Spectral Emission Properties Research Articles

Performance analysis of 1300 nm SLEDs – impact of temperature and length scaling

The impact of self-heating and cavity length on the spectral emission properties of SLEDs is investigated using a state-of-the-art simulation tool. Simulated data are compared to measurements for two InP-based benchmark devices operating around 1300 nm, and excellent agreement is achieved in either case.

High-Energy Particles in the Wind Nebula of Pulsar B1509-58 as Seen byINTEGRAL

We present observations with the INTEGRAL/IBIS telescope of the wind nebula powered by the young pulsar B1509-58 and we discuss the spatial and spectral properties of the unpulsed emission in the 20-200 keV energy band. The source extension and orientation along the northwest-southeast axis corresponds to the jet emission seen at keV and TeV energies. The hard X-ray spectrum is consistent with the earlier Beppo-SAX measurements. It follows a power law with a photon index alpha = -2.12 pm 0.05 up to 160 keV. A possible break at this energy is found at the 2.9 sigma confidence level. The 0.1-100 keV data are consistent with synchrotron aging of pairs in the jet and yield a magnetic field strength of 22-33 muG for a bulk velocity of 0.3-0.5c. The synchrotron cut-off energy thus corresponds to a maximum electron energy of 400-730 TeV.

Experimental investigation of the normal spectral emissivity and other thermophysical properties of pulse-heated Ni-Ti and Au-Ni alloys into the liquid phase

In a previous paper it was shown that the normal spectral emissivity at 684.5 nm of a binary alloy can be lower than that of the pure constituent components. For the actual probes it was found that the observed values of normal spectral emissivity of the alloys are in between or higher than those of the pure constituent components. Experiments were conducted on the alloy systems Ni-Ti and Au-Ni. Their emissivity as well as electrical resistivity and enthalpy as a function of temperature is presented.

NewChandraObservations of the Jet in 3C 273. I. Softer X‐Ray than Radio Spectra and the X‐Ray Emission Mechanism

The jet in 3C273 is a high-power quasar jet with radio, optical and X-ray emission whose size and brightness allow a detailed study of the emission processes acting in it. We present deep Chandra observations of this jet and analyze the spectral properties of the jet emission from radio through X-rays. We find that the X-ray spectra are significantly softer than the radio spectra in all regions of the bright part of the jet except for the first bright ''knot A'', ruling out a model in which the X-ray emission from the entire jet arises from beamed inverse-Compton scattering of cosmic microwave background photons in a single-zone jet flow. Within two-zone jet models, we find that a synchrotron origin for the jet's X-rays requires fewer additional assumptions than an inverse-Compton model, especially if velocity shear leads to efficient particle acceleration in jet flows.

Laboratory spectroscopic calibration of infrared tunable laser spectrometers for the in situ sensing of the Earth and Martian atmospheres

This paper reports the laboratory spectroscopic calibration of near- and mid- infrared tunable laser spectrometers used to determine in situ trace gases in the middle atmosphere of the Earth or in development for the investigation of the Martian atmosphere. The use of infrared absorption spectroscopy to measure gas concentrations requires a proper knowledge of the rotation–vibration spectra of the targeted molecules as well as a proper investigation of the tunable laser spectral emission properties. This last point is of particular importance for the use of new-generation lasers like quantum-cascade lasers or room-temperature multi-quantum wells laser diodes emitting between 2 and 3 μm. Purposely, we have developed various laboratory tunable laser set-ups to obtain accurate line strengths and pressure-broadening coefficients of atmospheric molecules and to test the performances of cutting-edge laser technology for trace gas sensing. In this paper, the spectroscopic calibration work is described. Several atmospheric applications of tunable laser are reported to stress the impact on concentration retrieval of a proper spectroscopic calibration work.

Long-lived visible luminescence of UV LEDs and impact on LED excited time-resolved fluorescence applications

We report the results of a detailed study of the spectral and temporal properties of visible emission from three different GaN-based ultraviolet (UV) light emitting diodes (UV LEDs). The primary UV emission in the 360–380 nm band decays rapidly (less than 1 µs) following switch-off; however, visible luminescence (470–750 nm) with a decay lifetime of tens of microseconds was observed at approximately 10−4 of the UV intensity. For applications of UV LEDs in time-resolved fluorescence (TRF) employing lanthanide chelates, the visible luminescence from the LEDs competes with the target Eu3+ or Tb3+ fluorescence in both spectral and temporal domains. A UV band-pass filter (Schott UG11 glass) was therefore used to reduce the visible luminescence of the UV LEDs by three orders of magnitude relative to UV output to yield a practical excitation source for TRF.

Spectral properties of nonthermal X-ray emission from the shell-type SNR RX J1713.7–3946 as revealed by XMM-Newton

We present the results of our morphological and spectral study of properties of the supernova remnant RX J1713.7-3946 based on data obtained with XMM-Newton. Highly inhomogeneous structures, such as the bright spots, filaments and dark voids, noted by Uchiyama et al. (2003), appear in the entire bright western portion of the shell. In addition two narrow rims are found which run parallel to each other from north to south in the western part of the remnant. No complex structures are seen in the interior region of the remnant. The X-ray spectra everywhere can be well represented with a power-law function of photon index ranging within Gamma = 2.0-2.8. A clear difference of spectra between the central dim region and the bright western portion is seen at lower energies. This differences can be ascribed either to an additional thermal component with electron temperature, kTe= 0.56keV from the center or, alternatively, to an increase in column density of Delta NH ~ 0.3 x 10^22 cm^-2 in the western region. In the context of the recent discovery by the NANTEN telescope of a molecular cloud apparently interacting with the western part of the supernova remnant, the second possibility seems to be the more likely scenario.

Surface-Plasmon-Coupled Emission of Quantum Dots

We studied surface plasmon-coupled emission (SPCE) of semiconductor quantum dots (QDs). These QDs are water-soluble ZnS-capped CdSe nanoparticles stabilized using lysine cross-linked mercaptoundecanoic acid. The QDs were spin-coated from 0.75% PVA solution on a glass slide covered with 50 nm of silver and a 5-nm protective SiO(2) layer. Excited QDs induced surface plasmons in a thin silver layer. Surface plasmons emitted a hollow cone of radiation into an attached hemispherical glass prism at a narrow angle of 48.5 degrees. This directional radiation (SPCE) preserves the spectral properties of QD emission and is highly p-polarized irrespective of the excitation polarization. The SPCE spectrum depends on the observation angle because of the intrinsic dispersive properties of SPCE phenomenon. The remarkable photostability can make QDs superior to organic fluorophores when long exposure to the intense excitation is needed. The nanosize QDs also introduce a roughness near the metal layer, which results in a many-fold increase of the coupling of the incident light to the surface plasmons. This scattered incident illumination transformed into directional, polarized radiation can be used simultaneously with SPCE to develop devices based on both quantum dot emission and light scattered from surface plasmons on a rough surface.

AChandraView of the Normal S0 Galaxy NGC 1332. II. Solar Abundances in the Hot Gas and Implications for Supernova Enrichment

Using a new Chandra ACIS-S3 observation of the normal, isolated, moderate-LX lenticular galaxy NGC 1332, we resolve the emission into ~75 point sources and a significant diffuse component. We present a detailed analysis of the spectral properties of the diffuse emission, constraining both the temperature profile and the metal abundances in the hot gas. The characteristics of the point-source population and the spatial properties of the diffuse emission are discussed in two companion papers. The diffuse component comprises hot gas with an ~isothermal temperature profile (~0.5 keV) and emission from unresolved point sources. In contrast with the cool cores of many groups and clusters, we find a small central temperature peak. We obtain emission-weighted abundance constraints within 20 kpc for several key elements: Fe, O, Ne, Mg, and Si. The measured iron abundance (ZFe = 1.1 in solar units; >0.53 at 99% confidence) strongly excludes the very subsolar values often historically reported for early-type galaxies. This continues, in a lower LX system, a trend in recent observations of bright galaxies and groups. The abundance ratios, with respect to Fe, of the other elements were also found to be ~solar, with the exception of ZO/ZFe, which was significantly lower (<0.4), as seen in several bright galaxies, groups, and clusters. Such a low O abundance is not predicted by simple models of ISM enrichment by Type Ia and Type II supernovae (SNe) and may indicate a significant contribution from primordial hypernovae. Revisiting Chandra observations of the moderate-LX, isolated elliptical galaxy NGC 720, we obtain similar abundance constraints (ZFe = 0.71, 90% confidence; ZO/ZFe = 0.23 ± 0.21). Adopting standard SNe Ia and SNe II metal yield models, our abundance ratio constraints imply that 73% ± 5% and 85% ± 6% of the Fe enrichment in NGC 1332 and NGC 720, respectively, arises from SNe Ia. Although these results are sensitive to the considerable systematic uncertainty in the SNe yields, they are in good agreement with observations of more massive systems. These two cases of moderate-LX early-type galaxies reveal a consistent pattern of metal enrichment from cluster scales to moderate LX/LB galaxies.

Submillimeter Observations of the Low-Metallicity Galaxy NGC 4214

Results of submillimeter (450 and 850 μm) observations of a nearby dwarf irregular galaxy NGC 4214 with SCUBA on JCMT are presented. We aimed at examining the far-infrared–to–submillimeter spectral energy distribution (SED) and properties of dust thermal emission in a low-metallicity environment by choosing NGC 4214, in which the gas metallicity (log O/H + 12) is 8.34. We found that the SED is quite similar to those of the IRAS Bright Galaxies Sample (IBGS), which are local bright star-forming galaxies with metallicities comparable to the solar abundance. The dust temperature and emissivity index for NGC 4214 obtained by a fitting to the single temperature graybody model are Td = 35 ± 0.8 K and β = 1.4 ± 0.1, respectively, which are typical values for IBGS galaxies. Compiling the previous studies on similar nearby dwarf irregular galaxies, we found that NGC 1569 shows similar results to those of NGC 4214, while NGC 4449 and IC 10 SE show different SEDs and low emissivity indices. There seems to be a variety of SEDs among metal-poor dwarf irregular galaxies. We examined the dependence on the intensity of interstellar radiation field, as well as a two-temperature model, but the origin of the difference is not clear. Some mechanism(s) other than metallicity and the interstellar radiation field must be responsible for controlling dust emission properties.

Revealing the X‐Ray Emission Processes of Old Rotation‐powered Pulsars:XMM‐NewtonObservations of PSR B0950+08, PSR B0823+26, and PSR J2043+2740

We have completed part of a program to study the X-ray emission properties of old rotation-powered pulsars with XMM-Newton in order to probe and identify the origin of their X-radiation. The X-ray emission from these old pulsars is largely dominated by nonthermal processes. None of the observed spectra required adding a thermal component consisting of either a hot polar cap or surface cooling emission to model the data. The X-ray spectrum of PSR B0950+08 is best described by a single power law of photon index α = 1.93. Taking optical data from the VLT FORS1 into account, a broken power-law model with the break point Ebreak = 0.67 keV and the photon indices α1 = 1.27 and α2 = 1.88 for E < Ebreak and E > Ebreak, respectively, is found to describe the pulsar's broadband spectrum from the optical to the X-ray band. Three σ temperature upper limits for possible contributions from a heated polar cap or the whole neutron star surface are T < 0.87 × 106 and T < 0.48 × 106 K, respectively. We also find that the X-ray emission from PSR B0950+08 is pulsed with two peaks per rotation period. The phase separation between the two X-ray peaks is ~144° (maximum to maximum), which is similar to the pulse peak separation observed in the radio band at 1.4 GHz. The main radio peak and the trailing X-ray peak are almost phase-aligned. The fraction of X-ray pulsed photons is ~30%. A phase-resolved spectral analysis confirms the nonthermal nature of the pulsed emission and finds no spectral variations as a function of pulse phase. Detailed pulse profile simulations using the polar gap, the outer gap, and the two-pole caustic model constrain the pulsar's emission geometry to be that of an almost orthogonal rotator, for which the two-pole caustic model can reproduce the observed doubly peaked X-ray pulse profile. The spectral emission properties observed for PSR B0823+26 are similar to those of PSR B0950+08. Its energy spectrum is very well described by a single power law with photon index α = 2.5. Three σ temperature upper limits for thermal contributions from a hot polar cap or from the entire neutron star surface are T < 1.17 × 106 and T < 0.5 × 106 K, respectively. There is evidence for pulsed X-ray emission at the ~97% confidence level with a pulsed fraction of 49% ± 22%. For PSR J2043+2740, which is located ~1° outside the boundary of the Cygnus Loop, we report the first detection of X-ray emission. A power-law spectrum or a combination of a thermal and a power-law spectrum both yield acceptable descriptions of its X-ray spectrum. No X-ray pulses are detected from PSR J2043+2740 and the sensitivity is low—the 2 σ pulsed fraction upper limit is 57% assuming a sinusoidal pulse profile.

Natural spectral bandwidth of electron cyclotron maser emission

We studied the spectral properties of the electron cyclotron maser emission generated by anisotropic distributions of fast electrons with power-law Magnitude distributions in solar flares. The 19 natural bandwidth of the generated spectral line depends significantly on the angle between the direction of the wave emission and the direction of the magnetic field in the Source. In addition, the line bandwidth depends on the parameters of the momentum and pitch-angle distribution functions for fast electrons. The 14 typical spectral bandwidths are shown to lie within the range 0.1-0.4%, in agreement with the minimum observable bandwidths of millisecond solar radio spikes. (C) 2004 MAIK"Nauka/lnterperiodica".

Spectral and timing properties of the X-ray emission from the millisecond pulsar PSR B1821-24

We report results on the timing and spectral analysis of observations of the millisecond pulsar PSR B1821−24 with RXTE, BeppoSAX and Chandra. The X-ray light curve is characterized by two narrow peaks at a phase distance of 0.452 ± 0.002. The average pulsed emission, over the range 1.6-20 keV, is well represented by a single power law with a photon index α = 1.30 −0.02 +0.05 and unabsorbed (2-10 keV) pulsed X-ray flux of 3.9 × 10 −13 erg cm −2 s −1 . We searched for a possible bunching of X-ray photons to verify if the X ray emission has a time structure similar to that of giant pulses and found a negative result.

Femtosecond X-ray pulses from a frequency-chirped SASE FEL

We discuss the temporal and spectral properties of self-amplified spontaneous emission (SASE) utilizing an energy-chirped electron beam. A short temporal pulse is generated by using a monochromator to select a narrow radiation bandwidth from the frequency-chirped SASE. For the filtered radiation, the minimum pulse length is limited by the intrinsic SASE bandwidth, while the number of modes and the energy fluctuation can be controlled through the monochromator bandwidth. Two cases are considered: (1) placing the monochromator at the end of a single long undulator; (2) placing the monochromator after an initial undulator and amplifying the short-duration output in a second undulator. We analyze these cases and show that tens of femtosecond X-ray pulses may be generated for the linac coherent light source.

A High Spatial Resolution X‐Ray and Hα Study of Hot Gas in the Halos of Star‐forming Disk Galaxies. I. Spatial and Spectral Properties of the Diffuse X‐Ray Emission

We present arcsecond resolution Chandra X-ray and ground-based optical Hα imaging of a sample of 10 edge-on star-forming disk galaxies (seven starburst and three spiral galaxies), a sample that covers the full range of star formation intensity found in disk galaxies. The X-ray observations make use of the unprecedented spatial resolution of the Chandra X-ray observatory to more robustly than before remove X-ray emission from point sources and hence obtain the X-ray properties of the diffuse thermal emission alone. We have combined the X-ray observations with existing, comparable-resolution, ground-based Hα and R-band imaging and present a mini-atlas of images on a common spatial and surface brightness scale to aid cross-comparison. In general, the morphology of the extraplanar diffuse X-ray emission is very similar to the extraplanar Hα filaments and arcs, on both small and large scales (scales of tens of parsecs and kiloparsecs, respectively). The most spectacular cases of this are found in NGC 1482 (for which we provide the first published X-ray observation) and NGC 3079. We provide a variety of quantitative measures of how the spectral hardness and surface brightness of the diffuse X-ray emission varies with increasing height z above the plane of each galaxy. Of the eight galaxies in which diffuse X-ray emitting halos are found (the starbursts and the normal spiral NGC 891), significant spatial variation in the spectral properties of the extraplanar emission (|z| ≥ 2 kpc) is only found in two cases: NGC 3628 and NGC 4631. In general, the vertical distribution of the halo-region X-ray surface brightness is best described as an exponential, with the observed scale heights of the sample galaxies lying in the range Heff ~ 2-4 kpc. The presence of extraplanar X-ray emission is always associated with the presence of extraplanar optical line emission of similar vertical extent. No X-ray emission was detected from the halos of the two low-mass normal spiral galaxies NGC 6503 and NGC 4244. Active galactic nuclei, where present, appear to play no role in powering or shaping the outflows from the starburst galaxies in this sample. The Chandra ACIS X-ray spectra of extraplanar emission from all these galaxies can be fitted with a common two-temperature spectral model with an enhanced α-to-iron element ratio. This is consistent with the origin of the X-ray emitting gas being either metal-enriched merged SN ejecta or shock-heated ambient halo or disk material with moderate levels of metal depletion onto dust. Our favored model is that SN feedback in the disks of star-forming galaxies create, via blow-out and venting of hot gas from the disk, tenuous exponential atmospheres of density scale height Hg ~ 4-8 kpc. The soft thermal X-ray emission observed in the halos of the starburst galaxies is either this preexisting halo medium, which has been swept up and shock-heated by the starburst-driven wind, or wind material compressed near the walls of the outflow by reverse shocks within the wind. In either case, the X-ray emission provides us with a powerful probe of the properties of gaseous halos around star-forming disk galaxies.

Effect of Random Inhomogeneities on Electron Cyclotron Maser Emission

The spectral properties of solar radio spikes are believed to be tightly related to the spike source inhomogeneity: in particular, the spikes display a rather large scatter of spectral bandwidth of the emission lines both within one event and from one event to another. This paper studies the effect of random magnetic and density inhomogeneities on the spectral properties of the electron cyclotron maser emission produced by superthermal electrons, which is likely responsible for solar radio spikes. Magnetic irregularities with a broad distribution over spatial scales are shown to provide considerable spectral broadening that is not necessarily small compared to the natural bandwidth, even for small magnetic inhomogeneities. The developed renormalization scheme allows us to describe quantitatively the spectral shape of the emission line when the broadening is large. Moreover, the presence of stronger magnetic inhomogeneities gives rise to the splitting of the emission line into two peaks, in agreement with the observed noninteger harmonic ratio between spectrally separated spike bands. Typical values of the spectral bandwidth are found to be fairly consistent with spike observations. The developed theory suggests new possibilities for random magnetic field diagnostics. The estimated magnitudes of the random magnetic field at the spike source look rather reasonable.

Numerical modelling of gamma radiation from galaxy clusters

We investigate the spatial and spectral properties of non-thermal emission from clusters of galaxies at γ-ray energies. We estimate the radiation flux between 10 keV and 10 TeV due to inverse-Compton (IC) emission, π 0 -decay and non-thermal bremsstrahlung (NTB) from cosmic ray (CR) ions and electrons accelerated at cosmic shocks as well as secondary e = generated in inelastic p-p collisions. We identify two main region of production of non-thermal radiation, namely the core (also bright in the thermal X-ray range) and the outskirts region where accretion shocks occur. We find that IC emission from shock-accelerated CR electrons dominate the emission at the outer regions of galaxy clusters, provided that at least a fraction of a per cent of the shock ram pressure is converted into CR electrons. A clear detection of this component and of its spatial distribution will allow us to probe the cosmic accretion shocks directly. In the cluster core, γ-ray emission above 100 MeV is dominated by the π 0 -decay mechanism. At lower energies, IC emission from secondary e ′ takes over. However, IC emission from shock-accelerated electrons projected on to the cluster core will not be negligible. We emphasize the importance of separating the aforementioned emission components for a correct interpretation of the experimental data and outline a strategy for that purpose. Failure to addresses this issue will produce unsound estimates of the intracluster magnetic field strength and CR ion content. According to our estimate future spaceborne and ground-based γ-ray facilities should be able to measure the whole non-thermal spectrum both in the cluster core and at its outskirts. The importance of such measurements in advancing our understanding of non-thermal processes in the intracluster medium is discussed.

Frequency chirped self-amplified spontaneous-emission free-electron lasers

We present a statistical analysis of the temporal and spectral properties of self-amplified spontaneous emission from an energy-chirped electron beam passing through a long undulator. It is found that the coherence time is independent of the chirp, while the range of spectral coherence is linearly proportional to it. We consider the use of a monochromator to pick out a small temporal slice of the radiation output. For the filtered radiation pulse, we determine the pulse duration, the number of modes, and the energy fluctuation. We apply our analysis to schemes proposed to generate short x-ray pulses at the Linac Coherent Light Source.

Thermal emission from undoped and degenerate silicon structures and from a metallic grating structure

The thermal spectral emission properties of three types of periodic grating structure were investigated: (1) a lightly doped (intrinsic-like) silicon grating, (2) a degenerate (metallic-like) silicon grating, and (3) silicon gratings coated with nickel metal. The structural dimensions of all samples were the same, with feature sizes comparable to the measurement wavelengths (2.5–25 μm). The measurement temperatures for all samples were in the range 27–740 °C. In general, it was found that the spectral emission of the metallic-like gratings depended on the parameters of the grating material and on the structural dimensions. A spectral oscillation in the wavelength range comparable to the structural dimension was observed.

Infrared-to-visible upconversion in K_5Nd(MoO_4)_4 stoichiometric laser crystal

We report the upconversion processes that produce violet, blue, green, orange, and red emissions in K5Nd(MoO4)4 stoichiometric crystal together with the dynamics and spectral properties of the laser emission. The influence of upconversion energy-transfer processes on the energy storage capacity through the reduction of fluorescence lifetimes of the metastable 4F3/2 level is investigated. The experiments were conducted in such a way that the dynamics of the infrared and visible fluorescence was performed under lasing and nonlasing conditions. The dynamics of the upconverted emission shows that both energy-transfer upconversion and excited-state absorption of the laser emission occur. A brief analysis about the polarization properties of the laser emission is presented.