Generation of Coherent Extreme-Ultraviolet Radiation from Bulk Sapphire Crystal

Abstract

Coherent extreme-ultraviolet (EUV) radiation produced by means of high-order harmonics generation (HHG) from intense laser pulses is used for various ultrafast pump–probe experiments. In this study, we test bulk sapphire as to its HHG capability as a new solid EUV emitter operating with moderate nJ-energy laser pulses obtained directly from an oscillator. Specifically, the high bandgap of sapphire (∼9 eV) permits EUV harmonics at wavelengths up to ∼60 nm for laser intensities of 1.31 TW cm–2 when irradiated by 12 fs pulses at 800 nm. The EUV output exceeds 107 photons per second without causing drastic thermal damage due to the high heat dissipation capabilities of bulk sapphire. In addition, the free-space EUV propagation can be steered by shaping the bulk surface without requiring extra grazing incidence mirrors. All these experimental findings prove the feasibility of using bulk sapphire as a desktop EUV source for relevant metrological applications.