Linking High Harmonics from gases and solids
When intense light interacts with an atomic gas, recollision between an ionizing electron and its parent ion creates high-order harmonics of the fundamental laser frequency. This sub-cycle effect generates coherent soft X-rays and attosecond pulses, and provides a means to image molecular orbitals. Here we generate high harmonics from bulk ZnO (a direct band gap semiconductor) and Si (an indirect band gap semiconductor) crystals and demonstrate their origin in a generalized recollision between electrons and their associated holes. In addition, we find that solid state high harmonics are perturbed by fields so weak that they are present in conventional electronic circuits, thus opening a route to integrate electronics with attosecond and high-harmonic technology. Finally, we devise a technique that extracts the solid’s band structure from the high harmonic signal. This all-optical technique will be applicable to study matter under extreme conditions, surface reactions at ambient pressures and ultrafast modifications to band structures.
- Anisotropic behaviour in isotropic crystal à microscopic origin yet to be explained
- Indirect band gap materials as good as direct band gap to sustain recollision process
- Electrons tunnel at the direct band gap
Vampa et al., PRL 113, 073901 (2014), Vampa et al., PRB 91, 064302 (2015)