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The laser induced dispersed fluorescence spectra (LIDFS) of CH 3 N radical from five different vibronic excited levels were recorded and assigned. The anharmonic constants of the ν″ 3 (CN stretching) mode were determined to be ω 0 = 1049 ± 2 cm −1 , ω 0 ξ 0 = 9 ± 0.5 cm −1 . The previous tentative assignment of 1 0 1 band in the excitation spectrum [J. Chem. Phys. 103 (1995) 4418] was confirmed by LIDFS. The lifetimes of different vibrational levels of the A 3 E state were measured and the radiative lifetimes of ν ′ = 0, ν ′ 3 = 1, ν ′ 2 = 1, ν ′ 3 = 2, ν ′ 3 = 3 and ν ′ 1 = 1 states were extrapolated as 415 ± 8, 341 ± 10, 231 ± 18, 219 ± 9, 170 ± 3 and 166 ± 7 ns, respectively.

High amplitude coherent electron‐trajectories have been seen in 3D particle‐in‐cell simulations of the colliding pulse injection scheme of laser‐wakefield accelerators in the bubble regime, and explained as a consequence of laser‐driven coherent betatron oscillation in our recent paper [K. Nemeth et al., Phys. Rev. Lett. 100, 095002 (2008)]. In the present paper we provide more details on the shape of the trajectories, their relationship to the phase velocity of the laser and indicate the dependence of the phenomenon on the accuracy of the numerical representation and choice of laser/plasma parameters.

The origin of beam disparity in emittance and betatron oscillation orbits, in and out of the polarization plane of the drive laser of laser-plasma accelerators, is explained in terms of betatron oscillations driven by the laser field. As trapped electrons accelerate, they move forward and interact with the laser pulse. For the bubble regime, a simple model is presented to describe this interaction in terms of a harmonic oscillator with a driving force from the laser and a restoring force from the plasma wake field. The resulting beam oscillations in the polarization plane, with period approximately the wavelength of the driving laser, increase emittance in that plane and cause microbunching of the beam. These effects are observed directly in 3D particle-in-cell simulations.

Recent efforts at the APS have focused on reducing beam loss during storage ring (SR) injection to minimize radiation damage to the APS undulators. Reducing beam loss at injection is particularly important during top-up operation where injection occurs once every two minutes. One way to potentially improve injection efficiency is to simply reduce the emittance of the beam from the APS booster, thereby allowing the beam to be brought closer to the injection septum. Recently several low-emittance operating modes for the APS booster have been studied. The emittance is lowered from the standard value by increasing the horizontal tune in stages. The vertical tune is simultaneously decreased to minimize the required defocusing sextupole strength for chromaticity correction. Calculations indicate that up to 29% reduction in emittance is possible-a result that has been achieved in studies. A lattice with emittance 17% lower than the standard lattice has been thoroughly commissioned and has been used for routine APS top-up operation since July 2002. Results of beam measurements and comparison to calculations for various low-emittance lattices are reported in this paper.

The triggering of wave-breaking in a three-dimensional laser plasma wake (bubble) is investigated. The Coulomb potential from a nanowire is used to disturb the wake field to initialize the wave-breaking. The electron acceleration becomes more stable and the laser power needed for self-trapping is lowered. Three-dimensional particle-in-cell simulations were performed. Electrons with a charge of about 100 pC can be accelerated stably to energy about 170 MeV with a laser energy of 460 mJ. The first step towards tailoring the electron beam properties such as the energy, energy spread, and charge is discussed. (C) 2007 American Institute of Physics.