Spectral Full Width Research Articles

Mn2+ doped Zn2SiO4 phosphors: A threefold-mode sensing approach for optical thermometry in the visible region at 525 nm

Optical functional materials such as nanostructured silicates have been studied for photonics applications involving energy conversion. In this scenario, we studied Zn2SiO4:Mn2+ nanostructured powders prepared by combustion synthesis for optical thermometry based on photon downshifting. The structural analysis showed that Zn2SiO4 particles were found embedded in clustered silica nanoparticles. The photoluminescence analysis showed that the samples exhibit intense green emission (centered around 525 nm), corresponding to the electronic transition 4T1 → 6A1 of Mn2+, when exposed to a low power ultraviolet lamp (centered around 255 nm). The temperature sensing performance of this material was evaluated using three different methodologies, i.e. the luminescence decay time constant, the spectral full width at half maximum, and the luminescence peak intensity from the 4T1 → 6A1 radiative transition. The thermometric analysis based on luminescence peak intensity provided a maximum relative sensitivity of ∼4.9x10−3 K−1 at 498 K, while the decay lifetime and the spectral width at half maximum provided maximum relative temperature sensitivities of ∼2.9x10−3 K−1 at 523 K and ∼1.7x10−3 K−1 at 298 K, respectively.

Multiple Enol-Keto Isomerization and Excited-State Unidirectional Intramolecular Proton Transfer Generate Intense, Narrowband Red OLEDs.

A novel series of excited-state intramolecular proton transfer (ESIPT) emitters, namely, DPNA, DPNA-F, and DPNA-tBu, endowed with dual intramolecular hydrogen bonds, were designed and synthesized. In the condensed phase, DPNAs exhibit unmatched absorption and emission spectral features, where the minor 0-0 absorption peak becomes a major one in the emission. Detailed spectroscopic and dynamic approaches conclude fast ground-state equilibrium among enol-enol (EE), enol-keto (EK), and keto-keto (KK) isomers. The equilibrium ratio can be fine-tuned by varying the substitutions in DPNAs. Independent of isomers and excitation wavelength, ultrafast ESIPT takes place for all DPNAs, giving solely KK tautomer emission maximized at >650 nm. The spectral temporal evolution of ESIPT was resolved by a state-of-the-art technique, namely, the transient grating photoluminescence (TGPL), where the rate of EK* → KK* is measured to be (157 fs)-1 for DPNA-tBu, while a stepwise process is resolved for EE* → EK* → KK*, with a rate of EE* → EK* of (72 fs)-1. For all DPNAs, the KK tautomer emission shows a narrowband emission with high photoluminescence quantum yields (PLQY, ∼62% for DPNA in toluene) in the red, offering advantages to fabricate deep-red organic light-emitting diodes (OLED). The resulting OLEDs give high external quantum efficiency with a spectral full width at half-maximum (FWHM) as narrow as ∼40 nm centered at 666-670 nm for DPNAs, fully satisfying the BT. 2020 standard. The unique ESIPT properties and highly intense tautomer emission with a small fwhm thus establish a benchmark for reaching red narrowband organic electroluminescence.

Comment on: Carbonaceous matter in ∼ 3.5 Ga black bedded barite from the Dresser Formation (Pilbara Craton, Western Australia) – Insights into organic cycling on the juvenile Earth

Weimann et al. (2024) offer important insights into carbonaceous matter (CM) preserved within bedded barite from the 3.48 billion-year-old Dresser Formation (Pilbara Craton). However, issues in the fitting of CM Raman spectra and the application of Raman CM thermometry cast doubts on the conclusion that 'CM in quartz veins yielded much lower temperatures of ∼ 220 °C, suggesting that quartz-vein associated CM entered the barite after 3.3 Ga' (Weimann et al., 2024). A primary concern is the inaccurate fitting of the CM's D1 band, whose spectral position (typically in the c. 1335–1355 cm−1 range) and full width at half maximum (FWHM) are indicators of thermal maturity (Kouketsu et al., 2014). This commentary emphasizes the implications of misfitting D1 and other issues in fitting the broader CM signals between 1100 and 1700 cm−1. Specifically, the omission of D4 (c. 1250 cm−1) resulted in a systematic overestimation of D1-FWHM and, consequently, unreasonably low thermal maturity estimates. We show that a more precise fitting including D4 – recognizing that CM spectra with a thermal maturity below 300 °C generally display a corresponding shoulder at c. 1250 cm−1 – yields much higher thermal maturity estimates that appear to align closely with the peak temperature (c. 290 °C) of the Dresser Formation's 3.3 Ga metamorphic event. This suggests a (near) syngenetic origin for the quartz-vein-hosted CM, challenging the notion of post-metamorphic infiltration. Consequently, these results also question Weimann et al.'s (2024) interpretation that the much higher thermal maturity (c. 350 °C) of a distinct CM generation, situated within the barite crystal’s growth zonations, stems from metamorphic overprinting. Instead, it can be reconciled with the thermal maturation of the CM during its transportation within the ancient Dresser hydrothermal system, prior to its concentration within the barite.

TADF deep-blue OLED with color index approaching Rec.2020 standard blue gamut achieved by a boron-based D–A type molecular skeleton

The ultra-high definition (UHD) displays in the market require organic light-emitting diodes (OLEDs) to meet the Rec.2020 color gamut standard, while it is still challenging to exploit ultra-deep-blue emitters that satisfy such blue standard. Herein, by substituting tCz (3,6-di(tert-butyl)carbazole) donor unit on the robust BOC (8,8,12,12-tetramethyl-8,12-dihydro-4-oxa-3a2-boradibenzo[cd,mn]pyrene) acceptor unit with high structural rigidity and appropriate energy levels, a novel boron-based D–A type thermally activated delayed fluorescence (TADF) ultra-deep-blue emitter, namely, tCz-BOC, was readily designed and synthesized. Inheriting from its rigid organoboron core, the emitter presents ultra-deep-blue emission with narrow spectral full width at half maximum (FWHM) of 54 nm and high photoluminescence quantum yield up to 73.7%. Additionally, tCz-BOC can effectively harvest T1 excitons through high-lying T2 mediated reverse intersystem crossing process. As a consequence, the fabricated OLED based on tCz-BOC exhibits a satisfactory ultra-deep-blue emission with λEL of 424 nm, narrow emission bandwidth with FWHM of 47 nm, excellent maximum external quantum efficiency (EQEmax) of 13.9%, as well as the CIEy coordinate of 0.047, which is fairly close to the Rec.2020 blue color gamut.

Efficient O-band emission from Pr3+ doped low phonon energy ZnF2-based glasses

Pr3+ doped ZnF2-based (ZnF2-BaF2-SrF2-YF3) glasses with a low phonon energy of ∼420 cm−1 are prepared by using a conventional melt-quenching method in dry N2 atmosphere. Under the excitation of a 980 nm laser diode, intense emission at ∼1310 nm is observed from the Pr3+ doped ZnF2-based glasses. The full spectral width at half maximum is 107 nm (1275–1382 nm), which is ∼7 nm wider than that of Pr3+ doped ZrF4-based glass (∼100 nm, 1279–1379 nm). The measured lifetime (∼183 μs) of the excited energy level 1G4 for Pr3+ ions in the ZnF2-based glass is also much longer than that of Pr3+ doped in ZrF4-based glass (∼110 μs). According to the theoretically calculated results, a positive gain of 31.7 dB at 1304 nm can be obtained from O-band optical amplifiers based on the Pr3+ doped ZnF2-based glass, which is 5 dB higher than that obtained from amplifiers based on Pr3+ doped ZrF4-based glass with a same pump condition. The corresponding bandwidth for a net gain of >20 dB is ∼51 nm (1277–1328 nm), and the noise figure is calculated to be < 5.8 dB in above spectral range. Our results indicate that Pr3+ doped ZnF2-based glasses have the potential for constructing efficient O-band optical amplifiers.

Effect of BaF2 and Y2O3 on the Raman scattering characteristics of fluorotellurite glasses

In this letter, we investigated the Raman scattering characteristics of a series of aTeO2-(90-a)BaF2-10Y2O3 (a = 85, 80, 75, 70, 65, 60, 55 mol%), bTeO2-(95-b)BaF2-5Y2O3 (b = 90, 85, 80, 75, 70, 65, 60, 55, 50 mol%) and cTeO2-(100-c)BaF2 (c = 95, 90, 85, 80, 75, 70, 65, 60 mol%) fluorotellurite glasses. With increasing the concentration of BaF2, the peak Raman gain coefficient at 785 cm−1 increased while the Raman gain bandwidth (full spectral width at half maximum of the Raman peaks around 785 cm−1) decreased, which was attributed to the increasing proportion of non-bridge oxygen bonds in the fluorotellurite glass systems. The same results were also observed for the case of the increasing of the concentration of Y2O3. In these samples, the 50TeO2-40BaF2-10Y2O3 glass has the largest Raman gain coefficient of 29.9 × 10−13 m/W, and the 95TeO2-5BaF2 glass has the widest Raman gain bandwidth of 7.35 THz for the pumping laser at 633 nm. Furthermore, the first-order Raman Stokes light peaked at ∼2373 nm was obtained by using fluorotellurite fiber based on the above glasses as Raman gain medium and a 2000nm picoseconds laser as pump light. Our results provide guidance for further improving the performance of Raman fiber lasers or amplifiers based on fluorotellurite fibers.

Effect of annealing on focused ion beam induced surface damages in silicon analyzed by micro-Raman spectroscopy

In this paper, we describe Raman spectroscopic study for evaluating the influence of vacuum annealing on the surface modification of the focused ion beam (FIB) induced damaged layer on a single crystalline Si (c-Si) substrate. The damaged layer consisting of amorphous silicon (a-Si) with implanted Ga ions is formed after irradiating FIB onto the c-Si surface. After vacuum annealing at 700 °C for 10 s, the Raman spectrum peak of poly crystalline Si (p-Si) appears. With increasing annealing time, the spectral parameters, peak shift, peak intensity, and full width at half maximum (FWHM), for p-Si and c-Si change. Through the comparison between the phase fraction of a-Si, p-Si, and c-Si in the FIB damaged layer and the mechanical properties of the FIB-processed Si nanowires obtained in the quasistatic tensile testing, a recovery of the damaged layer by annealing is discussed.

Temperature-Dependent Phonon Scattering and Photoluminescence in Vertical MoS2/WSe2 Heterostructures.

Transition metal dichalcogenide (TMD) monolayers and their heterostructures have attracted considerable attention due to their distinct properties. In this work, we performed a systematic investigation of MoS2/WSe2 heterostructures, focusing on their temperature-dependent Raman and photoluminescence (PL) characteristics in the range of 79 to 473 K. Our Raman analysis revealed that both the longitudinal and transverse modes of the heterostructure exhibit linear shifts towards low frequencies with increasing temperatures. The peak position and intensity of PL spectra also showed pronounced temperature dependency. The activation energy of thermal-quenching-induced PL emissions was estimated as 61.5 meV and 82.6 meV for WSe2 and MoS2, respectively. Additionally, we observed that the spectral full width at half maximum (FWHM) of Raman and PL peaks increases as the temperature increases, and these broadenings can be attributed to the phonon interaction and the expansion of the heterostructure's thermal coefficients. This work provides valuable insights into the interlayer coupling of van der Waals heterostructures, which is essential for understanding their potential applications in extreme temperatures.

Improved detection performance of self-driven InZnO / p-GaN heterojunction UV photodetector by lanthanum doping

By using the sol-gel spin-coating method, La-InZnO films with different La (0 at%, 2 at%, 4 at%, and 6 at%) doping concentrations were grown on p-GaN / sapphire film templates, and self-driven p-GaN / n-ZnO heterojunction ultraviolet (UV) detectors were prepared. The effects of La doping concentration on the microstructure, optical, and electrical properties of synthesized La-InZnO films were studied. In addition, the optical sensing characteristics and photoelectric response performance of four p-n heterojunction UV detectors were compared. La doping can decrease the content of oxygen vacancies. It also reduces the carrier concentration and mobility of the films. At zero bias voltage, the 2 at% doped device has the best performance, with a peak responsivity of 46 mA/W at 366 nm, a high spectral selectivity full width at half maximum (FWHM) of only 6.92 nm, and a fast response with the rise and decay times of 1.15 ms and 2.42 ms, respectively. This study demonstrates a feasible method for improving the performance of self-driven heterojunction UV detectors.

Erbium–bismuth-doped germanium silicate active optic glass for broad-band optical amplification

This work deals with research and optimization of the optical Ge–Si glass composition doped with Er3+, Yb3+ ions and bismuth optically active centers (BACs), which are optically active for implementation in a double C- and U-band planar optical amplifier. The intention was to increase the range of amplified wavelengths in the NIR band up to 1650 nm. Various types of glass with different content of GeO2, SiO2 and Er2O3, Yb2O3 ions Bi2O3 were prepared and the luminescence response in the 1500–1700 nm range was tested. The maxima of the luminescence intensity in the optical bands and the spectral full width at half maximum (FWHM) were determined by modified reflex spectrum method measurement. The prepared Ge–Si glass doped with Er3+ ions and BACs exhibited strong and balanced emission in the 1520–1680 nm range after pumping at 1480 nm. The specific balanced differential gain of up to 0.2 dB/cm in the C-band and simultaneously 0.2 dB/cm in the U-band was measured. Our results proved that the luminescence of BACs depends on the presence of optical active Er3+ ions and germanium in matrix of glass, pumped by radiation 1480 nm and energy transfer from erbium to BACs have been newly observed in the Ge–Si glass. It has also been found that high content of germanium, comparable with silicon content is required for this transfer. The results show that the germano-silicate glass doped with Er3+ and Bi ions is a perspective material for the fabrication of broad-band amplifiers in the C- and U-bands.

Modifying the coherence of vertical-cavity surface-emitting lasers using chaotic cavities

Vertical-cavity surface-emitting lasers (VCSELs) have been widely adopted in a variety of applications in recent years, with even more applications currently under research and development as a result of the emergence of visible-light VCSELs. Most of these applications make use of the ease of fabrication of large two-dimensional arrays of lasers, a feature unique to VCSELs that makes them scalable and versatile. However, applications that rely on the uniformity of the emitted beam in the transverse plane, such as illumination, projection, holography, and displays, suffer from the coherence artifacts (speckles) that reduce the quality of the formed images when coherent lasers are used. In this work, we show that, by using a chaotic-cavity D-shaped mesa, the coherence of broad-area VCSELs can be substantially reduced (the number of mutually incoherent modes is almost doubled, and the spectral full width at half-maximum is increased from ∼ 1.1 n m to ∼ 4.5 n m ), and the maximum achievable optical power is increased by up to 60%. The simplicity of implementing the reported design, which requires no additional fabrication steps, makes it a promising solution for applications that would benefit from the lower speckle density of the emitted light as well as those that rely on lower temporal coherence, such as time-domain optical coherence tomography and fiber-optic gyroscopes.

Yb:CaYAlO&lt;sub&gt;4&lt;/sub&gt; regenerative amplifier

Attosecond science is one of the driving forces for developing the femtosecond amplifiers of high average power and ultrashort pulse duration. In this work, the regenerative amplification is studied experimentally and theoretically based on Yb:CaYAlO&lt;sub&gt;4&lt;/sub&gt; crystal for the practical needs of high-repetition-rate attosecond light sources. In the theoretical study, a mode-tunable regenerative cavity with good thermal stability is designed based on the thermal lens calculations of Yb:CaYAlO&lt;sub&gt;4&lt;/sub&gt; crystal; the amplified output energy and spectra of &lt;i&gt;π&lt;/i&gt; and &lt;i&gt;σ&lt;/i&gt; polarization of the crystal are calculated. In the experiment, the &lt;i&gt;π&lt;/i&gt;-axis of Yb:CaYAlO&lt;sub&gt;4&lt;/sub&gt; crystal is parallel to the laser polarization, and the laser amplifier emits 1.61 mJ pulses with average power 16.1 W. Notably, the dip of the &lt;i&gt;π&lt;/i&gt;-polarization emission spectrum near 1025.1 nm compensates for the gain narrowing of the seed laser during amplification. Thus, the center wavelength and the spectral full width at a half maximum of the amplified laser are 1030 nm and 16 nm respectively. Using a grating-pair for compression, 149 fs pulses with peak power 9.5 GW are obtained. In comparison, the σ-polarization emission spectrum of Yb:CaYAlO&lt;sub&gt;4&lt;/sub&gt; crystal is relatively flat in a range from 1000 to 1050 nm, but with a larger gain cross-section. When the laser polarization is parallel to the &lt;i&gt;σ&lt;/i&gt;-axis of Yb:CaYAlO&lt;sub&gt;4&lt;/sub&gt; crystal, 2.87 mJ pulses at 10 kHz repetition rate are achieved, with an average power of 28.7 W. In this case, the center wavelength and the spectral full width at half maximum of the amplified laser are 1037 nm and 11 nm respectively. Using a grating-pair for compression, 178 fs pulses with peak power of 14.2 GW are obtained. The beam quality factor measured is 1.09 along the &lt;i&gt;x&lt;/i&gt;-axis of the amplified laser and 1.17 along the &lt;i&gt;y&lt;/i&gt;-axis. To the best of our knowledge, this is the highest average power and the maximum pulse energy obtained from the Yb:CaYAlO&lt;sub&gt;4&lt;/sub&gt; amplifier. For applications in high-repetition-rate attosecond light sources, terahertz generation and optical parametric amplification, subsequent laser outputs with average power 200 W, pulse energy 20 mJ and pulse duration less than 200 fs are expected to be achieved by adding two stages of traveling-wave amplification.

Experimental realization of short-wavelength infrared half wave retarder fabricated from ZnO single crystal plates

With increasing interest in studying fundamental phenomena at near-infrared (NIR) and short-wavelength infrared (SWIR) frequencies, it is essential to find optical devices which can alter polarization state in the NIR and SWIR radiation range. However, simple optical components such as wave plates capable of generating and controlling polarization sates in the NIR and SWIR radiation are rare. Therefore, our use of channelled spectra of polarized white photons is reported to extract the dispersion of the phase birefringence Δnp(λ) of the 112‾0 and 11‾00 plates of ZnO single crystal acting as multiple order wave plates. The phase birefringence Δnp(λ) of the 112‾0 and 11‾00 ZnO plates was extracted using a calculation procedure named the wavenumber difference method. The correctness of the birefringence data obtained was also confirmed by recalculating the plate thickness using the Jones matrix technique. Furthermore, the birefringence group velocity factor of the 112‾0 and 11‾00 ZnO plates was also extracted from the channelled spectra of polarized white photons using simple method. For both 112‾0 and 11‾00 ZnO plates, a broad spectral full width at half maximum (FWHM) is observed in SWIR region (1100–2500 nm), therefore, 112‾0 and 11‾00 ZnO plates can act as if they are functioning as a zero-order wave plate.

Sapphire Photonic Crystal Waveguides with Integrated Bragg Grating Structure

This contribution demonstrates photonic crystal waveguides generated within bulk planar sapphire substrates. A femtosecond laser is used to modify the refractive index in a hexagonal pattern around the pristine waveguide core. Near-field measurements reveal single-mode behavior at a wavelength of 1550 nm and the possibility to adapt the mode-field diameter. Based on far-field examinations, the effective refractive index contrast between the pristine waveguide core and depressed cladding is estimated to 3·10−4. Additionally, Bragg gratings are generated within the waveguide core. Due to the inherent birefringence of Al2O3, the gratings exhibit two distinct wavelengths of main reflection. Each reflection peak exhibits a narrow spectral full width at a half maximum of 130 pm and can be selectively addressed by exciting the birefringent waveguide with appropriately polarized light. Furthermore, a waveguide attenuation of 1 dB cm−1 is determined.

All-Polarization Maintaining Noise-Like Pulse From Mode-Locked Thulium-Doped Fiber Laser Based on Nonlinear Loop Mirror

In this paper, we present a figure-eight all-polarization maintaining thulium-doped mode-locked fiber laser based on a nonlinear optical loop mirror operating at noise-like pulse regimes. The total cavity length is 34.5 m, and the calculated net group delay dispersion is estimated to be ∼−2.616 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . At the maximum pump power, stable noise-like pulse centered at 1943 nm with a spectral full width at half maximum of 32 nm, a pulse energy of 13.51 nJ, and a coherence spike width of 236 fs is generated at a repetition rate of 5.96 MHz with the signal-to-noise ratio ∼64 dB. The polarization extinction ratio is > 15 dB at any mode-locking operation. The slope efficiency and the output power fluctuation of the laser are 5.16% and 0.039%, respectively. The laser does not require polarization state controllers, and it holds very high stability, which is insensitive to temperature changes or mechanical vibrations. Through further amplification, it will be a good laser source for real-time interrogation of fiber Bragg gratings and supercontinuum generation.

Hyperpolarized 129Xe MRI Abnormalities in Dyspneic Patients 3 Months after COVID-19 Pneumonia: Preliminary Results.

BackgroundSARS-CoV-2 targets angiotensin-converting enzyme 2 (ACE2) expressing cells in the respiratory tract. There are reports of breathlessness in patients many months post-infection.PurposeThis study aimed to determine if hyperpolarized 129Xe MRI (XeMRI) imaging could identify the possible cause of breathlessness in patients three months after hospital discharge following COVID-19 infection.Materials and MethodsThis prospective study was undertaken between August and December 2020, with patients and healthy control volunteers enrolled. All patients underwent: lung function tests; ventilation and dissolved phase XeMRI, with the mean Red Blood Cell (RBC):Tissue Plasma (TP) ratio to be calculated; and a low dose chest CT scored for the degree of post-COVID-19 abnormalities. Healthy controls underwent XeMRI. The intraclass correlation coefficient was calculated for volunteer and patient scans, to assess repeatability. A Wilcoxon rank-sum test and Cohen's effect size calculated to assess for differences between RBC:TP in patient and controls.Results9 patients (mean age 57±7 years, Male = 6) and 5 volunteers (29 ± 3 years, Female = 5) were enrolled. Patient mean time from hospital discharge was 169, range 116-254 days. There was a difference in RBC:TP between patients and controls (0.3 ± 0.1 versus 0.5 ± 0.1, respectively, p = 0.001, effect size = 1.36). There was significant difference between the RBC and gas phase spectral full width at half maximum (FWHM) between volunteers and patients (median ± 95 % confidence interval, 567 ± 1 vs 507 ± 81, p = 0.002 and 104 ± 2 vs 122 ± 17, p = 0.004, respectively). Results were reproducible with Intraclass Correlation Coefficients of 0.82 and 0.88 for patients and volunteers respectively. Participants had normal or near normal CT scans, mean 7/25, range 0-10/25.ConclusionXe MRI showed alveolar-capillary diffusion limitation in all 9 post COVID-19 pneumonia patients despite normal or nearly normal CT scans.See also the editorial by Dietrich.

Efficient third-harmonic generation of broadband picosecond radiation by employing spectrally noncritical phase-matching KDP crystal and cascaded LBO crystals

To improve the nonlinear frequency conversion efficiency of a broadband picosecond fiber laser, the spectrally noncritical phase matching for frequency doubling, dual-crystal cascaded design for frequency tripling is employed. By this method, we obtain 2.39 W of output power at the third-harmonic wavelength, when the spectral full width at half maximum of the fundamental light is 5.5 nm and the input fundamental light power is 8.6 W. The frequency conversion efficiency of IR-UV is 27.8%. To the best of our knowledge, this is the first time of the broadband third harmonic picosecond ultraviolet laser generation by the combination of the spectrally noncritical phase matching for frequency doubling and dual-crystal cascaded design for frequency tripling.

Femtosecond laser inscription of waveguides and Bragg gratings in transparent cyclic olefin copolymers.

We report on a femtosecond laser based fabrication technique that enables simultaneous single-step generation of optical waveguides and Bragg gratings inside bulk cyclic olefin copolymers. Due to the nonlinear absorption of focused and spatially modulated laser radiation with a wavelength of 514 nm and a pulse duration of 450 fs, a modification concluding a refractive index shift increase inside the substrate can be achieved. A sophisticated characterization of the generated waveguides by means of an elaborate cut-back method reveals a maximum attenuation of 3.2 dB/cm. Additionally, a Mach-Zehnder interferometer is used to examine the waveguide's refractive index profile. The integrated Bragg grating structures exhibit reflectivities up to 95 % and a spectral full width at half maximum of 288 pm, at a Bragg wavelength of 1582 nm, whereas the grating period can be deliberately chosen by adapting the fabrication parameters. Thus, due to its increased flexibility and the resulting dispensability of cost-intensive phase masks, this method constitutes an especially promising fabrication process for polymer Bragg gratings inside of bulk materials.

Long‐Term Observations of Stratosphere‐Troposphere Exchange Using MST Radar and Aura MLS Measurements Over a Tropical Station Gadanki

AbstractThis paper presents the climatology of stratospheric intrusion into the troposphere during the Indian Summer Monsoon (ISM) observed using the mesosphere‐stratosphere‐troposphere (MST) radar located at Gadanki (13.5°N, 79.2°E). The most significant and new observation is the presence of enhanced signal‐to‐noise ratio (SNR) of 3 dB and half‐power full spectral width of &gt;0.2 m s−1 in the vicinity of tropopause during the ISM. Downdrafts (updrafts) are dominated in the vicinity of tropopause from April to June (July to March). The result of stratospheric air intrusion is also supported with 10 years of ozone measurements obtained from Aura‐Microwave Limb Sounder (MLS) and 5 years of in situ ozonesonde observations. Detailed analysis shows that the horizontal advection along with turbulence in the vicinity of tropopause caused by the tropical easterly jet and tropopause altitude variability is the prime candidate for stratosphere to troposphere transport of ozone. In contrast, the tropical tropopause temperature plays a significant role in the troposphere to stratosphere transport of water vapor during the ISM. The significance of the present study is to qualitatively constitute the climatology of these exchange processes over Gadanki using Indian MST radar.

Optically Pumped Monolayer MoSe2 Excitonic Lasers from Whispering Gallery Mode Microcavities.

Developing integrable, nanoscale, and low-energy-consumption lasers is a crucial step toward on-chip optical communications and computing technologies. The strong exciton-photon interaction that emerged in monolayer transition metal dichalcogenides (TMDs) holds promise for engineering and integration. Herein, we prepare the MoSe2/microsphere cavities excitonic lasers by placing SiO2 microspheres on top of a monolayer MoSe2 film. By virtue of continuous-wave exciting MoSe2/microsphere whispering gallery mode (WGM) cavities, we realize multiple excitonic WGM lasing in the emission wavelength range of ∼750-875 nm at room temperature with tunable properties of free spectral range (FSR) and full width at half-maximum (fwhm) by varying the microsphere size. Theoretical calculations based on the finite element method (FEM) using COMSOL software were utilized to identify lasing modes and reveal the corresponding electric field distribution. These findings help to deepen fundamental understanding of excitonic WGM lasing and provide a promising research platform for integrable, scalable, and low-cost laser devices.