TY - JOUR A1 - Beke, S. A1 - Kobayashi, T. A1 - Sugioka, K. A1 - Midorikawa, K. A1 - Bonse, Jörn T1 - Time-of-flight mass spectroscopy of femtosecond and nanosecond laser ablated TeO2 crystals N2 - Single-pulse femtosecond (fs) (pulse duration ~200 fs, wavelength 398 nm) and nanosecond (ns) (pulse duration 4 ns, wavelength 355 nm) laser ablation have been applied in combination with time-of-flight mass spectrometer (TOFMS) to analyze the elemental composition of the plasma plume of single-crystalline telluria (c-TeO2, grown by the balance controlled Czochralski growth method). Due to the three-order difference of the peak intensities of the ns and fs-laser pulses, significant differences were observed regarding the laser-induced species in the plasma plume. Positive singly, doubly and triply charged Te ions (Te+, Te2+, Te3+) in the form of their isotopes were observed in case of both irradiations. In case of the ns-laser ablation the TeO+ formation was negligible compared to the fs case and there was no Te trimer (Te3+) formation observed. It was found that the amplitude of Te ion signals strongly depended on the applied laser pulse energy. Singly charged oxygen ions (O+) are always present as a byproduct in both kinds of laser ablation. KW - Time-of-flight mass spectroscopy KW - Tellurium dioxide crystals KW - second laser KW - Nanosecond laser KW - Ablation PY - 2011 U6 - https://doi.org/10.1016/j.ijms.2010.08.022 SN - 0168-1176 SN - 0020-7381 SN - 1387-3806 SN - 1873-2798 VL - 299 IS - 1 SP - 5 EP - 8 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-22490 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mermillod-Blondin, A. A1 - Mauclair, C. A1 - Bonse, Jörn A1 - Stoian, R. A1 - Audouard, E. A1 - Rosenfeld, A. A1 - Hertel, I.V. T1 - Time-resolved imaging of laser-induced refractive index changes in transparent media N2 - We describe a method to visualize ultrafast laser-induced refractive index changes in transparent materials with a 310 fs impulse response and a submicrometer spatial resolution. The temporal profile of the laser excitation sequence can be arbitrarily set on the subpicosecond and picosecond time scales with a pulse shaping unit, allowing for complex laser excitation. Time-resolved phase contrast microscopy reveals the real part of the refractive index change and complementary time-resolved optical transmission microscopy measurements give access to the imaginary part of the refractive index in the irradiated region. A femtosecond laser source probes the complex refractive index changes from the excitation time up to 1 ns, and a frequency-doubled Nd:YAG laser emitting 1 ns duration pulses is employed for collecting data at longer time delays, when the evolution is slow. We demonstrate the performance of our setup by studying the energy relaxation in a fused silica sample after irradiation with a double pulse sequence. The excitation pulses are separated by 3 ps. Our results show two dimensional refractive index maps at different times from 200 fs to 100 µs after the laser excitation. On the subpicosecond time scale we have access to the spatial characteristics of the energy deposition into the sample. At longer times (800 ps), time-resolved phase contrast microscopy shows the appearance of a strong compression wave emitted from the excited region. On the microsecond time scale, we observe energy transfer outside the irradiated region. KW - High-speed optical techniques KW - Light transmission KW - Neodymium KW - Optical harmonic generation KW - Optical pulse shaping KW - Refractive index KW - Self-induced transparency KW - Silicon compounds KW - Solid lasers PY - 2011 UR - http://rsi.aip.org/resource/1/rsinak/v82/i3/p033703_s1 U6 - https://doi.org/10.1063/1.3527937 SN - 0034-6748 SN - 1089-7623 VL - 82 IS - 3 SP - 033703-1 EP - 033703-8 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-23308 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Rosenfeld, A. A1 - Krüger, Jörg T1 - Implications of transient changes of optical and surface properties of solids during femtosecond laser pulse irradiation to the formation of laser-induced periodic surface structures N2 - The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of silicon wafer surfaces by linearly polarized Ti:sapphire femtosecond laser pulses (pulse duration 130 fs, central wavelength 800 nm) is studied experimentally and theoretically. In the experiments, so-called low-spatial frequency LIPSS (LSFL) were found with periods smaller than the laser wavelength and an orientation perpendicular to the polarization. The experimental results are analyzed by means of a new theoretical approach, which combines the widely accepted LIPSS theory of Sipe et al. with a Drude model, in order to account for transient (intra-pulse) changes of the optical properties of the irradiated materials. It is found that the LSFL formation is caused by the excitation of surface plasmon polaritons, SPPs, once the initially semiconducting material turns to a metallic state upon formation of a dense free-electron-plasma in the material and the subsequent interference between its electrical field with that of the incident laser beam resulting in a spatially modulated energy deposition at the surface. Moreover, the influence of the laser-excited carrier density and the role of the feedback upon the multi-pulse irradiation and its relation to the excitation of SPP in a grating-like surface structure is discussed. KW - Femtosecond laser ablation KW - Laser-induced periodic surface structures KW - (LIPSS) KW - Optical properties KW - Surface plasmon polaritons KW - Semiconductors KW - Silicon PY - 2011 U6 - https://doi.org/10.1016/j.apsusc.2010.11.059 SN - 0169-4332 SN - 1873-5584 VL - 257 IS - 12 SP - 5420 EP - 5423 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-23309 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rohloff, M. A1 - Das, S.K. A1 - Höhm, S. A1 - Grunwald, R. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Formation of laser-induced periodic surface structures on fused silica upon multiple cross-polarized double-femtosecond-laser-pulse irradiation sequences N2 - The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences consisting of five Ti:sapphire femtosecond (fs) laser pulse pairs (150 fs, 800 nm) is studied experimentally. A Michelson interferometer is used to generate near-equal-energy double-pulse sequences with a temporal pulse delay from -20 to +20 ps between the cross-polarized individual fs-laser pulses (~0.2 ps resolution). The results of multiple double-pulse irradiation sequences are characterized by means of Scanning Electron and Scanning Force Microscopy. Specifically in the sub-ps delay domain striking differences in the surface morphologies can be observed, indicating the importance of the laser-induced free-electron plasma in the conduction band of the solids for the formation of LIPSS. KW - Atomic force microscopy KW - Conduction bands KW - High-speed optical techniques KW - Laser beam effects KW - Scanning electron microscopy KW - Silicon compounds KW - Surface morphology PY - 2011 U6 - https://doi.org/10.1063/1.3605513 SN - 0021-8979 SN - 1089-7550 VL - 110 IS - 1 SP - 014910-1 - 014910-4 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-24049 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stegemann, B. A1 - Richter, M. A1 - Schultz, C. A1 - Pahl, H.-U. A1 - Endert, H. A1 - Bonse, Jörn A1 - Rau, B. A1 - Quaschning, V. A1 - Fink, F. T1 - One wavelength fits all N2 - Structuring of Thin-film Solar Cells with a Single Laser Wavelength Structuring of a PV module into a number of cells is necessary to lower the current and to increase the voltage, and is typically accomplished with nanosecond laser pulses of different wavelengths. Duetothe many available laser sources, complex and expensive scribing Setups are necessary. To overcome this a concept for laser structuring of thin-film PV modules using a single wavelength allows prediction ofthe ablation behaviourfor a given laser pulse energy. KW - Thin-film solar cells KW - Nanosecond laser ablation KW - 532 nm wavelength KW - Laser scribing KW - Damage threshold PY - 2011 SN - 1869-8913 VL - 2 IS - 6 SP - 46 EP - 48 PB - Hüthig CY - Heidelberg AN - OPUS4-24158 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -