Laser-plasma accelerator group

Abstract:

We report the use of wavelength-tuneable laser pulses from an optical parametric amplifier to generate high-order harmonics in a range of noble gases. The variation of the harmonic cut-off wavelength and phasematching pressure with gas species and fundamental wavelength were recorded. The experimental results are compared to a phenomenological model of the harmonic generation process, incorporating two separate models of photo-ionization. While the calculated phasematching pressure is generally insensitive to the ionization model, for the harmonic cut-off we obtain superior agreement between experiment and theory when the Yudin-Ivanov (YI) ionization model is used, compared to the commonly utilised Ammosov-Delone-Krainov (ADK) model.

Abstract:

Active plasma lensing is a compact technology for strong focusing of charged particle beams, which has gained considerable interest for use in novel accelerator schemes. While providing kT/m focusing gradients, active plasma lenses can have aberrations caused by a radially nonuniform plasma temperature profile, leading to degradation of the beam quality. We present the first direct measurement of this aberration, consistent with theory, and show that it can be fully suppressed by changing from a light gas species (helium) to a heavier gas species (argon). Based on this result, we demonstrate emittance preservation for an electron beam focused by an argon-filled active plasma lens.