[en] Geomechanical methods represent a very important part of the geological research. This paper gives a basic information about the geological situation in two main mining localities of the Mostecka uhelna, a.s. - Vrsany Mine and CSA Mine. Geomechanical characteristics, methods of prospecting work, a disintegration and a workability of overburden rocks including the total geomechanical rate of both the localities are main topics of this paper. (authors)

[en] The angular distributions of the (p,d), (d,t) and (³He,α) reactions on ¹³C were analyzed within the framework of DWBA in which additional information on nuclear vertex constants was introduced. Although all these reactions seem to represent a similar single nucleon transfer, their mechanism is shown to be quite different and so is the information extracted thereof. While from the (p,d) reactions spectroscopic factors may be extracted unambiguously, from the (d,t) reactions only the values of vertex constants can be directly obtained, which in turn are consistent with those determined by extrapolation of the experimental cross sections of the (p,d) reactions to the pole. In the case of (³He,α) reactions, however, the analysis indicates inadequacy of the DWBA concerning the calculations of central partial amplitudes. For a more reliable extraction of structural information, in addition to the correct normalization of peripheral amplitudes a contribution of more complex mechanisms must be taken into account. (author). 13 figs., 3 tabs., 21 refs

[en] In this paper, we briefly review a series of recent pioneering experiments on few-photon-induced multiple fragmentation of atoms and molecules performed at the free electron laser (FEL) at Hamburg (FLASH) using a 'reaction microscope', i.e. a coincident momentum imaging technique. For atoms we consider the most basic nonlinear process, namely direct or sequential two-photon double ionization (TPDI). In particular, benchmark data for theory are presented, such as recoil-ion momentum distributions for direct TPDI of He and Ne, and fully differential data for sequential TPDI of Ne. For molecules we show how one can identify contributions from different reaction channels by inspecting the measured kinetic energy and angular distributions of ionic fragments and even infer the time delay between the two-photon absorption events in TPDI by detailed comparison with theory. Finally, we describe a novel split mirror arrangement for EUV-pump-EUV-probe experiments and present the very first time-resolved data on the dynamics of N₂ molecules irradiated by the FLASH light.

[en] Two-photon double ionization of He and Ne by intense (10¹³-10¹⁴ W/cm²) short pulsed (∼ 25 fs) 44 eV radiation delivered by the free-electron LASer at Hamburg (FLASH) has been studied using a ^Reaction Microscope^. We observe characteristic signatures of direct (for He) and sequential (for Ne) ionization imprinted in different momentum distributions of the doubly charged ions. For Ne we also present kinematically complete data, extracting state-selective angular asymmetry parameters and an angular correlation function of both electrons, and compare them with recent theoretical predictions.

[en] Multiple ionization (MI), induced by a few EUV photons at energies of 28.2 eV, 38 eV and 44 eV from FLASH (the free-electron laser at Hamburg), has been studied for atoms (He, Ne, Ar) and N₂ molecules utilizing our multi-hit coincident technology-the reaction microscope. At comparably low intensities of I ≅ 10¹¹-10¹³ W cm^-2 we find the non-sequential (NS) MI mechanism dominating Ar³⁺ and Ar⁴⁺ production. Inspecting recoil ion and electron momentum distributions evidence is provided (i) for preferential back-to-back emission of electrons for NS double ionization of He and (ii) for angular entanglement between two outgoing electrons in sequential ionization (SI). In contrast to atoms, SI is observed to be most effective for MI of N₂ molecules at an intensity of ∼10¹³ W cm^-2 leading, among others, to N²⁺₂ → N⁺ + N⁺, N³⁺₂ → N²⁺ + N⁺, N⁴⁺₂ → N²⁺ + N²⁺ Coulomb explosion channels. Fragment ion momentum distributions are investigated and are demonstrated to allow tracing SI pathways.

[en] Using a reaction microscope, three-dimensional (3D) electron (and ion) momentum (P) spectra have been recorded for carrier-envelope-phase (CEP) stabilized few-cycle (∼5 fs), intense (∼4x10¹⁴ W/cm²) laser pulses (740 nm) impinging on He. Preferential emission of low-energy electrons (E_e<15 eV) to either hemisphere is observed as a function of the CEP. Clear interference patterns emerge in P space at CEPs with maximum asymmetry, interpreted as attosecond interferences of rescattered and directly emitted electron wave packets by means of a simple model.

[en] We carried out time-of-flight mass spectrometry for neon clusters that were exposed to intense free electron laser pulses with the wavelength of 62 nm, which induce optical transition from the ground state (2s² 2p⁶) to an excited state (2s² 2p⁵ nl ) in the Ne atoms. In contrast to Ne⁺ ions produced by two-photon absorption from isolated Ne atoms, the Ne⁺ ion yield from Ne clusters shows a linear dependence on the laser intensity (I). We discuss the ionization mechanisms which give the linear behaviour with respect to I and expected features in the electron emission spectrum. (paper)

[en] Using a split focusing mirror, XUV pump–probe measurements have been performed at the free-electron laser at Hamburg (FLASH). The obtained non-linear autocorrelation signals can be used to characterize the ultra-short photon pulses generated by the machine at different control parameters.

[en] Multiple photoionization processes of giant rare-gas clusters are investigated in the wavelength region of 51 to 61nm at Spring8. We report here some latest results of our investigation; the frustration of photoionization for giant xenon clusters and the charge transfer in Ar-core Ne-shell clusters.

[en] Here we present optical spectroscopy studies to examine structural and optical properties of active region of quantum cascade lasers grown fully by MOCVD technique. The active part is InGaAs/AlInAs based multilayer structure nominally lattice matched to InP substrate. In this communication we study a set of structures with different growth temperature of the cladding layers and its influence on the properties of active core. The x-ray spectroscopy (XRD) allowed to determine the widths of constituent layers and compare obtained values with nominal ones. Fourier-transformed photoluminescence (FTPL) and photoreflectance (PR) measurements provided high signal to noise spectra, proving good optical and structural properties of investigated samples. A model of atoms interdiffusion processes was presented to explain observed small energy shifts of the transitions energies within the investigated multilayer structures. (paper)