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ABSTRACT: In this paper we report on the experimental demonstration of using relativistic electron diffraction and an radiofrequency deflecting cavity to capture in a single shot the entire time-history of the ultrafast laser-induced heating and melting of a single crystal gold sample. By recording the time variation in the Bragg peaks on the streak image of a 16 ps long electron beam it is possible to reconstruct with 400 fs temporal resolution the evolution of the sample structure induced by a 35 mJ/cm2 400 nm laser pump pulse.
Journal of Applied Physics 12/2010; 108(11):114513-114513-5. · 2.17 Impact Factor
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ABSTRACT: We report the experimental demonstration of time-resolved relativistic electron diffraction. Single shot diffraction patterns from a single crystal gold sample were recorded using ultrashort 3.5 MeV electron bunches from a radio frequency photoinjector. By scanning the pump pulse time-delay, we studied the Bragg peaks amplitude change due to the laser-induced melting of the sample. The observed time scale matches the one predicted using a simple two temperature model of the heating of the thin foil. Time-resolved relativistic electron diffraction using megaelectronvolt electron beams with 107 particles in 100 fs bunch length opens exciting possibilities in ultrafast structural dynamics.
Applied Physics Letters 08/2010; 97(6):063502-063502-3. · 3.84 Impact Factor
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P Musumeci,
L Cultrera,
M Ferrario,
D Filippetto,
G Gatti, M S Gutierrez,
J T Moody,
N Moore,
J B Rosenzweig,
C M Scoby,
G Travish,
C Vicario
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ABSTRACT: In this Letter we report on the use of ultrashort infrared laser pulses to generate a copious amount of electrons by a copper cathode in an rf photoinjector. The charge yield verifies the generalized Fowler-Dubridge theory for multiphoton photoemission. The emission is verified to be prompt using a two pulse autocorrelation technique. The thermal emittance associated with the excess kinetic energy from the emission process is comparable with the one measured using frequency tripled uv laser pulses. In the high field of the rf gun, up to 50 pC of charge can be extracted from the cathode using a 80 fs long, 2 microJ, 800 nm pulse focused to a 140 mum rms spot size. Taking into account the efficiency of harmonic conversion, illuminating a cathode directly with ir laser pulses can be the most efficient way to employ the available laser power.
Physical Review Letters 02/2010; 104(8):084801. · 7.37 Impact Factor
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ABSTRACT: Single shot diffraction patterns using a 250-fs-long electron beam have been obtained at the UCLA Pegasus laboratory. High quality images with spatial resolution sufficient to distinguish closely spaced peaks in the Debye-Scherrer ring pattern have been recorded by scattering the 1.6 pC 3.5 MeV electron beam generated in the rf photoinjector off a 100-nm-thick Au foil. Dark current and high emittance particles are removed from the beam before sending it onto the diffraction target using a 1 mm diameter collimating hole. These results open the door to the study of irreversible phase transformations by single shot MeV electron diffraction.
The Review of scientific instruments 01/2010; 81(1):013306. · 1.52 Impact Factor
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ABSTRACT: We theoretically and experimentally investigate the possibility of using a rf streak camera to time resolve in a single shot structural changes at the sub-100 fs time scale via relativistic electron diffraction. We experimentally tested this novel concept at the UCLA Pegasus rf photoinjector. Time-resolved diffraction patterns from thin Al foil are recorded. Averaging over 50 shots is required in order to get statistics sufficient to uncover a variation in time of the diffraction patterns. In the absence of an external pump laser, this is explained as due to the energy chirp on the beam out of the electron gun. With further improvements to the electron source, rf streak camera based ultrafast electron diffraction has the potential to yield truly single shot measurements of ultrafast processes.
Review of Scientific Instruments 02/2009; · 1.37 Impact Factor
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ABSTRACT: Using an experimental scheme based on a vertically deflecting rf deflector and a horizontally dispersing dipole, we characterize the longitudinal phase space of the beam in the blow-out regime at the UCLA Pegasus rf photoinjector. Because of the achievement of unprecedented resolution both in time (50 fs) and energy (1.0 keV), we are able to demonstrate some important properties of the beams created in this regime such as extremely low longitudinal emittance, large temporal energy chirp, and the degrading effects of the cathode image charge in the longitudinal phase space which eventually leads to poorer beam quality. All of these results have been found in good agreement with simulations.
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ABSTRACT: At the Pegasus photoinjector laboratory, sub-mm elec-tron bunches interact with thin metal targets to produce diffraction patterns[1]. On account of the bunches' high brightness, suitable patterns can be obtained in only a sin-gle shot, making the bunches effective probes on the sub-ps scale. As detection improvements push the probes to the sub-100-fs regime, the ability to pump the sample with ul-trafast laser pulses opens the door for relativistic ultrafast electron diffraction to study femtosecond dynamics with a variety of applications. In lieu of a viable fs synchroniza-tion method, we review and explore a sub-100-fs electro-optic sampling setup to obtain single shot timing informa-tion about the pump-probe event.
