Spontaneous Emission Spectra Research Articles

Spontaneous emission from Λ-type three-level atom driven by bichromatic field in anisotropic double-band photonic crystals

The spontaneous emission property of Λ-type three-level atom driven by the bichromatic field in the anisotropic double-band photonic crystal is calculated by n-times iteration method. The influence of different parameters on atomic spontaneous emission is studied, and the phenomena of atomic spontaneous emission are explained in the dressed state representation. It is found that the spontaneous emission spectra of the atom driven by the bichromatic field presents a multi-peak comb structure. The position of the emission peak is determined by the initial state of the atom, and the interval between the neighboring emission peaks is the detuning δ of the bichromatic field. When the ratio between Rabi frequency intensity and the detuning δ of the bichromatic field remains unchanged, the intensity of each emitted peak remains invariant. The spontaneously emitted peak can be annihilated in the band gap and enhanced near the band edge in the anisotropic photonic crystals. Meanwhile, we also observe the fluorescence quenching phenomenon in the spontaneous emission spectra. The research in this paper provides the theoretical guidance for the control of atomic spontaneous emission.

In-situ measurement of combustion characteristics and potassium release concentration during torrefied biomass burning based on spontaneous emission spectroscopy

The orthogonal experiment designed in this paper investigated the effect of changes in experimental parameters such as biomass species, torrefaction temperature, torrefaction time, torrefaction oxygen concentration on the physicochemical properties and combustion characteristics of the torrefaction products. Two optical fiber spectrometers were used to capture the spontaneous emission spectra of the combustion flame of compressed pellets of torrefied biomass, and the in-situ measurement of pellet combustion temperature and K release concentration at high heating rate was realized by multi-spectral analysis algorithm. The experimental results indicate that for biomass, torrefaction will lead to a decrease of volatile and moisture content and an increase of fixed carbon and ash content in components, a decrease of O and H and an increase of C content in elements, a certain loss of biomass quality, an increase of high heat value, and each indicator move closer to coal. The effects of various experimental parameters on the volatile content, mass yield, high heat value increase rate and energy yield in biomass torrefaction products have similar laws, i.e., biomass species / torrefaction oxygen concentration > torrefaction temperature > torrefaction time. The mild torrefaction product pellets have a shorter ignition delay, increased volatile combustion flame height and peak temperature, longer volatile and char combustion duration, but lower peak char combustion temperature, among which the selected torrefaction products of rice straw and pine wood showed an increase in peak temperature of 0.56 % (11 K) and 0.61 % (12 K) for the volatile stage respectively, and a decrease of and 1.29 % (20 K) and 1.29 % (21 K) for the char stage respectively. In addition, the peak K release concentration during combustion of the mild torrefaction product pellets was reduced, among which the peak K release concentrations during the volatile and char stage were reduced by 43.22 % (3.89 ppm) and 52.93 % (51.55 ppm) of the rice straw torrefaction product respectively, and by 73.14 % (1.28 ppm) and 62.08 % (15.01 ppm) for the pine wood torrefaction product respectively. Biomass torrefaction products have fuel properties closer to coal, less K released from the combustion process, which have the potential to become an alternative to coal.

Magnetic dipole emission in resonant metal-dielectric-metal structures.

We explore a possibility to control magnetic dipole emission with plasmonic cavities, placing Eu3+ emitters inside profile-modulated metal-dielectric-metal structures. Significant variations in the branching ratio of the magnetic and electric dipole transitions are observed as the function of the thickness of the intermediate layer. The experimental results are confirmed with numerical simulations which account for cavity and gap plasmon resonances and predict modifications in the spontaneous emission spectrum as the function of the gap size and a strong directionality of the emission for small thicknesses of the intermediate layer. The implications of having a competition between electric and magnetic dipole relaxation channels in Eu3+ are discussed.

Superradiant emission spectra of a two-qubit system in circuit quantum electrodynamics

In this paper, we study the spontaneous emission spectra and the emission decay rates of a simplest atom system that exhibits sub- and superradiant properties: a system which consists of two artificial atoms (superconducting qubits) embedded in a one-dimensional open waveguide. The calculations are based on the method of the transition operator which was firstly introduced by R. H. Lehmberg to theoretically describe the spontaneous emission of two-level atoms in a free space. We obtain the explicit expressions for the photon radiation spectra and the emission decay rates for different initial two-qubit configurations with one and two excitations. For every initial state we calculate the radiation spectra and the emission decay rates for different effective distances between qubits. In every case, a decay rate is compared with a single qubit decay to show the superradiant or subradiant nature of a two-qubit decay with a given initial state.

The Efficacy of New Liquid Laser Dye Material – Chalcone: 1-(4-methylsulfonyl phenyl)-3-(4-N,N-dimethyl (amino phenyl)-2-propen-1-one (MSPPP)

This paper includes the efficacy of synthesis and characterization of a new liquid laser dye material – chalcone of 1-(4-methylsulfonyl phenyl)-3-(4-N,N-dimethyl (amino phenyl)-2-propen-1-one (MSPPP) and its application as a new laser medium. The absorption and fluorescence spectra of MSPPP were investigated under different solvents and concentrations. The study investigated the pump pulse energies of Nd: YAG laser (355 nm) and the amplified spontaneous emission (ASE) performance of MSPPP under various concentrations, and organic solvents. At identical conditions, the amplified spontaneous emission spectra of MSPPP in solution were compared with a conventional laser dye of coumarin 503. The fluorescence quantum yield and the gain of MSPPP were determined. The features are: (I) MSPPP has stellar photochemical stabilization., (II) ASE from the MSPPP was setting in the wavelength range between 515 and 548 nm. The molecular geometry was optimized and their HOMO– LUMO energy values were determined by SCM Software for Chemistry & Materials using DFTB (GGA BLYP) [Density-Functional based Tight-Binding] method.

Proper orthogonal decomposition of continuum-dominated emission spectra for simultaneous multi-property measurements

A novel spectrum calibration method is proposed for high-accuracy emission spectroscopy to extract quantitative gas property information from the spontaneous photon emission spectra. This is challenging, particularly in the presence of broadband emission, which smears the characteristic local spectral features that are often used as property indicators in conventional emission spectroscopy. Proper orthogonal decomposition (POD) can reduce the dimension (ND) of the broadband spectrum profile by selecting a number (NM≪ND) of dominant bases that span the gas-property-dependent spectrum space. Each POD-decomposed spectral basis represents critical broadband spectral features that are sensitive to the gas properties of interest. A reduced-order model (ROM) employing the kriging method correlates the entire emission spectrum profile that decomposed by the bases to multiple gas properties. To provide a spectrum database to train the ROM, chemiluminescence was captured from a flat flame with varied diluent gas compositions (N2 and CO2), fuel-oxidizer equivalence ratios, and pressures (1–5 bar). Subsequently, the ROM employing an emission spectrum can predict the gas properties under high-temperature and high-pressure conditions where conventional sensors are inapplicable. The average relative prediction errors obtained using this new analysis method were approximately 3.2% and 1.3% for the pressure and equivalence ratio, respectively.

Stimulated emission mechanism of aluminum nitride

Photoluminescence and stimulated emission spectroscopies were performed on transparent aluminum nitride (AlN) substrates grown by hydride vapor-phase epitaxy. The stimulated emission was observed from cryogenic to room temperatures and its origin was assigned on the basis of the spontaneous emission spectra and existing theories. Two stimulated emission mechanism crossovers were also found. One was a temperature-induced crossover from a purely excitonic mechanism to a carrier-involved mechanism, which is a universal behavior in semiconducting materials. The other was an excitation-power--induced crossover from an exciton--exciton scattering mechanism to a phonon-mediated mechanism, which is a unique behavior attributed to the peculiar excitonic structure (negative crystal-field splitting and positive electron--hole exchange interaction energies) of AlN.

Electrically driven whispering-gallery-mode microlasers in an n-MgO@ZnO:Ga microwire/p-GaN heterojunction.

In emerging miniaturized applications, semiconductor micro/nanostructures laser devices have drawn great public attentions of late years. The device performances of micro/nanostructured microlasers are highly restricted to the different reflective conditions at various side surfaces of microresonators and junction interface quality. In this study, an electrically driven whispering-gallery-mode (WGM) microlaser composed of a Ga-doped ZnO microwire covered by a MgO layer (MgO@ZnO:Ga MW) and a p-type GaN substrate is illustrated experimentally. Incorporating a MgO layer on the side surfaces of ZnO:Ga MWs can be used to reduce light leakage along the sharp edges and the ZnO:Ga/GaN interface. This buffer layer incorporation also enables engineering the energy band alignment of n-ZnO:Ga/p-GaN heterojunction and manipulating the current transport properties. The as-constructed n-MgO@ZnO:Ga MW/p-GaN heterojunction device can emit at an ultraviolet wavelength of 375.5 nm and a linewidth of about 25.5 nm, achieving the excitonic-related recombination in the ZnO:Ga MW. The broadband spectrum collapsed into a series of sharp peaks upon continuous-wave (CW) operation of electrical pumping, especially for operating current above 15.2 mA. The dominant emission line was centered at 378.5 nm, and the line width narrowed to approximately 0.95 nm. These sharp peaks emerged from the spontaneous emission spectrum and had an average spacing of approximately 5.5 nm, following the WGM cavity modes. The results highlight the significance of interfacial engineering for optimizing the performance of low-dimensional heterostructured devices and shed light on developing future miniaturized microlasers.

Polarization stabilization of the mean wavelength of erbium-doped super fluorescent fiber optic sources

We investigate the influence of polarization on the stability of a single-pass fiber super fluorescent light source (SFS) operating under the forward or reverse setup. The measurement of amplified spontaneous emission (ASE) spectra obtained using different values for the power and state of polarization (SOP) of the optical pump (980 nm) is the basis of the analysis. The mean wavelength was the stability evaluation criterion used for comparing the forward and backward SFS emission. The results indicate that both super fluorescent sources become insensitive to the polarization state when the pump power reaches a saturated absorption condition. The influence of the SFS spectral range is also analyzed, defining four spectral bands; Ctot band (1520–1570 nm), C band (1530–1560 nm), C+ band (1520–1540 nm), and C− band (1540–1560 nm). We show that the stability of the SFS improves by discriminating one of the two peaks of the ASE emission spectrum, reaching the performance required for inertial grade sensors.

Deep ultraviolet spectra from BGaN quantum dot structures

This work theoretically studies boron-containing ternary and quaternary lattice-matched quantum dot (QD) structures that emit ultraviolet (UV) wavelength by varying the boron mole fraction in the QD active region or the barrier. For BGaN and BAlGaN QD structures, matching to AlN, BAlN, AlGaN barriers and also BInGaN/AlN, the wide-bandgap AlN barrier imposes them to emit at 198–202 nm wavelength. For BInGaN QDs matching to the AlGaN, BAlN, the situation is different. They can emit at the range 252−291nm depending on the barrier and the efficiency of boron content in the barrier in redshifting the wavelength is deduced. The TE and TM gain and spontaneous emission spectra are high and increase under increasing boron in the active region or reducing boron content in the barrier region, exceeding its quantum-well counterpart and of central importance in light-emitting diode applications. Ultra-high gain is obtained from BInGaN/BAlN structure. Gain values are arranged according to the bandgap difference (ΔEg). The range of ΔEg is extended, in the studied structures, to ΔEg=1866−2856 meV, which is of practical importance in UV device applications. The total polarization is decreasing for the Al-containing systems, which is preferred.

Thermal resistance measurement of edge-emitting semiconductor lasers using spontaneous emission spectra

An improved technique for thermal resistance measurement of edge-emitting diode lasers using spontaneous emission spectra, collected through the opening in the n-contact within the range of operating currents, has been proposed. The advantage of the proposed technique is that systematic errors typical for measurements based on lasing spectra are excluded. The accuracy of the method was verified by measuring the dependence of the thermal resistance on the cavity length for diode lasers with 100 μm strip width. Obtained results are in good agreement with the model, and the minimum measurement error was ±0.1 K/W. The proposed technique can be used in metrological support of fabrication process of semiconductor lasers. Keywords: laser diode, thermal resistance, spontaneous emission.

Измерение теплового сопротивления торцевых полупроводниковых лазеров по спектрам спонтанного излучения

An improved technique for thermal resistance mea- surement of edge-emitting diode lasers using spontaneous emission spectra, collected through the opening in the n-contact within the range of operating currents, has been proposed. The advantage of the proposed technique is that systematic errors typical for measurements based on lasing spectra are excluded. The accuracy of the method was verified by measuring the dependence of the thermal resistance on the cavity length for diode lasers with 100 μm strip width. Obtained results are in good agreement with the model, and the minimum measurement error was ±0.1 K/W. The proposed technique can be used in metrological support of fabrication process of semiconductor lasers.

Расчет спектра фоторекомбинации при облучении атомов сильным лазерным полем на основе марковского приближения

We derived the spectrum of the photon spontaneous emission at the irradiation of atoms by a strong laser field. Our approach is based on the Markoff (factorization) approximation for the total density matrix of the system consisting of an atom, laser field and the vacuum electromagnetic field.

Nonreciprocal transition between two indirectly coupled energy levels

We propose a theoretical scheme to realize nonreciprocal transition between two energy levels that can not coupled directly. Suppose they are coupled indirectly by two auxiliary levels with a cyclic four-level configuration, and the four transitions in the cyclic configuration are controlled by external fields. The indirectly transition become nonreciprocal when the time reversal symmetry of the system is broken by the synthetic magnetic flux, i.e., the total phase of the external driving fields through the cyclic four-level configuration. The nonreciprocal transition can be identified by the elimination of a spectral line in the spontaneous emission spectrum. Our work introduces a feasible way to observe nonreciprocal transition in a wide range of multi-level systems, including natural atoms or ions with parity symmetry.

Theoretical investigation on the effect of terahertz wave on Ca2+ transport in the calcium channel

SummaryThe question of whether terahertz (THz) waves can interact with ions in channels of nerve cells and cause a further reaction has attracted much attention. To answer this question, we investigate the spontaneous radiation generated by Ca2+ moving in calcium channels and the effect of THz radiation on the transport of Ca2+ by solving the mathematical physical model through Brownian dynamics (BD) simulations. It is obtained that the moving Ca2+ in a calcium channel can generate electromagnetic radiation, the corresponding spectrum of which is concentrated in the THz range. Meanwhile, both the ion number in the channel and the background temperature are proved to have significant effects on the spontaneous emission spectra. The studies also show that external THz radiation can accelerate Ca2+ transport through the ion channel. These results are expected to provide a theoretical basis for the future treatment of THz waves in the neurological field.

Microscopic theory for the incoherent resonant and coherent off-resonant optical response of tellurium

An $\mathit{ab}\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathit{initio}$-based fully microscopic approach is applied to study the nonlinear optical response of bulk tellurium. The structural and electronic properties are calculated from first principles using the shLDA-1/2 method within density functional theory. The resulting band structure and dipole matrix elements serve as input for the quantum mechanical evaluation of the anisotropic linear optical absorption spectra, yielding results in excellent agreement with published experimental data. Assuming quasiequilibrium carrier distributions in the conduction and valence bands, absorption/gain and spontaneous emission spectra are computed from the semiconductor Bloch and luminescence equations. For ultrafast intense off-resonant excitation, the generation of high harmonics is evaluated and the emission spectra are calculated for samples of different thicknesses.

TD-DFT Simulation and Experimental Studies of a Mirrorless Lasing of Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)

In this work, we investigate the TD-DFT simulation, optical, and mirrorless laser properties of conjugated polymer (CP) Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)], also known as (PFO-co-PPV-MEHB) or ADS125GE. TD-DFT calculations were performed for three monomer units with truncated tails using time-dependent density functional theory (TD-DFT) calculations. The calculations showed a highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) structure and a very high oscillator strength of 6.434 for the singlet-singlet transition at 374.43 nm. Experimentally, the absorption and fluorescence spectra were examined at various concentrations in verity of solvents, such as benzene, toluene, and hexane. The experimental results obtained in hexane were comparable with theoretical UV-VIS spectra calculated under vacuum. Amplified spontaneous emission (ASE) spectra peaked at approximately 509 nm for CO PFO-co-PPV-MEHB in solution and were obtained at suitable concentrations and pump energies. Additionally, the photochemical stability of this CP and coumarin (C510) were compared. Time-resolved spectroscopy (TRS) studies with a sub-nanosecond resolution were performed for the CO under various pump energies. These results showed the excited state dynamics and single-pass optical gain of CO PFO-co-PPV-MEHB.

Optimized design of strain-compensated InxGa1-xN/GaN and InxGa1-xN/InYGa1-YN multiple-quantum-well laser diodes

We carried out a study of the strain-compensated InxGa1−xN/GaN and InxGa1-xN/InyGa1-yN multiple quantum wells, In order to carry out this analysis, we choose a set of three different types of samples. The optimization of this laser structure allowed us to determine the optimal values of the functional parameters, in order to adjust their performance and interest. We also studied the electronic and structural properties of compound semiconductor alloys used in wurtzite phase and we have presented a comparative theoretical study of both structures. Our studies show the improvement of the spontaneous emission spectra and better carrier confinement from the use of InxGa1-xN/InyGa1-yN MQW with higher In-content in barrier as active regions for diode lasers and this structure is useful for the design of new high performance Laser diodes emitting in the Blue/Violet range, and it’s also shows that the process of the electron-holes transition is strongly affected by the quantum well width and the Indium composition, and the InGaN lattice mismatch that increases with In-content causing the strain accumulation inside the QW structure. However, strain is undesirable as it can cause defects such as cracking at the interface.We can optimize the InGaN/GaN strained quantum well structures to achieve a reliable optoelectronic component. It suffices to incorporate small amounts of indium in the barrier enhances the annihilation of the defect and strain, thereby improving their structural properties.

Сужение спектра излучения GaAs светодиода за счет применения светофильтра InP (Ag)

АЛ115В LED emission spectrum at currents of 6.3 mA and 56 mA, as well as the emission spectrum using an InP (Ag) light filter at current 56 mA, are studied. A classical approximation of the spontaneous emission spectrum of a straight-band LED is presented (without taking into account the narrowing of the band gap due to the high degree of LED doping). The analytical and experimental widths of the LED band gap are estimated. The transmission spectrum of an InP (Ag) light filter is presented, taking into account reflection losses in the region of fundamental transitions. The spectral dependence (fragment) of the InP absorption coefficient is determined. The error is estimated. It is proposed to use АЛ115В with an InP (Ag) light filter in order to narrow the spectral band of radiation from 53 nm to 34 nm.

Amplification Lengths of Spectral Components of Intrinsic Stimulated Picosecond Emission. Dependence of the Characteristic Relaxation Time of These Components on Their Amplification Lengths. Relation Between Stimulated and Spontaneous Emission Spectra in GaAs

The high-power picosecond optical pumping of a thin GaAs layer generates intense picosecond stimulated emission. The emission spectrum is a light continuum. Based on the results of previous experimental work, the following is carried out. (a) The amplification lengths of the emission spectral components, i.e., the different distances over which different emission components are amplified in the active medium produced by pumping and (b) the dependences of the characteristic relaxation time of emission components on their gain lengths are estimated. It is shown that the spectrum of the product of the gain length and the gain linearly relates the spectra of the spontaneous and stimulated emission of GaAs. This relation is established upon gain saturation which is evidenced by a dip in the gain spectrum, “burned out” by intense emission.