https://doi.org/10.1140/epjd/s10053-021-00265-7
Regular Article - Ultraintense and Ultrashort Laser Fields
High harmonic generation in crystalline silicon irradiated by an intense ultrashort laser pulse
1
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
Received:
2
July
2021
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.
© The Author(s) 2021
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