{'fraction_non_alphanumeric': 0.016304347826086956, 'fraction_numerical': 0.005434782608695652, 'mean_word_length': 4.909090909090909, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Refractive and structural changes in silica glass induced by ultrashort laser pulses

We studied the behavior of filaments that are formed in the beam of ultrashort laser pulses via self-focusing effect. A refractive index change of 0.01 was confirmed by three independent image-analysis techniques. The waveguide structures were a few to 500 micrometers long depending on the numerical aperture (NA) of the ultrashort pulses. All the diameters were approximately two micrometers. We identified the conditions to produce one filament in one beam and produced waveguides using this single filament. By moving the focus along the optical axis, a longer straight waveguide can be produced. We also demonstrate that one can seize and translate voids formed by ultrashort laser pulses inside silica glass and can also merge two voids into one. We further present a clear evidence of a void and its surrounded region by showing scanning-electron-microscopic image of cleaved voids: we cleaved through the glass along a plane that includes the laser-ablated thin line on the surface and the voids formed inside.