulative fluence of 72J/cm2 at a wavelength of 248nm incident upon one arm through a 3-mm-long window, the MZI exhibits a phase shift of 8pi radians at wavelength λ = 1.55µm, corresponding to a saturated refractive index change of 2.1 x 10-3. Real time measurements of the MZI output during exposure are given and the UV-induced refractive index change is found to be negative
Recent progress in continuous-wave Ti:sapphire waveguide lasers
No full textA detailed study of the fabrication and continuous-wave laser operation of Ti:sapphire channel waveguides written with femtosecond (fs) and picosecond (ps) laser pulses in the bulk of a Ti:sapphire crystal is presented. The waveguides were produced using the double-line approach and the effect of parameters such as the laser pulse duration, repetition rate and interline spacing were investigated for optimizing the laser operation. Structures fabricated by fs-laser pulses (180 fs) exhibited superior performance delivering output powers up 143 mW with a slope efficiency of 23.5% and producing laser emission above a threshold of 84 mW. The emission wavelength was tuned over a wavelength range spanning from 700 to 920 nm using cavity optics with broadband transmission at the lasing wavelength in combination with a birefringent filter in an external cavity
Holographic recording mechanisms of gratings in indium oxide films using 325nm Helium-Cadmium laser irradiation
No full textUV (325 nm) holographic recording of gratings in indium oxide films fabricated by reactive pulsed laser deposition has been investigated as a function of growth temperature, oxygen pressure and angle of incidence of the plasma plume on the substrate. The influence of the ambient environment (air or vacuum) and the film temperature during recording has also been studied. Large steady state refractive index changes up to 6×10-3 were observed in layers grown at an oblique angle of 75°. About 77% of the magnitude of these changes residues after thermal annealing and is attributed to UV-induced permanent structural rearrangements. In contrast, refractive index changes in films grown at normal incidence were smaller in magnitude and completely reversible
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