Space- and time-resolved observation of extreme laser frequency upshifting during ultrafast-ionization

Abstract

A 65-fs, 800-nm, 2-TW laser pulse propagating through a nitrogen gas jet has been experimentally studied by 90 Thomson scattering. Time-integrated spectra of scattered light show unprecedented broadening towards the blue which exceeds 300 nm. Images of the scattering region provide for the first time a space- and time-resolved description of the process leading quite regularly to such a large upshift. The mean shifting rate was as high as dk/dt3A ̊/fs, never observed before. Interferometry shows that it occurs after partial laser defocusing. Numerical simulations prove that such an upshift is consistent with a laser-gas late interaction, when laser intensity has decreased well below relativistic values (a0 1) and ionization process involves most of the laser pulse. This kind of interaction makes spectral tuning of ultrashort intense laser pulses possible in a large spectral range. VC 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4818602

Self-phase modulation in various regimes of intense laser–plasma interactions

“…In this condition Giulietti et al. (2013) reported a 40–50 nm upshift, which was attributed to SPM through a combined effect of ionization and filamentation. Thomas et al.…”

“…The experiment we are going to describe (Giulietti et al. 2013) was somehow complementary to the one of Thomas et al. (2007).…”

“…A recent experiment (Giulietti et al. 2013) allowed observing a SPM-driven progressive laser-frequency up shift up to unprecedented values. The observation was indirect, through Thomson scattering of the laser light during the propagation, but this method provided a unique opportunity to ‘see’ the evolution of the laser spectrum in time and in space.…”

Narrow band and energy selectable plasma cathode for multistage laser wakefield acceleration

“…On the other hand, having short bunch durations, low emittance, and being potentially jitter-free, LWFA electron beams are considered a framework for ultrafast electron and x-ray imaging [7][8][9]. In the context of LWFA several techniques based on gas jets, gas-cell, and preformed channels have been proposed and tested experimentally [10][11][12][13][14][15][16][17][18].…”

“…However, during laser pulse propagation in a long distance its parameters usually essentially change. It happens because of pulse depletion, sensitivity of dephasing length to pulse parameters, various instabilities such as self-focusing, hosing, and others [5,11,12]. As a result, achieving necessary controllability and reproducibility of electron acceleration in the wakefield of such a pulse become difficult.…”