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Terahertz (THz) quantum cascade lasers (QCLs) are technologically important laser sources for the THz range but are complex to model. An efficient extended rate equation model is developed here by incorporating the resonant tunneling mechanism from the density matrix formalism, which permits to simulate THz QCLs with thick carrier injection barriers within the semi-classical formalism. A self-consistent solution is obtained by iteratively solving the Schrödinger–Poisson equation with this transport model. Carrier–light coupling is also included to simulate the current behavior arising from stimulated emission. As a quasi-ab initio model, intermediate parameters, such as pure dephasing time and optical linewidth, are dynamically calculated in the convergence process, and the only fitting parameters are the interface roughness correlation length and height. Good agreement has been achieved by comparing the simulation results of various designs with experiments, and other models such as density matrix Monte Carlo and non-equilibrium Green's function method that, unlike here, require important computational resources. The accuracy, compatibility, and computational efficiency of our model enable many application scenarios, such as design optimization and quantitative insights into THz QCLs. Finally, the source code of the model is also provided in the supplementary material of this article for readers to repeat the results presented here, investigate, and optimize new designs. [ABSTRACT FROM AUTHOR]

The rotational state resolved photodissociation dynamics of D2O via the C ̃ (010) state has been investigated by using the D-atom Rydberg tagging time-of-flight technique combined with a tunable vacuum ultraviolet light source. The D-atom action spectrum of the C ̃ (010) ← X ̃ (000) band and the corresponding time-of-flight (TOF) spectra of D-atom photoproducts formed following the excitation of D2O to individual rotational transition have been measured. By comparison with the action spectrum of the C ̃ (000) ← X ̃ (000) band, the bending vibrational constant of the C ̃ state for D2O can be determined to be v2 = 1041.37 ± 0.71 cm−1. From the TOF spectra, the product kinetic energy spectra, the vibrational state distributions of OD products, and the state resolved anisotropy parameters have been determined. The experimental results indicate a dramatic variation in the OD product state distributions for different rotational excitations. This illuminates that there are two distinctive coupling channels from the C ̃ (010) state to the low-lying electronic states: the homogeneous electronic coupling to the Ã1B1 state, resulting in vibrationally hot OD(X) products, and the Coriolis-type coupling to the B ̃ 1A1 state, producing vibrationally cold but rotationally hot OD(X) and OD(A) products. Furthermore, the three-body dissociation channel is confirmed, which is attributed to the C ̃ → 1A2 or C ̃ → Ã pathway. In comparison with the previous results of D2O photolysis via the C ̃ (000) state, it is found that the v2 vibration of the parent molecule enhances both the vibrational and rotational excitations of OD products. [ABSTRACT FROM AUTHOR]

Theoretical investigation of electro-absorption modulators in the mid-infrared range (>∼2 μm) is performed using asymmetric intra-step quantum wells based on Ge1−η1Snη1/Ge1−η2Snη2 heterostructures with SiGeSn outer barriers. After exploring the parameter space of the Sn content difference and width ratio of the intra-layers, a linear and much larger Stark shift is realized, compared to that of a square quantum well, without an increase of the total structure width. A modulator based on an optimized intra-step quantum well structure with a total well width of 12 nm is theoretically predicted to have both a larger peak shift per unit applied field and a larger absorption change than a 12 nm square quantum well device. By analyzing the device performance based on the two figures of merit: (1) absorption change per applied field and (2) absorption change per applied field squared, and taking 10 dB extinction ratio, a 44% higher bandwidth per volt and 46% lower power consumption per bit are achieved in intra-step than in a square well. Although the swing voltage for a square quantum well can be reduced by using a larger on-set applied field and performance could be improved, we found that the intra-step quantum well using zero on-set still retains its advantages when compared to the square quantum well which uses a 0.5 V on-set voltage. [ABSTRACT FROM AUTHOR]

This study aims to establish a highly sensitive and specific method for single cell screening and identification of KRAS+/epithelial cell adhesion molecules (EpCAMs)/vimentin+/pancreatic cancer circulating tumor cells (CTCs) and to explore the clinical implications in the diagnosis of pancreatic cancer. A single cell separation and identification system for pancreatic cancer CTCs was constructed based on the preparation of KRAS immunolipid magnetic spheres. The function of the system was evaluated, the physical parameters of the immunoliposomes (IMLs) were characterized, and the isolation effect of the IMLs on CTCs was studied and compared with EpCAM and vimentin phenotypic CTCs. CTCs in the peripheral blood of 50 patients with pancreatic cancer confirmed by preoperative CT diagnosis and postoperative pathology were isolated and identified. The isolated CTCs were stained with CK immune antibody, observed, and identified, the number of CTCs was counted, and the relationship between the CTC count and the clinical malignant grade markers and grade indicators was examined. The consistency of the KRAS mutation rate between CTCs and tissues was analyzed and compared. It was found that the circulating tumor cell sorting system with a high expression of KRAS-ML could effectively enrich the circulating tumor cells with a positive expression of KRAS in pancreatic cancer. The pancreatic cancer CTC sorting and single-cell gene detection system can be used as a new detection technology of peripheral blood CTCs in patients with pancreatic cancer. As a minimally invasive liquid biopsy method, this technology has significant clinical practice implications for pancreatic cancer detection and effectiveness assessment. [ABSTRACT FROM AUTHOR]

Giant-permittivity CaCu3Ti4O12 has been modeled by nature at an atomic or electronic scale. Notably, the relation between the imaginary part of the complex dielectric value and the frequency of the applied A.C. electric field is found to deviate from the universal dielectric response in the frame of classic mechanics. Only the deviation is elucidated based on the model, and thus, a clue to quantum dielectric physics appears. [ABSTRACT FROM AUTHOR]

In this article, we describe an experimental setup for studying tunable vacuum ultraviolet photochemistry using the H-atom Rydberg tagging time-of-flight technique. In this apparatus, two vacuum ultraviolet laser beams were used: one is generated by using a nonlinear four-wave mixing scheme in a Kr gas cell and fixed at 121.6 nm wavelength to probe the H-atom product through the Lyman α transition and the other beam, produced by a seeded free electron laser facility, can be continuously tunable for photodissociating molecules in the wavelength range of 50-150 nm with extremely high brightness. Preliminary results on the H2O photodissociation in the 4d (000) Rydberg state are reported here. These results suggest that the experimental setup is a powerful tool for investigating photodissociation dynamics in the vacuum ultraviolet region for molecules involving H-atom elimination processes. [ABSTRACT FROM AUTHOR]

Photodissociation dynamics of H2O via the F ̃ state at 111.5 nm were investigated using the high resolution H-atom Rydberg “tagging” time-of-flight (TOF) technique, in combination with the tunable vacuum ultraviolet free electron laser at the Dalian Coherent Light Source. The product translational energy distributions and angular distributions in both parallel and perpendicular directions were derived from the recorded TOF spectra. Based on these distributions, the quantum state distributions and angular anisotropy parameters of OH (X) and OH (A) products have been determined. For the OH (A) + H channel, highly rotationally excited OH (A) products have been observed. These products are ascribed to a fast direct dissociation on the B ̃ 1A1 state surface after multi-step internal conversions from the initial excited F ̃ state to the B ̃ state. While for the OH (X) + H channel, very highly rotationally excited OH (X) products with moderate vibrational excitation are revealed and attributed to the dissociation via a nonadiabatic pathway through the well-known two conical intersections between the B ̃ -state and the X ̃ -state surfaces. [ABSTRACT FROM AUTHOR]

The shape of the photoluminescence line registered from a side edge of InP wafer is studied as a function of the distance from the excitation spot. The observed redshift in the luminescence maximum is well described by radiation filtering and is consistent with the absorption spectra. Our method provides an independent and accurate determination of the Urbach tails in moderately doped semiconductors. [ABSTRACT FROM AUTHOR]

The rotational state resolved photodissociation dynamics of D 2 O via the C̃(010) state has been investigated by using the D-atom Rydberg tagging time-of-flight technique combined with a tunable vacuum ultraviolet light source. The D-atom action spectrum of the C̃(010) ← X̃(000) band and the corresponding time-of-flight (TOF) spectra of D-atom photoproducts formed following the excitation of D 2 O to individual rotational transition have been measured. By comparison with the action spectrum of the C̃(000) ← X̃(000) band, the bending vibrational constant of the C̃ state for D 2 O can be determined to be v 2 = 1041.37 ± 0.71 cm -1 . From the TOF spectra, the product kinetic energy spectra, the vibrational state distributions of OD products, and the state resolved anisotropy parameters have been determined. The experimental results indicate a dramatic variation in the OD product state distributions for different rotational excitations. This illuminates that there are two distinctive coupling channels from the C̃(010) state to the low-lying electronic states: the homogeneous electronic coupling to the à 1 B 1 state, resulting in vibrationally hot OD(X) products, and the Coriolis-type coupling to the B̃ 1 A 1 state, producing vibrationally cold but rotationally hot OD(X) and OD(A) products. Furthermore, the three-body dissociation channel is confirmed, which is attributed to the C̃ → 1 A 2 or C̃ → à pathway. In comparison with the previous results of D 2 O photolysis via the C̃(000) state, it is found that the v 2 vibration of the parent molecule enhances both the vibrational and rotational excitations of OD products.

We study the vacuum ultraviolet photodissociation dynamics of N 2 O via the C 1 Π state by using the time-sliced velocity map ion imaging technique. Images of N( 2 D j=5/2, 3/2 ) products from the N atom elimination channels were acquired at a set of photolysis wavelengths from 142.55 to 148.19 nm. Vibrational states of the NO(X 2 Π) co-fragments were partially resolved in experimental images. From these images, the product total kinetic energy release distributions (TKERs), branching ratios of the vibrational states of NO(X 2 Π) co-fragments, and the vibrational state specific angular anisotropy parameters ( β ) have been determined. Notable features were found in the experimental results: the TKERs show that the NO(X 2 Π) co-fragments are highly vibrationally excited. For the highly vibrationally excited state of NO(X 2 Π), a bimodal rotational structure is found at all the studied photolysis wavelengths. Furthermore, the vibrational state specific β values of both spin-orbit channels (j = 3/2, 5/2) clearly show a monotonic decrease as the vibrational quantum number of NO(X 2 Π) increases. These observations suggest that multiple dissociation pathways play a role in the formation of the N( 2 D j=5/2, 3/2 ) + NO(X 2 Π) products: one corresponds to a fast dissociation pathway through the linear state (the C 1 Π state) following the initial excitation to a slightly bent geometry in the vicinity of the linear C 1 Π configuration, leading to the low rotationally excited components with relatively large β values; the other corresponds to a relatively slow dissociation pathway through the bent C(3 1 A') or C(3 1 A″) state, leading to moderately rotationally excited NO(X 2 Π) products with smaller β values.

Photodissociation dynamics of H 2 O via the F̃ state at 111.5 nm were investigated using the high resolution H-atom Rydberg "tagging" time-of-flight (TOF) technique, in combination with the tunable vacuum ultraviolet free electron laser at the Dalian Coherent Light Source. The product translational energy distributions and angular distributions in both parallel and perpendicular directions were derived from the recorded TOF spectra. Based on these distributions, the quantum state distributions and angular anisotropy parameters of OH (X) and OH (A) products have been determined. For the OH (A) + H channel, highly rotationally excited OH (A) products have been observed. These products are ascribed to a fast direct dissociation on the B̃ 1 A 1 state surface after multi-step internal conversions from the initial excited F̃ state to the B̃ state. While for the OH (X) + H channel, very highly rotationally excited OH (X) products with moderate vibrational excitation are revealed and attributed to the dissociation via a nonadiabatic pathway through the well-known two conical intersections between the B̃-state and the X̃-state surfaces.

Photodissociation dynamics of HOD from the B̃ state has been studied using H/D atom Rydberg "tagging" time-of-flight technique. Both the OD + H and OH + D channels have been investigated. Product kinetic energy distributions, internal state distributions of the OD/OH product, as well as the OD/OH quantum state specific angular anisotropy parameters have been determined. Overall, the photodissociation dynamics of HOD via the B̃ state is qualitatively similar to that of the H2O and D2O, with quantitative differences arising probably from the change in masses. At different photolysis energies, similar rovibrational distributions and state-resolved angular distributions have been observed for the OH/OD(X) product, while remarkable differences have been observed in the rovibrational distributions and state-resolved angular distributions of the OH/OD(A) product.