Channel guiding for laser wakefield accelerators

Abstract

Experimental investigations of laser guiding in plasma channels at LBNL are reported. Intense (> 2 × 10 17 W/cm 2 ), short (60 fs) laser pulses have been injected and guided in slab or cylindrical channels. The channels are produced in H 2 gas, delivered by a high pressure gasjet, with the dual-pulse Ignitor-Heater technique [1]. Using cylindrical focusing optics, a first ultrashort (< 100 fs) laser pulse (Ignitor), is brought to a line focus to ionize the gas jet. A second 160 ps long laser pulse (Heater) is subsequently used to heat the existing spark via inverse Bremsstrahlung. The hydrodynamic shock expansion creates a channel. The channel profile is diagnosed with time resolved longitudinal interferometry. The effects of laser beam size and divergence mismatch at the channel entrance and leakage of the laser energy out of the channel are studied in 1D and 2D.

Hadron Therapy Based on Laser Acceleration in the Plasma Channel Using Oxygen Ionization

“…Optical guiding of short and intense laser pulses in plasma channels can be used in a variety of applications, including plasma-based accelerators. In the laser Wakefield accelerator, plasma wave excitation requires laser intensities on the order of 10 18 W cm 2 [35], and based on Eq. 5, implies µm-scale spot sizes for TW -level laser powers (Z R ∼ = 300µm, for w 0 = 10µm and λ = 1µm).…”

“…If the index of refraction peaks on the axis, ∂η R ∂w < 0, a plasma channel can provide optical guiding which can be obtained by a plasma density profile with a local minimum on the axis, ∂n p ∂w > 0. Specifically, a channel with a radially parabolic density profile of the form n p (w) = n 0 + nw 2 w 2 0 , can guide a laser pulse with a constant radiation radius w 0 , provided that the channel depth n, satisfies n = n c , where, n c = 1 πr e w 2 0 shows the critical channel depth, and r e = e 2 m e c 2 , shows the classical electron radius, also, e and m e , show the electron charge and mass, respectively [35].…”