Efficient and high-throughput ablation of platinum using high-repetition rate radially and azimuthally polarized sub-picosecond laser pulses.

A highly productive ablation process of 100 nm thick platinum films with a processed area rate of up to 378 cm2/min is presented using radially and azimuthally polarized laser beams. This was achieved by developing a laser amplifier generating 757 fs long laser pulses at a maximum average power of 390 W and a repetition rate of 10.6 MHz with adjustable polarization states, i.e., linear, radial, and azimuthal polarization on the work piece. The pulse train emitted from the laser was synchronized to a custom-designed polygon scanner and directed into an application machine.

The Impact of Ultrashort Pulse Laser Structuring of Metals on In-Vitro Cell Adhesion of Keratinocytes.

Besides the need for biomaterial surface modification to improve cellular attachment, laser-structuring is favorable for designing a new surface topography for external bone fixator pins or implants. The principle of this study was to observe how bioinspired (deer antler) laser-induced nano-microstructures influenced the adhesion and growth of skin cells. The goal was to create pins that allow the skin to attach to the biomaterial surface in a bacteria-proof manner. Therefore, typical fixator metals, steel, and titanium alloy were structured using ultrashort laser pulses, which resulted in periodical nano- and microstructures. Surface characteristics were investigated using a laser scanning microscope and static water contact angle measurements. In vitro studies with human HaCaT keratinocytes focused on cell adhesion, morphology, actin formation, and growth within 7 days. The study showed that surface functionalization influenced cell attachment, spreading, and proliferation. Micro-dimple clusters on polished bulk metals (DC20) will not hinder viability. Still, they will not promote the initial adhesion and spreading of HaCaTs. In contrast, additional nanostructuring with laser-induced periodic surface structures (LIPSS) promotes cell behavior. DC20 + LIPSS induced enhanced cell attachment with well-spread cell morphology. Thus, the bioinspired structures exhibited a benefit in initial cell adhesion. Laser surface functionalization opens up new possibilities for structuring, and is relevant to developing bioactive implants in regenerative medicine.

Thermal and laser properties of Yb:LuAG for kW thin disk lasers.

Thin disk laser experiments with Yb:LuAG (Yb:Lu(3)Al(5)O(12)) were performed leading to 5 kW of output power and an optical-to-optical efficiency exceeding 60%. Comparative analyses of the laser relevant parameters of Yb:LuAG and Yb:YAG were carried out. While the spectroscopic properties were found to be nearly identical, investigations of the thermal conductivities revealed a 20% higher value for Yb:LuAG at Yb(3+)-doping concentrations of about 10%. Due to the superior thermal conductivity with respect to Yb:YAG, Yb:LuAG offers thus the potential of improved performance in high power thin disk laser applications.

Diode-pumped mode-locked Yb:LuScO(3) single crystal laser with 74 fs pulse duration.

The mode locking of the mixed sesquioxide single crystal Yb:LuScO(3) is demonstrated. This crystal is locally disordered and has the broadest emission spectrum of all sesquioxides known so far. Pulse durations as short as 111 and 74 fs were obtained using the semiconductor saturable absorber mirror and Kerr-lens mode locking, respectively. The latter regime was reached using a two-section distributed Bragg-reflector tapered diode laser as a pump source.

Femtosecond thin-disk laser with 141 W of average power.

We present a semiconductor saturable absorber mirror mode-locked thin disk laser based on Yb:Lu(2)O(3) with an average power of 141 W and an optical-to-optical efficiency of more than 40%. The ideal soliton pulses have an FWHM duration of 738 fs, an energy of 2.4 microJ, and a corresponding peak power of 2.8 MW. The repetition rate was 60 MHz and the beam was close to the diffraction limit with a measured M(2) below 1.2.

Study of the tribological properties of surface structures using ultrashort laser pulses to reduce wear in endoprosthetics.

BACKGROUND: Loosening of prostheses and functional disorders represent a far-reaching problem in the clinic, and the long-term outcomes are essentially determined by wear. Despite all advances, up to 10% of prostheses still fail after 10 years. In particular, more active patients show increased revision rates. METHODS: The objective of this thesis is to examine whether the applied microstructures of the articulating surfaces can lead to a reduction in abrasion. Three different structural geometries (dimples, offset lines, grid lines) were defined. In an experimental test setup according to DIN ISO 6474 (Deutsches Institut für Normung, International Organization for Standardization), a tribological test of metal and ceramic pairings was performed using two-dimensional ring-on-disc (RoD) tests. RESULTS: In both material groups, the structuring had a positive effect on the wear behaviour. In the ceramic group, an abrasion reduction of 22.6% was achieved. However, it is important to take into account the limited informative value due to the hardness of the material. Two of the three Cobalt-Chrome-Molybdenum (CoCrMo) structure geometries (grids, offset lines) also showed a significant reduction in abrasion compared to the reference group, with a maximum wear reduction of 55.5%. CONCLUSION: By reducing abrasion, surface structuring could be used to extend the life of prostheses and minimise the number of revisions.

227-fs pulses from a mode-locked Yb:LuScO3 thin disk laser.

We report on the first mode-locked thin disk laser based on Yb:LuScO(3). This new mixed gain material combines the emission peaks of two sesquioxides, leading to a gain bandwidth of more than 20 nm. We achieve 7.2 W average output power in 227-fs pulses, which is shorter than for any previous ultrafast thin disk laser. The output power was limited by a growth defect near the center of the thin disk.

Broadly tunable high-power Yb:Lu(2)O(3) thin disk laser with 80% slope efficiency.

We report on efficient laser operation of high quality crystalline Yb(3+):Lu(2)O(3) in thin disk configuration. Using doping concentrations between 1 at.% to 3 at.% and disk thicknesses between 0.08mm and 0.45mm the optimum crystal parameters have been determined. Pumped at 976 nm the laser operates at 1034 nm and 1080 nm. With a 0.25mm thick 3 at.% Yb:Lu(2)O(3) disk 32.6W of output power at 45.3W incident pump power with a slope efficiency of 80% and a resulting optical-to-optical efficiency of 72% have been realized. These are the highest values in terms of slope efficiency as well as optical-to-optical efficiency for an Yb-doped thin disk laser reported so far. Using an 1mm birefringent filter continuous tuning from 987 nm to 1127 nm with more than 10Wof output power over a tuning range of 90 nm has been achieved.

Ultrashort pulse Yb:LaSc(3)(BO(3))(4) mode-locked oscillator.

Passive mode-locked laser operation based on an Yb-doped lanthanum scandium borate crystal is demonstrated. Pulse durations as short as 58 fs and 67 fs were achieved applying a Ti:sapphire- and a diode-laser pump source, respectively. The average output powers were 73 mW and 39 mW at a repetition rate of 90 MHz. The laser was broadly tunable from 1028 to 1057 nm in the sub-200 fs pulse regime.

Model for the calculation of radiation trapping and description of the pinhole method.

Radiation trapping is a well-known process that results in the lengthening of observed fluorescence lifetimes in laser materials with significant overlap in their emission and absorption spectra. The pinhole method is a measurement technique that allows the intrinsic fluorescence lifetime of an excited state to be determined in a nondestructive manner. A theoretical description of this method is proposed. A model is developed that identifies the lifetime extrapolated to a zero radius pinhole as the intrinsic fluorescence lifetime. The application of this method to bulk materials and thin discs is discussed.