Modifications and Color Markings in Glasses by UV Laser Radiation
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Modifications and Color Markings in Glasses by UV Laser Radiation M. Talkenberg1, G. Falkenberg2, M. Krauss3 and E. W. Kreutz1, 4 1
Lehrstuhl für Lasertechnik, Rheinisch-Westfälische Technische Hochschule Aachen, Aachen, Germany Hamburger Synchrotronstrahlungslabor, Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany 3 Fraunhofer-Institut Silicatforschung, Würzburg, Germany 4 Fraunhofer-Institut für Lasertechnik, Aachen, Germany 2
ABSTRACT Rare earth-, transition metal- and metal doped soda lime-, BK7- and photosensitive lithium aluminosilicate glass are irradiated by pulsed UV laser radiation (wavelength λL = 355nm, pulse length tp = 10 to 80 ns) as a function of repetition rate, pulse energy and overlap between successive pulses. The solid state laser radiation is focused into the volume to fluences below the removal-threshold. Depending on the chemical composition, the laser parameters, and the processing variables the laser radiation is absorbed by optically- and photochemically active polyvalent ions with conversion of the optical energy into fluorescence stimulation and ionization as well as color center formation resulting in modifications and/or color markings in the VIS. The absorption and concentration changes of the polyvalent ions are probed by optical spectroscopy and transient absorption spectroscopy. The photochemical and -physical processes such as oxidation and reduction of polyvalent ions and/or color center generation underlying the modifications and color markings are discussed.
INTRODUCTION The interaction of laser radiation with dielectric materials has been investigated since the beginning of laser material processing. Puzzling effects of optical breakdown, avalanche ionization, multiphoton ionization or laser-induced absorption center formation especially in glasses claim for research until now. Glass is a material of major technological interest for design, production, and application, for example, of microsystems for numerous applications in chemistry, pharmacy, medicine, and biotechnology (e. g. micromixers and microreaction chambers) as well as in integrated optics (e. g. waveguides, active and passive optical devices as well as Bragg-gratings). Selected optical glasses combine high optical transmission in the UV to IR with low material production costs. However, the processing of undoped and doped glasses using laser radiation is limited by laser radiation induced modifications on the surface and in the volume such as the generation of absorption centers or the formation of cracks, for example. The focus is on the modification of rare earth-, transition metal-, and metal doped soda lime-, and photosensitive lithium aluminosilicate glass [1, 2, 3] after irradiation with UV-laser radiation at the wavelength 355 nm and fluences below the material removal threshold with respect to the formation of laser radiation induced cracks on the surface and in the volume of the glass. The laser-induced modifications are investigated by optical spectroscopy, transient optical spectroscop
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