2018 Physics/Theoretical Colloquium Thursday, November 1st, 2018 3:45 – 4:45 p.m. Rosen Auditorium (TA-53, Bldg. 1) Refreshments at 3:15 pm Speaker: Prof. Jorge J. Rocca Department of Electrical and Computer Engineering, and Department of Physics Colorado State University, Fort Collins, CO “Highly Relativistic Ultrashort Pulse Laser Interaction with Ordered Nanowire Arrays: X-ray and Neutron Generation ” Abstract: The trapping of femtosecond laser pulses of relativistic intensity deep within ordered nanowire arrays can volumetrically heat dense matter into a new ultra-hot plasma regime. Electron densities more than 100 times greater than the critical density and multi-keV temperatures are achieved using ultrashort laser pulses of only one Joule energy. Extraordinarily high degrees of ionization (e.g. 52 times ionized Au) were observed with gigabar pressures only exceeded in the laboratory in the central hot-spot of highly compressed thermonuclear fusion plasmas [1,2]. I will discuss the fundamental physics of relativistic laser pulse interactions with nanostructures and their promising applications. The large electron density, which results in an increase collisional rate and shorter radiative lifetime, combined with the large plasma volume that increases the hydrodynamic cooling time allow for greatly increased conversion into x-rays. Recent experiments in which gold nanowire arrays were heated by ultra-high contrast pulses at intensities of ~ 4 x 1019 W cm-2 produced record 20 percent conversion efficiency into picosecond x-ray pulses [3]. In a different set of experiments the acceleration of deuterons from a dense deuterated nanowire array to MeV energies resulted in a record number of monochromatic fusion neutrons per Joule for a compact laser. The neutron production was 500 times larger than that obtained irradiating flat solid targets of the same material (CD2) with the same laser pulses [4]. These results and those of new experiments conducted at increased intensities of ~ 5 x 10 21 W cm-2 conducted using ultra-high contrast pulses from a frequency-doubled petawatt-class laser will be presented and compared with 3-D relativistic particle-in-cell simulations. Work supported by the U.S. Department of Energy, Fusion Science program of the Office of Science and by the Air Force Office of Scientific Research 1. M. A. Purvis, V. N. Shlyaptsev, R. Hollinger, C. Bargsten, A. Pukhov, A. Prieto, Y. Wang, B. Luther, L. Yin, S. Wang, J. J. Rocca, “Relativistic plasma nano-photonics for ultra-high energy density physics” , Nature Photonics 7, 796 (2013). 2. B. Bargsten et al., “ Energy penetration into arrays of aligned nanowires irradiated with relativistic intensities: scaling to terabar pressures”, Science Advances, 3, e1601558 (2017). 3. R. Hollinger, et al. R. Hollinger, B. Bargsten, V.N. Slyaptsev, V. Kaymak, A. Pukhov, M.G.Capeluto, S.Wang, A. Rockwood, Y. Wang, A. Towsend, A.Prieto, J.J. Rocca , “Efficient picosecond X-ray pulses from plasma in the radiation dominated regime”, Optica, 4, 1344, (2017) 4. Curtis. C. Calvi, J. Tinsley, R. Hollinger, V. Kaymak, A. Pukhov, S. Wang, A. Rockwood, Y. Wang, V.N. Shlyaptsev, J.J. Rocca, , “Micro-scale fusion in dense relativistic nanowire array plasmas”, Nature Communications, 9 ,art. 1077, (2018)