Nonadiabatic redshifts in high-order harmonic generation from solids

Area of Science:

• Solid-state physics
• Quantum optics
• Attosecond science

Background:

• High-order harmonic generation (HHG) is a key phenomenon in nonlinear optics.
• Understanding HHG in solids is crucial for developing advanced light sources.
• Previous studies have explored HHG in solids, but the mechanisms in multi-plateau spectra require further investigation.

Purpose of the Study:

• To numerically investigate the multi-plateau high-order harmonic generation (HHG) spectra in solids.
• To elucidate the underlying physical mechanisms responsible for spectral shifts and the presence of even-order harmonics.
• To validate numerical findings against recent experimental results.

Main Methods:

• Numerical simulations of HHG in solids.
• Analysis of HHG spectra, including redshift and Full Width at Half Maximum (FWHM).
• Investigation of electron dynamics in k-space and time domains.

Main Results:

• Redshifted HHG spectra observed in the second and higher plateaus for short laser pulses, attributed to nonadiabatic effects.
• Increasing FWHMs with harmonic order suggest step-by-step excitation of higher conduction bands.
• Presence of even-order harmonics explained by broken symmetry in k-space and time domains, despite coordinate space symmetry.

Conclusions:

• The study provides a comprehensive numerical understanding of multi-plateau HHG in solids.
• The findings confirm the importance of nonadiabatic effects and the indirect step-by-step excitation model.
• Numerical results align well with experimental observations, validating the proposed mechanisms.