Fig. 2: Experiment.
From: Onset of Bloch oscillations in the almost-strong-field regime
a Two fundamental beams (red) are focused into a crystal (crossing angle α = 1. 1∘, beam waist 120 μm). Beams in the DUV (blue) are emitted from the laser-induced grating both collinearly to the fundamental beams and in the interstitial space. The wavefronts of the fundamental pulses A and B, which originate by beam splitting of one laser pulse, are highlighted in red. Cross-phase modulation scans (XPMS) are used for experimental pulse retrieval23 and indicate a center wavelength of 700 nm and a pulse duration of 8 fs. The DUV beams contain two pulses (wavefronts highlighted in blue), of which the front pulses travel at the pace of the fundamental pulses, whereas the rear pulses propagate at a speed corresponding to the DUV dispersion and are thus delayed due to the refractive index mismatch at Vis–IR and DUV wavelengths. The spectrometer records the DUV spectrum emitted collinearly to A. The experiment is carried out in a vacuum, inhibiting nonlinear interactions with air. b The raw spectrum I(ω) (black) and the Fourier filtered spectrum Ir(ω) (blue) at IB = 3.5 TW/cm2 from SiO2(001). c The Fourier filtered spectrum Ir(ω) as a function of intensity.
