Formation of subwavelength periodic structures on tungsten induced by ultrashort laser pulses
ABSTRACT The evolution of surface morphology of tungsten irradiated by single-beam femtosecond laser pulses is investigated. Ripplelike periodic structures have been observed. The period of these ripples does not show a simple relation to the wavelength and angle of incidence. The orientation of ripples is aligned perpendicularly to the direction of polarization for linearly polarized light. Surprisingly, we find that the alignment of the ripple structure turned left or right by 45 degrees with respect to the incident plane when using right and left circularly polarized light, respectively. The period of the ripple can be controlled by the pulse energy, the number of pulses, and the incident angle. We find a clear threshold for the formation as a function of pulse energy and number of pulses. The mechanism for the ripple formation is discussed, as well as potential applications in large-area structuring of metals.
SourceAvailable from: K. M. Tanvir Ahmmed[Show abstract] [Hide abstract]
ABSTRACT: Femtosecond laser micromachining has emerged in recent years as a new technique for micro/nano structure fabrication because of its applicability to virtually all kinds of materials in an easy one-step process that is scalable. In the past, much research on femtosecond laser micromachining was carried out to understand the complex ablation mechanism, whereas recent works are mostly concerned with the fabrication of surface structures because of their numerous possible applications. The state-of-the-art knowledge on the fabrication of these structures on metals with direct femtosecond laser micromachining is reviewed in this article. The effect of various parameters, such as fluence, number of pulses, laser beam polarization, wavelength, incident angle, scan velocity, number of scans, and environment, on the formation of different structures is discussed in detail wherever possible. Furthermore, a guideline for surface structures optimization is provided. The authors’ experimental work on laser-inscribed regular pattern fabrication is presented to give a complete picture of micromachining processes. Finally, possible applications of laser-machined surface structures in different fields are briefly reviewed.Micromachines 11/2014; 5(4):1219-1253. DOI:10.3390/mi5041219 · 1.29 Impact Factor
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ABSTRACT: In this paper, precise P3 scribing of thin-film solar cells (AZO/CIGS/Mo/Glass) via a picosecond laser is investigated. A parametric study is carried out for P3 scribing to study the effects of laser fluence and overlap ratio on ablation depth and slot quality, supported by the numerical prediction using a two-temperature model. The optimum scribing conditions are determined, and the potential processing speed is increased. Laser induced periodic surface structures are also presented after the scribing process, which can potentially enhance the absorption of the cell surface and consequently increase the cell efficiency.06/2014; 2(3):031007. DOI:10.1115/1.4027733
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ABSTRACT: Formation of self-induced gratings on a metal surface scanned by a focused femtosecond laser beam has been investigated. It is experimentally shown that application of femtosecond IR radiation allows one to form more ordered self-induced gratings as compared with the gratings formed by visible light. The dependence of the tilt of grating lines with respect to the beam polarisation direction on the distance between tracks and the beam motion direction in adjacent tracks is analysed. Formation of two-dimensional periodic gratings during double laser beam passage along the same trajectory but with a small difference in the beam polarisation directions has been found for the first time.Quantum Electronics 04/2014; 44(4):330. DOI:10.1070/QE2014v044n04ABEH015376 · 0.89 Impact Factor