Optical properties and potential of LB4 for THz wave generation

Optical properties of a Li2B4O7 (LB4) crystal are determined in the spectral range 0.2-1.6 THz. Dispersion of the refractive index components for o- and e-wave are approximated in the form of Sellmeier equations. They are subsequently used to determine the possible interaction types and to calculate the phase-matching angles to get THz waves by difference frequency generation. The damage threshold is determined as well as the coherence length for all possible types of three wave interactions under the pump by fs Ti: Sapphire laser pulses at 950 nm. The efficiency of the processes is estimated. Using trains of hundreds of pulses at 950 nm it was found to be 1.32 times of that for β-BBO crystal laser pump

Dynamics and control of active sites in hierarchically nanostructured cobalt phosphide/chalcogenide-based electrocatalysts for water splitting

The rational design of efficient electrocatalysts for industrial water splitting is essential to generate sustainable hydrogen fuel. However, a comprehensive understanding of the complex catalytic mechanisms under harsh reaction conditions remains a major challenge. We apply a self-templated strategy to introduce hierarchically nanostructured “all-surface” Fe-doped cobalt phosphide nanoboxes (Co@CoFe–P NBs) as alternative electrocatalysts for industrial-scale applications. Operando Raman spectroscopy and X-ray absorption spectroscopy (XAS) experiments were carried out to track the dynamics of their structural reconstruction and the real catalytically active intermediates during water splitting. Our operando analyses reveal that partial Fe substitution in cobalt phosphides promotes a structural reconstruction into P–Co–O–Fe–P configurations with low-valence metal centers (M0/M+) during the hydrogen evolution reaction (HER). Results from density functional theory (DFT) demonstrate that these in situ reconstructed configurations significantly enhance the HER performance by lowering the energy barrier for water dissociation and by facilitating the adsorption/desorption of HER intermediates (H*). The competitive activity in the oxygen evolution reaction (OER) arises from the transformation of the reconstructed P–Co–O–Fe–P configurations into oxygen-bridged, high-valence CoIV–O–FeIV moieties as true active intermediates. In sharp contrast, the formation of such CoIII/IV–O–FeIII/IV moieties in Co–FeOOH is hindered under the same conditions, which outlines the key advantages of phosphide-based electrocatalysts. Ex situ studies of the as-synthesized reference cobalt sulfides (Co–S), Fe doped cobalt selenides (Co@CoFe–Se), and Fe doped cobalt tellurides (Co@CoFe–Te) further corroborate the observed structural transformations. These insights are vital to systematically exploit the intrinsic catalytic mechanisms of non-oxide, low-cost, and robust overall water splitting electrocatalysts for future energy conversion and storage

Terahertz birefringence and dichroism of KTA crystal

For the first time, we present the spectra of all three components of the refractive index and absorption coefficient of the KTiOAsO4 (KTA) crystal measured by the means of terahertz time-domain spectroscopy in the range of 0.3–2.1 THz. The dispersion of the refractive index is approximated and presented in the form of the Sellmeier equation. We observe a large birefringence ΔnZ-X ≈ 0.76 and dichroism which is attributed to a strong absorption peak in the vicinity of ~1.23–1.25 THz for the Z-axis. However, the crystal can be considered as almost uniaxial due to a close value of nX and nY as well as αX ≈ αY in the region below 0.5 THz. Moreover, KTA crystals can satisfy the phase-matching condition in principal XZ-plane for THz emission on difference frequency generation mechanism. Therefore, the crystal could be considered as an efficient candidate for terahertz wave generator under intense laser pump

Optical properties of vanadium and nitrogen doped 4H and 6H-SiC

Linear optical properties of vanadium (V) and nitrogen (N) doped single-crystal sub-millimeter wafers of 4H-S1C and 6H-S1C grown for industrial applications in optics and electronics are studied in detail within transparency window and from 0.2 THz to 2.1 THz range to reveal usability in parametric frequency conversion. Manufactured wafers are found not uniform in polytype composition. Optical properties of majority of wafers indicated applicability for THz wave generation by optical rectification method. The wafers demonstrated large optical damage threshold exceeding that for widely used crystals GaSe at least for from 3 to 5 times and up to 10 times lower (from a few tens to below 1 cm') absorption coefficient in the THz range. Birefringence of doped 4H-S1C are still close to that for pure crystals, i.e. suitable for phase matched frequency conversion within the transparency window or into the THz region. Polytype 6H seems suitable for phase matched down-conversion into the THz range. Nevertheless, absolute values of refractive indices are seriously varying wafer to wafer

Optical properties of vanadium and nitrogen doped 4H and 6H-SiC

Linear optical properties of vanadium (V) and nitrogen (N) doped single-crystal sub-millimeter wafers of 4H-S1C and 6H-S1C grown for industrial applications in optics and electronics are studied in detail within transparency window and from 0.2 THz to 2.1 THz range to reveal usability in parametric frequency conversion. Manufactured wafers are found not uniform in polytype composition. Optical properties of majority of wafers indicated applicability for THz wave generation by optical rectification method. The wafers demonstrated large optical damage threshold exceeding that for widely used crystals GaSe at least for from 3 to 5 times and up to 10 times lower (from a few tens to below 1 cm') absorption coefficient in the THz range. Birefringence of doped 4H-S1C are still close to that for pure crystals, i.e. suitable for phase matched frequency conversion within the transparency window or into the THz region. Polytype 6H seems suitable for phase matched down-conversion into the THz range. Nevertheless, absolute values of refractive indices are seriously varying wafer to wafer

Remote imaging by nanosecond terahertz spectrometer with standoff detector

Creation and application of the remote imaging spectrometer based on high power nanosecond terahertz source with standoff detector is reported. 2D transmission images of metal objects hided in nonconductive (dielectric) materials were recorded. Reflection images of metal objects mounted on silicon wafers are recorded with simultaneous determination of the wafer parameters (thickness/material)

Remote imaging by nanosecond terahertz spectrometer with standoff detector

Creation and application of the remote imaging spectrometer based on high power nanosecond terahertz source with standoff detector is reported. 2D transmission images of metal objects hided in nonconductive (dielectric) materials were recorded. Reflection images of metal objects mounted on silicon wafers are recorded with simultaneous determination of the wafer parameters (thickness/material)

Geoscience model service integrated workflow for rainstorm waterlogging analysis

This paper proposed a geoscience model service integrated workflow-based rainstorm waterlogging analysis method to overcome the defects of conventional waterlogging analysis systems. In this research, we studied a general OGC WPS service invoking strategy, an automatic asynchronous invoking mechanism of WPS services in the BPEL workflow, and a distributed waterlogging analysis services integrated workflow to realize the reconstruction of a waterlogging analysis model based on the proposed method. The proposed method can make use of the flexible adjustment capability of the workflow and not only overcomes the inherent defects of conventional geoscience analysis methods but also realizes the integration and calculation of distributed geospatial data, models and computing resources automatically. The method has better construction convenience, execution reliability, extensibility and intelligence potential than a conventional method and has important value for dealing with more natural disasters and environmental challenges