The interaction of focused femtosecond laser pulses at 810 nm and 1 kHz repetition rate with bulk fused silica is studied. Ultra-short pulse-induced optical breakdown (OB) and filamentation (FL) are two electronic excitation mechanisms leading to photo-structural modifications (e.g. uniform refractive index change) based on plasma formation inside transparent materials. Beyond a certain input power associated with the focusing geometry, the localized OB plasma formed around the geometrical focus can lead to structural damage characterized by a void-like morphology with a non-uniform high index contrast, while the modifications caused by plasma generation in the FL process usually give rise to a moderate index change. However, the formation of multiple filaments at certain higher powers using long focal lengths might be a drawback for waveguide applications. In this work, the thresholds of FL and its associated supercontinuum (SC), OB, and structural damage are measured as a function of focusing geometry. Consequently, various tracks were written and characterized in terms of writing geometry (parallel or perpendicular), focusing condition, pulse energy, and translation speed. In the parallel configuration, waveguides with a circular core of 3-6 m, and index change as large as 5 x 10-3 were achieved. Furthermore, the influence of self-focusing and filamentation on the shape of index modifications for the waveguides written perpendicularly under a very tight focusing, together with the observed pulse refocusing are also investigated.
We have investigated the writing of waveguides in pure fused silica glass with femtosecond Ti:sapphire laser at 1 kHz repetition rate. The obtained results were compared for two writing configurations with pulse durations of 200 fs and 45 fs, and with different exposure energies and translation speeds of the sample. The magnitude of the refractive-index changes in the glass was measured as a function of light exposure, where index changes as large as 5×10-3 were achieved.
Recently, the chalcogenide glasses (ChG) have attracted much attention in the field of optical
communication and integrated optics. High transparency in the infrared spectral region, low phonon
energy, high nonlinear properties, and high photosensitivity at near band-gap (Eg 2.35 eV,
a 1-2 x iO cm1 at 5 14 nm) are important characteristics of these glasses. In particular, the
photosensitive effects, among them photodarkening and giant photoexpansion (2-5%) , have been
extensively studied and several holographic elements, such as microlenses, diffraction and Bragg
gratings, and channel waveguides have been realized in fiber, bulk, and thin film forms of these
materials [2-4]. In this work, we report for the first time to our knowledge, the observation and study of
the strong polarization dependent photoinduced surface relief gratings in As2S3 thin films. A model to
describe the observed phenomena is also presented.
Chalcogenide glasses (ChG) based on As, S and Se are transparent in the infrared and have found applications in bulk, planar and fiber waveguide optical components. Due to their recent use in planar channel waveguide devices, a study to assess how structural variations imposed by processing conditions (film deposition) lead to changes in linear and nonlinear optical properties, is ongoing in our group. High resolution, near infrared (NIR) ((lambda) equals 840 nm) Raman spectroscopy has been employed to characterize changes in bonding between bulk glass specimens and glass in planar form. To obtain spectroscopic and spatially resolved information on chemical bonding, a microscope attachment has been constructed and is characterized as to its spatial resolution. Measurements are presented on single layer films prepared using processing and illumination conditions such as those used in fabricating waveguide components. These data are discussed in comparison to spectra obtained on bulk glass materials.