We investigate the average power scaling of two diode-pumped Yb-doped fiber amplifiers emitting a diffraction-limited beam. The first fiber under investigation with a core diameter of 30 µm was able ...to amplify a 10 W narrow linewidth seed laser up to 2.8 kW average output power before the onset of transverse mode instabilities (TMI). A further power scaling was achieved using a second fiber with a smaller core size (23µm), which allowed for a narrow linewidth output power of 3.5 kW limited by stimulated Brillouin scattering (SBS). We mitigated SBS using a spectral broadening mechanism, which allowed us to further increase the output power to 4.3 kW only limited by the available pump power. Up to this power level, a high slope efficiency of 90% with diffraction-limited beam quality and without any sign of TMI or stimulated Raman scattering for a spectral dynamic range of higher than -80 dB was obtained.
Although Sc doped AlN (ScAlN) has been used extensively in micro-electro-mechanical systems (MEMS) devices and more recently in optical devices, there have not been thorough studies of its intrinsic ...optical losses. Here we explore the optical losses of the Sc
Al
N waveguide system by observing racetrack resonator waveguide quality factors. Using a partial physical etch, we fabricate waveguides and extract propagation losses as low as 1.6 ± 0.3 dB/cm at wavelengths around 1550 nm, mostly dominated by intrinsic material absorption from the Sc
Al
N thin film layer. The highest quality factor of the resonators was greater than 87,000. The propagation loss value is lower than any value previously published and shows that this material can be broadly used in optical modulators without significant loss.
AvrBs3, the founding member of the Xanthomonas transcription-activator-like effectors (TALEs), is translocated into the plant cell where it localizes to the nucleus and acts as transcription factor. ...The DNA-binding domain of AvrBs3 consists of 17.5 nearly-identical 34 amino acid-repeats. Each repeat specifies binding to one base in the target DNA via amino acid residues 12 and 13 termed repeat variable diresidue (RVD). Natural target sequences of TALEs are generally preceded by a thymine (T0), which is coordinated by a tryptophan residue (W232) in a degenerated repeat upstream of the canonical repeats. To investigate the necessity of T0 and the conserved tryptophan for AvrBs3-mediated gene activation we tested TALE mutant derivatives on target sequences preceded by all possible four bases. In addition, we performed domain swaps with TalC from a rice pathogenic Xanthomonas because TalC lacks the tryptophan residue, and the TalC target sequence is preceded by cytosine. We show that T0 works best and that T0 specificity depends on the repeat number and overall RVD-composition. T0 and W232 appear to be particularly important if the RVD of the first repeat is HD ('rep1 effect'). Our findings provide novel insights into the mechanism of T0 recognition by TALE proteins and are important for TALE-based biotechnological applications.
We report on a newly designed and fabricated ytterbium-doped large mode area fiber with an extremely low NA (~0.04) and related systematic investigations on fiber parameters that crucially influence ...the mode instability threshold. The fiber is used to demonstrate a narrow linewidth, continuous wave, single mode fiber laser amplifier emitting a maximum output power of 3 kW at a wavelength of 1070 nm without reaching the mode-instability threshold. A high slope efficiency of 90 %, excellent beam quality, high temporal stability, and an ASE suppression of 70 dB could be reached with a signal linewidth of only 170 pm.
Abstract
HVAC systems are among the biggest energy consumers in buildings and therefore in the focus of optimal control research. In practice, rule-based control and PID controllers are typically ...used and implemented at the beginning of the building operation. Since this approach neither guarantees optimal or even good control, optimal control algorithms (which can be predictive and adaptive) are in the focus of research. The problem with most of the approaches is that a model of the system is often needed which comes with high engineering efforts. Further, the required computing power can quickly exceed the capacities, even in modern buildings. Therefore, in this paper we investigate the application of a state-of-the-art Reinforcement Learning (RL) algorithm, as a self-calibrating valve controller for two water-air heat exchangers of a real-world air handling unit. We choose a generic problem formulation to pre-train the algorithm with a simulation of an admixing heater and use it to control an injection heater and a throttle cooler. Our results show that after only 70 hours, the control quality significantly increases. Therefore, it seems evident that with pre-trained RL algorithms, a self-improving HVAC automation can be realized with little hardware requirements and without extensive modelling of the system dynamics.
We discuss a recently proposed quantity, called transfer entropy, which uses time series data to measure the amount of information transferred from one process to another. In order to understand its ...foundation, merits, and limitations, we review some aspects of information theoretic functionals. While for symbol sequences these measures have an intuitive interpretation, their application to continuous state processes and, in particular, their estimation from finite data sets is problematic. For mutual information, finite length scale estimates converge from below and can thus be used to reject the assumption that the observed processes are independent. However, mutual information does not provide any directional information. Conversely, transfer entropy does resolve the directionality of information exchange but no similar monotonic convergence seems to hold. Thus, only in the case of zero transfer entropy in one direction we can reliably infer an asymmetry of the information exchange.
The discovery of proteins with programmable DNA-binding specificities triggered a whole array of applications in synthetic biology, including genome editing, regulation of transcription, and ...epigenetic modifications. Among those, transcription activator-like effectors (TALEs) due to their natural function as transcription regulators, are especially well-suited for the development of orthogonal systems for the control of gene expression. We describe here the construction and testing of libraries of synthetic TALE-activated promoters which are under the control of a single TALE with a given DNA-binding specificity. These libraries consist of a fixed DNA-binding element for the TALE, a TATA box, and variable sequences of 19 bases upstream and 43 bases downstream of the DNA-binding element. These libraries were cloned using a Golden Gate cloning strategy making them usable as standard parts in a modular cloning system. The broad range of promoter activities detected and the versatility of these promoter libraries make them valuable tools for applications in the fine-tuning of expression in metabolic engineering projects or in the design and implementation of regulatory circuits.
We report on an air-clad large-core single-transverse-mode ytterbium-doped photonic crystal fiber with a mode-field-diameter of 35 microm, corresponding to a mode-field-area of ~1000 microm(2). In a ...first experiment this fiber is used to amplify 10-ps pulses to a peak power of 60 kW without significant spectral broadening due to self-phase modulation allowing for the frequency up-conversion of these pulses using narrow-bandwidth phase matched nonlinear crystals.
High-power ultrafast fiber laser systems Limpert, J.; Roser, F.; Schreiber, T. ...
IEEE journal of selected topics in quantum electronics,
03/2006, Letnik:
12, Številka:
2
Journal Article
Recenzirano
The recent demonstration of rare-earth-doped fiber lasers with a continuous wave output power well above the kilowatt level with diffraction-limited beam quality has proven that fiber lasers ...constitute a power-scalable solid-state laser concept. To generate intense pulses from a fiber, several fundamental limitations have to be overcome. Nevertheless, novel experimental strategies and fiber designs offer an enormous potential toward laser systems with high average powers and high pulse energies. This paper reviews the challenges, achievements, and perspectives of ultrashort pulse generation and amplification in fibers.
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