SEARCH · Engineering Papers
Results for “STIMULATED EMISSION”
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.
Circularly Polarized Stimulated Emission from a Chiral Cavity Based on Apparent Circular Dichroism Organic Thin-Films
Explore the source record for details and available documents.
Investigation of HgCdTe waveguide structures with quantum wells for long-wavelength stimulated emission
The photoluminescence and stimulated emission during interband transitions in quantum wells based on HgCdTe placed in an insulator waveguide based on a wide-gap CdHgTe alloy are studied. Heterostructures with quantum wells based on HgCdTe are of interest for the development of long-wavelength lasers in the range of 25–60 μm, which is currently unattainable for quantum-cascade lasers. Optimal designs of quantum wells for attainment of long-wavelength stimulated emission under optical pumping are discussed. It is shown that narrow quantum wells from pure HgTe appear to be more promising for long-wavelength lasers in comparison with wide (potential) wells from the alloy due to the suppression of Auger recombination. It is demonstrated that molecular-beam epitaxy makes it possible to obtain structures for the localization of radiation with a wavelength of up to 25 μm at a high growth rate. Stimulated emission is obtained for wavelengths of 14–6 μm with a threshold pump intensity in the range of 100–500 W/cm{sup 2} at 20 K.
Multiple stimulated emission fluorescence photoacoustic sensing and spectroscopy
Multiple stimulated emission fluorescence photoacoustic (MSEF-PA) phenomenon is demonstrated in this letter. Under simultaneous illumination of pumping light and stimulated emission light, the fluorescence emission process is speeded up by the stimulated emission effect. This leads to nonlinear enhancement of photoacoustic signal while the quantity of absorbed photons is more than that of fluorescent molecules illuminated by pumping light. The electronic states' specificity of fluorescent molecular can also be labelled by the MSEF-PA signals, which can potentially be used to obtain fluorescence excitation spectrum in deep scattering tissue with nonlinearly enhanced photoacoustic detection. In this preliminary study, the fluorescence excitation spectrum is reconstructed by MSEF-PA signals through sweeping the wavelength of exciting light, which confirms the theoretical derivation well.
Properties of Stimulated Emission of the РМ567 Dye in Pores of Anodized Aluminum Oxide
Properties of the stimulated emission of the РМ567 dye in porous aluminum oxide are investigated. It is established that when РМ567 molecules are doped into aluminum oxide pores, a small part of dye molecules forms aggregates. The quantum yield of fluorescence of РМ567 in Al{sub 2}O{sub 3} is Ф{sub f} = 0.85. The stimulated emission of РМ567 in the Al{sub 2}O{sub 3} film is observed in the short-wavelength maximum of the fluorescence band. The threshold of the stimulated emission is 2 MW/cm{sup 2}. The kinetics of the decay of stimulated emission is measured. It is demonstrated that low-Q lasing of the stimulated emission of РМ567 in the film with Q ≥ 1·10{sup 2} is caused by the fact that the geometry of rays in pores does not correspond to that of complete internal reflection, and hence, the radiative losses increase. The efficiency of lasing of РМ567 in Al{sub 2}O{sub 3} is 0.3%.
Stimulated emission, photoluminescence, and localisation of nonequilibrium charge carriers in ultrathin (monolayer) GaN/AlN quantum wells
The stimulated emission and photoluminescence of ultrathin GaN quantum wells with a nominal thickness of 1.5 – 2 monolayers (MLs) and AlN barrier layers 4 – 6.66 ML thick, obtained by plasma-activated molecular beam epitaxy on c-sapphire substrates, are studied. The stimulated emission of TE polarisation in ultrathin GaN/AlN quantum wells is obtained under pumping directly into quantum wells. The wavelength of stimulated emission varied from 262 to 290 nm, depending on the thickness of the wells and barriers. It is shown that stimulated emission is achieved on localised GaN states with a thickness of 2 and 3 ML in ultrathin quantum wells with a nominal thickness of 1.5 and 2 ML, respectively. The minimum excitation threshold of stimulated emission was 700 kW cm{sup −2} at λ = 270 nm. (paper)
Aggregation‐Induced Stimulated Emission of 100% Dye Microspheres
Dyes with aggregation-induced emission (AIE) properties have gained interest due to their bright luminescence in solid-state aggregates. While fluorescence from AIE dyes is widely exploited, relatively little is known about aggregation-induced stimulated emission. Here, stimulated emission of tetraphenylethene (TPE)-based organoboron AIE dyes, TPEQBN, in thin films and in microcavity lasers is investigated. Using femtosecond pump–probe spectroscopy, gain coefficients up to 230 cm -1 at 500 nm are measured. Using rate equations, concentration- and pump-dependent gain dynamics as well as laser build-up dynamics are analyzed. During laser oscillation, radiative stimulated emission allows high instantaneous quantum yield greater than 90% to be achieved. Solid-state microspheres made of 100% AIE dyes are fabricated via microfluidic emulsion and solvent evaporation method. Coupled with high gain and high refractive index of 1.76, microspheres as small as 2 µm in diameter show lasing by nanosecond pumping with a threshold of ≈10 pJ µm –2 . Polymer coated, but not bare, microspheres are internalized by live cells and generate narrowband cavity-mode emission from within the cytoplasm. This work shows the potential of AIE dyes as laser materials.
Strain–Activated Stimulated Emission from Multilayer MoSe 2 in a Narrow Operation Window
Herein, photoluminescence (PL) and fluorescence lifetime imaging (FLIM) in multilayer MoSe 2 are studied. Strain-activated stimulated emission via defect levels in multilayer MoSe 2 under laser excitation is observed, for the first time in defects of transition metal dichalcogenides. The stimulated emission is indicated by a threshold behavior of PL emission intensity with respect to laser intensity, strong polarization effects, achieved population inversion with a difference in lifetimes of two competing excited states, and localization of the stimulated emission zone as observed in FLIM. Here, the presented results not only demonstrate strain-activated stimulated emission and highlight the necessity of strain engineering in tailoring 2D layered materials for optoelectronic applications, but also shed light on the design of stimulated emission in transition metal dichalcogenide's defects to tailor for potential single-photon emission behavior.
Transverse stimulated emission in liquids.
Stimulated Brillouin scattering emission transverse to laser beam in liquids external to laser cavity, using specially designed ruby laser system
On the line profile coefficient for stimulated emission
It is pointed out that the line profile coefficients for spontaneous and stimulated emission are identical in low-intensity radiation fields. In more intense radiation fields, however, the stimulated emission profiles in the radiative transfer equation and in the rate equations for the atomic level populations may differ from each other, owing to their different physical nature. A seeming discrepancy between the stimulated emission profiles of the usual semi-classical aproach and a recent quantum mechanical approach by Cooper et al. (1982), which should also be valid for intense 'broadband' fields, is discussed and shown to have negligible consequences for low-intensity radiation fields.
Long wavelength stimulated emission up to 9.5 μm from HgCdTe quantum well heterostructures
Stimulated emission from waveguide HgCdTe structures with several quantum wells inside waveguide core is demonstrated at wavelengths up to 9.5 μm. Photoluminescence line narrowing down to kT energy, as well as superlinear rise in its intensity evidence the onset of the stimulated emission, which takes place under optical pumping with intensity as small as ∼0.1 kW/cm{sup 2} at 18 K and 1 kW/cm{sup 2} at 80 K. One can conclude that HgCdTe structures potential for long-wavelength lasers is not exhausted.
Stimulated emission of Cooper pairs in a high-temperature cuprate superconductor
The concept of stimulated emission of bosons has played an important role in modern science and technology, and constitutes the working principle for lasers. In a stimulated emission process, an incoming photon enhances the probability that an excited atomic state will transition to a lower energy state and generate a second photon of the same energy. It is expected, but not experimentally shown, that stimulated emission contributes significantly to the zero resistance current in a superconductor by enhancing the probability that scattered Cooper pairs will return to the macroscopically occupied condensate instead of entering any other state. Here, we use time- and angle-resolved photoemission spectroscopy to study the initial rise of the non-equilibrium quasiparticle population in a Bi 2 Sr 2 CaCu 2 O 8+δ cuprate superconductor induced by an ultrashort laser pulse. Our finding reveals significantly slower buildup of quasiparticles in the superconducting state than in the normal state. The slower buildup only occurs when the pump pulse is too weak to deplete the superconducting condensate, and for cuts inside the Fermi arc region. We propose this is a manifestation of stimulated recombination of broken Cooper pairs, and signals an important momentum space dichotomy in the formation of Cooper pairs inside and outside the Fermi arc region.
Pulse-stimulated emission from plasma columns.
Pulse stimulated emission from plasma columns, discussing decaying ringing at electron- cyclotron frequency
Observation of hyperfine level crossing in stimulated emission.
Level crossing effect in stimulated emission and application to determination of hyperfine splitting in Xe 129 excited electronic state during laser transition
Stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on GaAs and Ge/Si(001) substrates
We report the observation of stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on Si(001) substrates with the application of a relaxed Ge buffer layer. Stimulated emission is observed at 77 K under pulsed optical pumping at a wavelength of 1.11 μm, i.e., in the transparency range of bulk silicon. In similar InGaAs/GaAsSb/GaAs structures grown on GaAs substrates, room-temperature stimulated emission is observed at 1.17 μm. The results obtained are promising for integration of the structures into silicon-based optoelectronics.
Carrier thermalization under stimulated emission in In{sub 0.17}Ga{sub 0.83}N epilayer at room temperature
We elucidate a strong room temperature stimulated emission (SE) of In{sub 0.17}Ga{sub 0.83}N epilayer grown by molecular beam epitaxy under the subpicosecond pulse excitation. The SE peak at 428 nm emerges on the higher energy side of the spontaneous emission in photoluminescence spectra when the excitation density exceeds the threshold of ∼3.68 mJ/cm{sup 2}. Nondegenerate transient differential reflectivity measurements show that a multi-stage carrier thermalization from excited states to localized edge states and stimulated emission dominate the decay processes of photogenerated carriers under various excitation densities. Our results indicate that the existence of phonon bottleneck effect could result in a slow thermalization process in the InGaN material even under the condition of stimulated emission.
Stimulated Emission and Optical Properties of Solid Solutions of Cu(In,Ga)Se{sub 2} Direct Band Gap Semiconductors
Stimulated emission, optical properties, and structural characteristics of non-irradiated and proton-irradiated Cu(In,Ga)Se{sub 2} thin films deposited on soda lime glass substrates using co-evaporation of elements in a multistage process were investigated. X-ray diffraction analysis, scanning electron microscopy, X-ray spectral analysis with energy dispersion, low-temperature photoluminescence, optical transmittance and reflectance were used to study the films. Stimulated emission at low temperatures of ~20 K was found in non-irradiated and proton-irradiated Cu(In,Ga)Se{sub 2} thin films upon excitation by laser pulses of nanosecond duration with a threshold power density of ~20 kW/cm{sup 2}. It was shown that the appearance and parameters of the stimulated emission depend strongly on the concentration of ion-induced defects in Cu(In,Ga)Se{sub 2} thin films.