Abstract
An open challenge in the important field of femtosecond laser material processing is the controlled internal structuring of dielectric materials. Although the availability of high energy high repetition rate femtosecond lasers has led to many advances in this field, writing structures within transparent dielectrics at intensities exceeding 1013 W/cm2 has remained difficult as it is associated with significant nonlinear spatial distortion. This letter reports the existence of a new propagation regime for femtosecond pulses at high power that overcomes this challenge, associated with the generation of a hollow uniform and intense light tube that remains propagation invariant even at intensities associated with dense plasma formation. This regime is seeded from higher order nondiffracting Bessel beams, which carry an optical vortex charge. Numerical simulations are quantitatively confirmed by experiments where a novel experimental approach allows direct imaging of the 3D fluence distribution within transparent solids. We also analyze the transitions to other propagation regimes in near and far fields. We demonstrate how the generation of plasma in this tubular geometry can lead to applications in ultrafast laser material processing in terms of single shot index writing, and discuss how it opens important perspectives for material compression and filamentation guiding in atmosphere.
Highlights
An open challenge in the important field of femtosecond laser material processing is the controlled internal structuring of dielectric materials
The availability of high energy high repetition rate femtosecond lasers has led to many advances in this field, writing structures within transparent dielectrics at intensities exceeding 1013 W/cm[2] has remained difficult as it is associated with significant nonlinear spatial distortion
We demonstrate how the generation of plasma in this tubular geometry can lead to applications in ultrafast laser material processing in terms of single shot index writing, and discuss how it opens important perspectives for material compression and filamentation guiding in atmosphere
Summary
An open challenge in the important field of femtosecond laser material processing is the controlled internal structuring of dielectric materials. This letter reports the existence of a new propagation regime for femtosecond pulses at high power that overcomes this challenge, associated with the generation of a hollow uniform and intense light tube that remains propagation invariant even at intensities associated with dense plasma formation This regime is seeded from higher order nondiffracting Bessel beams, which carry an optical vortex charge. For the first time to our knowledge, ultra-intense light pulses are shown to be able to propagate as a ‘‘light tube’’ in dielectrics without deformation, generating a tubular plasma distribution that reaches optical breakdown densities This novel tubular geometry for delivery of energy from femtosecond pulses in a propagation-invariant way is expected to generate novel breakthroughs in femtosecond laser material processing. Experimental results have applied this propagation-invariance of zero-order femtosecond Bessel beams to single shot laser processing of nanochannels in glass with high aspect ratios from 10051 to 10005115,16
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