Terahertz master-oscillator power-amplifier quantum cascade laser with a grating coupler of extremely low reflectivity

A terahertz master-oscillation power-amplifier quantum cascade laser (THz-MOPA-QCL) is demonstrated where a grating coupler is employed to efficiently extract the THz radiation. By maximizing the group velocity and eliminating the scattering of THz wave in the grating coupler, the residue reflectivity is reduced down to the order of 10−3. A buried DFB grating and a tapered preamplifier are proposed to improve the seed power and to reduce the gain saturation, respectively. The THz-MOPA-QCL exhibits single-mode emission, a single-lobed beam with a narrow divergence angle of 18° × 16°, and a pulsed output power of 136 mW at 20 K, which is 36 times that of a second-order DFB laser from the same material

Efficient solid-state emission and reversible mechanofluorochromism of a tetraphenylethene-pyrene-based β-diketonate boron complex

A new twisted dye (BF2-TP) was synthesized, it possesses distinct mechanofluorochromism with large spectral shift of 62 nm.</p

Enhanced Catalytic Performance of Sn Single-Atom Doped CuO with Oxygen Vacancies for Efficient Epoxidation of &alpha;-Olefins

Epoxidation of long-chain &alpha;-olefins (LAOs) is a process of paramount importance, particularly in the preparation of epoxides. Traditional epoxidation methods, such as the chlorohydrin method and peracid method, suffer from issues such as poor selectivity, by-product formation, and environmental pollution. Mukaiyama epoxidation, with its mild reaction conditions and exceptional selectivity, has attracted widespread attention and considerable research. Transition metal oxide catalysts show potential in the reaction; however, the catalytic efficiency still require substantial improvement due to dilemma of substance activation. In this study, a synergistic enhancement method was employed, achieved through the creation of oxygen vacancies and the electron-rich nature of Cu. The substitution of Cu with Sn in CuO facilitates the creation of oxygen vacancy (Vo), thereby enhancing absorption and activation of O2. The conversion for O2 activation paves the way for the formation of benzoyl peroxy radicals. Moreover, the interaction between Sn and Cu promotes charge transfer from Sn to Cu, resulting in an electron-rich Cu surface that significantly accelerates the dehydrogenation of benzaldehyde. The synergistic enhancement protocol exhibits near-quantitative performance, delivering an oxide yield of 92.9%. This study introduces an innovative dual-promotion catalytic strategy for Mukaiyama epoxidation utilizing readily available O2, providing profound insights into the optimization design of transition metal oxide catalysts and beyond

The roles of La content on the microstructure, corrosion resistance and discharge behavior of as-extruded Mg–6Al–3Pb alloy bars: Actual experiments and first-principles calculations

The microstructure, corrosion resistance and discharge properties of as-extruded Mg–6Al–3Pb-xLa (x = 0.5, 1.0 wt%) alloy bars in the transverse direction (TD) and extrusion direction (ED) were systemically investigated and compared. With the increase of La content, the second phase (mainly Al11La3, LaAl3) was gradually increased from 3.69 % to 4.19 %–6.82 % and 5.59 %. However, their average grain size was similar, from 24.42 μm to 25.66 μm–21.31 μm and 23.05 μm. The microstructure was different between the different directions (ED or TD), (1) the distribution characteristic of second phase: The second phase was uniformly distributed in the TD-samples, whereas the counterparts in the ED-samples were irregularly distributed in bands, predominantly along the ED. (2) the distribution characteristic of texture: the color of grains in the TD-samples was blue or green (mainly composed of non-basal plane orientations.), whereas the counterparts in the ED-samples were red or purple (The basal plane orientation is predominant). Regarding corrosion behaviors, the AP63-1La alloy presented the better corrosion resistance compared to the AP63-0.5La alloy, mainly be ascribed to the increased volume fraction of Al11La3 and LaAl3 phase. The essence was that both of them had higher potentials/better corrosion resistance than the Mg-matrix, which was verified by the calculation of work function (Al11La3: 4.18, LaAl3: 4.49, Mg: 3.70) via DFT calculation. In terms of discharge properties, the AP63-1La (TD) alloy had the best discharge properties with an average discharge potential of −1.707 V (vs. SCE)

Supplementary document for Continuous-wave terahertz quantum cascade microlaser arrays operating on various bound states in the continuum - 6502248.pdf

Measurements and simulation detail

Modeling and improving the output power of terahertz master-oscillator power-amplifier quantum cascade lasers

A model based on carrier rate equations is proposed to evaluate the gain saturation and predict the dependence of the output power of a terahertz master-oscillator power-amplifier quantum cascade laser (THz-MOPA-QCL) on the material and structure parameters. The model reveals the design rules of the preamplifier and the power extractor to maximize the output power and the wall-plug efficiency. The correction of the model is verified by its agreement with the experiment results. The optimized MOPA devices exhibit single-mode emission at ∼ 2.6 THz with a side mode suppression ratio of 23 dB, a pulsed output power of 153 mW, a wall-plug efficiency of 0.22%, and a low divergence angle of ∼6°×16°, all measured at an operation temperature of 77 K. The model developed here is helpful for the design of MOPA devices and semiconductor optical amplifiers, in which the active region is based on intersubband transitions.</jats:p