Transient field-resolved reflectometry at 50-100 THz

Transient field-resolved spectroscopy enables studies of ultrafast dynamics in molecules, nanostructures, or solids with sub-cycle resolution, but previous work has so far concentrated on extracting the dielectric response at frequencies below 50 THz. Here, we implemented transient reflectometry 50–100 THz (3–6 µm) MHz repetition rate employing 800 nm few-cycle excitation pulses that provide sub-10 fs temporal resolution. The capabilities technique are demonstrated photorefractive changes semiconductors Ge and GaAs, where high frequency range permits to explore resonance-free Drude response. extended can further enable inaccessible transitions, including intramolecular vibrations a large systems.