Single-mode characteristic of a supermode microcavity Raman laser

Microlasers in near-degenerate supermodes lay the cornerstone for studies of non-Hermitian physics, novel light sources, and advanced sensors. Recent experiments of the stimulated scattering in supermode microcavities reported beating phenomena, interpreted as dual-mode lasing, which, however, contradicts their single-mode nature due to the clamped pump field. Here, we investigate the supermode Raman laser in a whispering-gallery microcavity and demonstrate experimentally its single-mode lasing behavior with a side-mode suppression ratio (SMSR) up to 37 dB, despite the emergence of near-degenerate supermodes by the backscattering between counterpropagating waves. Moreover, the beating signal is recognized as the transient interference during the switching process between the two supermode lasers. Self-injection is exploited to manipulate the lasing supermodes, where the SMSR is further improved by 15 dB and the laser linewidth is below 100 Hz.

A Novel Dual-Mode Dual-Band Bandpass Filter Based on a Single Ring Resonator

In this paper, a dual-mode bandpass filter that operates in two different bands is proposed. A circular patch with a small circular hole is set as the basic resonator, and, as the circular hole moves, the linewidth of the ring resonator becomes non-uniform. Consequently, the ring resonator is structurally asymmetric and exhibits a dual-mode characteristic. A gap is formed in the middle of the resonator, a pair of inductors and capacitors is applied to the gap, and the proposed dual-mode structure operates as a dual-band filter. The first resonant frequency <i>f</i>₁ is determined by the inductor and capacitor values, and the second resonant frequency <i>f</i>₂ is determined by the capacitor values. In addition, the frequency ratio (<i>f</i>₂/<i>f</i>₁) can be adjusted by an appropriate combination of inductor and capacitor values.

A Performance Prediction Model for Pumps as Turbines (PATs)

In recent years, the interest towards the use of pumps operating as turbines (PATs) for the generation of electrical energy has increased, due to the low cost of implementation and maintenance. The main issue that inhibits a wider use of PATs is the lack of corresponding characteristic curves, because manufacturers usually provide only the pump-mode performance characteristics. In the PAT selection phase, the lack of turbine-mode characteristic curves forces users to expend expensive and time-consuming efforts in laboratory testing. In the technical literature, numerous methods are available for the prediction of PAT turbine-mode performance based on the pump-mode characteristics, but these models are usually calibrated making use of few devices. To overcome this limit, a performance database called Redawn is presented and the data collected are used to calibrate novel PAT performance models.

Investigation of Recessed Gate AlGaN/GaN MIS-HEMTs with Double AlGaN Barrier Designs toward an Enhancement-Mode Characteristic

In this work, recessed gate AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with double AlGaN barrier designs are fabricated and investigated. Two different recessed depths are designed, leading to a 5 nm and a 3 nm remaining bottom AlGaN barrier under the gate region, and two different Al% (15% and 20%) in the bottom AlGaN barriers are designed. First of all, a double hump trans-conductance (gm)–gate voltage (VG) characteristic is observed in a recessed gate AlGaN/GaN MIS-HEMT with a 5 nm remaining bottom Al0.2Ga0.8N barrier under the gate region. Secondly, a physical model is proposed to explain this double channel characteristic by means of a formation of a top channel below the gate dielectric under a positive VG. Finally, the impacts of Al% content (15% and 20%) in the bottom AlGaN barrier and 5 nm/3 nm remaining bottom AlGaN barriers under the gate region are studied in detail, indicating that lowering Al% content in the bottom can increase the threshold voltage (VTH) toward an enhancement-mode characteristic.

Directional Goldstone waves in polariton condensates close to equilibrium

Quantum fluids of light are realized in semiconductor microcavities using exciton-polaritons, solid-state quasi-particles with a light mass and sizeable interactions. Here, we use the microscopic analogue of oceanographic techniques to measure the excitation spectrum of a thermalised polariton condensate. Increasing the fluid density, we demonstrate the transition from a free-particle parabolic dispersion to a linear, sound-like Goldstone mode characteristic of superfluids at equilibrium. Notably, we reveal the effect of an asymmetric pumping by showing that collective excitations are created with a definite direction with respect to the condensate. Furthermore, we measure the critical sound speed for polariton superfluids close to equilibrium.

The Aristotelian Psychology of Tragic Mimesis

This paper argues that the psychology of mimesis presupposed by Poetics 4 is immediately relevant to Aristotle’s psychology of tragic mimesis. µανθάνειν καὶ συλλογίζεσθαι at 1448b16 involve a cognitive mode characteristic of Aristotelian induction that joins particulars with universals through spontaneous, non-discursive noetic predication. Aristotle’s view of the cognition of tragic mimesis can be subsumed under the practice of theōria: the inductive re‑cognition of ethical universals is a ‘theoric’ exercise of philosophical reflection on the particulars of the tragic action, an associative intellection that actualizes the subject’s knowledge by joining ethical universals with the particular mimetic praxeis they regard.