Spontaneous Emission Measurements Research Articles

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.

Spatio-temporal analysis of power deposition and vibrational excitation in pulsed N2 microwave discharges from 1D fluid modelling and experiments

Vibrational excitation of N2 beyond thermodynamic equilibrium enhances the reactivity of this molecule and the production of radicals. Experimentally measured temporal and spatial profiles of gas and vibrational temperature show that strong vibrational non-equilibrium is found in a pulsed microwave discharges at moderate pressure (25 mbar) in pure N2 outside the plasma core and as an effect of power pulsing. A one dimensional radial time-resolved self-consistent fluid model has been developed to study the mechanism of formation of vibrationally excited N2. In addition to the temperature maps, time-resolved measurements of spontaneous optical emission, electron density and electron temperature are used to validate the model and the choice of input power density. The model reveals two regions in the plasma: a core where chemistry is dominated by power deposition and where vibrational excitation starts within the first ∼10 µs and an outer region reliant on radial transport, where vibrational excitation is activated slowly during the whole length of the pulse (200 µs). The two regions are separated by a sharp gradient in the estimated deposited power density, which is revealed to be wider than the emission intensity profile used to estimate the plasma size. The low concentration of excited species outside the core prevents the gas from heating and the reduced quenching rates prevent the destruction of vibrationally excited N2, thereby maintaining the observed high non-equilibrium.

Propagation loss in polyfluorene waveguides due to nanometer-roughness at their interfaces, studied by amplified spontaneous emission measurements

The propagation loss in single-mode asymmetric waveguides due to interface nanometer-roughness was studied using amplified spontaneous emission (ASE) measurements. Poly(9,9-dioctylfluorene) (F8) was used as the organic gain medium and the structure of the asymmetric waveguide was quartz glass substrate/F8/air. The propagation loss was measured at the ASE wavelength (447 nm) of amorphous F8, and the surface roughness of the substrate and F8 was measured using an atomic force microscope. The propagation losses of F8 waveguides with different F8 slab thicknesses were in good agreement with those calculated using an analytical expression for single-mode asymmetric waveguides with nanometer-roughness interfaces. The results presented herein will be useful for the design of high-performance organic lasers and organic optoelectronic integration systems.

Optical Properties of Perovskite-Organic Multiple Quantum Wells.

A comprehensive study of the optical properties of CsPbBr3 perovskite multiple quantum wells (MQW) with organic barrier layers is presented. Quantum confinement is observed by a blue‐shift in absorption and emission spectra with decreasing well width and agrees well with simulations of the confinement energies. A large increase of emission intensity with thinner layers is observed, with a photoluminescence quantum yield up to 32 times higher than that of bulk layers. Amplified spontaneous emission (ASE) measurements show very low thresholds down to 7.3 µJ cm−2 for a perovskite thickness of 8.7 nm, significantly lower than previously observed for CsPbBr3 thin‐films. With their increased photoluminescence efficiency and low ASE thresholds, MQW structures with CsPbBr3 are excellent candidates for high‐efficiency perovskite‐based LEDs and lasers.

Investigating spray flames for nanoparticle synthesis via tomographic imaging using multi-simultaneous measurements (TIMes) of emission.

Tomographic imaging using multi-simultaneous measurements (TIMes) of spontaneous light emission was performed on various operating conditions of the SpraySyn burner to analyse the flame morphology and its potential impact on spray flame pyrolysis. Concurrent instantaneous and time-averaged three-dimensional measurements of CH* chemiluminescence (flame front indicator) and atomic Na emission from NaCl dissolved in the injected combustible liquid (related to hot burnt products of the spray flame) were reconstructed employing a 29-camera setup. Overlapping regions of CH* and Na are presented using isosurface visualisation, local correlation coefficient fields and joint probability distributions. The instantaneous results reveal the complex nature of the reacting flow and regions of interaction between the flame front with the hot gases that originate from the spray stream. The averaged reconstructions show that the spray flames tested are slightly asymmetric near the burner exit but develop into symmetric bell-shaped distributions at downstream locations. The changes in the flame structure for different operating conditions are analysed in light of previous studies, helping in the better understanding of the nanoparticle synthesis process. Furthermore, the importance of using measurements from two views for significantly improved alignment of the burner based on the originally proposed procedure are discussed in light of the reconstructions. This is an important aspect since the SpraySyn is intended for use as a well-defined standardised burner for nanoparticle synthesis, which is being investigated numerically and experimentally across different research groups.

Amplified spontaneous emission and optical gain characteristics of sexithiophene single crystals

This paper reports optical properties of a single crystal thiophene/phenylene co-polymer 5,5ʺʺ'-diphenyl-2,2′:5′,2ʺ:5ʺ,2ʺ′:5ʺ′,2ʺʺ:5ʺʺ, 2ʺʺ'-sexithiophene (P6T). The P6T crystals demonstrate high charge carriers’ mobility and large photoluminescence quantum efficiency (PLQE). Herein, the stimulated emission of P6T is studied within wide range of pump energies –refers to energy per pulse – (from 19 ± 0.5 μJ/cm2 to 64.2 ± 0.5 μJ/cm2) through amplified spontaneous emission (ASE) measurements by using Nd-YAG femtoseconds tunable pulsed laser at 445 nm excitation wavelength (λexc). ASE measurements exhibit lower threshold energy density (Eth) i.e., ~26 ± 0.5 μJ/cm2 which confirms optical amplification in P6T at 632 nm emission wavelength. The ASE characteristics of P6T are also studied as a function of different λexc ranging from 425 to 475 nm to find the wavelength for optimum amplification. It is observed that the maximum optical amplification for P6T occurs at a λexc of 445 nm. These crystals exhibit large optical gains which are measured to be 69 cm−1, 53 cm−1 and 29 cm−1 at excitation energies of 91 ± 0.5 μJ/cm2, 66 ± 0.5 μJ/cm2 and 43 ± 0.5 μJ/cm2, respectively. PL measurements of P6T crystals demonstrate large value of the PLQE ~57.36%. This study suggests the potential of P6T single crystal as one of the good candidates among high optical gain materials of its kind for its possible applications in solid-state lasers, photodetectors and optical amplifiers.

Deep Blue Light Amplification from a Novel Triphenylamine Functionalized Fluorene Thin Film.

The development of high performance optically pumped organic lasers operating in the deep blue still remains a big challenge. In this paper, we have investigated the photophysics and the optical gain characteristics of a novel fluorene oligomer functionalized by four triphenylamine (TPA) groups. By ultrafast spectroscopy we found a large gain spectral region from 420 to 500 nm with a maximum gain cross-section of 1.5 × 10−16 cm2 which makes this molecule a good candidate for photonic applications. Amplified Spontaneous Emission measurements (ASE) under 150 fs and 3 ns pump pulses have revealed a narrow emission at 450 nm with a threshold of 5.5 μJcm−2 and 21 μJcm−2 respectively. Our results evidence that this new fluorene molecule is an interesting material for photonic applications, indeed the inclusion of TPA as a lateral substituent leads to a high gain and consequently to a low threshold blue organic ASE.

The characteristic of otoacoustic emissions in full-term neonates according to ABO blood groups

IntroductionPrevious research has suggested that individuals with different blood groups show varied incidences of noise-induced hearing loss. The reduced otoacoustic emissions amplitudes indicate the higher possibilities of outer hair cell damage for noise exposure. ObjectiveThe objective is to analyze the characteristics of otoacoustic emissions, including the occurrence of spontaneous otoacoustic emission and the amplitudes of distortion product otoacoustic emission at certain frequencies in full term neonates with different ABO blood groups. MethodsA total of 80 selected full-term female neonates who passed the initial newborn hearing screen were enrolled into the study, with equal number of participants in four ABO blood groups (Blood Group A, Blood Group B, Blood Group AB, Blood Group O). Measurements of spontaneous otoacoustic emission and distortion product otoacoustic emission were performed in both ears for all participants. Results(1) The blood group O participants showed significantly fewer spontaneous otoacoustic emission occurrences than the other three blood groups (A=70%, B=80%, AB=67%, O=25%, p< 0.05). (2) The blood group O participants showed lower DPOAE amplitudes at 1257 Hz (M = 4.55 dB, SD = 8.36), 1587 Hz (M = 11.60 dB, SD = 6.57), 3174 Hz (M = 7.25 dB, SD = 5.99), 5042 Hz (M = 13.60, SD = 6.70) than participants with the other three blood groups in left ears (p < 0.05). In right ears, the blood group O participants showed reduced amplitudes at 1257Hz (M=6.55dB, SD=8.36), 1587Hz (M=13.60dB, SD=6.57), 3174Hz (M=7.65dB, SD=6.43), 5042Hz (M=13.65dB, SD=6.50) than participants from non-O blood groups (p<0.05). ConclusionFemale individuals with blood group O have lower otoacoustic emissions values than individuals with the other three blood groups. We need to further investigate the possible relationships between ABO blood group and cochlear function, including the potential influences of noise damage on cochlear outer hair cells.

Amplified Spontaneous Emission and Optical Gain in Organic Single Crystal Quinquethiophene

In this paper, we report optical characteristics of an organic single crystal oligomer 5,5⁗-diphenyl-2,2′:5′,2″:5″,2‴:5‴,2⁗-quinquethiophene (P5T). P5T crystal is a thiophene/phenylene co-oligomer that possesses better charge mobility as well as photoluminescence quantum efficiency (PLQE) as compared to other organic materials. Stimulated emission in P5T is investigated via amplified spontaneous emission (ASE) measurements within broad pump energies ranging from 35.26 to 163.34 µJ/cm2. An Nd-YAG femtosecond-tunable pulsed laser is used as a pump energy source for the ASE measurements of P5T crystals at an excitation wavelength of 445 nm. The ASE spectra exhibit optical amplification in P5T crystals at a 625 nm peak wavelength with a lower threshold energy density (Eth) ≈ 52.64 μJ/cm2. P5T also demonstrates higher optical gain with a value of 72 cm−1, that is calculated by using the variable stripe-length method. The value of PLQE is measured to be 68.24% for P5T. This study proposes potential applications of P5T single crystals in organic solid state lasers, photodetectors, and optical amplifiers.

Theory for frequent measurements of spontaneous emissions in a non-Markovian environment: Beyond the Lorentzian spectrum

The measurement-result-conditioned evolution of a system (e.g., an atom) with spontaneous emissions of photons is described by the quantum trajectory (QT) theory. In this work we generalize the associated QT theory from an infinitely wide bandwidth Markovian environment to the finite bandwidth non-Markovian environment. In particular, we generalize the treatment for an arbitrary spectrum, which is not restricted by the specific Lorentzian case. We rigorously prove the general existence of a perfect scaling behavior jointly defined by the bandwidth of the environment and the time interval between successive photon detections. For a couple of examples, we obtain analytic results to facilitate the QT simulations based on the Monte-Carlo algorithm. For the case where the analytical result is not available, a numerical scheme is proposed for practical simulations.

Diagnostic method based on spontaneous emission to evaluate the detonation cycle

A study on a hydrogen-fuelled single-cycle pulse detonation device, through pressure and spontaneous emission measurements, was carried out. Detonation initiation was effectively achieved by applying a 65 J microsecond discharge associated with the Shchelkin spiral with very small errors in the diagnostic method. OH* and H2O* temporal emission measurements were applied at the nozzle exit to establish correlations to specific impulses, determined from pressure curves. OH* emission images were also captured to verify detonation propagation at the exhaust. Both the OH* and H2O* emitters correlated well with the specific impulses, and the integrated areas under emission peak maxima resulted in improved correlations. It was found that the OH* amount per kilogram of fuel grows exponentially with the specific impulse based on fuel, while the H2O* emission area per kilogram of mixture decays exponentially with the specific impulse, based on the mixture. The OH* images demonstrate stable detonation propagations and validate the established correlations. Furthermore, a new optical method was developed for detonation cycle diagnostics.

Spontaneous Emission Measurements of Selected Alkali Radicals during the Combustion of a Single Biomass Pellet

Spontaneous emission intensities of Na*, Ca*, and K* during the combustion of single wood and straw pellets doped with known concentrations of Na, Ca, and K were measured using optical bandpass filters mounted on an intensified charge-coupled device camera. The impregnated biomass pellets were suspended in a natural gas flat flame at 750 and 1000 °C. Before the pellets were made, the biomass samples were washed and soaked to demineralize and doped with different concentrations of Na, Ca, and K (0.5, 2, and 5 wt %). During the experiments, the temperature at the center of the pellets was measured with a thermocouple and the combustion stages were identified with the help of the temperature derivative. The results reveal that, at the lower gas temperature, the emission of the selected alkalis is marginal, in agreement with previous studies. At the higher gas temperature, the emission profiles reveal that K and Na are released distinctively in the volatile combustion and char combustion stages. The presence of large amounts of silica and alumina may trap the alkalis in the solid phase, leading to a reduced emission of these species during the char combustion. Calcium does not evaporate at the tested temperature conditions, but the temperature is high enough to promote the decomposition of calcium oxalate in the outer layer of the pellet, leading to a flat emission profile during the combustion stages. Finally, the total integrated emission increased proportionally with the increase of the doping concentration for all species.

Widely Tunable Laser Using Reflecting Fabry–Perot Filters With Lossy Half-Wave Trenches

We report the design and experimental results of a widely tunable three-section laser by using reflecting Fabry–Perot filters with deeply etched lossy half-wave coupling trenches. Good performance in side-mode suppression ratio and wavelength tuning range has been demonstrated experimentally. By introducing moderate coupling loss in the half-wave coupling trenches, high-mode selectivity can be achieved. The single-mode selectivity can be further improved by introducing slight gain in the Fabry–Perot filters. Electrical tuning of 12 channels covering as large as 84-nm wavelength range with side-mode suppression ratio up to 48 dB has been demonstrated. The large wavelength tuning range is a result of large temperature induced gain spectrum shift, which is verified by amplified spontaneous emission measurements

Multidimensional photon correlation spectroscopy of cavity polaritons

The strong coupling of atoms and molecules to radiation field modes in optical cavities creates dressed matter/field states known as polaritons with controllable dynamical and energy transfer properties. We propose a multidimensional optical spectroscopy technique for monitoring polariton dynamics. The response of a two-level atom to the time-dependent coupling to a single-cavity mode is monitored through time-and-frequency-resolved single-photon coincidence measurements of spontaneous emission. Polariton population and coherence dynamics and its variation with cavity photon number and controlled by gating parameters are predicted by solving the Jaynes-Cummings model.

Highly Reliable Low-Threshold InAs Quantum Dot Lasers on On-Axis (001) Si with 87% Injection Efficiency

Quantum dot lasers epitaxially grown on Si are promising for an efficient light source for silicon photonics. Recently, considerable progress has been made to migrate 1.3 μm quantum dot lasers from off-cut Si to on-axis (001) Si substrates. Here, we report significantly improved performance and reliability of quantum dot lasers enabled by a low threading dislocation density GaAs buffer layer. Continuous-wave threshold currents as low as 6.2 mA and output powers of 185 mW have been achieved at 20 °C. Reliability tests after 1500 h at 35 °C showed an extrapolated mean-time-to-failure of more than a million hours. Direct device transparency and amplified spontaneous emission measurements reveal an internal optical loss as low as 2.42 cm–1 and injection efficiency of 87%. This represents a significant stride toward efficient, scalable, and reliable III–V lasers on on-axis Si substrates for photonic integrate circuits that are fully compatible with CMOS foundries.

Gain optimization, bleaching, and e-beam structuring of IR-140 doped PMMA and integration with plasmonic waveguides

The optimal IR-140 weight ratio concentration producing maximum gain in amplified spontaneous emission measurements in the near-infrared (~880 nm) is determined. The structures investigated consist of PMMA polymer thin films, doped with IR-140 dye molecules in 4 different concentrations (0.7%, 0.8%, 0.9% and 1.0%), spin-coated on a silica layer grown on silicon wafers. The maximum material gain was obtained for the 0.9% weight ratio sample. The polarization dependence of the gain medium was also investigated, and the gain found to be similar in the TE and TM orientations. Bleaching of the gain medium, characterized by a decrease in the material gain due to pumping, was also explored and found to be rapid for thin films. However, bleaching is reduced as the pump energy density is reduced, creating a trade-off between gain and film longevity. The bleaching disappears at a low pump repetition rate. The gain films were structured via e-beam lithography to demonstrate the feasibility of this method for integration of structured doped polymers within optical devices. Amplification of the long-range surface plasmon guided by a gold stripe covered by the gain medium is also demonstrated and the modal gain measured was measured (~65 cm−1) from which the material gain was deduced (~300 cm−1). The material should prove useful for demonstrating device ideas and concepts in plasmonics and nano-photonics.

Measurement of the X-ray Spectrum of a Free Electron Laser with a Wide-Range High-Resolution Single-Shot Spectrometer

We developed a single-shot X-ray spectrometer for wide-range high-resolution measurements of Self-Amplified Spontaneous Emission (SASE) X-ray Free Electron Laser (XFEL) pulses. The spectrometer consists of a multi-layer elliptical mirror for producing a large divergence of 22 mrad around 9070 eV and a silicon (553) analyzer crystal. We achieved a wide energy range of 55 eV with a fine spectral resolution of 80 meV, which enabled the observation of a whole SASE-XFEL spectrum with fully-resolved spike structures. We found that a SASE-XFEL pulse has around 60 longitudinal modes with a pulse duration of 7.7 ± 1.1 fs.

Temperature- and current-dependent spontaneous emission study on 2 µm InGaSb/AlGaAsSb quantum well lasers

Spontaneous emission measurements, as a function of injection current and temperature, were carried out from the sidewall of a working 2 µm InGaSb/AlGaAsSb quantum well laser. The local Z power parameter was extracted to investigate the carrier recombination behaviors. A model involving the activation energy is presented to interpret the carrier loss mechanisms. Our findings show that the majority of the injected carriers recombine radiatively at low injection currents, and that Auger nonradiative recombination increases significantly with injection current. More importantly, no obvious temperature dependence of Z is observed from 20 to 80 °C.

Bounds on collapse models from cold-atom experiments

The spontaneous localization mechanism of collapse models induces a Brownian motion in all physical systems. This effect is very weak, but experimental progress in creating ultracold atomic systems can be used to detect it. In this paper, we considered a recent experiment [1], where an atomic ensemble was cooled down to picokelvins. Any Brownian motion induces an extra increase of the position variance of the gas. We study this effect by solving the dynamical equations for the Continuous Spontaneous Localizations (CSL) model, as well as for its non-Markovian and dissipative extensions. The resulting bounds, with a 95% of confidence level, are beaten only by measurements of spontaneous X-ray emission and by experiments with cantilever (in the latter case, only for rC > 10^(-7) m, where rC is one of the two collapse parameters of the CSL model). We show that, contrary to the bounds given by X-ray measurements, non-Markovian effects do not change the bounds, for any reasonable choice of a frequency cutoff in the spectrum of the collapse noise. Therefore the bounds here considered are more robust. We also show that dissipative effects are unimportant for a large spectrum of temperatures of the noise, while for low temperatures the excluded region in the parameter space is the more reduced, the lower the temperature.

Ultra-weak Photon Emissions Differentiate Malignant Cells from Non- Malignant Cells In Vitro

A fast, inexpensive, and accurate method for differentiating normal (non-malignant) cells from malignant cells could facilitate diagnosis and subsequently treatment. Although blood constituents are the current dominant indicators, we have found that Spectral Power Densities (SPD) obtained from only 100 s of measurements of spontaneous ultra-weak photon emissions (UPE) from cell cultures significantly differentiated malignant from non-malignant states. Breast cells were particularly differentiable from nonbreast cells according to their SPD profiles. More critically the combination of only 3 discrete frequency increment changes in SPD profiles accurately classified 85% of malignant breast cells from normal breast cells in culture. These results confirm results from our mouse experiments and preliminary observations from our human measurements that appropriately analyzed and interpreted SPD from very brief samples of UPE may be a viable tool for early detection of malignancy.