The photocatalytic water oxidation activity of hematite (α-Fe2O3) has been greatly enhanced by incorporating hematite nanoparticles on the reduced graphene oxide (rGO) nanosheets. Photoelectrochemical measurement results show that coupling the hematite nanoparticles with the rGO greatly increases the photocurrent and reduces the charge recombination rate. Transient absorption spectroscopy and time-domain terahertz spectroscopy have provided the direct evidence that the photogenerated electrons have transferred as the mobile carriers from α-Fe2O3 to rGO, which enhances the charge separation and suppresses the charge recombination. This work has provided new insight into the mechanism of photocatalysis enhancement by reduced graphene oxide, which has implications in the design of semiconductor/graphene heterojunction photocatalysts.

The CEBAF Large Acceptance Spectrometer for operation at 12 GeV beam energy (CLAS12) in Hall B at Jefferson Laboratory is used to study electro-induced nuclear and hadronic reactions. This spectrometer provides efficient detection of charged and neutral particles over a large fraction of the full solid angle. CLAS12 has been part of the energy-doubling project of Jefferson Lab's Continuous Electron Beam Accelerator Facility, funded by the United States Department of Energy. An international collaboration of over 40 institutions contributed to the design and construction of detector hardware, developed the software packages for the simulation of complex event patterns, and commissioned the detector systems. CLAS12 is based on a dual-magnet system with a superconducting torus magnet that provides a largely azimuthal field distribution that covers the forward polar angle range up to 35 • , and a solenoid magnet and detector covering the polar angles from 35 • to 125 • with full azimuthal coverage. Trajectory reconstruction in the forward direction using drift chambers and in the central direction using a vertex tracker results in momentum resolutions of <1% and <3%, respectively. Cherenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data-acquisition rates allow operation at a luminosity of 10 35 cm −2 s −1 . These capabilities are being used in a broad program to study the structure and interactions of nucleons, nuclei, and mesons, using polarized and unpolarized electron beams and targets for beam energies up to 11 GeV. This paper gives a general description of the design, construction, and performance of CLAS12.

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The exclusive electroproduction process ep → e p π 0 was measured in the range of photon virtualities Q 2 = 0.4−1.0 GeV 2 and the invariant mass range of the pπ 0 system of W = 1.1−1.8 GeV. These kinematics are covered in exclusive π 0 electroproduction off the proton with nearly complete angular coverage in the pπ 0 center-of-mass system and with high statistical accuracy. Nearly 36000 cross section points were measured, and the structure functions σT + σL, σLT , and σT T , were extracted via fitting the φ π 0 dependence of the cross section. A Legendre polynomial expansion analysis demonstrates the sensitivity of our data to high-lying N * and ∆ * resonances with M > 1.6 GeV. As part of a broad effort to determine the electrocouplings of the N * and ∆ * resonances using both single-and double-pion electroproduction, this dataset is crucial for the reliable extraction of the high-lying resonance electrocouplings from the combined isospin analysis of the N π and π + π − p channels.PACS numbers:

Optical rectification is demonstrated in (110)-cut ZnGeP 2 (ZGP) providing broadband terahertz (THz) generation. The source is compared to both GaP and GaAs over a wavelength range of 1150 nm to 1600 nm and peak intensity range of 0.5 GW/cm 2 to 40 GW/cm 2 . ZGP peak-to-peak field amplitude is larger than in the other materials due to either lower nonlinear absorption or larger second order nonlinearity. This material is well suited for broadband THz generation across a wide range of infrared excitation wavelengths.Over the last decade, broadband sources of intense THz pulses have received significant attention due to the possibility of accessing a diverse range of light-matter interactions and the potential for creating high-speed electronics. For a recent review of the progress see Ref.[1] and references therein. Large-area zincblende ̅ crystals are commonly used in time-domain terahertz spectroscopy as sources and electrooptic (EO) samplers [2] due to large second-order nonlinear coefficients. A common issue with materials like GaAs and ZnTe is that the optimum wavelength for THz and optical velocity matching is poorly positioned with respect to the onset of two-photon absorption.Here we generate broadband THz pulses in ZnGeP2, a chalcopyrite (pnictide) crystal with ̅ symmetry, by optical rectification. Optical rectification is a second-order nonlinear optical process that generates a transient D.C. polarization, which typically creates THz radiation for short excitation pulses. In previous work, ZnGeP2 has only been used as a source of narrow-band and tuneable THz radiation through parametric down conversion [3,4]. This work verifies that ZGP has a suitable coherence length, high laserdamage threshold [3] and nonlinear figure-of-merit [5] for optical rectification. ZGP's generation efficiency surpasses that of high-quality and high-resistivity wafers of GaAs and GaP across the infrared, including the datacoms C-band around 1550 nm. This study complements the recent resurgence of interest in ZGP as a nonlinear material driven by high-quality growth [6,7].Undoped ZGP single crystals were grown by the horizontal gradient freeze technique [6]. Samples were cut in the (110) plane and double-side polished for optical transmission measurements. Sample thicknesses are 0.33 mm and 0.93 mm for the short and long crystals respectively. The orientation of the crystals was verified by electron paramagnetic resonance (EPR), ensuring that the z-axis is in the plane of the plate. EPR measures the phosphorus hyperfine signal associated with the zinc-vacancy acceptor in asgrown ZGP, differentiating the 100 and 001 directions [8]. ZGP is birefringent due to a ~2% lattice compression in the z-axis, which complicates the THz generation for pump polarizations that are not parallel or perpendicular to this axis. Measurements were performed at normal incidence with the crystal rotated in the plane to maximize the THz signal. The rotation results in the pump being polarized perpendicular to the z-axis of the ZGP crystal, such th...