Spontaneous Emission Spectra Research Articles

Modulation of High-Intensity Optical Properties in CdS/CdSe/CdS Spherical Quantum Wells by CdSe Layer Thickness.

Spherical quantum wells (SQWs) have proven to be excellent materials for suppressing Auger recombination due to their expanded confinement volume. However, research on the factors and mechanisms of their high-intensity optical properties, such as multiexciton properties and third-order optical nonlinearities, remains incomplete, limiting further optimization of these properties. Here, a series of CdS/CdSe (xML)/CdS SQWs with varying CdSe layer thicknesses were prepared. The modulation effects of CdSe shell variations on the PL properties, defect distribution, biexciton binding energy, and third-order optical nonlinearities of the SQWs were investigated, and their impact on the material's multiexciton properties was further analyzed. Results showed that the typical CdS/CdSe(3ML)/CdS sample exhibited a large volume-normalized two-photon absorption cross-section (18.17 × 102 GM/nm3) and favorable biexciton characteristics. Optical amplification was observed at 12.4 μJ/cm2 and 1.02 mJ/cm2 under one-photon (400 nm) and two-photon (800 nm) excitation, respectively. Furthermore, different amplified spontaneous emission spectra were observed for the first time under one/two-photon excitation. This phenomenon was attributed to thermal effects overcoming the biexciton binding energy. This study provides valuable insights for further optimizing multiexciton gain characteristics in SQWs and developing optical gain applications.

Er3+/Yb3+ Co-Doped Fluorotellurite Glass Fiber with Broadband Luminescence.

In order to address the 'capacity crisis' caused by the narrow bandwidth of the current C band and the demand for wide-spectrum sensing sources and tunable fiber lasers, a broadband luminescence covering the C + L bands using Er3+/Yb3+ co-doped fluorotellurite glass fiber is investigated in this paper. The optimal doping concentrations in the glass host were determined based on the intensity, lifetime, and full width at half maximum (FWHM) of the fluorescence centered at 1.5 µm, which were found to be 1.5 mol% Er2O3 and 3 mol% Yb2O3. We also systematically investigated this in terms of optical absorption spectra, absorption and emission cross-sections, gain coefficients, Judd-Ofelt parameters, and up-conversion fluorescence. The energy transfer (ET) mechanism between the high concentrations of Er3+ and Yb3+ was summarized. In addition, a step-indexed fiber was prepared based on these fluorotellurite glasses, and a wide bandwidth of ~112.5 nm (covering the C + L bands from 1505.1 to 1617.6 nm) at 3 dB for the amplified spontaneous emission (ASE) spectra has been observed at a fiber length of 0.57 m, which is the widest bandwidth among all the reports based on tellurite glass. Therefore, this kind of Er3+/Yb3+ co-doped fluorotellurite glass fiber has great potential for developing broadband C + L band amplifiers, ultra-wide fiber sources for sensing, and tunable fiber lasers.

Resonant inelastic x-ray scattering in warm-dense Fe compounds beyond the SASE FEL resolution limit

Resonant inelastic x-ray scattering (RIXS) is a widely used spectroscopic technique, providing access to the electronic structure and dynamics of atoms, molecules, and solids. However, RIXS requires a narrow bandwidth x-ray probe to achieve high spectral resolution. The challenges in delivering an energetic monochromated beam from an x-ray free electron laser (XFEL) thus limit its use in few-shot experiments, including for the study of high energy density systems. Here we demonstrate that by correlating the measurements of the self-amplified spontaneous emission (SASE) spectrum of an XFEL with the RIXS signal, using a dynamic kernel deconvolution with a neural surrogate, we can achieve electronic structure resolutions substantially higher than those normally afforded by the bandwidth of the incoming x-ray beam. We further show how this technique allows us to discriminate between the valence structures of Fe and Fe2O3, and provides access to temperature measurements as well as M-shell binding energies estimates in warm-dense Fe compounds.

Evaluation of an Erbium-Doped Fiber Ring Laser as an Edge Filtering Device for Fiber Bragg Grating Sensor Interrogation

An easy-to-implement and cost-effective Fiber Bragg Grating (FBG) sensor interrogation technique based on a ring Erbium-Doped Fiber Laser (EDFL) topology is proposed and experimentally assessed. The FBG sensor is part of the EDFL cavity and must have a central wavelength located within the linear region of the EDF’s amplified spontaneous emission (ASE) spectrum, which occurs at between 1530 and 1540 nm. In this manner, the wavelength-encoded response of the FBG under strain is converted to a linear variation in the laser output power, removing the need for spectrum analysis as well as any limitations from the use of external edge-filtering components. In addition, the laser linewidth is significantly reduced with respect to the FBG bandwidth, thus improving the resolution of the system, whereas its sensitivity can be controlled through pumping power. The performance of the system has been characterized by modeling and experiments for EDFs with different lengths, doping concentrations, and pumping power levels. The influence of mode-hopping in the laser cavity on the resolution and accuracy of the system has also been investigated.

Nonlocal effects in plasmon-emitter interactions

Abstract Nonlocal and quantum mechanical phenomena in noble metal nanostructures become increasingly crucial when the relevant length scales in hybrid nanostructures reach the few-nanometer regime. In practice, such mesoscopic effects at metal–dielectric interfaces can be described using exemplary surface-response functions (SRFs) embodied by the Feibelman d-parameters. Here we show that SRFs dramatically influence quantum electrodynamic phenomena – such as the Purcell enhancement and Lamb shift – for quantum light emitters close to a diverse range of noble metal nanostructures interfacing different homogeneous media. Dielectric environments with higher permittivities are shown to increase the magnitude of SRFs calculated within the specular-reflection model. In parallel, the role of SRFs is enhanced in noble metal nanostructures characterized by large surface-to-volume ratios, such as thin planar metallic films or shells of core–shell nanoparticles, for which the spill-in of electron wave functions enhances plasmon hybridization. By investigating emitter quantum dynamics close to such plasmonic architectures, we show that decreasing the width of the metal region, or increasing the permittivity of the interfacing dielectric, leads to a significant change in the Purcell enhancement, Lamb shift, and visible far-field spontaneous emission spectrum, as an immediate consequence of SRFs. We anticipate that fitting the theoretically modelled spectra to experiments could allow for experimental determination of the d-parameters.

Controllable spontaneous emission spectrum in an artificial giant atom: Dark lines and bound states

We study the spontaneous emission spectra of a few-level giant atom strongly coupled to a one-dimensional waveguide by employing variational and analytical approaches, which are beyond the rotating-wave approximation and the Markovian approximation. We show that the interference effects due to the multiple coupling points result in dark lines in spontaneous emission spectra of either two-level or three-level giant atoms regardless of whether there is a bound state or not. We illustrate that the generation of dark lines depends on the distance between the coupling points and their number. In the absence of a bound state, the dark lines can be used to suppress emission at a certain frequency in the spectrum. In the presence of a bound state, the total intensity of the emission spectrum can be significantly suppressed. The present results offer the possibility of control over the spontaneous emission with the dark lines due to the destructive interference in giant atoms. Published by the American Physical Society 2024

Tailoring two-photon spontaneous emission: Framework and nanoantenna design for interference and directionality

We develop a framework that computes two-photon spontaneous emission (TPSE) spectra of a quantum emitter near an arbitrarily shaped nanostructure. The model considers the interaction up to the electric quadrupolar order, which is relevant for nanophotonic structures sustaining strongly confined fields that are used to enhance and to tailor spontaneous emission processes. Moreover, we consider interference effects between multipolar two-photon emission channels, for the first time to our knowledge. First, we show for a s → s transition of a hydrogen atom placed under a silver plasmonic nanodisk a substantial enhancement in the photon-pair emission rates by 5 and 11 orders of magnitude for the two-electric dipole (2ED) and two-electric quadrupole (2EQ) transitions, respectively. Then for the same emitter under a plasmonic graphene nanotriangle, we demonstrate a breakdown of the electric dipole approximation in the TPSE process where the interference between the 2ED and 2EQ transitions is important, as it increases the total rate by 63 %. Third, we explore platforms where entangled photons of different energy are emitted in the far-field in different directions. In the end, our framework is a complete tool to design emitters and nanostructures for the TPSE process, leading to a rich assortment of functional nanoantennas.

Simulation Analysis on Optimization of Optical Fiber Communication Based on L+ Band

Nowadays, L+ band (1600-1650 nm) is widely used in optical communication, however, the traditional fiber amplifiers for L+ band can no longer meet the increasing demand, and it is crucial to select more suitable materials and optimize the peak power of the output spectrum. In this work, we determine the rate equation and power propagation equation corresponding to the three-energy-level structure by Er3+ doping phosphate glass, and select the appropriate pumping wavelength and power, and calculate the variation of amplified spontaneous emission spectra with the length of the fiber and the doping concentration using MATLAB programming. Finally, on this basis, genetic algorithm is used to optimize the fiber length and doping concentration, and the parameter values to maximize the peak power of the output spectrum are successfully obtained, and the performance is compared with that of the traversing parameter method, which provides a reference for the design and optimization of fiber amplifiers.

Optimization of the Peak Power of the Output Spectrum of Spontaneous Emission Spectrum Amplified by O-Band Fiber

As the demand for information and communication continues to increase, the optimization and improvement of optical fiber communication has been a key focus of scientific research, with profound impacts on multiple fields, including military, aerospace, industrial, and daily communications. Based on the in-depth understanding and establishment of the rate equation and power propagation equation of each energy level system, this study explores the influence of fiber length and doping concentration on amplifying spontaneous emission spectrum under certain pump power. With a comprehensive understanding of its characteristics, analog annealing algorithms are employed to optimize the length and doping concentration of the fiber to maximize the peak power of the output spectrum. This research provides an important contribution to the further development and efficiency improvement of optical fiber communication in the future. It is concluded that for the O-band, the output peak of high power can provide greater signal strength, thereby increasing the transmission distance and bandwidth capacity of the signal. This is essential for applications such as long-distance communications, high-speed data transmission, and multi-channel transmission.

Design and output spectral peak power optimization of E-band fiber-amplified spontaneous emission spectra

Design and output spectral peak power optimization of E-band fiber-amplified spontaneous emission spectra

Integrated Optical Sensing and Communication (IOSAC) System Based on Hybrid‐Waveguide Structures

AbstractAdvanced silicon photonic technologies enable integrated optical sensing and communication (IOSAC) in real time for the emerging application requirements of simultaneous sensing and communication for next‐generation networks. Herein, an IOSAC system is proposed and demonstrated on the silicon nitride (Si3N4) photonics platform. The IOSAC devices leveraging microring resonators excel in real‐time monitoring of analyte fluctuations and efficiently transmit this data to the terminal, positioning them as viable alternatives to bulk optics in applications that demand both high precision and speed. By directly integrating Si3N4 ring resonators with optical communication networks, simultaneous sensing and optical communication are demonstrated by an optical signal transmission experimental system using especially filtering amplified spontaneous emission spectra. The refractive index (RI) sensing ring with a sensitivity of 172 nm RIU−1, a figure of merit (FOM) of 1220, and a detection limit (DL) of 8.2 × 10−6 RIU is demonstrated. Simultaneously, the 1.25 Gbps optical on‐off‐keying (OOK) signal is transmitted at the concentration of different NaCl solutions, indicating the bit‐error‐ratio (BER) decreases with the increase in concentration. The novel IOSAC technology shows the potential to realize high‐performance simultaneous biosensing and communication in real time and further accelerate the development of IoT and 6G networks.

Theory and optimisation of radiative recombination in broken-gap InAs/GaSb superlattices

We present a theoretical analysis of mid-infrared radiative recombination in InAs/GaSb superlattices (SLs). We employ a semi-analytical plane wave expansion method in conjunction with an 8-band Hamiltonian to compute the SL electronic structure, paying careful attention to the identification and mitigation of spurious solutions. The calculated SL eigenstates are used directly to compute spontaneous emission spectra and the radiative recombination coefficient . We elucidate the origin of the relatively large coefficients in InAs/GaSb SLs which, despite the presence of spatially indirect (type-II-like) carrier confinement, are close to that of bulk InAs and compare favourably to those calculated for mid-infrared type-I pseudomorphic and metamorphic quantum well structures having comparable emission wavelengths. Our analysis explicitly quantifies the roles played by carrier localisation (specifically, partial delocalisation of bound electron states) and miniband formation (specifically, miniband occupation and optical selection rules) in determining the magnitude of and its temperature dependence. We perform a high-throughput optimisation of the room temperature coefficient in InAs/GaSb SLs across the 3.5–7 m wavelength range, quantifying the dependence of on the relative thickness of the electron-confining InAs and hole-confining GaSb layers. This analysis provides guidance for the growth of optimised SLs for mid-infrared light emitters. Our results, combined with the expected low non-radiative Auger recombination rates in structures having spatially indirect electron and hole confinement, corroborate recently observed high output power in prototype InAs/GaSb SL inter-band cascade light-emitting diodes.

Spontaneous emission spectrum from a V-type artificial atom in a strong-coupling regime: Dark lines and line narrowing

Spontaneous emission spectrum from a V-type artificial atom in a strong-coupling regime: Dark lines and line narrowing

Spectral-broadness simulation of a Littman/Metcalf external cavity diode laser with a dynamic-curvature end mirror.

We propose a dynamic-spectral-broadness Littman/Metcalf external cavity diode laser, which replaces the flat end mirror of the external cavity with a curved one with a tunable radius of curvature (RoC). The concept was verified via simulation; first, the frequency selectivity of the cavity was calculated for each RoC using Gaussian-beam optics combined with ray tracing, and second, laser oscillation and amplified spontaneous-emission (ASE) spectra were obtained using the transmission-line laser model. The simulation revealed a tuning range with spectral broadness: 250 kHz for single-mode operation, 1.2-47 GHz for multi-mode operation, and 50 GHz-3.9 THz for ASE.

Theoretical Study of Spontaneous Emission Spectra in GaAsBi/GaAs Quantum Wells

GaAsBi/GaAs heterojunctions have a type II band arrangement, and the band structure energy of GaAs alloys with diluted Bi content provides a wide range for designing effective band gaps. In this paper, we calculate the electronic energy band structure of GaAsBi/GaAs quantum wells (QWs) with different Bi concentrations under the 8-band K · P model. The calculated results show that the Bi concentration has a great influence on the band gap, valence band, conduction band, and other structures of GaAsBi/GaAs QWs. Based on the band structure, we make systematical simulations on the effects of different quantum well widths, different Bi concentrations, different carrier densities, and different temperatures on the spontaneous emission spectra (SES) of GaAsBi/GaAs QWs. We find that the peaks of SES reduce with the increase of temperature and well width of the quantum well structure. The full width at half maximum (FWHM) of SES at 300 K is 0.1 eV, which is much broader than that at 100 K. The increasing Bi concentration is found to give rise to the blue shift of SES. Finally, the carrier concentration in the quantum well is found to be an important factor that can enhance the SES peak values. The findings in this work are helpful in the design of GaAsBi/GaAs-based optoelectronic devices.

Exploring the photodynamic profile of laser-generated exciplex from a conjugated polymer

In this work, we investigated the impact of the concentration on the spectral and amplified spontaneous emission spectra (ASE) of a conducting polymer of poly(2,5-di(3,7-dimethyloctyloxy) cyanoterephthalylidene) (PDDCP) in tetrahydrofuran (THF). The findings demonstrate that the absorption spectra exhibited two peaks at 330 and 445 nm across the concentration range (1–100 µg/mL). Irrespective of the optical density, altering the concentrations did not affect the absorption spectrum. Also, the analysis indicated that the polymer did not agglomerate in the ground state for any of the concentrations mentioned. However, changes in the polymer had a substantial effect on its photoluminescence spectrum (PL), likely due to the formation of exciplexes and excimers. Also, the energy band gap also varied as a function of concentration. At a certain concentration (25 µg/mL) and pump pulse energy (3 mJ), PDDCP produced a superradiant ASE peak at 565 nm with a remarkably narrow full width at half maximum (FWHM). These findings can provide insight into the optical characteristics of PDDCP, which may have potential applications in the fabrication of tunable solid-state laser rods, Schottky diodes, and solar cell applications.

Characterization of laser dye concentrations in ZnO nanostructures for optimization of random laser emission performance

Many nanoforms of zinc oxide (ZnO) structures can be synthesized, such as spheres, rods, flowers, disks and walls, as scatter centers in random laser. However, nanoflower and nanowire shapes in this work have received particular interest due to their wide range of applications, including biological, medical cancer cell detection, gas sensors, and biosensors. In this paper, we investigate the optical and morphological properties of two-shaped nanoparticles as scatter centers in the laser active medium on the performance emission of a random laser. Fluorescence and absorption spectra show that 10[Formula: see text][Formula: see text]M for R6G dye and [Formula: see text][Formula: see text]cm[Formula: see text] ZnO NPs are the optimal nanocomposite film concentrations for R6G dye. With excitation energies ranging from 3.44[Formula: see text]mJ to 28.34[Formula: see text]mJ and a repetition rate of 2[Formula: see text]Hz, second-harmonic generation Nd: YAG laser Amplified spontaneous emission (ASE) spectra of the nanocomposite films were observed. The results indicated a minimum bandwidth (Full width at half maximum (FWHM)) of 13[Formula: see text]nm at a threshold energy of 8.65[Formula: see text]mJ for ZnO NW (nanowire) nanocomposite films at [Formula: see text][Formula: see text]cm[Formula: see text] with R6G dye at 10[Formula: see text][Formula: see text]M and Poly(methyl methacrylate) (PMMA). The ZnO NF (nanoflower) nanocomposite film had an FWHM of 11[Formula: see text]nm and a threshold energy of 4.8[Formula: see text]mJ at the same concentrations of R6G dye on PMMA.

Ultra‐broadband and thermally stable NIR emission in Bi‐doped glasses and fibers enabled by a metal reduction strategy

AbstractBismuth (Bi)‐doped glasses with broadband near‐infrared (NIR) emission have been drawing increasing interest due to their potential applications in tunable fiber lasers and broadband optical amplifiers. Yet, the implementation of highly efficient and ultra‐broadband Bi NIR emission covering the whole telecommunication window remains a daunting challenge. Here, via a metal reduction strategy to simultaneously create a chemically reductive environment during glass melting and enhance the local network rigidity, a super broadband (FWHM ≈ 600 nm) NIR emission covering the entire telecommunications window with greatly enhanced intensity was achieved in Bi‐doped germanate glasses. More importantly, due to the excellent thermal stability, the super broadband Bi NIR emission can be well retained after the glass was drawn into an optical fiber. Furthermore, the transmission loss of 0.066 dB/cm at 1310 nm and an obvious broadband amplified spontaneous emission spectrum spanning a range of 1000–1600 nm were observed in this fiber. This work can strengthen our comprehension of the complicated Bi NIR luminescence behaviors and offer a feasible and universal way to fabricate tunable fiber lasers and broadband optical amplifiers based on Bi‐doped multicomponent glasses.

Frustrated Spontaneous Emission near the Edge of a Photonic Band Gap

The novel dynamical and spectral features of (single photon) spontaneous emission from an atomic transition near a photonic band edge are investigated by frustrating these features by spontaneous emission through another atomic transition far from the photonic band edge and deep in the photon continuum, the two atomic transitions forming the two dipole-allowed transitions of a three-level atom in a Λ configuration. Though spontaneous emission through the atomic transition far from the photonic band edge (the “far” transition) is not directly affected by the photonic band gap (PBG), it is indirectly affected by the PBG through its coupling to the atomic transition near the photonic band edge (the “near” transition) via the Λ configuration. As a result of this coupling, spontaneous emission through the “far” transition can be used as a probe to measure the strength of the effects of the PBG on spontaneous emission through the “near” transition. We have shown that the effects of the PBG on spontaneous emission via the “near” transition are strongly affected (and, therefore, can be controlled by) not only by the detuning of the “near” transition from photonic band edge but also by the vacuum decay rate of spontaneous emission through the “far” transition which is coupled to the “near” transition through the Λ configuration. In particular, we have shown that the oscillatory behavior of spontaneous emission near a photonic band edge as well as the Autler-Townes doublet of the spontaneous emission spectrum (due to the splitting of the atomic level near the photonic band edge) are strongly dependent on the decay rate of spontaneous emission through the probe transition which is far from the band edge.

Influence of indium content and carrier density on spontaneous emission spectra of wurtzite InGaN/GaN quantum wires with screening effects

Spontaneous emission spectra of wurtzite (WZ) InxGa1−xN/GaN quantum wires (QWRs) with screening effects are investigated as a function of an In content and a carrier density. The screening potentials rapidly increase with increasing carrier density. However, for a given carrier density, the magnitude of the screening potential is nearly irrespective of the In content. In the case of the InGaN/GaN quantum well (QW) structures, the peak intensity gradually decreases with increasing In content owing to the increase in an internal field by piezoelectric (PZ) and spontaneous (SP) polarizations. On the other hand, the peak intensity of the InGaN/GaN QWR structure is less sensitive to an internal field and rapidly increases owing to the increase in the carrier confinement with increasing In content. However, it is reduced due to the decrease in a quasi-Fermi level separation when the In content further increases.