Fig. 1
From: Multi-petahertz electron interference in Cr:Al2O3 solid-state material
Experimental setup and properties of Cr:Al2O3. a Schematic view of experimental setup for the Fourier transform extreme ultraviolet attosecond spectroscopy (FTXUV) based on transient absorption spectroscopy. An IAP with 192-as duration (44-eV center photon energy) and a NIR pulse with 7-fs duration (1.55-eV center photon energy) were used. The target is 36-nm-thick bulk single-crystalline α-Al2O3 with Cr dopant. The transmitted IAP from the target was detected by an extreme ultraviolet (XUV) spectrometer. b Measured absorption coefficient α in the target (red filled circles and solid line). For comparison, the red dashed line shows that of the high-purity Al2O3 sample from ref. 8. The inset shows (αħω0)2 as a function of energy. The ħ and ω0 are the Dirac constant and the angular frequency of the injected light source in the absorption spectroscopy. The Urbach energy E0 of the initial donor-like state and bandgap energy Eg of the Al2O3 host material are 5 eV (orange arrow) and 8.7 eV (purple arrow), respectively. c Energy level diagram of the target. The green shaded area is the VB of the Al2O3 at K, Γ, A, and H points in wave vector14. The orange shaded area corresponds to the Cr donor-like state. The purple shaded area is the CB state of Al2O3 host material. Blue and red arrows show the IAP and NIR pulse, respectively
