Tailored Beam Shaping for Laser Spot Joining of Highly Conductive Thin Foils

AbstractLaser spot joining of thin metallic foils in the order of 100 micrometer and below has a number of interesting applications in electronic industry. However, high thermal conductivity and thermal expansion of common materials largely prohibit spot joints with a sufficiently large contact area needed to satisfy mechanical and electrical requirements. Of the numerous possibilities to positively influence the process of such joints we investigateusing a pulsed Nd:YAG laser to generate spot joints of thin foils in combination with a beam shaping optic to tailor the temperature profile during laser spot joining of thin foils. This allows for increased contact area, stabilized process behavior and offers the potential for joining ultra thin foils far below 100 μm. Different configurations are examined, results are presentedand discussed, mainly in terms of their generalimpact on the micro joining process

Laser als Werkzeug für die Mikro- und Nanostrukturierung : und die darin aufgeführten wissenschaftlichen Publikationen E1-E51

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Detection of per- and polyfluoroalkyl water contaminants with multiplexed 4D microcavities sensor

The per- and polyfluoroalkyl substances (PFAS) constitute a group of organofluorine chemicals treated as the emerging pollutants and currently are of particularly acute concern. These compounds have been employed intensively as surfactants over multiple decades and are already to be found in surface and ground waters at amounts sufficient to have an effect on the human health and ecosystems. Because of the carbon-fluorine bonds the PFAS have an extreme environmental persistence and their negative impact accumulates with further production and penetration into the environment. In Germany alone, more than thousands sites have been identified to be contaminated with PFAS and thus timely detection of PFAS residues is becoming a high-priority task. In this paper we report on the high performance optical detection method based on whispering gallery modes microcavities applied for the first time for detection of the PFAS contaminants in aqueous solutions. A self-sensing boosted 4D microcavity fabricated with two-photon polymerization is employed as an individual sensing unit. On example of the multiplexed imaging sensor with multiple hundreds of simultaneously interrogated microcavities we demonstrate the possibility to detect the PFAS chemicals representatives at the level of down to 1 ppb

Comparative analysis of quantum cascade laser modeling based on density matrices and non-equilibrium Green's functions

We study the operation of an 8.5 mu m quantum cascade laser based on GaInAs/AlInAs lattice matched to InP using three different simulation models based on density matrix (DM) and non-equilibrium Green's function (NEGF) formulations. The latter advanced scheme serves as a validation for the simpler DM schemes and, at the same time, provides additional insight, such as the temperatures of the sub-band carrier distributions. We find that for the particular quantum cascade laser studied here, the behavior is well described by simple quantum mechanical estimates based on Fermi's golden rule. As a consequence, the DM model, which includes second order currents, agrees well with the NEGF results. Both these simulations are in accordance with previously reported data and a second regrown device. (C) 2014 AIP Publishing LLC