Nanochannel structures with a feature size deeply under the diffraction limit and a high aspect ratio hold huge biomedical significance, which is especially challenging to be realized on hard and brittle materials, such as silica, diamond, and sapphire. By simultaneously depositing the pulse energy on the surface and inside the sample, nanochannels with the smallest feature size of 18 nm (∼1 / 30λ) and more than 200 aspect ratios are achieved inside silica, the mechanism of which can be concluded as the surface assisting material ejection effect. Both the experimental and theoretical results prove that the coaction of the superficial “hot domain” and internal hot domain dominates the generation of the nanochannels, which gives new insights into the laser-material interacting mechanisms and potentially promotes the corresponding application fields.
We theoretically investigated the ultrafast thermal excitation behaviors on Au films surface irradiated by polarization-shaped femtosecond laser. The spatio-temporal dynamics of temperature evolution in Au film with polarization-shaped femtosecond laser excitation are obtained based on Finite Element Method (FEM). It is revealed that the phonon temperature fields can be flexibly adjusted by optimizing the polarization state combinations of polarization-shaped double femtosecond laser pulses. The results are attributed to pulse synthetic effect, which closely depends on the polarization state combinations of double femtosecond laser pulses. The study provides the basic for understanding of the thermal excitation dynamics for optimizing laser micro and nano-fabrications via tailoring the polarization state of temporally shaped femtosecond laser.
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