2014, McFarland, B.K., Berrah, N., Bostedt, C., Bozek, J., Bucksbaum, P.H., Castagna, J.C., Coffee, R.N., Cryan, J.P., Fang, L., Farrell, J.P., Feifel, R., Gaffney, K.J., Glownia, J.M., Martinez, T.J., Miyabe, S., Mucke, M., Murphy, B., Natan, A., Osipov, T., Petrovic, V.S., Schorb, S., Schultz, T., Spector, L.S., Swiggers, M., Tarantelli, F., Tenney, I., Wang, S., White, J.L., White, W., Gühr, M.

Free electron laser (FEL) based x-ray sources show great promise for use in ultrafast molecular studies due to the short pulse durations and site/element sensitivity in this spectral range. However, the self amplified spontaneous emission (SASE) process mostly used in FELs is intrinsically noisy resulting in highly fluctuating beam parameters. Additionally timing synchronization of optical and FEL sources adds delay jitter in pump-probe experiments. We show how we mitigate the effects of source noise for the case of ultrafast molecular spectroscopy of the nucleobase thymine. Using binning and resorting techniques allows us to increase time and spectral resolution. In addition, choosing observables independent of noisy beam parameters enhances the signal fidelity.

2015, Iablonskyi, D., Nagaya, K., Fukuzawa, H., Motomura, K., Kumagai, Y., Mondal, S., Tachibana, T., Takanashi, T., Nishiyama, T., Matsunami, K., Johnsson, P., Piseri, P., Sansone, G., Dubrouil, A., Reduzzi, M., Carpeggiani, P., Vozzi, C., Devetta, M., Negro, M., Faccialà, D., Calegari, F., Trabattoni, A., Castrovilli, M., Ovcharenko, Y., Möller, T., Mudrich, M., Stienkemeier, F., Coreno, M., Alagia, M., Schütte, B., Berrah, N., Callegari, C., Plekan, O., Finetti, P., Spezzani, C., Ferrari, E., Allaria, E., Penco, G., Serpico, C., De Ninno, G., Diviacco, B., Di Mitri, S., Giannessi, L., Prince, K.., Yao, M., Ueda, K.

We present a comprehensive analysis of autoionization processes in Ne clusters (~5000 atoms) after multiple valence excitations by free electron laser radiation. The evolution from 2-body interatomic Coulombic decay (ICD) to 3-body ICD is demonstrated when changing from surface to bulk Frenkel exciton excitation. Super Coster-Kronig type 2-body ICD is observed at Wannier exciton which quenches the main ICD channel.

2014, Haessler, S., Balciunas, T., Fan, G., Andriukaitis, G., Pugžlys, A., Baltuška, A., Witting, T., Squibb, R., Zaïr, A., Tisch, J.W.G., Marangos, Chipperfield, L.E.

Quasifree field-driven electron trajectories are a key element of strong-field dynamics. Upon recollision with the parent ion, the energy transferred from the field to the electron may be released as attosecondduration extreme ultaviolet emission in the process of high-harmonic generation. The conventional sinusoidal driver fields set limitations on the maximum value of this energy transfer and the efficient return of the launched electron trajectories. It has been predicted that these limits can be significantly exceeded by an appropriately ramped-up cycle shape [L. E. Chipperfield et al., Phys. Rev. Lett. 102, 063003 (2009)]. Here, we present an experimental realization of similar cycle-shaped waveforms and demonstrate control of the high-harmonic generation process on the single-atom quantum level via attosecond steering of the electron trajectories.With our improved optical cycles, we boost the field ionization launching the electron trajectories, increase the subsequent field-to-electron energy transfer, and reduce the trajectory duration. We demonstrate, in realistic experimental conditions, 2 orders of magnitude enhancement of the generated extreme ultraviolet flux together with an increased spectral extension. This application, which is only one example of what can be achieved with cycle-shaped high-field light waves, has significant implications for attosecond spectroscopy and molecular self-probing.

2015, Andrianov, A.V., Zakhar'in, A.O., Zhukavin, R.K., Shastin, V.N., Abrosimov, N.V.

We report on experimental observation and study of terahertz emission from lithium doped silicon crystals under continuous wave band-to-band optical excitation. It is shown that radiative transitions of electrons from 2P excited states of lithium donor to the 1S(A1) donor ground state prevail in the emission spectrum. The terahertz emission occurs due to capture of nonequilibrium electrons to charged donors, which in turn are generated in the crystal as a result of impurity assisted electron-hole recombination. Besides the intracentre radiative transitions the terahertz emission spectrum exhibits also features at about 12.7 and 15.27 meV, which could be related to intraexciton transitions and transitions from the continuum to the free exciton ground state.

2015, Schütte, Bernd, Arbeiter, Mathias, Fennel, Thomas, Jabbari, Ghazal, Kuleff, Alexander I., Vrakking, Marc J. J., Rouzée, Arnaud

We report on a novel correlated electronic decay process following extensive Rydberg atom formation in clusters ionized by intense near-infrared fields. A peak close to the atomic ionization potential is found in the electron kinetic energy spectrum. This new contribution is attributed to an energy transfer between two electrons, where one electron decays from a Rydberg state to the ground state and transfers its excess energy to a weakly bound cluster electron in the environment that can escape from the cluster. The process is a result of nanoplasma formation and is therefore expected to be important, whenever intense laser pulses interact with nanometer-sized particles.