Laser-plasma accelerator group

Abstract:

We present the latest results on the development of a high power fibre laser system for a laser-wire measuring electron beam emittance in an ILC-specification environment. The laser consists of a commercial Ytterbium (Yb) doped fibre laser system producing 1μJ pulses at 6.49MHz, which can be locked to an external frequency reference. This output has been amplified in a single 70cm rod type photonic crystal fibre (PCF), producing ~ 100μJ pulses in a burst mode at 2Hz (limited by diagnostics).

Abstract:

Hydrodynamic optically-field-ionized (HOFI) plasma channels up to 100mm long are investigated. Optical guiding is demonstrated of laser pulses with a peak input intensity of $6\times10^{17}$ W cm$^{-2}$ through 100mm long plasma channels with on-axis densities measured interferometrically to be as low as $n_{e0} = (1.0\pm0.3)\times10^{17}$cm$^{-3}$. Guiding is also observed at lower axial densities, which are inferred from magneto-hydrodynamic simulations to be approximately $7\times10^{16}$cm$^{-3}$. Measurements of the power attenuation lengths of the channels are shown to be in good agreement with those calculated from the measured transverse electron density profiles. To our knowledge, the plasma channels investigated in this work are the longest, and have the lowest on-axis density, of any free-standing waveguide demonstrated to guide laser pulses with intensities above $>10^{17}$ W cm$^{-2}$.

Abstract:

We present the first results from the commissioning of the upgraded laser-wire experiment at the Accelerator Test Facility 2 (ATF-II) at KEK. A new laser transport line and beam diagnostics were used to collide 150 mJ, 167 ps long laser pulses with 1.28 GeV, 30 ps long electron bunches to measure the vertical transverse size. Additionally, a new detector was installed with a reduced area for lower background. Initial scans showing a convoluted beam size of 18.4 ± 0.4 μm were used to tune the electron beam optics and reduce this down to 8.0 ± 0.3 μm. Laser pulse energy and charge dependency were investigated showing a linear relationship in both with a minimum laser energy of 20 mJ required for adequate signal to make a laser-wire scan.

Abstract:

We present the successful development of a new fibre laser system for a laser-wire electron beam emittance diagnostic, suitable for intra-train scanning in an ILC-specification environment. The system is based on the amplification of a commercial Ytterbium (Yb) fibre laser with a repetition rate of 6.49MHz in rod type Yb doped photonic crystal fibre (PCF). We demonstrate world leading laser performance, with amplification of pulses from 1.5uJ to 268uJ and a beam quality factor M2 < 1.1, in 1ms bursts at 2Hz.