2013, Kornilov, O., Eckstein, M., Rosenblatt, M., Schulz, C.P., Motomura, K., Rouzée, A., Klei, J., Foucar, L., Siano, M., Lübcke, A., Schapper, F., Johnsson, P., Holland, D.M.P., Schlathölter, T., Marchenko, T., Düsterer, S., Ueda, K., Vrakking, M.J.J., Frasinski, L.J.

Single-shot time-of-flight spectra for Coulomb explosion of N2 and I2 molecules have been recorded at the Free Electron LASer in Hamburg (FLASH) and have been analysed using a partial covariance mapping technique. The partial covariance analysis unravels a detailed picture of all significant Coulomb explosion pathways, extending up to the N 4+-N5+ channel for nitrogen and up to the I 8+-I9+ channel for iodine. The observation of the latter channel is unexpected if only sequential ionization processes from the ground state ions are considered. The maximum kinetic energy release extracted from the covariance maps for each dissociation channel shows that Coulomb explosion of nitrogen molecules proceeds much faster than that of the iodine. The N 2 ionization dynamics is modelled using classical trajectory simulations in good agreement with the outcome of the experiments. The results suggest that covariance mapping of the Coulomb explosion can be used to measure the intensity and pulse duration of free-electron lasers.

2015, Barillot, T., Magrakvelidze, M., Loriot, V., Bordas, C., Hervieux, P.-A., Gisselbrecht, M., Johnsson, P., Laksman, J., Mansson, E.P., Sorensen, S., Canton, S.E., Dahlström, J.M., Dixit, G., Madjet, M.E., Lépine, F., Chakraborty, H.S.

We perform time-dependent local density functional calculations of the time delay in C60 HOMO and HOMO-1 photoionization at giant plasmon energies. A semiclassical model is used to develop further insights.

2010, Mauritsson, J., Remetter, T., Swoboda, M., Klünder, K., L'Huillier, A., Schafer, K.J., Ghafur, O., Kelkensberg, F., Siu, W., Johnsson, P., Vrakking, M.J.J., Znakovskaya, I., Uphues, T., Zherebtsov, S., Kling, M.F., Lépine, F., Benedetti, E., Ferrari, F., Sansone, G., Nisoli, M.

We present an interferometric pump-probe technique for the characterization of attosecond electron wave packets (WPs) that uses a free WP as a reference to measure a bound WP. We demonstrate our method by exciting helium atoms using an attosecond pulse (AP) with a bandwidth centered near the ionization threshold, thus creating both a bound and a free WP simultaneously. After a variable delay, the bound WP is ionized by a few-cycle infrared laser precisely synchronized to the original AP. By measuring the delay-dependent photoelectron spectrum we obtain an interferogram that contains both quantum beats as well as multipath interference. Analysis of the interferogram allows us to determine the bound WP components with a spectral resolution much better than the inverse of the AP duration. © 2010 The American Physical Society.

2011, Gademann, G., Kelkensberg, F., Siu, W.K., Johnsson, P., Gaarde, M.B., Schafer, K.J., Vrakking, M.J.J.

We show that high harmonic generation driven by an intense nearinfrared (IR) laser can be temporally controlled when an attosecond pulse train (APT) is used to ionize the generation medium, thereby replacing tunnel ionization as the first step in the well-known three-step model. New harmonics are formed when the ionization occurs at a well-defined time within the optical cycle of the IR field. The use of APT-created electron wave packets affords new avenues for the study and application of harmonic generation. In the present experiment, this makes it possible to study harmonic generation at IR intensities where tunnel ionization does not give a measurable signal.

2013, Leitner, T., Buchner, F., Luebcke, A., Rouzée, A., Rading, L., Johnsson, P., Odelius, M., Karlsson, H.O., Vrakking, M., Wernet, P.

Time and energy resolved photoelectron distributions of photo-excited Nal are presented. A splitting in the photo-excited state suggested by calculations of the intramolecular potential energy surfaces could be confirmed experimentally for the first time.

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, Boll, R., Rouzée, A., Adolph, M., Anielski, D., Aquila, A., Bari, S., Bomme, C., Bostedt, C., Bozek, J.D., Chapman, H.N., Christensen, L., Coffee, R., Coppola, N., De, S., Decleva, P., Epp, S.W., Erk, B., Filsinger, F., Foucar, L., Gorkhover, T., Gumprecht, L., Hömke, A., Holmegaard, L., Johnsson, P., Kienitz, J.S., Kierspel, T., Krasniqi, F., Kühnel, K.-U., Maurer, J., Messerschmidt, M., Moshammer, R., Müller, N.L.M., Rudek, B., Savelyev, E., Schlichting, I., Schmidt, C., Scholz, F., Schorb, S., Schulz, J., Seltmann, J., Stener, M., Stern, S., Techert, S., Thøgersen, J., Trippel, S., Viefhaus, J., Vrakking, M., Stapelfeldt, H., Küpper, J., Ullrich, J., Rudenko, A., Rolles, D.

This paper gives an account of our progress towards performing femtosecond time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe setup combining optical lasers and an X-ray free-electron laser. We present results of two experiments aimed at measuring photoelectron angular distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C8H5F) and dissociating, laser-aligned 1,4-dibromobenzene (C6H4Br2) molecules and discuss them in the larger context of photoelectron diffraction on gas-phase molecules. We also show how the strong nanosecond laser pulse used for adiabatically laser-aligning the molecules influences the measured electron and ion spectra and angular distributions, and discuss how this may affect the outcome of future time-resolved photoelectron diffraction experiments.