Semiconductor compounds are widely used for photocatalytic hydrogen production applications, where photogenerated electron–hole pairs are exploited to induce catalysis. Recently, powders of a metallic oxide (Sr 1-x NbO 3 , 0.03$<$x$<$0.20) were reported to show competitive photocatalytic efficiencies under visible light, which was attributed to interband absorption. This discovery expanded the range of materials available for optimized performance as photocatalysts. Here we study epitaxial thin films of SrNbO 3+δ and find that their bandgaps are ~4.1 eV. Surprisingly, the carrier density of the conducting phase exceeds 10 22 cm -3 and the carrier mobility is only 2.47 cm 2 V -1 s -1 . Contrary to earlier reports, the visible light absorption at 1.8 eV (~688 nm) is due to the plasmon resonance, arising from the large carrier density. We propose that the hot electron and hole carriers excited via Landau damping (during the plasmon decay) are responsible for the photocatalytic property of this material under visible light irradiation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2016

Status And Upgrades of the NLCTA for Studies of Advanced Beam Acceleration, Dynamics, And Manipulation

Abstract Not Provided

Accelerators,ACCPHY↗

DOE OSTI2016

Echo-enabled harmonics up to the 75th order from precisely tailored electron beams

The production of coherent radiation at ever shorter wavelengths has been a long-standing challenge since the invention of lasers1, 2 and the subsequent demonstration of frequency doubling3. Modern X-ray free-electron lasers (FELs) use relativistic electrons to produce intense X-ray pulses on few-femtosecond timescales4, 5, 6. However, the shot noise that seeds the amplification produces pulses with a noisy spectrum and limited temporal coherence. To produce stable transform-limited pulses, a seeding scheme called echo-enabled harmonic generation (EEHG) has been proposed7, 8, which harnesses the highly nonlinear phase mixing of the celebrated echo phenomenon9 to generate coherent harmonic density modulations in the electron beam with conventional lasers. Here, we report on a demonstration of EEHG up to the 75th harmonic, where 32 nm light is produced from a 2,400 nm laser. We also demonstrate that individual harmonic amplitudes are controlled by simple adjustment of the phase mixing. Results show the potential of laser-based manipulations to achieve precise control over the coherent spectrum in future X-ray FELs for new science10, 11.

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

Measurements of Terahertz Generation in a Metallic, Corrugated Beam Pipe

Abstract Not Provided

Accelerators,ACCPHY↗

DOE OSTI2015

A tunable, linac based, intense, broad-band THz source forpump-probe experiments

We propose an intense THz source with tunable frequency and bandwidth that can directly interact with the degrees of freedom that determine the properties of materials and thus provides a new tool for controlling and directing these ultrafast processes as well as aiding synthesis of new materials with new functional properties. This THz source will broadly impact our understanding of dynamical processes in matter at the atomic-scale and in real time. Established optical pumping schemes using femtosecond visible frequency laser pulses for excitation are extended into the THz frequency regime thereby enabling resonant excitation of bonds in correlated solid state materials (phonon pumping), to drive low energy electronic excitations, to trigger surface chemistry reactions, and to all-optically bias a material with ultrashort electric fields or magnetic fields. A linac-based THz source can supply stand-alone experiments with peak intensities two orders of magnitude stronger than existing laser-based sources, but when coupled with atomic-scale sensitive femtosecond x-ray probes it opens a new frontier in ultrafast science with broad applications to correlated materials, interfacial and liquid phase chemistry, and materials in extreme conditions.

36 MATERIALS SCIENCE↗

DOE OSTI2014