Fig. 2: 1D simulation results.

a, b are seed field envelopes after an interaction, for positively and negatively chirped pump pulses, respectively. The back-scattering produced in advance of the seed pulse is shown in orange, the amplified seed pulse in purple, and the scattered light trailing the seed pulse in green. Inset I shows the initial seed envelope. Insets II, III display the amplified seed pulses (purple region) on a magnified scale. c, d present the spectra obtained from a and b, respectively. The colour scheme associates spectra with temporal segments. The dotted black curve represents the initial seed spectrum. All spectra are normalised to the same value. e, f are the electron density spectra for positive and negative frequency chirp, respectively. Spectra are calculated at the time the seed pulse exits the plasma (seed propagates from top to bottom). The wave numbers are given in units of approximately the inverse beat wavelength, 2/λ₀ = 1/400 nm⁻¹. g, h are similar to e and f, but correspond to the ion density spectra. The electron density spectral amplitudes have been multiplied by factor four to be visible on the same scale as the ion density spectra. In f and h no spectral signature of the grating is visible when presented on the same scale as e and g.