A phonon scattering assisted injection and extraction based terahertz quantum cascade laser

A novel lasing scheme for terahertz quantum cascade lasers, based on consecutive phonon-photon-phonon emissions per module, is proposed and experimentally demonstrated. The charge transport of the proposed structure is modeled using a rate equation formalism. An optimization code based on a genetic algorithm was developed to find a four-well design in the $\mathrm{GaAs/Al_{0.25}Ga_{0.75}As}$ material system that maximizes the product of population inversion and oscillator strength at 150 K. The fabricated devices using Au double-metal waveguides show lasing at 3.2 THz up to 138 K. The electrical characteristics display no sign of differential resistance drop at lasing threshold, which suggests - thanks to the rate equation model - a slow depopulation rate of the lower lasing state, a hypothesis confirmed by non-equilibrium Green's function calculations.Comment: 11 pages, 10 figure

A phonon scattering assisted injection and extraction based terahertz quantum cascade laser

A novel lasing scheme for terahertz quantum cascade lasers, based on consecutive phonon-photon-phonon emissions per module, is proposed and experimentally demonstrated. The charge transport of the proposed structure is modeled using a rate equation formalism. An optimization code based on a genetic algorithm was developed to find a four-well design in the $\mathrm{GaAs/Al_{0.25}Ga_{0.75}As}$ material system that maximizes the product of population inversion and oscillator strength at 150 K. The fabricated devices using Au double-metal waveguides show lasing at 3.2 THz up to 138 K. The electrical characteristics display no sign of differential resistance drop at lasing threshold, which suggests - thanks to the rate equation model - a slow depopulation rate of the lower lasing state, a hypothesis confirmed by non-equilibrium Green's function calculations.Comment: 11 pages, 10 figure

Electrically switching transverse modes in high power THz quantum cascade lasers.

The design and fabrication of a high power THz quantum cascade laser (QCL), with electrically controllable transverse mode is presented. The switching of the beam pattern results in dynamic beam switching using a symmetric side current injection scheme. The angular-resolved L-I curves measurements, near-field and far-field patterns and angular-resolved lasing spectra are presented. The measurement results confirm that the quasi-TM(01) transverse mode lases first and dominates the lasing operation at lower current injection, while the quasi-TM(00) mode lases at a higher threshold current density and becomes dominant at high current injection. The near-field and far-field measurements confirm that the lasing THz beam is maneuvered by 25 degrees in emission angle, when the current density changes from 1.9 kA/cm(2) to 2.3 kA/cm(2). A two-dimension (2D) current and mode calculation provides a simple model to explain the behavior of each mode under different bias conditions

A case report and literature review of the late presenting congenital diaphragmatic hernia

Late presenting congenital diaphragmatic hernia is a disease associated with defective diaphragm and penetration of different organs into the thoracic cavity. In the present case, a 3-year-old boy was referred to our hospital complaining of acute abdominal pain. No other gastrointestinal symptoms including nausea, vomiting, or constipation were observed. The patient represented no respiratory problems such as dyspnea or respiratory distress syndrome. Radiograph of the thoracic and abdominal cavities showed bowel loops occupying the entire space of the left hemithorax and right-shifted mediastinum. The patient was referred to the pediatric surgery center. The defect was resolved by prompt surgical intervention. A follow-up radiograph within 6 months of surgery showed complete recovery. © 2018 Annals of Pediatric Surgery

Effects of interface roughness scattering on device performance of indirectly pumped terahertz quantum cascade lasers

The impacts of interface roughness (IR) scattering on device performance of indirectly-pumped (IDP) terahertz quantum cascade lasers are studied. Three different active region designs with almost the same lasing frequency at threshold and comparable oscillator strength are experimentally investigated and the measurement data are analyzed and compared with numerical simulation. The simulation results show that all structures suffer from the detrimental effect of intersubband roughness scattering in terms of threshold current density, and probably operating temperature. The intrasubband IR scattering time could also to be a limiting factor in the IDP structures due to the employed high energetic barrier.Peer reviewed: YesNRC publication: Ye

Rate equation analysis of three phonon-photon-phonon terahertz quantum cascade lasers

A rate equation model is presented to analyze the performance of terahertz quantum cascade lasers based on consecutive phonon-photon-phonon emissions. Devices lased up to 128.5, 138, and 144 K at 2.5, 3.2 and 2.6 THz, respectively. \ua9 Optical Society of America.Peer reviewed: YesNRC publication: Ye

Nanoscopically resolved dynamic charge-carrier distribution in operating interband cascade lasers

Abstract Dynamic charge carriers play a vital role in active photonic quantum/nanodevices, such as electrically pumped semiconductor lasers. Here we present a systematic experimental study of gain-providing charge-carrier distribution in a lasing interband cascade laser. The unique charge-carrier distribution profile in the quantum-well active region is quantitatively measured at nanometer scales by using a noninvasive scanning voltage microscopy technique. Experimental results clearly confirm the accumulation and spatial segregation of holes and electrons in the beating heart of the device. The measurement also shows that the charge-carrier density is essentially clamped in the presence of stimulated emission at low temperatures. The threshold charge-carrier density exhibits a linear but fairly weak temperature dependence, in contrast to the exponential temperature dependence of the threshold current. The experimental approach will lead to a deeper understanding of fundamental processes that govern the operation and performance of nanoelectronic devices, quantum devices and optoelectronic devices

On metal contacts of terahertz quantum cascade lasers with a metal-metal waveguide

This paper reports an experimental study of the effects of different metal claddings on the performance of terahertz quantum cascade lasers. The experimental results show that by using a metal cladding made of Ta/Cu/Au to replace that of Pd/Ge/Ti/Pt/Au, the maximum lasing temperature of the devices is increased from 132 to 172 K, and the threshold current density of the devices at 10 K can be reduced from 0.74 to 0.68 kA cm 122. The improvement of the device performance is attributed to lower optical losses associated with the metal cladding layers. The different effects of the metal contacts on device optical properties and electrical properties are also discussed.Peer reviewed: YesNRC publication: Ye