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Item type:Publication, Access status: without files , 3D nano and micro structures in transparent materials by in-volume femtosecond laser processing(Laser Inst. of America, 2010-03); ; ; ; Nano as well as micro structuring in the volume of transparent materials is enabled by ultrafast laser radiation. By laser radiation with pulse durations in the fs and ps regime multi photon processes are efficiently induced resulting in a high resolution of less than 1 μm3, a very low heat input and a high writing flexibility in all three dimensions. High transparent materials such as sapphire and glasses are locally modified in the volume to change the refractive index for optical applications or to increase the corrodibility selectively for the manufacturing of micro channels and micro structured parts for the use in micro systems and medical technology. The miniaturization of products for micro optics, the medical technology and micro systems engineering requires transparent components with structure sizes in the micrometer range and accuracies of approx. 100 nm. In-volume Selective Laser-induced Etching (ISLE) is an appropriate manufacturing process for micro machining of transparent materials such as sapphire and glasses, e.g. fused silica. By focusing the laser radiation (wavelength 1040 nm, pulse duration 500 fs, repetition rate 0.1-5 MHz, pulse energy <1 μJ) in the volume the material is locally modified. By scanning the laser focus with pulse overlap inside the material, connected volumes of modified material are created. The modified volumes are subsequently removed by chemical etching in a second processing step using aqueous solution of e.g. HF or KOH. Periodical nano structures (ripples, nanoplanes) are fabricated inside transparent materials exploiting fs-laser induced nano optics with potential applications such as nano sieves for filtering, optical gratings or functionalized internal surfaces. Direct laser writing of waveguides in transparent materials by fs laser radiation is well known. Further applications include crack-free 3D micro markings in transparent materials consisting e.g. of micro-gratings, which result in a colorful experience in the observers eye due to diffraction and interference. To exploit the high manufacturing velocities possible with ultrafast lasers with repetition rates of several MHz a high speed scanning system with large numerical aperture and pre-compensation of spherical aberrations has been developed for in-volume nano and micro structuring. With this system high writing velocities (50-400 mm/s), small focus size (0.6-2.2 mm) and high precision (100-400 nm) are combined for the first time on rather large scanning fields (0.6-1.5 mm) and material depth of up to 2 mm.Publicationtype: Conference Paper14 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , High-power ultra-short pulse laser radiation: new sources as key enablers for emerging applications (plenary session keynote)(Laser Inst. of America, 2010-03); ; ; ; Ultrafast laser sources with pulse durations in the sub-picosecond regime enable a precise machining of various materials. Pulse durations shorter than the electron phonon-coupling time lead to a low thermal load or even non-thermal ablation processes. Exploiting non-linear absorption processes, the absorption becomes nearly material independent when laser pulses of several microjoule energy and high beam quality are focused on the materials surface. Low pulse energies and intensities well above the vaporization threshold and therefore an eduction of the absorbed energy within the ablation product enables a high-precision cutting, ablation and drilling of, even weakly absorbing materials, multi-component and multi-layer systems. Additional, the focusing of ultrafast laser pulses in the volume of transparent dielectrics allows a localized modification of the bulk material. Specifically, defined refractive index changes in glasses and crystals can be utilized for waveguiding and beam-forming applications. A combined approach of material modification followed by chemical etching provides the possibility to manufacture micro-channels or 3D-micro mechanical parts. The 3D-capability of the in-volume material processing originates from the non-linear absorption of light in the initially transparent material. To achieve high process efficiencies in material processing, laser sources delivering high average power are necessary. High average power is achieved either by high pulse energies and low repetition rates or high pulse repetition rates and moderate pulse energies. The optimum set of parameters is strongly depending on the process, the material and the application. In this paper, we present compact laser sources with a high flexibility in pulse energy and pulse repetition rate and an average power of several hundreds of Watt. Additional, a broad range of applications, from micro- and nanostructuring of various materials to volume processing of dielectrics will be presented.Publicationtype: Conference Paper15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Advantages of adaptive optics for laser metal deposition in comparison to conventional opticsLaser Metal Deposition with adaptive optics and zoom-optics allows variable beam diameters at a constant working distance guarantying a constant powder focus on the work piece surface. The zoom-optic presented in this paper is an alternative if a variation of the laser beam diameter for producing different track widths is needed. The extensive adjustment of a powder nozzle to the working point (Tool Center Point) is unnecessary with a fixed working distance. The variation of the laser beam diameters is generated by adjusting the lens positions. In the interaction zone the laser beam diameter can be varied from d = 0.6 mm to d = 2.4 mm. The power density distribution produced corresponds as closely as possible to a top-hat distribution which is best for Laser Metal Deposition. Two examples using this zoom-optic are presented. In a first application an increase of the productivity of a two-dimensional cladding is demonstrated by cladding an outer frame with a lower and an inner filling with a higher deposition rate. In a second application laser metal deposition of a simulated blade tip is carried out using a variation of the laser beam diameter and adaption of laser power during the cladding.Publicationtype: Conference Paper13