Frequency shift of an intense laser pulse induced by plasma wave

Spectral modification of an intense (≥1018Wcm−2) laser pulse propagating in a helium gas target was studied using Thomson scattering diagnostic. The spectra recorded at 90° to the laser propagation and polarization direction show a significant modulation and modification of the incident laser pulse during its interaction and propagation through the helium gas target. Simulations suggest that such a modulation in the spectrum of the laser pulse could arise due to its interaction with the self excited plasma waves.