High-harmonic generation with ultra-low threshold and extraordinary photon flux in CdTe

Abstract An ultra-low pump threshold and high photon flux have been long pursuits of high harmonic generation (HHG) in solids, which would benefit various applications such as attosecond generation, ultrafast electron dynamics studies, extreme ultraviolet spectroscopy, and coherent diffraction imaging. Here, we report non-perturbative HHG with extraordinary characteristics from a cadmium telluride (CdTe) bulk crystal exhibiting a flat shape of band dispersion near the Fermi level and high carrier mobility. The measured pump intensity threshold for the 12th and 31st harmonics is only 30 and 75 GW/cm2, respectively, one order of magnitude lower than that of other pristine crystals including two-dimensional materials reported so far. The HHG output grows with the pump intensity up to 4.5 TW/cm2 without saturation. A comparative measurement shows CdTe has two-to-three orders of magnitude stronger HHG than silicon does. This work opens up exciting possibilities for developing compact coherent light sources across the spectrum and attosecond photonics devices.