Browsing by Subject "Laser-material processing"
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Item Open Access The universality of self-organisation: a path to an atom printer?(Springer Science and Business Media Deutschland GmbH, 2023-04-07) Ilday, S.; Ilday, F. ÖmerMore than 30 years ago, Donald Eigler and Erhard Schweizer spelt the letters IBM by positioning 35 individual xenon atoms at 4 K temperature using a scanning tunnelling microscope. The arrangement took approximately 22 h. This was an outstanding demonstration of control over individual atoms. Since then, 3D printers developed into a near-ubiquitous technology. Nevertheless, with typical resolutions in the micrometres, they are far from the atomic scale of control that the IBM demonstration seemed to herald. Even the highest resolution achieved with ultrafast lasers driving two-photon polymerisation barely reaches 100 nm, three orders of magnitude distant from the atomic scale. Here, we adopt a long-term view when we ask about the possibility of a 3D atom printer, which can build an arbitrarily shaped object of macroscopic dimensions with control over its atomic structure at room temperature and within a reasonable amount of time. After discussing the state-of-the-art technology based on direct laser writing, we identify three fundamental challenges to overcome. The first is the fat fingers problem, which refers to laser wavelengths being much larger than the size of the atoms. The second one is complexity explosion, namely, the number of processing step scales with the inverse cube of the resolution, leading to prohibitively long processing times. The third challenge is the increasing strength of random fluctuations as the size of the smallest volume element to be printed approaches the atomic scale. This requires control over the fluctuations, which we call mischief of fluctuations. Although direct-writing techniques offer sufficient resolution, speed, and excellent flexibility for the mesoscopic scale, each of the three fundamental problems above appears enough to render the atomic scale unreachable. Each of these arise out of a need to control each atom individually and with precision. In contrast, the three challenges of direct writing are not fundamental limitations to self-organisation, this chapter proposes a potential path to a 3D atom printer, where laser-driven self-organisation can complement direct-writing techniques by bridging the atomic and mesoscopic scales.Item Open Access Ultrafast laser-material processing in the ablation-cooled regime(Bilkent University, 2020-07) Arony, Nazifa TasnimRecently, a new regime of material ablation using ultrashort laser pulses has been demonstrated. In this regime, thousands of pulses collectively interact and ablate the material, if the time between subsequent pulses is much less than the time for heat diffusion. . Ablation results in the violent ejection from the surface of the material exceeding a critical temperature. As a result, there moval of heat through ablation becomes dominant over thermal diffusion, and this process is called the ablation-cooled laser-material removal. It was shown that ablation efficiency could be significantly increased while simultaneously reducing the pulse energy by several ordersof magnitude if the pulses’ repetition rate is increased to several GHz. This thesis explores the scaling of the repetition rate upto 100 GHz. Our results indicate that with increasing repetition rate, the efficiency gains of this regime can be maintained along, while further decreasing the pulse energy requirements by 1-2 orders of magnitude. Dramatically, we find that few-nanojoule pulses at 50-100 GHz ablate more efficiently than tens of microjoule pulses at sub-MHz repetition rates. We present systematic results on crystalline silicon and exploratory studies on several technical materials of industrial relevance. The presently reported pulse energies could easily be obtained directly from mode-locked lasers, potentially eliminating the need for costly and complicated laser amplifiers. Therefore, our results are suggestive of a radical transformation of the laser technology required for ultrafast ablation.