High-resolution Emission Spectroscopy Research Articles

ESPRESSO reveals blueshifted neutral iron emission lines on the dayside of WASP-76 b

Context. Ultra hot Jupiters (gas giants with Teq > 2000 K) are intriguing exoplanets due to the extreme physics and chemistry present in their atmospheres. Their torrid daysides can be characterised using ground-based high-resolution emission spectroscopy. Aims. We search for signatures of neutral and singly ionised iron (Fe I and Fe II, respectively) in the dayside of the ultra hot Jupiter WASP-76 b, as these species were detected via transmission spectroscopy in this exoplanet. Furthermore, we aim to confirm the existence of a thermal inversion layer, which has been reported in previous studies, and attempt to constrain its properties. Methods. We observed WASP-76 b on four epochs with ESPRESSO at the VLT, at orbital phases shortly before and after the secondary transit, when the dayside is in view. We present the first analysis of high-resolution optical emission spectra for this exoplanet. We compare the data to synthetic templates created with petitRADTRANS, using cross-correlation function techniques. Results. We detect a blueshifted (−4.7 ± 0.3 km s−1) Fe I emission signature on the dayside of WASP-76 b at 6.0σ. The signal is detected independently both before and after the eclipse, and it is blueshifted in both cases. The presence of iron emission features confirms the existence of a thermal inversion layer. Fe II was not detected, possibly because this species is located in the upper layers of the atmosphere, which are more optically thin. Thus the Fe II signature on the dayside of WASP-76 b is too weak to be detected with emission spectroscopy. Conclusions. We propose that the blueshifted Fe I signature is created by material rising from the hot spot to the upper layers of the atmosphere, and discuss possible scenarios related to the position of the hotspot. This work unveils some of the dynamic processes ongoing on the dayside of the ultra hot Jupiter WASP-76 b through the analysis of the Fe I signature from its atmosphere, and complements previous knowledge obtained from transmission studies. It also highlights the ability of ESPRESSO to probe the dayside of this class of exoplanets.

Detection of Fe and Ti on the dayside of the ultrahot Jupiter MASCARA-1b with CARMENES

Ultrahot Jupiters are a type of gaseous exoplanet that orbit extremely close to their host star, resulting in significantly high equilibrium temperatures. In recent years, high-resolution emission spectroscopy has been broadly employed in observing the atmospheres of ultrahot Jupiters. We used the CARMENES spectrograph to observe the high-resolution spectra of the dayside hemisphere of MASCARA-1b in both visible and near-infrared. Through cross-correlation analysis, we detected signals of Fe I and Ti I. Based on these detections, we conducted an atmospheric retrieval and discovered the presence of a strong inversion layer in the planet’s atmosphere. The retrieved Ti and Fe abundances are broadly consistent with solar abundances. In particular, we obtained a relative abundance of [Ti/Fe] as −1.0 ± 0.8 under the free retrieval and −0.4−0.8+0.5 under the chemical equilibrium retrieval, suggesting the absence of significant titanium depletion on this planet. Furthermore, we considered the influence of planetary rotation on spectral line profiles. The resulting equatorial rotation speed was determined to be 4.4−2.0+1.6 km s−1, which agrees with the rotation speed induced by tidal locking.

The PEPSI Exoplanet Transit Survey (PETS) – IV. Assessing the atmospheric chemistry of KELT-20b

ABSTRACT Most ultra-hot Jupiters (UHJs) show evidence of temperature inversions, in which temperature increases with altitude over a range of pressures. Temperature inversions can occur when there is a species that absorbs the stellar irradiation at a relatively high level of the atmospheres. However, the species responsible for this absorption remains unidentified. In particular, the UHJ KELT-20b is known to have a temperature inversion. Using high resolution emission spectroscopy from LBT/PEPSI we investigate the atomic and molecular opacity sources that may cause the inversion in KELT-20b, as well as explore its atmospheric chemistry. We confirm the presence of Fe i with a significance of 17σ. We also report a tentative 4.3σ detection of Ni i. A nominally 4.5σ detection of Mg i emission in the PEPSI blue arm is likely in fact due to aliasing between the Mg i cross-correlation template and the Fe i lines present in the spectrum. We cannot reproduce a recent detection of Cr i, while we do not have the wavelength coverage to robustly test past detections of Fe ii and Si i. Together with non-detections of molecular species like TiO, this suggests that Fe i is likely to be the dominant optical opacity source in the dayside atmosphere of KELT-20b and may be responsible for the temperature inversion. We explore ways to reconcile the differences between our results and those in literature and point to future paths to understand atmospheric variability.

Electric-Field Fluctuations as the Cause of Spectral Instabilities in Colloidal Quantum Dots.

Spectral diffusion (SD) represents a substantial obstacle toward implementation of solid-state quantum emitters as a source of indistinguishable photons. By performing high-resolution emission spectroscopy for individual colloidal quantum dots at cryogenic temperatures, we prove the causal link between the quantum-confined Stark effect and SD. Statistically analyzing the wavelength of emitted photons, we show that increasing the sensitivity of the transition energy to an applied electric field results in amplified spectral fluctuations. This relation is quantitatively fit to a straightforward model, indicating the presence of a stochastic electric field on a microscopic scale, whose standard deviation is 9 kV/cm, on average. The current method will enable the study of SD in multiple types of quantum emitters such as solid-state defects or organic lead halide perovskite quantum dots, for which spectral instability is a critical barrier for applications in quantum sensing.

Space-resolved line shape model for sputtered atoms of finite-size targets

High-resolution emission spectroscopy provides valuable information on the physical sputtering process during plasma-wall interaction. Up to now, analyzing the observed spectral lines during sputtering did not account for the finite size of the targets. It becomes crucial if the size of the target becomes comparable with the distance the sputtered atoms travel before emitting the photons. So, for example, the generally used standard emission model based on an infinite target or the point source approximation breaks for observations using two lines of sight: parallel and perpendicular to the normal of the target. It is impossible to achieve consistent results for energy and angular distribution of sputtered atoms. The new space-resolved emission model for finite-size targets developed in this work removes this gap. It incorporates the space-velocity transformation for the distribution function and includes the finite lifetime of excited states. The model was validated using emission spectra of sputtered atoms from a polycrystalline tungsten sample bombarded by monoenergetic Ar+ with kinetic energies of 100 eV to 140 eV at normal incidence in the linear plasma device PSI-2. Using the new model enables the simultaneous fitting of the line shapes of sputtered tungsten for both observation angles. The optimization process is performed using the standard Thompson distribution by separating the energy-dependent parameter and the angular distribution.

High-resolution emission spectroscopy retrievals of MASCARA-1b with CRIRES+: strong detections of CO, H2O, and Fe emission lines and a C/O consistent with solar

ABSTRACT The characterization of exoplanet atmospheres has proven to be successful using high-resolution spectroscopy. Phase curve observations of hot/ultra-hot Jupiters can reveal their compositions and thermal structures, thereby allowing the detection of molecules and atoms in the planetary atmosphere using the cross-correlation technique. We present pre-eclipse observations of the ultra-hot Jupiter, MASCARA-1b, observed with the recently upgraded CRIRES+ high-resolution infrared spectrograph at the VLT. We report a detection of Fe (≈ 8.3σ) in the K-band and confirm previous detections of CO (>15σ) and H2O (>10σ) in the day-side atmosphere of MASCARA-1b. Using a Bayesian inference framework, we retrieve the abundances of the detected species and constrain planetary orbital velocities, T–P profiles, and the carbon-to-oxygen ratio (C/O). A free retrieval results in an elevated CO abundance ($\log _{10}(\chi _{\rm {{}^{12}CO}}) = -2.85^{+0.57}_{-0.69}$), leading to a supersolar C/O ratio. More realistically, allowing for vertically-varying chemistry in the atmosphere by incorporating a chemical-equilibrium model results in a C/O of $0.68^{+0.12}_{-0.22}$ and a metallicity of $[\rm M/H] = 0.62^{+0.28}_{-0.55}$, both consistent with solar values. Finally, we also report a slight offset of the Fe feature in both Kp and vsys that could be a signature of atmospheric dynamics. Due to the 3D structure of exoplanet atmospheres and the exclusion of time/phase dependence in our 1D forward models, further follow-up observations and analysis are required to confirm or refute this result.

High-resolution Emission Spectroscopy of the Ultrahot Jupiter KELT-9b: Little Variation in Day- and Nightside Emission Line Contrasts

The transmission spectrum of the ultrahot Jupiter KELT-9b (T eq ∼ 4000 K) exhibits absorption by several metal species. We searched for atomic and molecular lines in its emission spectrum by observing partial phase curves with the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs (R ∼ 80,000–95,000). We find evidence for emission by Si i in the atmosphere of KELT-9b for the first time. Additionally we find evidence for emission by Mg i and Ca ii, which were previously detected in transmission, and confirmed earlier detections of Fe i emission. Conversely, we find no evidence for dayside emission from Al i, Ca i, Cr i, FeH, Fe ii, K i, Li i, Mg ii, Na i, OH, Ti i, TiO, V i, V ii, VO, and Y i. By employing likelihood mapping, we find indications of there being little variation in emission line contrast between the day- and nightsides—suggesting that KELT-9b may harbor iron emission on its nightside. Our results demonstrate that high-resolution ground-based emission spectroscopy can provide valuable insights into exoplanet atmospheres.

Analysis of site symmetries of Er3+ doped CaF2 and BaF2 crystals by high resolution photoluminescence spectroscopy

The understanding of complex relationships between luminescent properties, local symmetry of an emitting center, and the host crystal structure provides a better insight into optical properties of materials. In this work, the alkaline earths CaF2 and BaF2 fluoride crystals doped with 0.1 mol% ErF3 were investigated. The crystals structure has been studied using a synchrotron and laboratory X-ray diffraction. The C3v and C4v sites symmetry were determined using erbium probed high resolution emission spectroscopy (HRPL) at low temperature (LT) of 10 K. The considerable difference in room temperature (RT) optical properties for CaF2 compared to BaF2 crystals was observed. Such difference in absorption intensity of 4.7 times of erbium 4G11/2 manifold in UV, and 7.5 times in green emission from 4S3/2 manifold, could be due to the distinction in the host crystals cationic radius (ΔrCa,Ba) and the dopant-host ionic radius (ΔrCa-Er, ΔrBa-Er). Those Δr differences influence the structure and lead to the following symmetry formation: In CaF2, the C4v and C3v isolated centers were identified, with the determined Er3+- F−i bond lengths of 2.734 Å and 4.735 Å respectively; In BaF2, only C3v isolated centers were identified with the determined Er3+- F−i bond lengths of 5.380 Å. The present work is the first study that takes into account correlations of optical properties, the local symmetry and the structure in mentioned fluorides crystals, and it could be a step forward in the lanthanide doped optical materials systematics.

High-resolution time-resolved spectroscopy based on hybrid asynchronous optical sampling

The capability of characterizing arbitrary and non-repetitive emission spectra with a high resolution in real-time is of great merit in various research fields. Optical frequency combs provide precise and stable frequency grids for the measurement of a single spectral line with high accuracy. Particularly, dual-comb spectroscopy enables spectral measurement with a large bandwidth spanning tens of nanometers, but it is limited to measuring absorption spectra and has to trade-off spectral resolution vs the acquisition frame rate set by the repetition rate. Here, to alleviate these restrictions, we propose and demonstrate time-resolved spectroscopy for an emission spectrum based on hybrid asynchronous optical sampling, which features a spectral resolution of 0.63 pm, a frame rate of 1 MHz, and a measurement bandwidth of 13.6 nm, simultaneously. A mode-locked fiber comb with a repetition frequency of f1 is harnessed to interrogate emission spectral features with high resolution via optical Fourier transform achieved using a time-lens. Subsequently, a soliton microcomb of repetition frequency f2s ≈ 1000f1 serving as a probe pulse implements hybrid asynchronous optical sampling, thus significantly increasing the acquisition rate by nearly 3 orders of magnitude. As a proof-of-concept demonstration, the frequency trajectory of a rapidly scanning laser with a linear chirp of 6.2 THz/s is tracked. We believe that chip-scale microcombs will make the fast and high-resolution emission spectroscopy presented here a powerful tool for widespread applications.

Detection of iron emission lines and a temperature inversion on the dayside of the ultra-hot Jupiter KELT-20b

Ultra-hot Jupiters (UHJs) are gas giants with very high equilibrium temperatures. In recent years, multiple chemical species, including various atoms and ions, have been discovered in their atmospheres. Most of these observations have been performed with transmission spectroscopy, although UHJs are also ideal targets for emission spectroscopy due to their strong thermal radiation. We present high-resolution thermal emission spectroscopy of the transiting UHJ KELT-20b/MASCARA-2b. The observation was performed with the CARMENES spectrograph at orbital phases before and after the secondary eclipse. We detected atomic Fe using the cross-correlation technique. The detected Fe lines are in emission, which unambiguously indicates a temperature inversion on the dayside hemisphere. We furthermore retrieved the temperature structure with the detected Fe lines. The result shows that the atmosphere has a strong temperature inversion with a temperature of 4900 ± 700 K and a pressure of 10−4.8−1.1+1.0 bar at the upper layer of the inversion. A joint retrieval of the CARMENES data and the TESS secondary eclipse data returns a temperature of 2550−250+150 K and a pressure of 10−1.5−0.6+0.7 bar at the lower layer of the temperature inversion. The detection of such a strong temperature inversion is consistent with theoretical simulations that predict an inversion layer on the dayside of UHJs. The joint retrieval of the CARMENES and TESS data demonstrates the power of combing high-resolution emission spectroscopy with secondary eclipse photometry in characterizing atmospheric temperature structures.

High-performance NiMoS hydrodesulfurization catalysts by one-pot hydrothermal synthesis using Ni(acac)2 for sulfur-free liquid fuels

A straightforward hydrothermal synthesis of NiMoS active phases loaded on SBA-15 was attempted. We initially prepared a catalyst by impregnating metal precursors sequentially onto SBA-15 and the subsequent hydrothermal treatment with sublimed sulfur. To obtain the one-pot catalyst, we performed the hydrothermal treatment of a mechanical mixture containing metal precursors, sublimed sulfur, and SBA-15. The catalysts were characterized by powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, N2 adsorption-desorption study, and high-resolution transmission emission spectroscopy. Compared to impregnation-assisted synthesis, the one-pot synthesis promoted the generation of dispersed shorter MoS2 slabs with desirable average stacking number, i.e., increased number of edge and rim sites. Therefore, the one-pot catalyst enabled the ultra-deep sulfur removal (~100%) in the dibenzothiophene hydrodesulfurization. Unlike Ni(acac)2, the utilization of Ni(NO3)2 inhibits the sulfidation of molybdenum and the dispersion of MoS2 layers, decreasing the hydrodesulfurization activity. The one-pot catalyst was able to achieve ~80% sulfur removal even after six consecutive catalytic runs under batch reactor conditions (320 °C, 6 MPa (H2), 500 ppmw S, 100 mg (mcat)) due to the persistent stability of NiMoS active phases.

Quantification of Cr in Lu1-xSrxFe0.5Cr0.5O3 (0 ≤ x ≤ 1) samples containing impurities using X-ray techniques in combination with several data treatment methodologies

Wet chemical method was applied with the intention of obtaining Lu1-xSrxFe0.5Cr0.5O3 (0 ≤ x ≤ 1) perovskites in polycrystalline form. A systematic study of the crystal structure of the main perovskite phase obtained as well as a characterization of impurities was performed by X-ray techniques: powder diffraction (PXRD), high resolution emission spectroscopy (HR-XES), and photoelectron spectrometry (XPS). The PXRD data of Lu1-xSrxFe0.5Cr0.5O3 (0 ≤ x ≤ 1) were refined using Pbnm orthorhombic unit cell for the perovskite structure. Only samples with x = 0 and x = 0.1 resulted pure; as the amount of Sr increases, it is segregated as impurities, first as SrCrO4 and then as SrFe12O19. The mean oxidation state of Cr in the analyzed samples was obtained from HR-XES by quantifying spectral changes in the Cr-Kβ" and Cr-Kβ2,5 regions by different methodologies: statistical parameters and multivariate methods. The results were compared with the ones obtained by PXRD and XPS. With the last technique Cr6+ ionic concentrations were obtained through the spectral analysis in the region Cr2p3/2–580eV. Similar Cr6+ ionic compositions were obtained using the three X-ray techniques.

Ro-vibrational population distribution in the ground state of hydrogen isotopologues in LHD peripheral plasmas deduced from emission spectroscopy

Wide wavelength range with high-resolution emission spectroscopy was applied to LHD peripheral plasmas. All measured Fulcher-a band Q-branches spectra (600–630 nm) were measured with a single shot exposure time of 100–200 ms for all investigated discharges. Ro-vibrational populations up to v = 2 and N = 11 for H2 and up to v = 3 and N = 14 for D2 in the 3p3Πu state were estimated, where v and N are vibrational and rotational quantum numbers, respectively. It was found that the rotational population of every vibrational state follows two-temperature Boltzmann distribution. From the calculation with a coronal model, ro-vibrational populations distribution up to such high N quantum numbers in the ground state are deduced.

Europium-Doped Ceria-Gadolinium Mixed Oxides: PARAFAC Analysis and High-Resolution Emission Spectroscopy under Cryogenic Conditions for Structural Analysis.

Gadolinium-doped ceria or gadolinium-stabilized ceria (GDC) is an important technical material due to its ability to conduct O2- ions, e.g., used in solid oxide fuel cells operated at intermediate temperature as an electrolyte, diffusion barrier, and electrode component. We have synthesized Ce1-xGdxO2-y:Eu3+ (0 ≤ x ≤ 0.4) nanoparticles (11-15 nm) using a scalable spray pyrolysis method, which allows the continuous large-scale technical production of such materials. Introducing Eu3+ ions in small amounts into ceria and GDC as spectroscopic probes can provide detailed information about the atomic structure and local environments and allows us to monitor small structural changes. This study presents a novel approach to structurally elucidate europium-doped Ce1-xGdxO2-y:Eu3+ nanoparticles by way of Eu3+ spectroscopy, processing the spectroscopic data with the multiway decomposition method parallel factor (PARAFAC) analysis. In order to perform the deconvolution of spectra, data sets of excitation wavelength, emission wavelength, and time are required. Room temperature, time-resolved emission spectra recorded at λex = 464 nm show that Gd3+ doping results in significantly altered emission spectra compared to pure ceria. The PARAFAC analysis for the pure ceria samples reveals a high-symmetry species (which can also be probed directly via the CeO2 charge transfer band) and a low-symmetry species. The GDC samples yield two low-symmetry spectra in the same experiment. High-resolution emission spectra recorded under cryogenic conditions after probing the 5D0-7F0 transition at λex = 575-583 nm revealed additional variation in the low-symmetry Eu3+ sites in pure ceria and GDC. The total luminescence spectra of CeO2-y:Eu3+ showed Eu3+ ions located in at least three slightly different coordination environments with the same fundamental symmetry, whereas the overall hypsochromic shift and increased broadening of the 5D0-7F0 excitation in the GDC samples, as well as the broadened spectra after deconvolution point to less homogeneous environments. The data of the Gd3+-containing samples indicates that the average charge density around the Eu3+ ions in the lattice is decreased with increasing Gd3+ and oxygen vacancy concentration. For reference, the Judd-Ofelt parameters of all spectra were calculated. PARAFAC proves to be a powerful tool to analyze lanthanide spectra in crystalline solid materials, which are characterized by numerous Stark transitions and where measurements usually yield a superposition of different contributions to any given spectrum.

MCDHF calculations of isotope shifts in neutral antimony

Ab initio multiconfiguration Dirac–Hartree–Fock (MCDHF) calculations have been carried out in order to determine the isotope shift (IS) electronic parameters of transitions belonging to electric dipole (E1) transition arrays 5s25p3−5s25p26s,5s25p26s−5s25p26p and 5s25p26s−5s25p27p in neutral antimony, Sb I. In a correlation model limited to single and double excitations from the valence shells, these parameters, combined with the changes in mean-square nuclear charge radius δ⟨r2⟩123,121 compiled by Angeli and Marinova [3] produce isotope shifts values in good agreement with the most recent measurements by high-resolution emission and optogalvanic absorption spectroscopy of Sobolewski et al. [5] but not with the old measurements of Buchholz et al. [4] for 5p3−5p26s. However, our analysis does not allow to reject the latter due to the large uncertainty affecting δ⟨r2⟩123,121, i.e. 0.072 ± 0.048 fm2 [3]. This shows the need of a more accurate determination of this nuclear parameter. Although improving excitation energies, the inclusion of core-valence correlation limited to one hole in the 4d core subshell destroyed the theory-experiment agreement on the IS parameters.

Production of hydrogen negative ions in an ECR volume source: balance between vibrational excitation and ionization

The operation of an ECR-driven (2.45 GHz) hydrogen negative ion source is studied. Electron densities and temperatures are investigated with electrostatic probes and negative ion densities are measured with laser photodetachment. Vacuum ultraviolet irradiance measurements are focused on molecular transitions to the ground state while high-resolution visible emission spectroscopy is used to study the transitions between excited states for both molecules and atoms. The standalone operation of the source is found to be more efficient in higher pressures (12 mTorr) where negative ion densities are as high as 4 × 109 cm−3. Further investigation on the operation of the source reveals a rich vibrational spectrum. On the other hand, a limitation on the production of negative ions which is attributed to a lack of low-energy electrons becomes apparent. The underlying mechanisms that lead to this behavior are discussed along with possible solutions to this issue. Finally, the rates of different negative ion destruction processes are estimated and compared.

Retrieval of exoplanet emission spectra with HyDRA

Thermal emission spectra of exoplanets provide constraints on the chemical compositions, pressure-temperature (P-T) profiles, and energy transport in exoplanetary atmospheres. Accurate inferences of these properties rely on the robustness of the atmospheric retrieval methods employed. While extant retrieval codes have provided significant constraints on molecular abundances and temperature profiles in several exoplanetary atmospheres, the constraints on their deviations from thermal and chemical equilibria have yet to be fully explored. Our present work is a step in this direction. We report HyDRA, a disequilibrium retrieval framework for thermal emission spectra of exoplanetary atmospheres. The retrieval code uses the standard architecture of a parametric atmospheric model coupled with Bayesian statistical inference using the Nested Sampling algorithm. For a given dataset, the retrieved compositions and P-T profiles are used in tandem with the GENESIS self-consistent atmospheric model to constrain layer-by-layer deviations from chemical and radiative-convective equilibrium in the observable atmosphere. We demonstrate HyDRA on the Hot Jupiter WASP-43b with a high-precision emission spectrum. We retrieve an H2O mixing ratio of log(H2O) = -3.54^{+0.82}_{-0.52}, consistent with previous studies. We detect H2O and a combined CO/CO2 at 8-sigma significance. We find the dayside P-T profile to be consistent with radiative-convective equilibrium within the 1-sigma limits and with low day-night redistribution, consistent with previous studies. The derived compositions are also consistent with thermochemical equilibrium for the corresponding distribution of P-T profiles. In the era of high precision and high resolution emission spectroscopy, HyDRA provides a path to retrieve disequilibrium phenomena in exoplanetary atmospheres.

Spectroscopy and perturbation analysis of the A1π (v=0) state of 13 C16 O

ABSTRACTThe lowest v = 0 level of the A1Π state of the 13C16O isotopologue of carbon monoxide has been reinvestigated with a variety of high-resolution spectroscopic techniques. The A1Π −X1Σ+(0, 0) band has been studied by vacuum-ultraviolet Fourier-transform absorption spectroscopy, using the SOLEIL synchrotron as a radiation source. Spectra were obtained under quasi-static gas conditions at liquid-nitrogen temperature, room temperature and at an elevated temperature of 900 K, with absolute accuracies of 0.01−0.03 cm−1. Two-photon Doppler-free laser spectroscopy has been applied to a limited number of transitions in the A1Π −X1Σ+(0, 0) band, under collision-free circumstances of a molecular beam, yielding an absolute accuracy of 0.002 cm−1. The third technique is high-resolution Fourier-transform emission spectroscopy in the visible region applied to the B1Σ+ −A1Π(0, 0) band in a gas discharge, at an absolute accuracy of up to 0.003 cm−1. With these methods, rotational levels of A1Π (0) could be studied in both parity components up to a rotational quantum number of J = 46. The frequencies of 397 transitions were used to analyse the perturbations between the A1Π(0) level by vibrational levels of the D1Δ, e3Σ−, d3Δ, and a′3Σ+ states.

Isotope shifts in Sb I

The isotope shifts of eight lines of Sb I covering the UV–NIR spectral range have been measured. We used two different experimental techniques: high-resolution emission spectroscopy and optogalvanic absorption spectroscopy with a tunable dye ring laser system. Recurring to pseudo-relativistic Hartee–Fock estimates, the field and specific mass shifts of numerous configurations were evaluated. The comparison between experimental and ab initio line shift values is very satisfactory.

High-resolution emission spectroscopy of random lasing in GaN films pumped by UV-pulsed laser

We report on room temperature photoluminescence on GaN films grown by metal organic chemical vapor deposition (MOCVD). A NdYAG pulsed-laser at 266nm illuminates the films. Two components, at 363nm and 370nm, are identified in the near band edge structure on the spectra. A laser threshold of 700±150kWcm−2 is evidenced and corresponds to random lasing in the GaN film. A drastic narrowing of the spectral bandwidth from 5.2 to 1.8nm is observed at 370nm. High-resolution spectroscopy measurements show laser mode widths thinner than 50pm leading to a high quality factor Q=7750. Low-resolution measurements show redshift from 370.0 to 373.1nm for one component and from 363.1nm to 363.9nm for the other. Interpretation of this redshift is discussed.