Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Cascade”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Frequency combs in optically injected terahertz ring quantum cascade lasers

Quantum cascade lasers (QCLs) have emerged as promising candidates for generating chip-scale frequency combs in mid-infrared and terahertz wavelengths. In this work, we demonstrate frequency comb formation in ring terahertz QCLs using the injection of light from a distributed feedback (DFB) laser. The DFB design frequency is chosen to match the modes of the ring cavity (near 3.3 THz), and light from the DFB is injected into the ring QCL via a bus waveguide. By controlling the power and frequency of the optical injection, we show that combs can be selectively formed and controlled in the ring cavity. Numerical modeling suggests that this comb is primarily frequency-modulated in character, with the injection serving to trigger comb formation. We also show that the ring can be used as a filter to control the output of the DFB QCL, potentially being of interest in terahertz photonic integrated circuits. Our work demonstrates that waveguide couplers are a compelling approach for injecting and extracting radiation from ring terahertz combs and offer exciting possibilities for the generation of new comb states in terahertz, such as frequency-modulated waves, solitons, and more.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Interband cascade light-emitting diodes grown on silicon substrates using GaSb buffer layer

Interband cascade light-emitting diodes (ICLEDs) offer attractive advantages for infrared applications, which would greatly expand if high-quality growth on silicon substrates could be achieved. Here, this work describes the formation of threading dislocations in ICLEDs grown monolithically on GaSb-on-Silicon wafers. The epitaxial growth is done in two stages: the GaSb-on-Silicon buffer is grown first, followed by the ICLED growth. The buffer growth involves the nucleation of a 10-nm-thick AlSb buffer layer on the silicon surface, followed by the GaSb growth. The AlSb nucleation layer promotes the formation of 90° and 60° interfacial misfit dislocations, resulting in a highly planar morphology for subsequent GaSb growth that is almost 100% relaxed. The resulting GaSb buffer for growth of the ICLED has a threading dislocation density of ~10 7 /cm 2 after ~3 μm of growth. The fabricated LEDs showed variations in device performance, with some devices demonstrating comparable light–current–voltage curves to those for devices grown on GaSb substrates, while other devices showed somewhat reduced relative performance. Cross-sectional transmission electron microscopy observations of the inferior diodes indicated that the multiplication of threading dislocations in the active region had most likely caused the increased leakage current and lower output power. Enhanced defect filter layers on the GaSb/Si substrates should provide more consistent diode performance and a viable future growth approach for antimonide-based ICLEDs and other infrared devices.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Thermoradiative energy conversion in infrared interband cascade InAs/GaSb/AlInSb/GaSb type-II superlattice diodes

Thermoradiative energy conversion presents a means for the direct conversion of thermal energy through radiative transfer to a cold scene. However, much of the study of thermoradiative principles has been based on theory and simulations, with only sparse reports on the experimental demonstration of the concept. This work studies thermoradiative energy conversion in InAs/GaSb/AlInSb/GaSb type-II superlattice cascade devices. The devices exhibit a cutoff wavelength of 3.2 μm at 300 K, corresponding to a bandgap of 0.39 eV. Testing under a temperature-controlled chamber and scene demonstrates a maximum power density of 2.9 mW/m2 at a cell temperature of 121 °C. It is consistent with expected values for device operation limited by Shockley–Read–Hall non-radiative recombination. This result is a significant step in providing an experimental demonstration of thermoradiative energy conversion and a means to characterize cell performance, providing a foundation for further development to achieve practical values for power generation.

Islam, Md Toriqul (ORCID:0000000249871320)↗
DOE OSTI2010

Calculation of gain and luminescence spectra of quantum-cascade laser structures taking into account asymmetric emission line broadening

The energy levels, wave functions, and matrix elements of optical dipole transitions are calculated numerically for superlattice quantum-cascade structures. The effect of spectral broadening on the shape of emission spectra is estimated and semiphenomenological asymmetric profiles of emission line broadening are proposed. It is shown that the electroluminescence spectra well agree with the calculated spontaneous recombination spectra. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Efficient cascade quasi-synchronous parametric generation with up-conversion

We report efficient cascade up-conversion generation due to two simultaneous quasi-synchronous processes of parametric decay {omega}{sub 3{yields}{omega}1}+ {omega}{sub 2} of pump quanta at the frequency {omega}{sub 3} and up-conversion of one of the generated waves {omega}{sub 1}+{omega}{sub 3{yields}{omega}4}>{omega}{sub 3} at the frequency {omega}{sub 1} in a medium with a quadratic nonlinearity. It is found that the necessary condition for this generation is the requirement |{gamma}{sub 1}|{sup 2}>({omega}{sub 2}/{omega}{sub 1})|{gamma}{sub 1}|{sup 2}, where {gamma}{sub 1,2} are the averaged constants of the nonlinear coupling for the processes {omega}{sub 1}+{omega}{sub 2,3{yields}{omega}3,4}, respectively. If this requirement is fulfilled, the plane monochromatic pump wave is completely depleted, while the limiting (the noise seed intensity is I{sub 10,20{yields}}0 at the input) efficiency of the energy conversion into radiation at the frequency {omega}{sub 4} is independent of I{sub 10,20} and determined only by the relations between |{gamma}{sub 1,2}|{sup 2} and the frequencies of the interacting waves. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Cascaded second-harmonic generation, summation of the wave vectors of the bulk defect-deformation waves, and generation of multimode micro- and nanostructures by laser irradiation of solids

We consider for the first time three-wave interactions of bulk quasi-static defect-deformation (DD) waves (generation of the second DD harmonic and summation of the wave vectors), similar to three-wave interactions in nonlinear optics and acoustics, leading to cascaded broadening of the spectrum of spatial DD harmonics. Based on the theory developed, we interpret the recently observed effect of laser-induced generation of the bulk periodic structure of silver nanoparticles with a discrete spatial spectrum, extending from micro- to nanometres. (nonlinear optical phenomena)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Two-cascade acousto-optic dispersive delay line for ultrashort laser pulses

An optical dispersive delay line for controlling the spectral composition and phase of ultrashort laser pulses is considered. To control independently the spectral amplitude and spectral phase of pulses, it is proposed to use the cascade arrangement of two acousto-optic cells with different control signals. (letters)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Cascade amplification of self-similar frequency-modulated pulses in normal group velocity dispersion active fibres

This paper examines the possibility of efficient amplification of self-similar frequency-modulated wave packets in longitudinally inhomogeneous active fibres. We analyse the dynamics of parabolic pulses with a constant frequency modulation rate and derive algorithms for optimising the group velocity dispersion profile in order to ensure self-similar propagation of such pulses. We demonstrate that the use of a cascade scheme can ensure efficient amplification of individual subpicosecond pulses of this type. (optical fibres, lasers and amplifiers. properties and applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Broadening and splitting of emission spectra of a GaInAs/AlInAs quantum cascade laser in a quantising magnetic field

We have studied the effect of a relatively weak quantising magnetic field on emission spectra of a GaInAs/AlInAs quantum cascade laser near 10 K. The results demonstrate that, as the magnetic field induction increases to 7 T, the spectra broaden (to 5 meV) and split into three emission bands. As a result, we observe simultaneously up to 80 longitudinal lasing modes in the three bands and the integrated laser output intensity increases 70 times. The presence of bands in the emission spectra can be accounted for in terms of the magnetic quantisation of the laser levels into spinsplit Landau levels. The increase in emission intensity is attributable primarily to phonon resonance adjustment in a magnetic field. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Fabrication-tolerant integrated polarisation splitter based on cascaded Mach–Zehnder interferometers

We report a fabrication-tolerant polarisation splitter based on cascaded Mach – Zehnder interferometers. This configuration enables a factor of 2 – 3 increase (at the 20 dB level) in the tolerance to the phase difference in comparison with a single interferometer. As an example, we present numerical simulation of a splitter with a centre wavelength of 650 nm, based on a planar waveguide from Si{sub 3}N{sub 4}. The permissible channel waveguide width deviation from calculation results (20-dB extinction coefficient bandwidth) is ∼8% (∼30 nm) for the TE polarisation and ∼30% (100 nm) for the TM polarisation. (fiber and integrated optics)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Equivalent circuit-level model and improvement of terahertz quantum cascade lasers

An equivalent circuit-level model of terahertz (THz) quantum cascade lasers (QCLs) is developed by using rate equations. This model can be employed to investigate the characteristics of THz QCLs accurately and to improve their design. We use the circuit-level model to analyse a new active structure, which can improve the performance of THz QCLs by means of enhancing carrier injection. The simulation result shows that THz QCLs with the new active structure have a much higher performance compared with conventional THz QCLs. The high-performance THz QCLs are expected to be operated at higher temperatures. (lasers)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Quantum cascade laser based on GaAs/Al{sub 0.45}Ga{sub 0.55}As heteropair grown by MOCVD

A pulsed quantum cascade laser emitting in the wavelength range 9.5–9.7 μm at 77.4 K is developed based on the GaAs/Al{sub 0.45}Ga{sub 0.55}As heteropair. The laser heterostructure was grown by MOCVD. The threshold current density was 1.8 kA cm{sup -2}. The maximum output power of the laser with dimensions of 30 μm × 3 mm and with cleaved mirrors exceeded 200 mW. (lasers)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Generation of linearly polarised light near 1.4 μm in a cascaded, random distributed feedback Raman laser

We have demonstrated efficient generation of linearly polarised light by a random distributed feedback laser based on stimulated Raman scattering in a 1.8-km-long fibre, pumped by linearly polarised radiation of an ytterbium-doped fibre laser with a lasing wavelength near 1.06 μm. Cascaded generation up to the fifth Stokes component (1.4 μm) with wavelength tuning by changing the pump wavelength is obtained. The output power of the fourth Stokes component reached 5 W at λ=1.34 μm. The problems related to the further mastering of the long-wavelength region are discussed. (paper)

42 ENGINEERING↗
DOE OSTI2017

Equivalent circuit-level model of quantum cascade lasers with integrated hot-electron and hot-phonon effects

We report a study of the effects of hot-electron and hot-phonon dynamics on the output characteristics of quantum cascade lasers (QCLs) using an equivalent circuit-level model. The model is developed from the energy balance equation to adopt the electron temperature in the active region levels, the heat transfer equation to include the lattice temperature, the nonequilibrium phonon rate to account for the hot phonon dynamics and simplified two-level rate equations to incorporate the carrier and photon dynamics in the active region. This technique simplifies the description of the electron–phonon interaction in QCLs far from the equilibrium condition. Using the presented model, the steady and transient responses of the QCLs for a wide range of sink temperatures (80 to 320 K) are investigated and analysed. The model enables us to explain the operating characteristics found in QCLs. This predictive model is expected to be applicable to all QCL material systems operating in pulsed and cw regimes. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

A GaInAs/AlInAs quantum cascade laser with an emission wavelength of 5.6 μm

A quantum cascade laser based on a strain-compensated Ga{sub 0.4}In{sub 0.6}As/Al{sub 0.58}In{sub 0.42}As heteropair is developed, which operates in the pulse regime in the wavelength range of 5.5–5.6 μm at temperatures of up to at least 350 K. It became possible due to an increase in the quantum well depth and to the usage of the two-phonon depopulation mechanism for the lower lasing level. The calculated voltage defect is about 100 meV. The laser epitaxial hetero-structure was grown by the MOVPE method. It was investigated by the high-resolution X-ray diffraction technique. It is shown that the heterostructure has a high quality with bandwidths of main satellite peaks of 55 arcsec. The threshold current density is 1.6 kA cm{sup –2} at 300 К. The characteristic temperature is T{sub 0} = 161 K for the temperature interval of 200 – 350 K. For the laser of size 20 μm × 3 mm with cleaved mirrors, the maximum pulsed power is 1.1 W at 80 K and 130 mW at 300 K. The bibliography includes 13 references. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Mode loss spectra in THz quantum-cascade lasers with gold- and silver-based double metal waveguides

Spectra of the waveguide loss coefficient for THz radiation of a quantum-cascade laser with a gold- and silver-based double metal waveguide (DMW) are calculated based on the measurements of resistivity of the metals for different temperatures. It is shown that, taking into account the absorption of THz radiation by free carriers and optical phonons, the spectrum of total mode losses has a broad minimum in the range of 3 – 6 THz, which shifts to higher frequencies with increasing temperature. The minimum losses in the Au-based waveguide increase from 8 to 27 cm{sup –1} as temperature increases from 100 to 300 K. The use of an Ag-based DMW makes it possible to decrease the losses by 2 – 4 cm{sup –1} compared to the Au-based DMW. The bibliography includes 21 references. (terahertz radiation)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Balance-equation method for simulating terahertz quantum-cascade lasers using a wave-function basis with reduced dipole moments of tunnel-coupled states

A model based on a system of balance equations for localised and continuum states is developed to calculate the current − voltage (I − V) and power characteristics of quantum-cascade lasers (QCLs) operating in the terahertz (THz) range. A method for modifying the eigenbasis of the Schrödinger equation by reducing the dipole moments of tunnel-coupled states is proposed to take into account the effect of dephasing on the carrier transport. The calculated and experimental data on the current − voltage characteristics and the dependence of the integrated radiation intensity on current for the THz QCLs lasing at 2.3 THz are compared. The calculated and measured values of the threshold current, lasing current range, and maximum operating temperature T{sub max} are found to be in good agreement. It is shown that T{sub max} can be increased by 25 % by reducing the thickness of the top contact layer n{sup +}-GaAs of the laser structure under study from 800 to 100 nm. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗