Particle-beam-driven plasma wakefield acceleration (PWFA) enables various novel high-gradient techniques for powering future compact light-source and high-energy physics applications. Here, a driving particle bunch excites a wakefield response in a plasma medium, which may rapidly accelerate a trailing witness beam. In this Letter, we present the measurement of ratios of acceleration of the witness bunch to deceleration of the driver bunch, the so-called transformer ratio, significantly exceeding the fundamental theoretical and thus far experimental limit of 2 in a PWFA. An electron bunch with ramped current profile was utilized to accelerate a witness bunch with a transformer ratio of 4.6_{-0.7}^{+2.2} in a plasma with length ∼10 cm, also demonstrating stable transport of driver bunches with lengths on the order of the plasma wavelength.
A backlight for liquid-crystal-display illumination is presented, in which s-polarized light is preferentially coupled out by micro-optical structures in a birefringent layer. In the experiments, contrasts higher than 15 have been obtained. A polarization dependent ray-tracing model has been developed. Important guidelines for finding an optimal backlight configuration have been derived from the calculations.
Self-modulation of an electron beam in a plasma has been observed. The propagation of a long (several plasma wavelengths) electron bunch in an overdense plasma resulted in the production of multiple bunches via the self-modulation instability. Using a combination of a radio-frequency deflector and a dipole spectrometer, the time and energy structure of the self-modulated beam was measured. The longitudinal phase space measurement showed the modulation of a long electron bunch into three bunches with an approximately 200 keV/c amplitude momentum modulation. Demonstrating this effect is a breakthrough for proton-driven plasma accelerator schemes aiming to utilize the same physical effect.
A backlight for liquid crystal display illumination is presented, consisting of a commercial birefringent liquid crystalline polymeric layer innovatively laminated onto a micro‐structured plastic light guide. S‐polarized light is preferentially extracted from the light guide, and the efficiency was measured to be 1.78 time higher than in for a conventional unpolarized light emitting backlight.
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