R. S. Taylor

Polarization-selective etching in femtosecond laser-assisted microfluidic channel fabrication in fused silica.

We fabricate microchannels in fused silica by femtosecond laser irradiation followed by etching in diluted hydrofluoric acid. We show a dramatic dependence of the etch rate on the laser polarization, spanning 2 orders of magnitude. We establish the existence of an energy-per-pulse threshold at which etching of the laser-modified zones becomes highly polarization selective. The enhanced selective etching is due to long-range, periodic, polarization-dependent nanostructures formed in the laser-modified material.

Pulse duration dependence of femtosecond-laser-fabricated nanogratings in fused silica

Femtosecond laser radiation tightly focused in bulk fused silica is used to generate self-ordered nanogratings when the sample is translated under the lens at constant speed. The nanogratings are preserved over a length scale of millimeters. We demonstrate that nanogratings are formed for all pulse durations tested, ranging from 40to500fs, and that the pulse energy threshold for this phenomenon increases with decreasing pulse duration. We use high spatial resolution diagnostics based upon selective chemical etching followed by atomic force microscopy and scanning electron microscopy to reveal the morphology of the nanogratings.

Femtosecond laser-induced refractive index modification in multicomponent glasses

We present a comprehensive study on femtosecond laser-induced refractive index modification in a wide variety of multicomponent glasses grouped as borosilicate, aluminum–silicate, and heavy-metal oxide glasses along with lanthanum–borate and sodium–phosphate glasses. By using high-spatial resolution refractive index profiling techniques, we demonstrate that under a wide range of writing conditions the refractive index modification in multicomponent glasses can be positive, negative, or nonuniform, and exhibits a strong dependence on the glass composition. With the exception of some aluminum–silicate glasses all other glasses exhibited a negative/nonuniform index change. We also demonstrate direct writing of waveguides in photosensitive Foturan® glass with a femtosecond laser without initiating crystallization by thermal treatment. Upon ceramization of lithium–aluminum–silicate glasses such as Foturan®, Zerodur®, and Robax® we observe switching of laser-induced refractive index change from being positive t...

Excimer laser angioplasty: Tissue ablation, arterial response, and fiber optic delivery

The results of recent work directed towards the application of excimer lasers to angioplasty are presented. Several laser-tissue interactions are examined, including the effect of the XeCl laser optical pulse duration (7-300 ns) on the threshold fluence for ablation of arterial wall and on the quality of the cut in human postmortem artery, the potential for altering the ablation threshold fluence of arterial plaque in swine by treatment with hematoporphyrin derivative, and the healing response of swine arterial wall to surgical irradiation with an argon laser and a pulsed XeCl laser. The dependence of damage thresholds and transmission properties of selected commercial fused silica fibers on the laser pulsewidth and wavelength are determined.

High-resolution study of photoinduced modification in fused silica produced by a tightly focused femtosecond laser beam in the presence of aberrations

An ultrahigh-resolution (20nm) technique of selective chemical etching and atomic force microscopy has been used to study the photoinduced modification in fused silica produced at various depths by tightly focused femtosecond laser radiation affected by spherical aberration. We demonstrate that shapes of the irradiated zones near the threshold for modification can be predicted by taking proper account of spherical aberration caused by the refractive index mismatched air–silica interface. We establish a depth dependence of the pulse energy required to initiate modification and characterize the relationship between numerical aperture of the writing lens and practically achievable writing depth. We also show that spatial characteristics of the laser-modified zones can be controlled by a specially designed focusing system which allows correction for a variable amount of spherical aberration.

Dependence of the nonlinear transmission properties of fused silica fibers on excimer laser wavelength

The nonlinear transmission properties of commercially available fused silica fibers have been determined as a function of excimer laser wavelength. Accurate two‐photon absorption coefficients have been measured and the influence of color center formation is discussed. Two‐photon absorption and color center formation dominate the ArF and KrF transmission at high intensities while both of these effects are negligible at the XeCl and XeF laser wavelengths.

Stress in femtosecond-laser-written waveguides in fused silica.

We identify two states of stress induced in waveguides fabricated by femtosecond lasers in fused silica and show how they can be relieved by annealing. In-plane stress and stress concentration are revealed through birefringence and loss measurements. Another kind of laser-induced stress appears in the form of swelling of the glass surface when waveguides are written near the surface and is a manifestation of confined rapid material quenching. By annealing the sample we reduce the losses by approximately 30% (at 633 nm) and decrease the birefringence by a factor of 4 in fused silica.

Effect of optical pulse duration on the XeCl laser ablation of polymers and biological tissue

Photoacoustic spectroscopy was used to measure the pulse duration dependence of the XeCl laser ablation of polyimide, polyethylene terephthalate, and post‐mortem human aorta. It was observed that the ablation threshold exhibited only a weak dependence on pulse duration. Photoablation etch depth measurements of polyimide as a function of XeCl laser fluence indicated that over a practical etch depth range of 0.1 to 1 μm per laser pulse the etch depth was independent of the pulse duration.

Ultra-high resolution index of refraction profiles of femtosecond laser modified silica structures

Ultra-high spatial resolution index of refraction profiles of femtosecond laser modified structures in silica glass have been measured using the combination of chemical etching and atomic force microscopy.

Particle trapping in 3-D using a single fiber probe with an annular light distribution

A single optical fiber probe has been used to trap a solid 2 ìm diameter glass bead in 3-D in water. Optical confinement in 2-D was produced by the annular light distribution emerging from a selectively chemically etched, tapered, hollow tipped metalized fiber probe. Confinement of the bead in 3-D was achieved by balancing an electrostatic force of attraction towards the tip and the optical scattering force pushing the particle away from the tip.