Mapping the electron band structure by intraband high-harmonic generation in solids

High-harmonic generation (HHG) has recently been extended to solids, enabling all-optical reconstruction of electron band structure. However, material absorption of above-the-bandgap interband harmonics used for this purpose in earlier work limits the applicability of this promising technique. Here, sub-100-fs mid-infrared pulses tunable within the range of wavelengths from 5.0 to 6.7 μm are used to study HHG in ZnSe. Below-the-bandgap high-order harmonics generated by such driver pulses fall within the transparency range of a solid material, thus removing absorption-related limitations on the depth of HHG. Such harmonics are shown to be ideally suited to probe the nonlinearities of electron bands, enabling an all-optical mapping of the electron band structure in bulk solids.