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Ultrafast laser processing has diverse scientific, industrial and medical applications. Until recently, this process has been idealized as a one-way interaction — the laser beam modifies the material, which would be the end of the story. The idea of the material modifying the laser beam, in return, and that this could open new doors appears to have been overlooked. In many cases, such two-way interactions either did not occur, or were unnoticed, if present, and actively prevented, if noticed.
Our approach is to explicitly design for and exploit such interactions, and this approach has already led to several striking advances. Here, we invoke nonlinearities in the form of positive feedback between laser beam-induced changes in the material and material change-induced effects back on the laser beam. We first showed that we could create laser-induced spatial nanostructures on various material surfaces with unprecedented uniformity (Ilday et al., Nature Photon., 2013), which we later extended to creation of self-organized 3D structures inside silicon (Ilday et al., Nature Photon., 2017). This perspective also led to the extremely efficient regime of ablation-cooled laser-material ablation (Ilday et al., Nature, 2016), self-assembly of colloidal nanoparticles (Ilday et al., Nature Commun., 2017), and intracavity optical trapping, where the trap is placed inside the cavity of a laser, giving rise to nonlinear feedback forces (arXiv:1808.07831).These demonstrations will be discussed, compared and contrasted.
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