11 research outputs found
VUV frequency combs from below-threshold harmonics
Recent demonstrations of high-harmonic generation (HHG) at very high
repetition frequencies (~100 MHz) may allow for the revolutionary transfer of
frequency combs to the vacuum ultraviolet (VUV). This advance necessitates
unifying optical frequency comb technology with strong-field atomic physics.
While strong-field studies of HHG have often focused on above-threshold
harmonic generation (photon energy above the ionization potential), for VUV
frequency combs an understanding of below-threshold harmonic orders and their
generation process is crucial. Here we present a new and quantitative study of
the harmonics 7-13 generated below and near the ionization threshold in xenon
gas. We show multiple generation pathways for these harmonics that are
manifested as on-axis interference in the harmonic yield. This discovery
provides a new understanding of the strong-field, below-threshold dynamics
under the influence of an atomic potential and allows us to quantitatively
assess the achievable coherence of a VUV frequency comb generated through below
threshold harmonics. We find that under reasonable experimental conditions
temporal coherence is maintained. As evidence we present the first explicit VUV
frequency comb structure beyond the 3rd harmonic.Comment: 16 pages, 4 figures, 1 tabl
Surface Versus Bulk State Transitions in Inkjet-Printed All-Inorganic Perovskite Quantum Dot Films
The anion exchange of the halides, Br and I, is demonstrated through the direct mixing of two pure perovskite quantum dot solutions, CsPbBr3 and CsPbI3, and is shown to be both facile and result in a completely alloyed single phase mixed halide perovskite. Anion exchange is also observed in an interlayer printing method utilizing the pure, unalloyed perovskite solutions and a commercial inkjet printer. The halide exchange was confirmed by optical absorption spectroscopy, photoluminescent spectroscopy, X-ray diffraction, and X-ray photoemission spectroscopy characterization and indicates that alloying is thermodynamically favorable, while the formation of a clustered alloy is not favored. Additionally, a surface-to-bulk photoemission core level transition is observed for the Cs 4d photoemission feature, which indicates that the electronic structure of the surface is different from the bulk. Time resolved photoluminescence spectroscopy indicates the presence of multiple excitonic decay features, which is argued to originate from states residing at surface and bulk environments