Continuous Emission Spectrum Research Articles

Ignition of Coal Microparticles by Laser Pulses of The Second Harmonic of a Ndodymium Laser in the Q-Switched Regime

The ignition of pelletized samples of hard coals of the long-flame gas (DG), gas (G), fat (L), coke (K) grades with particle sizes ≤63 μm by laser pulses (λ = 532 nm, τi = 10 ns) was studied. When the critical radiation energy density Hcr(1), specific for each grade of coal, is exceeded, an optical breakdown occurs and a dense plasma with a continuous emission spectrum is formed. As the plasma expands and rarefies, the spectra show the emission of carbon ions CII, excited nitrogen atoms N, excited carbon molecules C2, and carbon monoxide CO. The plasma glow intensity peaks at the end of the laser pulse, and the glow relaxation time is ~1 μs. The plasma glow amplitude increases nonlinearly with increasing laser pulse energy density. At radiation energy density H ≥ Hcr(2), specific for each grade of coal, thermochemical reactions are initiated in the volume of microparticles and coal particles are ignited in a submillisecond time interval.

Different LED light intensity and quality change perennial ryegrass (Lolium perenne L.) physiological and growth responses and water and energy consumption.

Light intensity and spectral composition highly affect plant physiology, growth, and development. According to growing conditions, each species and/or cultivar has an optimum light intensity to drive photosynthesis, and different light spectra trigger photosynthetic responses and regulate plant development differently. For the maintenance of natural sports pitches, namely professional football competitions, turf quality is a key condition. Due to the architecture of most football stadiums, the lawns receive low intensities of natural light, so supplementary artificial lighting above the turf is required. The use of light-emitting diodes (LEDs) can have a higher cost-benefit ratio than traditional high-pressure sodium lamps. The continuous emission spectrum, combined with high spectral selectivity and adjustable optical power, can be used to optimize plant growth and development. Thus, perennial ryegrass (Lolium perenne L.) plants, commonly used for lawns, were primarily grown at three different intensities (200, 300, and 400 μmol m-2 s-1) of cool white light. Despite the higher water and energy consumption, 400 μmol m-2 s-1 maximizes the plant's efficiency, with higher photosynthetic rates and foliar pigment concentration, and more foliar soluble sugars and aboveground biomass accumulation. Then, it was evaluated the perennial ryegrass (Double and Capri cultivars) response to different spectral compositions [100% cool white (W), 80% Red:20% Blue (R80:B20), 90% Red:10% Blue (R90:B10), and 65% Red:15% Green:20% Blue (R65:G15:B20)] at 400 μmol m-2 s-1. Both cultivars exhibited similar responses to light treatments. In general, W contributed to the better photosynthetic performance and R90:B10 to the worst one. Water consumption and aboveground biomass were equal in all light treatments. R80:B20 allows energy savings of 24.3% in relation to the W treatment, showing a good compromise between physiological performance and energy consumption.

Polymer‐Encapsulated Halide Perovskite Color Converters to Overcome Blue Overshoot and Cyan Gap of White Light‐Emitting Diodes

AbstractCurrently, the most popular way to manufacture white light‐emitting diodes (WLEDs) is based on blue‐emitting InGaN LED chips (440–460 nm) and yellow‐emitting phosphor coating (520–700 nm) to produce white light lighting. However, because conventional white WLEDs lack the uniformly distributed continuous emission spectrum compared to natural sunlight: “blue overshoot” (extra 440–460 nm blue‐light can cause damage to the retina) and “cyan gap” (470–520 nm wavelength range). Here, a novel strategy to “kill two birds with one stone” is reported: using the stable and bright polymer encapsulated perovskite nanocrystals (PNCs) composite films as the cyan color converters that efficiently absorb the “blue overshoot” and effectively emit the cyan light to fill the “cyan gap”. A series of polymer‐encapsulated PNC films is achieved that can reach very high photoluminescence quantum yield (PL QY) of 90–95% under 450 nm blue‐light excitation. Importantly, both 370 nm UV‐excited WLED and 455 nm blue‐excited WLED devices are constructed that exhibit smoothly and evenly distributed white light without blue overshoot and cyan gap, which was not achieved before for blue‐excited cyan‐emissive materials. This study paves the way toward the application of PNC color converters in the next generation full‐visible‐spectrum WLED lighting that mimic the natural daylight.

Testbed for Studying the Efficiency of Plants Photosynthetic Irradiation Based on Measuring Carbon Dioxide Concentration in the Air

The work is devoted to the description of a testbed that allows studying the efficiency of photosynthetic irradiation of plants by measuring the level of carbon dioxide concentration in the air, which in turn determines the intensity of photosynthetic processes in plants. This method makes it possible to significantly increase the speed of comparative research of the effect of irradiation modes on crop yields. The developed testbed is based on the ESP8266 microcontroller with sensors for measuring carbon dioxide concentration, temperature, air humidity, and a microcontroller implementing the control of plant irradiation modes. Measurement of carbon dioxide concentration was carried out using the MH-Z16 sensor, the principle of which is based on the measurement of non-dispersive infrared radiation (NDIR). In the testbed LED irradiators with a continuous emission spectrum and LED irradiators with a combined emission spectrum (white light + “red” radiation) were used. The testbed allowed us to study the dependence of the efficiency of photosynthesis on the conditions of irradiation by varying the spectral composition of radiation, irradiance intensity. The measurement of carbon dioxide concentration in the phytotron showed its significant dependence on the irradiation conditions. Since the rate of change in the concentration of carbon dioxide occurs over a sufficiently long period of time, research into the irradiation efficiency was carried out on the basis of an assessment of the dynamics of carbon dioxide concentration. Another variant of the research was the consistent comparison of changes in the concentration of carbon dioxide under different irradiation conditions.

Compact ultrabroadband light-emitting diodes based on lanthanide-doped lead-free double perovskites

Impurity doping is an effective approach to tuning the optoelectronic performance of host materials by imparting extrinsic electronic channels. Herein, a family of lanthanide (Ln3+) ions was successfully incorporated into a Bi:Cs2AgInCl6 lead-free double-perovskite (DP) semiconductor, expanding the spectral range from visible (Vis) to near-infrared (NIR) and improving the photoluminescence quantum yield (PLQY). After multidoping with Nd, Yb, Er and Tm, Bi/Ln:Cs2AgInCl6 yielded an ultrabroadband continuous emission spectrum with a full width at half-maximum of ~365 nm originating from intrinsic self-trapped exciton recombination and abundant 4f–4f transitions of the Ln3+ dopants. Steady-state and transient-state spectra were used to ascertain the energy transfer and emissive processes. To avoid adverse energy interactions between the various Ln3+ ions in a single DP host, a heterogeneous architecture was designed to spatially confine different Ln3+ dopants via a “DP-in-glass composite” (DiG) structure. This bottom-up strategy endowed the prepared Ln3+-doped DIG with a high PLQY of 40% (nearly three times as high as that of the multidoped DP) and superior long-term stability. Finally, a compact Vis–NIR ultrabroadband (400~2000 nm) light source was easily fabricated by coupling the DiG with a commercial UV LED chip, and this light source has promising applications in nondestructive spectroscopic analyses and multifunctional lighting.

ОБ ОЦЕНКЕ ЭФФЕКТИВНОСТИ ПРОЦЕССА ВЫСОКОИНТЕНСИВНОГО ОКИСЛЕНИЯ

The EEO parameter is commonly used as a figure-of-merit of ultraviolet-based advanced oxidation processes (UV AOPs). It represents the energy input into the UV AOPs that can achieve an order of magnitude decrease in the target contaminant concentration in a unit volume. This paper focuses on factors, that influence on the EEO parameter and should be reported with it to compare the efficiency of different reactors or UV AOPs: the identity and concentration of the target pollutant, as well as the concentration of scavengers; the amount of hydrogen peroxide or other oxidizing agent, source of UV radiation etc. Decays of phenol, sodium dodecyl sulfate and petroleum products in UV AOP were used to show how various conditions affect on the EEO parameter. The studies were carried out on model solutions with an initial concentration of pollutants of 10 mg/l. As a source of ultraviolet radiation, a pulsed xenon lamp was used. It has a continuous emission spectrum in the range of 200 – 1000 nm, the average energy consumption was about 200 W, the radiation energy in the range of 200–300 nm was 2.7 J. Hydrogen peroxide was used as an oxidizing agent, it concentration varied from 10 to 340 mg/L. The modified parameter of UV AOP efficiency is proposed. It considers electrical energy input with reagents consumption. It is proposed to express the costs of the oxidant in physical values and include them in the modified parameter with a weighting factor.

Gas-discharge plasma diagnostics by a continuous spectrum of optical radiation

In the present work, plasma diagnostics method based on the measurement and theoretical analysis of continuous emission spectrum of a gas discharge was discussed. Using the method, electron temperatures of a DC glow discharge and ferromagnetic enhanced inductive discharge were determined for inert gases in the gas pressure range of 20–200 Pa. Experimental results were compared with the results of numerical calculations for the ferromagnetic enhanced inductive discharge and DC glow discharge. A satisfactory agreement between the optically measured and numerically calculated values of electron temperature was shown.

Localization of a Motionless Sound Source by Simultaneous Suppression of Interference Using Incoherent Aperture Synthesis

We consider the problem of direction finding of a motionless sound source by using aperture synthesis. The emitted signal of the source is assumed to be time incoherent. This scenario is most interesting from the practical point of view, since the real sources mainly have a continuous emission spectrum. It was assumed that in addition to the sea noise, the receiving system was also affected by onboard interference caused by the mechanisms inside the carrier ship. The power of onboard interference greatly exceeded the power of the useful signal. The results of testing of the proposed algorithms using numerical and lake experiments are presented. It has been shown that, depending on the length and type of the trajectory of the carrier ship, different accuracies are achieved for the measured coordinates of a motionless source.

On the uniqueness of the solution of the problem of reconstructing a continuous soft X-ray emission spectrum by the iterative method

Abstract The question on the uniqueness of the solution of the problem of reconstructing a continuous soft X-ray emission spectrum by the iterative method [Nuclear Inst. and Methods in Physics Research A, 916 (2019) 313–321] from spectrograms obtained with a transmission diffraction grating is considered. It is shown that, despite the presence of a potentially infinite number of solutions of this problem, only one of them has the physical sense.

Triple Cherenkov probe measurements on FTU: calibration and runaway energy spectra

Characterization and calibration measurements of two Cherenkov probes have been performed in ENEA Frascati’s laboratories. Different kinds of radiation have been used, from visible light to x-rays, in order to evaluate possible spurious responses of the probes. Moreover, a preliminary calibration is presented, as well as a first evaluation of the minimum single probe’s detectable flux performed through an electron beam of 2.3 MeV. Additional results have been obtained thanks to spectrometry analysis, which gave deeper insights of the phenomena occurring inside the probes. In particular, a continuous emission spectrum, associated to cathodoluminescence, has been observed to dominate in the Cherenkov range, showing that scintillating phenomena are not negligible in this kind of probes. Results on non-thermal electron losses from recent FTU experimental campaigns are also presented. The signals acquired are compared to those from other diagnostics like x-rays, neutron and gamma detectors or plasma magnetic activity, showing good correlation between them. The analysis focuses on the capability and sensitivity of the probes to measure runaway electrons losses with energy discrimination in presence of perturbations due to kinetic and magnetic reconnection phenomena.

Understanding VCSEL-Based Gain Switching Optical Frequency Combs: Experimental Study of Polarization Dynamics

In this paper, we carry out an experimental study on the polarization properties of a vertical-cavity surface-emitting laser (VCSEL) working under gain switching (GS) regime and the characteristics of the resulting optical frequency comb signal. We have observed that each of the two polarization modes presented in the VCSEL continuous wave emission spectrum generate a separate optical frequency comb (OFC) whose modes are phase correlated thanks to the GS regime. We study how these combs associated with the main and orthogonal polarization modes, respectively, vary depending on the input parameters to the VCSEL (bias current and radio-frequency power and frequency). The correlation between both OFCs in the best operation point as defined by the OFC characteristics is also evaluated. Therefore, this study demonstrates that two orthogonally polarized combs are generated that exhibit a high correlation between each other that combine to produce a wider overall optical comb. Hence, we can predict the feasibility of dual-polarization VCSEL-based OFC generators in the few gigahertz repetition frequency rates, with highly correlated modes and continuously tunable distance between them, in a compact and energy- and cost-efficient system that can find application in ultrafast laser dynamics studies and or in polarization-division multiplexing optical communications.

Influence of annealing in Zn vapor on the luminescence of MgZnO ceramics

AbstractZnO‐based compounds that exhibit a number of strongly overlapping emission bands in visible spectral region are promising materials for white‐light emitters with continuous emission spectrum. Defect‐related emission in doped with different impurities ZnO, however, spreads from green to red spectral region, so its shift toward shorter wavelengths is required. We supposed that this problem can be solved due to broadening of ZnO band gap by alloying ZnO with MgO. The enhancement of visible emission brightness is also an important problem. In this work, MgxZn1‐xO ceramics with x =0 and x=0.2 were sintered both in air and Zn vapor at 950 oC. Emission and Raman scattering spectra were measured at 300 K using 325 nm line of He‐Cd laser as excitation source. In samples sintered in air, bright UV emission and weak visible one took place, adding MgO to ZnO resulting in blue‐shift of the latter. Sintering in Zn vapor was found to weaken UV emission and to increase drastically the brightness of visible one especially in blue‐green spectral region. As a result, bright blue radiation was observed from MgZnO ceramics under excitation by considerably week UV light. Obtained effects were accounted for by the shift of “green” centers energetic level with respect to involved band edge as a result of band‐gap broadening and by the increase of this center density due to annealing in Zn vapor. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultra-wide electroluminescence spectrum of LED heterostructures based on GaPAsN semiconductor alloys

In this paper, we present the results of the white light-emitting diodes (LEDs) construction based on GaPAsN semiconductor alloys on a GaP substrate. Heterostructure electroluminescence with a continuous emission spectrum in the range from 350 nm to 1050 nm is observed. The output of light through the side walls and the face side of the sample enabled us to achieve white light emission by means of ultra-wide electroluminescence spectrum covering all visible spectrum and part of the near IR spectral range. While extracting emission through substrate, the short-wavelength part of the visible spectra is absorbed at GaP layer.

Rate-equations based model for the 2D-0D direct channel in quantum dot lasers under CW and gain-switching

Direct capture of carriers from the wetting layer to the most confined states is discussed in this paper. This channel for carrier scattering was recently used to fit typical P-I curves of quantum dot lasers. Here new numerical expressions for the escape times accounting for the carriers added by the direct channel are introduced and evaluated, and insights of the influence of these additional carriers on the continuous and pulsed laser emission spectrum are given.

Continuous Emission Spectrum Measurement for Electron Temperature Determination in Low-Temperature Collisional Plasmas

Continuous emission spectrum measurement is applied for the inconvenient diagnostics of low-temperature collisional plasmas. According to the physical mechanism of continuous emission, a simplified model is presented to analyze the spectrum in low temperature plasma. The validity of this model is discussed in a wide range of discharge parameters, including electron temperature and ionization degree. Through the simplified model, the continuous emission spectrum in a collisional argon internal inductively coupled plasma is experimentally measured to determine the electron temperature distribution for different gas pressures and radio-frequency powers. The inverse Abel transform is also applied for a better spatially resoluted results. Meanwhile, the result of the continuous emission spectrum measurement is compared to that of the electrostatic double probes, which indicates the effectiveness of this method.

Formation of the continuous visible emission spectrum of pulsed discharge in cesium vapor

The formation of a continuous emission spectrum of pulsed discharge in high-pressure cesium vapor (P ≤ 1 bar) has been experimentally studied under conditions of increased power deposited in discharge. Experimental data well agree with the results of theoretical calculations. Physical mechanisms underlying the observed phenomenon are discussed. It is shown that, as the pumping current pulse amplitude is increased from 15 to 80 A, a discrete line spectrum transforms into the continuous spectrum. This is accompanied by an increase in the light yield (from 15 to 85 lm/W) and color-rendering index (from 86 to 98).

Use of short-wavelength synchrotron radiation to measure luminescence quantum yield and the luminescence excitation spectrum of polymers

We describe an optical diagnostics module and the instrumental and methodological features of ultrahigh vac- uum experiments investigating the optical characteristics of condensed media in the short-wavelength (hν ~ 3.5-25 eV) range of the spectrum of probing synchrotron radiation. We give a brief presentation of the re- sults of an experimental determination of the spectral dependence of the luminescence quantum yield and the luminescence excitation spectrum of ablatable polymer dielectrics on the Kurchatov synchrotron radiation source at values of the probing radiation power density (I0 ~ 10 12 photons/cm 2 ⋅sec) that are below threshold for extended surface vaporization and a surface temperature of the condensed targets equal to 77-300 K. Introduction. In photonic power systems with high power density (optical accelerators and plasmatrons, laser plasma injectors, thermionic plasma optical converters, etc.) (1-3), plasma active media, including optical ablation media, at high temperatures (Te ~ 1-5 eV), are a source of broadband short-wavelength radiation with maximum in- tensities in the UV (UVC) and vacuum UV (VUV) regions of the spectrum. The temperature of the structural ele- ments of such power systems in the cycle for different pulsed periodic conditions may vary from cryogenic to phase transition temperatures. Therefore to calculate the heat and mass exchange characteristics, here we need data on the spectral reflection and absorption coefficients, the luminescence quantum yield for the structural materials in the UV- VUV regions of the spectrum over a broad temperature range, taking into account the technologically attainable level of surface treatment. As we know, measurement of the optical characteristics of condensed media in the vacuum UV region of the spectrum presents significant experimental complications, first of all due to the lack of sufficiently bright (at least 1 μW/mrad 2 ⋅nm) and broadband radiation sources in this region of the spectrum and secondly due to the need to make precision measurements under vacuum. Spectroscopy studies of condensed media in the vacuum UV region of the spectrum are conducted mainly using gas-discharge sources with a line emission spectrum, which limits the experimen- tal options in this spectral range both with respect to the number of available frequencies and with respect to the spectral brightness of the probing sources (2, 3). Using synchrotron radiation helps solve this problem. The high spec- tral density, the continuous (from the IR to the x-ray region) emission spectrum, the sharp directionality, and the high degree of polarization, the possibility for accurate determination of the spectral and energy characteristics of the source of probing radiation enable efficient use of synchrotron emitters as a working tool in optics and metrology with the maximum degree of monochromatization of short-wavelength radiation for existing vacuum UV monochromators. The goal of this work was to analyze the instrumental and methodological features of study under ultrahigh vacuum of luminescence excitation spectra and luminescence quantum yield of polymers over a broad range of photon energies for UV-VUV radiation and over a broad temperature range.

Luminescence of Ca(NbO 3) 2:Pr 3+ at ambient and high hydrostatic pressure

In this contribution, photoluminescence and time-resolved photoluminescence spectra of Ca(NbO 3) 2 doped with Pr 3+ obtained at high hydrostatic pressure up to 72 kbar applied in a diamond anvil cell are presented. At ambient conditions, the emission spectrum obtained in the time interval 0–1 μs is dominated by spin-allowed transitions from the 3P 0 state. On the other hand, transitions from 1D 2, characterized by a decay time equal to 30 μs dominate the steady-state luminescence. At pressures lower than 60 kbar, the continuous wave emission spectrum consists of sharp lines peaking between 600 and 625 nm, related to the 1D 2→ 3H 4 transition and three lines at 500, 550 and 650 nm related to emission transitions originating from the 3P 0 level of Pr 3+. The emission from the 1D 2 excited state depends weakly on the pressure. Its decay time decreases from 33 μs at ambient pressure to less than 22 μs at 68 kbar. On the other hand, the 3P 0 emission is strongly pressure dependent. At pressures of 60 kbar and higher, the Pr 3+ emission intensity from the 3P 0 state decreases. This is accompanied by a strong shortening of the luminescence decay time. The observed pressure quenching of the f–f emission transitions and the concomitant lifetime shortening have been attributed to increasing crossover from the 3P 0 state of Pr 3+ to a Pr 3+-trapped exciton state.

Optical spectroscopy of laser plasma in a deep crater

The time dynamics of plasma-emission spectra is studied experimentally at different stages of the drilling of a steel plate by 100-fs and 5-ps laser pulses: from a shallow crater to a hole. The change in the time dependence of the plasma temperature caused by variations in the irradiated surface geometry is analysed. It is found that the time interval needed to reach a particular temperature (about 8000 K) drastically increases from 40–50 to 150–200 ns when a specific crater depth is achieved. The opposite tendency is observed as the crater depth grows further and a hole is produced. Strong self-absorption in a plasma plume inside a deep crater is experimentally confirmed which results in the appearance of line absorption against a continuous emission spectrum.

Spectra and Kinetics of Emission from the Products of Explosive Decomposition of Silver Azide

The spectrum and kinetics of optical emission from the products of explosive decomposition of silver azide (AgN3) initiated by a pulsed electron beam (0.5 MeV, 1 kA/cm2, 20 ns) have been experimentally studied. The stage of preexplosion luminescence is followed by the formation of a continuous emission spectrum due to a dense plasma of decomposition products. This spectrum exhibits variations within a time interval of 0.6–0.9 μs, which can be related to the self-heating of plasma from 3000 to 3600 K as a result of the exothermal reaction 2N3 → 3N2.