Regular Article - Ultraintense and Ultrashort Laser Fields
High harmonic generation in crystalline silicon irradiated by an intense ultrashort laser pulse
Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Tsarigradsko Chausse 72, 1784, Sofia, Bulgaria
2 Institute for Advanced Physical Studies, New Bulgarian University, 1618, Sofia, Bulgaria
Accepted: 6 September 2021
Published online: 6 October 2021
We investigate the high harmonic generation in bulk silicon irradiated by intense near-infrared laser pulses with pulse duration 100 fs. For peak field strength of the applied laser is below 1 V/Å, the spectral intensity of the emitted harmonics follows the prediction of perturbative nonlinear optics—the frequency comb consists of a series of discrete peaks at odd harmonic orders. For a pulse duration longer than 30 fs and peak laser field strength exceeding 1 V/Å, non-perturbative effects and generation of even order harmonics occur. The appearance of even harmonics is due to optical rectification of the transmitted pulse, which includes weak quasi-DC component with electric field as low as 3 V/m. In the strong coupling regime, when the peak field strength inside vacuum exceeds 1.5 V/Å, the laser creates dense breakdown plasma of electron–hole pairs, which in turn results in severe spectral broadening of the transmitted pulse. The harmonic spectrum superimposes onto a continuous background, the spectral width of individual harmonics is substantially broadened, and their central wavelength undergoes a blue shift that covers the spacing between adjacent harmonic orders.
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