Tag Archives: femtosecond laser pulses

Real-Time Control of Polarization in High-Aspect-Ratio Ultra-Short-Pulse Laser Micro-Machining

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By: O. J. Allegre, W. Perrie, K. Bauchert, G. Dearden, K. G. Watkins

Laser Group, School of Engineering, University of Liverpool, UK
Boulder Nonlinear Systems, Inc., Colorado

The past decade has seen the development of ultra-short pulse lasers, with processes based on femtosecond and picosecond pulse durations becoming increasingly widespread. Thanks to the ultra-short timescale on which laser energy is coupled to the material, high precision machining of metals has been achieved with very little thermal damage. Industrial applications include the very precise drilling of holes for fuel-injection nozzles in the automotive industry. Polarization plays a particularly important role in drilling high-aspect-ratio (depth/diameter) microscopic holes in metal. Drilling with a linear polarized laser beam produces distorted hole profiles due to the anisotropic reflectivity of linear polarization. This paper describes the use of a liquid-crystal polarization rotator developed by Boulder Nonlinear Systems, Inc. to improve drilling quality by removing the distortions associated with static linear polarization. This flexible device allows rapid switching of the linear polarization of a laser beam between two orthogonal directions during micro-drilling. As a proof of principle, helical drilling tests were performed on stainless steel, using a 775 nm, 200 femtosecond pulse laser.

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Texturing structures of Ti films by multiple femtosecond laser pulses

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By: Yongguang Huang

Femtosecond laser texturing has proved to be a particularly powerful method for creating a wide variety of surface structures on the metal films, such as a hollow microbump-nanojet sturcture and disk-column-nanodroplet structure on the gold films. The process of femtosecond laser texturing does not rely on material removal, but on hydrodynamic flow produced by inhomogeneous heating and film deformation. Femtosecond laser texturing the metal films demonstrates different behaviors depending on films property such as electron-phone coupling, electron thermal diffusion parameters and film thickness. In our work, we concentrated on the surface structures of the Ti films by cumulative femtosecond pulses texturing. With increasing laser average power, the pits structure, the bump structure and the crater structure were induced in order by cumulative pulses with the pulse energy of 0.2nJ/pulse to 2nJ/pulse from a femtosecond oscillator, as shown in Fig.1-2. It is worth noting that for forming the pits structure and the bump structure, the temperature of the Ti film is below than its melting point. And what force causes the film ablation and swelling? More detailed results and discussion will be presented at the conference.

Fig.1 Three-dimensional topography image by a non-contact three dimension surface profiler. The serial numbers a1,a2 to p correspond to the surface structure in the top. Their corresponding laser parameters and corresponding morphology curves are shown in Fig.2.

Fig.2 Left: Surface profiles of the surface structure of Ti films after laser irradiation 0.1s which were measured by a three dimension surface profiler. The correspond average power used are (a) 18mW, (b) 22mW, (c) 27mW (d) 32mW, (e) 36mW, ( f) 40mW, (g) 45mW, (h) 50mW, (i) 60mW, (j) 70mW, (k) 80 mW, (l) 90 mW, (m) 100mW, (n) 110mW, (o) 120mW, (p) 130mW.  The distance between the ticks on the ordinate axis corresponds to 100nm. Right: Atomic force microscope image of the crater structure (I), the bump structure (II) and the pits structure (III).

The above brief overview was extracted from its original abstract and paper presented at The International Congress on Applications of Lasers & Electro-Optics (ICALEO) in Orlando, FL. To order a copy of the complete proceedings from this conference click here

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