Laser Wakefield Excitation and Measurement by Femtosecond Longitudinal Interferometry

Abstract

Plasma density oscillations (Langmuir waves) in the wake of an intense (Ipeak-3 x 1017W/cm2) laser pulse (100 fs) are measured with ultrafast time resolution using a longitudinal interferometric technique. Phase shifts consistent with large amplitude (Sne/ne-1) density waves at the electron plasma frequency were observed in a fully tunnel-ionized He plasma, corresponding to longitudinal electric fields of-10 GV/m. Strong radial ponderomotive forces enhance the density oscillations. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, , manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the *

Optical Frequency Domain Visualization of Electron Beam Driven Plasma Wakefields

“…Such diagnostics have already been demonstrated in the case of the laser wakefield accelerator (LWFA) [2,3,6]. The imaging of laser-driven wakes in plasmas of density 1.7 to 3  10 17 cm -3 has been demonstrated using the multishot technique of Frequency Domain Interferometry (FDI) [3] and in plasmas of density 10 18 cm -3 to 10 19 cm -3 using the single shot technique of Frequency Domain Holography (FDH) [2].…”

“…The imaging of laser-driven wakes in plasmas of density 1.7 to 3  10 17 cm -3 has been demonstrated using the multishot technique of Frequency Domain Interferometry (FDI) [3] and in plasmas of density 10 18 cm -3 to 10 19 cm -3 using the single shot technique of Frequency Domain Holography (FDH) [2]. Both techniques require two laser pulses: a reference preceding the plasma wave, and a probe co-propagating with the plasma wave and recording its refractive index.…”

Laser wakefield accelerated electron beam monitoring and control

“…Due the dependence of the spectra on electron plasma density, electron energy, and betatron oscillation amplitude this measurement needs to be coupled with other measurements of the laser-plasma interaction such as an electron energy spectrograph, frequency domain interferometry [32,33,34,35], and frequency domain holography [36]. Such simultaneous measurements have been previously used to measure the normalized transverse electron beam emittance from a LWFA where the x-ray emission was used to measure the electron transverse bunch size [37].…”

Electron Acceleration by a Laser Pulse with a Rising Propagation Speed

“…Preaccelerated electrons can be accelerated to high energy and can be extracted easily. Although this direct acceleration scheme is less than ideal, because the pulse can generate a parasitic wake (Marqes et al 1996;Siders et al 1996), its simplicity is noteworthy. However, like many other laser-driven acceleration schemes Sprangle et al 1996), dephasing between the particle and the pulse (Mckinstrie and Startsev 1997) always exists because the propagation speed of the pulse is assumed to be constant.…”