Solid-state harmonic generation: Broadband PI-FROSt characterization and driving mechanisms

We present the comprehensive characterization of a series of harmonic fields generated in a ZnO crystal by a few-cycle MIR driving pulse that spans the visible to mid-infrared (MIR) spectral region. The characterization is conducted using the recently developed Plasma-Induced Frequency Resolved Optical Switching (PI-FROSt) technique. We demonstrate the ability of this method to accurately characterize the MIR driving field (λ = 3.2 μm), as well as both odd and even harmonics up to the fifth order. The total spectral bandwidth extends over an exceptionally wide range of 2.6 octaves. All assessments validate the high precision of the field reconstructions and confirm the suitability of the PI-FROSt method for the metrology of over-octave-spanning waveforms. The results offer valuable insights into the fundamental mechanisms governing harmonic generation and emphasize the crucial influence of propagation and cascading.