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- Physikingenieurwesen (PHY) (518) (remove)
We present a novel unimorph deformable mirror with a diameter of only 10 mm that will be used in adaptive resonators of high power solid state lasers. The relationship between applied voltage and deformation of a unimorph mirror depends on the piezoelectric material properties, layer thicknesses, boundary conditions, and the electrode pattern. An analytical equation for the deflection of the piezoelectric unimorph structure is derived, based on the electro-elastic and thin plate theory. The validity of the proposed analytical model has been proven by numerical finite-element modelling and experimental results. Our mirror design has been optimized to obtain the highest possible stroke and a high resonance frequency.
Adaption of the NDIR-technology to 13CO2-breath tests under increased inspiratory O2 concentrations
(2009)
The mechanisms of femtosecond laser-induced transient melting and atomic mixing in a target composed of a 30 nm Au film deposited on a bulk Cu substrate are investigated in a series of atomistic simulations. The relative strength and the electron temperature dependence of the electron-phonon coupling of the metals composing the layered target are identified as major factors affecting the initial energy redistribution and the location of the region(s) undergoing transient melting and resolidification. The higher strength of the electron-phonon coupling in Cu, as compared to Au, results in a preferential sub-surface heating and melting of the Cu substrate, while the overlaying Au film largely retains its original crystalline structure. The large difference in the atomic mobility in the transiently melted and crystalline regions of the target makes it possible to connect the final distributions of the components in the resolidified targets to the history of the laser-induced melting process, thus allowing for experimental verification of the computational predictions. (C) 2009 Elsevier B. V. All rights reserved.
Redistribution of deep selenium and sulfur impurities in silicon upon surface doping with phosphorus
(2009)
The study is concerned with the effect of short-term high-temperature heating on Si:Se and Si:S samples, whose surface layers are doped with phosphorus to high concentrations. It is found that the resistivity of the wafers substantially increases deep in the bulk within up to similar to 10 mu m. The experimental data suggest that this effect is due to enhanced diffusion of chalcogen in the presence of the phosphorus-doped surface region. The mechanism of the effect is the injection of nonequilibrium interstitial silicon atoms from the layer heavily doped with phosphorus to the bulk of the sample. This results in a shift of the equilibrium between the concentrations of substitutional and interstitial impurity atoms towards higher concentrations of interstitials and, as a consequence, towards the increase in the relative content of the fast-diffusing interstitial component of the impurity.
A new simple design of a high-efficiency low-transport-time cell for laser ablation is presented. The main feature of the design is that the particles are transported by a laminar spiral gas flow into the outlet without any contact with the cell walls. The efficiency of the particle transport and the dependence of the ICP-MS peak shape on experimental conditions were measured. The peak duration on the 10% level was found to be as short as 30 ms and the transport efficiency reached 100% when analysing a standard brass sample. As an example of application to real samples with fine inhomogeneities, the profiles of C-13, Ca-44 and Pb-208 were measured by LA-ICP-MS across a tree core. As a result, the very quick particle transport time of the cell enabled the fine, seasonal variation in wood composition to be resolved.
The production of free-standing large aspect ratio metal nanofilms by femtosecond laser separation
(2009)
We demonstrate a new method for the production of free-standing metal films of thickness down to several tens of nanometres. Films of different metals as well as multilayer structures have been produced by means of femtosecond laser-induced separation of evaporated layers from a plane glass surface. This technology enables the production of large-area films with different properties for optical or nanotechnological applications. We study the properties of the film and demonstrate the possibility of high-pass filtering of electrons with an energy of several keV by means of the free-standing films. The physical mechanisms leading to the film separation under femtosecond laser radiation are discussed.
Over the past 5 years we have developed a new type of unimorph deformable mirror. The main advantages of this mirror technology are · very low surface scattering due to the use of superpolished glass · excellent coatings, even suitable for high power lasers, can be applied · active diameter of the mirrors can be between 10 mm and 100 mm · large strokes can be achieved even for small mirror diameters · integrated monolithic tip/tilt functionality based on a spiral arm design We have modeled these mirrors by analytical models as well as by the finite element method. This allows us to quickly design new mirrors tailored to specific applications. One example is a mirror for laser applications that has a diameter of 10 mm and can achieve a stroke in defocus mode of 5 μm. The stroke for these mirrors scales as the square of the mirror diameter, meaning that we can achieve, for example, a stroke of 125 μm for a mirror of 50 mm diameter. We will present design criteria and tradeoffs for these mirrors. We characterize our mirrors by the maximum stroke they can deliver for various Zernike modes, under the boundary condition that the Zernike mode has to be created with a certain fidelity, usually defined by the Maréchal criterion.
A New Combined Optical and Robotic Testing System to Evaluate Multisegmental Spinal Kinematics
(2010)
Investigation of multisegmental spinal biomechanics with a combined optical and robotic test setup
(2010)
The need for portable and on site screening methods for viruses is evident in face of virus infections that can spread lastly in a heavily connected world. A robust and efficient method for detecting viruses is a novel technique called Plasmon Assisted Microscopy of Nanoobjects. It is based on the acquisition of images from a sensor surface exploiting the behavior of surface plasmons in the presence of nanoobjects. In this paper an efficient image analysis approach with respect to the requirements of the sensor is presented and an embedded image processing system for this purpose is introduced. The processing pipeline comprises three steps and starts with restorating the images by removing the background and filtering artifacts. The acquired image series is analyzed pixel by pixel in a second pipeline step in order to detect pixels containing nanoobjects. In a last step pixels are aggregated to nanoobject structures. The paper introduces in the context of this virus detection method a configurable embedded system that was used for rapid prototyping of the image analysis algorithms in a flexible way. (C) 2010 Elsevier B.V. All rights reserved.
In this manuscript, a new approach in surface plasmon resonance microscopy is presented. The method provides optical real-time detection of single nanoparticles on surfaces. The potential of the method is demonstrated recording spherical dielectric particles as small as 40 nm in diameter and single HIV virus-like particles having diameters of similar to 100 nm both immobilized on functionalized surfaces. The surface plasmon resonance signal in the binding spots was found to be almost linearly proportional to the size of the particles and, therefore, surpasses the intensity of Mie scattering on spherical particle (dependence similar to r(-6)) by orders of magnitude for small objects. The physical reason leading to this strong effect is discussed.
Efficient quasi-three-level laser operation requires the generation of the highest possible pump rate from a given pump source. We derive the fundamental scaling laws for the pump rate and we extract optimization criteria for pump concepts from these laws. The analysis is then applied to the thin-disk laser. Based on the results, a novel pump concept for thin-disk lasers is proposed, which allows for several tens of pump beam passes and reduces the optical complexity of conventional pump concepts. Furthermore, the beam quality of the pump source is preserved almost completely, facilitating the highest possible pump rate.
Novel unimorph deformable mirror with monolithic tip-tilt functionality for solid state lasers
(2011)
We present a new type of unimorph deformable mirror with monolithic tip-tilt functionality. The tip-tilt actuation is based on a spiral arm design. The mirror will be used in high-power laser resonators for real-time intracavity phase control. The additional tip-tilt correction with a stroke up to 6 μm simplifies the resonator alignment significantly. The mirror is optimized for a laser beam footprint of about 10 mm. We have modeled and optimized this mirror by finite element calculations and we will present design criteria and tradeoffs for this mirrors. The mirror is manufactured from a super-polished glass substrate with very low surface scattering and excellent dielectric coating.
The role of homophase and heterophase interfaces on transport properties in structured materials
(2011)
Analytical features of particle counting sensor based on plasmon assisted microscopy of nano objects
(2011)
It has been shown that the beam quality and the efficiency of high-power solid-state lasers could be enhanced by the use of deformable mirrors in order to compensate for optical aberrations. An intracavity compensation requires a deformable mirror which is capable of handling very high laser intensities. The active diameter of the deformable mirror should be a few millimeters in order to match typical fundamental mode laser beam diameters. There is a wide variety of commercially available deformable mirrors, but neither meets all requirements.
We have developed a new type of unimorph deformable mirror for the correction of low-order Zernike modes. The mirror features a clear aperture of 50 mm combined with large peak-to-valley amplitudes of up to 35 μm. Newly developed fabrication processes allow the use of prefabricated, coated, super-polished glass substrates. The mirror's unique features suggest the use in several astronomical applications like the compensation of atmospheric aberrations seen by laser beacons, low light astronomy, and the use in woofer-tweeter systems. Additionally, the design enables an efficient correction of the inevitable wave-front error imposed by the floppy structure of primary mirrors in future large space telescopes. We have modeled the mirror by using analytical as well as finite element models. We will present design, key features and manufacturing steps of the deformable mirror.
Characterization of a miniaturized unimorph deformable mirror for high power cw-solid state lasers
(2012)
We have developed a new type of unimorph deformable mirror for real-time intra-cavity phase control of high power cw-lasers. The approach is innovative in its combination of super-polished and pre-coated highly reflective substrates, the miniaturization of the unimorph principle, and the integration of a monolithic tip/tilt functionality. Despite the small optical aperture of only 9 mm diameter, the mirror is able to produce a stroke of several microns for low order Zernike modes, paired with a residual static root-mean-square aberration of less than 0.04 µm. In this paper, the characteristics of the mirror such as the influence functions, the dynamic behavior, and the power handling capability are reported. The mirror was subjected to a maximum of 490 W of laser-light at a wavelength of 1030 nm. Due to the high reflectivity of over 99.998 percent the mirror is able to withstand intensities up to 1.5 MW/cm2.
We have developed a new type of unimorph deformable mirror, designed to correct for low-order Zernike modes. The mirror has a clear optical aperture of 50 mm combined with large peak-to-valley Zernike amplitudes of up to 35 μm. Newly developed fabrication processes allow the use of prefabricated super-polished and coated glass substrates. The mirror's unique features suggest the use in several stronomical applications like the precompensation of atmospheric aberrations seen by laser beacons and the use in woofer-tweeter systems. Additionally, the design enables an efficient correction of the inevitable wavefront error imposed by the floppy structure of primary mirrors in future large space-based telescopes. We have modeled the mirror by using analytical as well as finite element models. We will present design, key features and manufacturing steps of the deformable mirror.
26.3.-30.3.: DPG spring meeting Berlin: Modeling the morphogenesis of brine channels in sea ice
(2012)
26.3.-30.3.: DPG spring meeting Berlin: Instability of a repulsive Bose gas near the BEC transition
(2012)
We report on interferometric measurements of the thermo-optical aberrations of the laser medium of an Yb:YAG thin-disk laser in pumped and cw lasing conditions at several pump-power levels with a mean repeatability of 5 nm. These measurements build the basis for future intracavity compensation of the aberrations with our deformable mirror in order to improve the fundamental-mode efficiency.
Quasiparticle parametrization of meanfields, Galilei invariance and conserving response functions
(2013)
Concepts for future large space telescopes require an active optics system to mitigate aberrations caused by thermal deformation and gravitational release. Such a system would allow on-site correction of wave-front errors and ease the requirements for thermal and gravitational stability of the optical train. In the course of the ESA project "Development of Adaptive Deformable Mirrors for Space Instruments" we have developed a unimorph deformable mirror designed to correct for low-order aberrations and dedicated to be used in space environment. We briefly report on design and manufacturing of the deformable mirror and present results from performance verifications and environmental testing.