In situ laser irradiation of WC-Co hard metals inside an SEM. Part 2. Behaviour of the cobalt binder.

Cemented carbides with higher binder contents were irradiated with a CO2-pulse laser within a SEM to investigate the structural development in more detail. The decisive medium is the melting binder which dissolves the refractory carbide phase. In this way a superficial layer of an oversaturated solid solution with highly dispersed secondary carbides is produced. At higher pulse numbers a periodic structure is engraved in the surface by local evaporation as result of a self-amplifying resonance phenomenon

In situ laser irradiation of WC-Co hardmetals inside an SEM. Part 1. General features of surface modification.

Samples of WC-6% Co hardmetals were irradiated with a pulsed CO2 laser inside a scanning electron microscope in order to study the mechanisms and development of surface modification in microscopic detail. The photon emission of the irradiated surface was measured simultaneously. Samples with surfaces prepared in different ways were irradiated in a multiple pulse regime. The laser power density was somewhat lower than that which would lead to a melting of the polished surface. It is shown that under such irradiation conditions the decisive step in surface modification is the successive solution of the carbide in the lower melting binder phase. Above a critical number of laser pulses, in the order of a thousand, this leads to the onset of large-scale melting, pointing to a marked rise of absorbency. These alterations of surface state are well reflected in the photon emission measurements. The influence of the original binder distribution within the surface layer, changed by grinding or p olishing, is investigated

The influence of underdense polymer target with/without high-Z nanoparticles on laser radiation absorption and energy transport

Fabrication methods for low-density fine-structure (cell size $<$1 $\mu$m) 3-D networks of cellulose triacetate (TAC) are developed. Target densities ranged 4-20 mg/cc, similar polymer structures were produced both with no load and with high-Z cluster dopant with concentration up to 30%. Foams of varying density down to 0.25 plasma critical density at the third harmonic of iodine laser wavelength are supplied for laser shots. Experiments with underdense foam targets with and without clusters irradiated on the PALS laser facility are analyzed preliminary, showing strong influence of target structure on process of laser light absorption. Heat and radiation transport in such targets are considered

High-frequency electromagnon in GdMnO 3

Results of far-infrared transmittance are reported for GdMnO 3, a multiferroic perovskite manganite. The spectra allow to obtain position and intensity of the high-frequency electromagnon (~75 cm -1 ) in this material. We present a comparative analysis of the high- and low-frequency electromagnons across the phase diagram of GdMnO 3. The traces of the electromagnon excitation can be detected even deeply in the paramagnetic state, which is attributed to magnetic fluctuations. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011