Simultaneous spatial and temporal focusing (SSTF) provides precise control of the pulse front tilt necessary to achieve nonreciprocal writing in glass. The magnitude of the pulse front tilt may be adjusted over several orders of magnitude. Nonreciprocal writing was observed for a larger range of focal depths within the sample using SSTF, and nonreciprocal ablation patterns on the surface were revealed. Further, the lower numerical aperture (0.04 NA) utilized with SSTF increases the rate of writing. This technique allows channels in microfluidic devices to be prototyped an order of magnitude faster than with current methods.

We analyze the structure of space-time focusing of spatially-chirped pulses using a technique where each frequency component of the beam follows its own Gaussian beamlet that in turn travels as a ray through the system. The approach leads to analytic expressions for the axially-varying pulse duration, pulse-front tilt, and the longitudinal intensity profile. We find that an important contribution to the intensity localization obtained with spatial-chirp focusing arises from the evolution of the geometric phase of the beamlets.

Simultaneous spatial temporal focusing (SSTF) is used to deliver microjoule femtosecond pulses with low numerical aperture geometries (<0.05 NA) with characteristics that are significantly improved compared to standard focusing paradigms. Nonlinear effects that would normally result in focal plane shifts and focal spot distortion are mitigated when SSTF is employed. As a result, it is shown that SSTF will enable surgical implementations that are presently inhibited.

Femtosecond laser exposure of fused silica in the nonablative regime can lead to various localized bulk modifications of the material structure. In this paper, we show that these laser-induced modifications can be used to tune silica thermal expansion properties permanently. In particular, we demonstrate that a given exposer regime leads to lower thermal expansion than the bulk, while other exposure conditions yield the opposite results. This remarkable property enables the possibility to engineer a given thermal expansion behavior by selectively exposing a material volume to a femtosecond laser beam. This finding opens up opportunities for a variety of integrated precision instruments and optical devices for which inertness to thermal fluctuations is essential.

Abstract:We analyze the structure of space-time focusing of spatiallychirped pulses using a technique where each frequency component of the beam follows its own Gaussian beamlet that in turn travels as a ray through the system. The approach leads to analytic expressions for the axiallyvarying pulse duration, pulse-front tilt, and the longitudinal intensity profile. We find that an important contribution to the intensity localization obtained with spatial-chirp focusing arises from the evolution of the geometric phase of the beamlets.