244 research outputs found
High-intracavity-power thin-disk laser for the alignment of molecules
We propose a novel approach for strong alignment of gas-phase molecules for
experiments at arbitrary repetition rates. A high-intracavity-power
continuous-wave laser will provide the necessary ac electric field of
- . We demonstrate thin-disk lasers
based on Yb:YAG and Yb:LuO in a linear high-finesse resonator providing
intracavity power levels in excess of 100~kW at pump power levels on the order
of 50~W. The multi-longitudinal-mode operation of this laser avoids
spatial-hole burning even in a linear standing-wave resonator. The system will
be scaled up as in-vacuum system to allow for the generation of fields of
. This system will be directly applicable for
experiments at modern X-ray light sources, such as synchrotrons or
free-electron lasers, which operate at various very high repetition rates. This
would allow to record molecular movies through temporally resolved diffractive
imaging of fixed-in-space molecules, as well as the spectroscopic investigation
of combined X-ray-NIR strong-field effects of atomic and molecular systems
Kerr-lens mode-locked Tm^3+:Sc_2O_3 single-crystal laser in-band pumped by an Er:Yb fiber MOPA at 1611 nm
We demonstrate a Kerr-lens mode-locked Tm3+:Sc2O3single-crystal laser in-band pumped by an Er3+:Yb3+ fiber master oscillator power amplifier at 1611 nm. Pulses as short as 166 fs with an average output power of 440 mW are obtained. The spectral bandwidth and center wavelength are 29.3 and 2124 nm, respectively. At a longer pulse duration of 298 fs, we obtain 1 W of average output power. The repetition rate is 95 MHz, and the conversion efficiency against the absorbed pump power is as high as 47%. To the best of our knowledge, this is the first Kerr-lens mode-locked Tm3+-doped solid state laser
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Sub-6 optical-cycle Kerr-lens mode-locked Tm:Lu2O3 and Tm:Sc2O3 combined gain media laser at 2.1 μm
We present a combined gain media Kerr-lens mode-locked laser based on a Tm:Lu2O3 ceramic and a Tm:Sc2O3 single crystal. Pulses as short as 41 fs, corresponding to less than 6 optical cycles, were obtained with an average output power of 42 mW at a wavelength of 2.1 μm and a repetition rate of 93.3 MHz. Furthermore, a maximum average power of 316 mW with a pulse duration of 73 fs was achieved
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Laser cooling in Yb:KY3F10: a comparison with Yb:YLF
Laser cooling by anti-Stokes fluorescence is a technology to realize all-solid-state optical cryocoolers. We grew Yb3+-doped KY3F10 (Yb:KYF) crystals as novel laser cooling media and compare their cooling performance to Yb3+-doped LiYF4 (Yb:YLF) crystals also grown in our institute. We present temperature-dependent absorption and emission cross sections as well as the fluorescence lifetime of Yb:KYF, and calculate its material figure-of-merit for laser cooling. Yb:KYF exhibits a higher figure-of-merit than Yb:YLF at temperatures below 200 K. This is because, in contrast to Yb:YLF, the excitation transition from the second-highest Stark level of the ground state is best-suited for cryogenic cooling in Yb:KYF. Thus, it has the potential to achieve unprecedentedly low temperatures below the boiling point of liquid nitrogen. In this work, we observe the first laser cooling of Yb:KYF, and obtain a background absorption coefficient of ∼10−4 cm−1, which is among the lowest ever reported for Yb3+-doped fluoride crystals. A simple model calculation predicts that our Yb:KYF and Yb:YLF crystals can potentially be cooled down to ≈100 K in a high-power cooling setup. Our Yb:KYF crystals still leave room for further improvement through the optimization of the growth process and the use of purer raw materials
Schalentragwerke mit funktionaler Gradierung
Betone für schlanke Schalentragwerke weisen zur Sicherstellung ausreichender Zugfestigkeiten oft einen hohen Stahlfasergehalt auf. Dies ist mit hohen ökologischen und monetären Kosten verbunden. Das Ziel war es daher, die Voraussetzungen für die Herstellung effizienter Schalentragwerke aus funktional fasergradierten Betonfertigteilen zu schaffen.Concrete for slender load-bearing shell structures often has a high steel fibre content to ensure sufficient tensile strength. This is associated with high ecological and financial costs. Thus, the aim of this project was to create the prerequisites for the production of efficient shell structures made of functional fibre-graded precast concrete elements
Yellow laser performance of Dy in co-doped Dy,Tb:LiLuF
We present laser results obtained from a Dy-Tb co-doped
LiLuF crystal, pumped by a blue emitting InGaN laser diode, aiming for
the generation of a compact 578 nm source. We exploit the yellow Dy
transition F H to generate
yellow laser emission. The lifetime of the lower laser level is quenched via
energy transfer to co-doped Tb ions in the fluoride crystal. We report
the growth technique, spectroscopic study and room temperature continuous wave
(cw) laser results in a hemispherical cavity at 574 nm and with a highly
reflective output coupler at 578 nm. A yellow laser at 578 nm is very relevant
for metrological applications, in particular for pumping of the forbidden
SP Ytterbium clock transition, which is
recommended as a secondary representation of the second in the international
system (SI) of units. This paper was published in Optics Letters and is made
available as an electronic reprint with the permission of OSA. The paper can be
found at the following URL on the OSA website:
http://dx.doi.org/10.1364/OL.39.006628. Systematic or multiple reproduction or
distribution to multiple locations via electronic or other means is prohibited
and is subject to penalties under law.Comment: 8 pages, 5 figure
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Diode-Pumped Laser Operation of Tb3+:LiLuF4 in the Green and Yellow Spectral Range
Here, a diode-pumped laser based on trivalent terbium (Tb3+) as the active ion is reported. Optical pumping of a Tb3+-doped lithium-lutetium-fluoride (LiLuF4) crystal with up to 200 mW from a diode laser emitting at a wavelength of 488.2 nm enables continuous-wave lasing directly in the green and in the yellow. At an emission wavelength of 542 nm, the laser reaches an output power of up to 43.8 mW with a high slope efficiency of 52% with respect to the absorbed pump power. The yellow laser at 587 nm exhibits a slope efficiency of 22% and the output power of 13.8 mW is only limited by the available pump power. Laser thresholds as low as 14 and 27 mW of absorbed pump power are observed for the green and yellow, respectively. The investigations toward further optimization of the laser performance reveal that highly Tb3+-doped materials are suitable for compact, efficient, and affordable diode-pumped solid-state lasers with direct emission in the visible spectral range. These results are of high relevance, as in particular for the yellow spectral range such systems are currently not available. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Effect of Pre-Shear on Agglomeration and Rheological Parameters of Cement Paste
Cementitious pastes are multiphase suspensions that are rheologically characterized by viscosity and yield stress. They tend to flocculate during rest due to attractive interparticle forces, and desagglomerate when shear is induced. The shear history, e.g., mixing energy and time, determines the apparent state of flocculation and accordingly the particle size distribution of the cement in the suspension, which itself affects suspension's plastic viscosity and yield stress. Thus, it is crucial to understand the effect of the mixing procedure of cementitious suspensions before starting rheological measurements. However, the measurement of the in-situ particle agglomeration status is difficult, due to rapidly changing particle network structuration. The focused beam reflectance measurement (FBRM) technique offers an opportunity for the in-situ investigation of the chord length distribution. This enables to detect the state of flocculation of the particles during shear. Cementitious pastes differing in their solid fraction and superplasticizer content were analyzed after various pre-shear histories, i.e., mixing times. Yield stress and viscosity were measured in a parallel-plate-rheometer and related to in-situ measurements of the chord length distribution with the FBRM-probe to characterize the agglomeration status. With increasing mixing time agglomerates were increasingly broken up in dependence of pre-shear: After 300 s of pre-shear the agglomerate sizes decreased by 10 µm to 15 µm compared to a 30 s pre-shear. At the same time dynamic yield stress and viscosity decreased up to 30% until a state of equilibrium was almost reached. The investigations show a correlation between mean chord length and the corresponding rheological parameters affected by the duration of pre-shear
A diffuse interface model for quasi-incompressible flows: Sharp interface limits and numerics
In this contribution, we investigate a diffuse interface model for quasi-incompressible flows. We determine corresponding sharp interface limits of two different scalings. The sharp interface limit is deduced by matched asymptotic expansions of the fields in powers of the interface. In particular, we study solutions of the derived system of inner equations and discuss the results within the general setting of jump conditions for sharp interface models. Furthermore, we treat, as a subproblem, the convective Cahn-Hilliard equation numerically by a Local Discontinuous Galerkin scheme
Distinct Kinin-Induced Functions Are Altered in Circulating Cells of Young Type 1 Diabetic Patients
We aimed to understand early alterations in kinin-mediated migration of circulating angio-supportive cells and dysfunction of kinin-sensitive cells in type-1 diabetic (T1D) patients before the onset of cardiovascular disease.Total mononuclear cells (MNC) were isolated from peripheral blood of 28 T1D patients free from cardiovascular complications except mild background retinopathy (age: 34.8+/-1.6 years, HbA(1C): 7.9+/-0.2%) and 28 age- and sex-matched non-diabetic controls (H). We tested expression of kinin receptors by flow cytometry and migratory capacity of circulating monocytes and progenitor cells towards bradykinin (BK) in transwell migration assays. MNC migrating towards BK (BK(mig)) were assessed for capacity to support endothelial cell function in a matrigel assay, as well as generation of nitric oxide (NO) and superoxide (O(2) (-)*) by using the fluorescent probes diaminofluorescein and dihydroethidium.CD14(hi)CD16(neg), CD14(hi)CD16(pos) and CD14(lo)CD16(pos) monocytes and circulating CD34(pos) progenitor cells did not differ between T1D and H subjects in their kinin receptor expression and migration towards BK. T1D BK(mig) failed to generate NO upon BK stimulation and supported endothelial cell network formation less efficiently than H BK(mig). In contrast, O(2) (-)* production was similar between groups. High glucose disturbed BK-induced NO generation by MNC-derived cultured angiogenic cells.Our data point out alterations in kinin-mediated functions of circulating MNC from T1D patients, occurring before manifest macrovascular damage or progressed microvascular disease. Functional defects of MNC recruited to the vessel wall might compromise endothelial maintenance, initially without actively promoting endothelial damage, but rather by lacking supportive contribution to endothelial regeneration and healing
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