Absorption Cross-section Spectra Research Articles

The Radiative Efficiency and Global Warming Potential of HCFC-132b.

Hydro-chloro-fluoro-carbons (HCFCs) are potent greenhouse gases which strongly absorb the infrared (IR) radiation within the 8-12 μm atmospheric windows. Despite international policies schedule their phasing out by 2020 for developed countries and 2030 globally, HCFC-132b (CH2ClCClF2) has been recently detected with significant atmospheric concentration. In this scenario, detailed climate metrics are of paramount importance for understanding the capacity of anthropogenic pollutants to contribute to global warming. In this work, the radiative efficiency (RE) of HCFC-132b is experimentally measured for the first time and used to determine its global warming potential (GWP) over 20-, 100- and 500-year time horizon. Vibrational- and rotational-spectroscopic properties of this molecule are first characterized by exploiting a synergism between Fourier-transform IR (FTIR) spectroscopy experiments and quantum chemical calculations. Equilibrium geometry, rotational parameters and vibrational properties predicted theoretically beyond the double-harmonic approximation are employed to assist the vibrational assignment of the experimental trace. Finally, FTIR spectra measured over a range of pressures are used to determine the HCFC-132b absorption cross section spectrum from 150 to 3000 cm-1, from which istantaneous and effective REs are derived and, in turn, used for GWP evaluation.

In silico modelling of radiative efficiencies of anthropogenic greenhouse gases

Radiative efficiency (RE) is a climate metric adopted in international reports on climate change to quantify the greenhouse capacity of gases, and hence to guide decision-making processes and drive transitions in the production and utilization of chemicals in different application fields. Key quantities for the determination of the RE of a gas are the atmospheric irradiance profile and the infrared (IR) absorption cross section spectrum. The latter is usually measured experimentally, even though acquiring high-quality IR spectra can pose severe challenges, sometimes limiting the accuracy or the accessible spectral range. While computational quantum chemistry methods have emerged as valuable tools to simulate IR absorption properties, their application to REs estimation is still limited to the use of the double-harmonic approximation, which presents fundamental limitations. In this work, a cost-effective quantum chemical (QC) workflow including non-empirical anharmonic contributions to spectral properties and an automatic identification of conformer distribution is presented for the accurate evaluation of REs using a range of atmospheric irradiance profiles. Different levels of theory are considered, according to the current state-of-the-art, and the accuracy of the QC RE tool is demonstrated with reference to a number of representative halocarbons widely used in refrigeration, manufacturing, and pharmaceutical fields. The results show that REs can be computed with an average accuracy of 5% using double-hybrid functionals, which overshoot the widely used B3LYP method. Finally, the QC methodology is applied to determine the REs of selected halocarbons for which data is limited, or to address some contradictory results appeared in the literature for some species. The outcomes of this work demonstrate that QC anharmonic IR cross section spectra can be used to estimate REs with an accuracy on par with that of experimental measurements, hence applicable to challenging cases for providing data for policymakers as well for screening purposes when seeking new replacement compounds.

Exploring the two-photon absorption response in short π-chain organic compounds: Hydrazones and pyrazolines derivatives

We compared the experimental two-photon absorption spectra of two hydrazone derivatives of chalcone (HDC-1 and HDC-2) and two pyrazoline derivatives of dibenzylideneacetone and chalcone (PD-1 and PD-2). The compounds were synthesized by the Claisen-Schmidt reaction and characterized using NMR, FTIR, and UV–Vis. Using femtosecond pulses, the Z-scan technique recorded two-photon absorption cross-section (σ2PA) spectra of the investigated compounds, which presented values of σ2PA, ranging from ∼12 GM to ∼50 GM. Such σ2PA difference is generally associated with the conjugated chain length and the different functional and peripherical groups used. For example, increasing the π-chain and peripherals donor groups p-OCH3 from HDC-1 to HCD-2 led to a change in the σ2PA magnitude (σHDC−12PA∼35GM, σHDC−22PA∼50GM). The modification on the pyrazoline derivatives, i.e., increasing the conjugated chain and adding p-OCH3 in both phenyls in the PD-2 compared to compound PD-1 doubled the σ2PA magnitude (σPD−12PA∼12GM, σPD−22PA∼22GM). According to the obtained results and considering the investigated compounds' short π-chain, we could claim that these classes of organic molecules promise nonlinear optical materials for optical limiting due to optical transparency ranging from 450 nm for pyrazolines to 550 nm for hydrazone derivatives.

Growth, characterization, and efficient laser operation of Czochralski- and micro-pulling-down-grown Yb3+:YScO3 mixed sesquioxides

We report on the growth, spectroscopy and laser operation of Yb3+-doped mixed sesquioxide crystals. Various Yb3+-doped crystals with compositions close to (Y0.5Sc0.5)2O3 have been successfully grown by the Czochralski method and by the micro-pulling down (µ-PD) method. Our spectroscopic investigations reveal broadened stimulated emission and absorption cross-section spectra originating from the structural disorder of the mixed crystals. We find the peak wavelengths to shift by ∼1.6 nm between Y:Sc-ratios of 54:46 and 46:54 and confirm a linear relation of the peak position with the lattice constant of the host composition. In the laser experiments, we obtain highly efficient continuous-wave laser operation under pumping with an optically-pumped semiconductor laser (OPSL) at ∼975 nm, reaching slope efficiencies of up to 89% at optical-to-optical efficiencies exceeding 80% at laser wavelengths between 1037 nm and 1086 nm.

LiNbO3:Tm3+ Crystal: Material for Radiation-Balanced Laserin the Wave length Range of 1650 – 2000 nm

The absorption and emission cross-section spectra of LiNbO3:Tm3+ crystals were investigated within the wavelength range of at room temperature. This study delves into the potential for achieving radiation-balanced lasing. Optimal parameters for both the pump and emission wavelengths, denoted as and , respectively, were determined. At these wavelengths, the corresponding optimal values for gain and radiation-balanced generation efficiency were identified. These findings underscore the feasibility of radiation-balanced lasing in LiNbO3:Tm3+ crystals under the specified conditions.

Influence of peripherical modifications in linear and nonlinear photophysical properties of imidazo[4,5-b]pyridine derivatives

This study reports a wide study on linear and nonlinear optical properties of six imidazo[4,5-b]pyridines derivates. The compounds are coupled with a series of peripheral groups forming different dipolar structures (D-π-A and A-π-A). Photophysical parameters such as the anisotropy coefficient, transition dipole moment, and permanent dipole moment difference were determined using spectroscopic techniques. The two-photon absorption (2PA) cross-section spectra were obtained by the tunable femtosecond Z-scan technique. In addition, quantum chemical calculations and the Sum Over States (SOS) model for two energy levels were applied to support the experimental data. A single 2PA band, with 2PA cross-section varying from 70 to 110 GM, was observed in the 2PA cross-section spectra in the molecules with only acceptor groups. In addition, the presence of a second band around 660 nm and an increase in 2PA cross-section values (around 110 to 130 GM in the principal band) was observed for the molecules with a combination of the methoxy radical (OMe) with halogen groups (D-π-A structure). These results indicate that the non-centrosymetric A-Imp-D structures facilitate the polarizability and internal charge transfer processes, resulting in photophysical and two-photon absorption properties enhancement compared to A-Imp-A structures.

Crystalline Phase, Cross-Section, and Temporal Characteristics of Erbium-Ion in Lu3Ga5O12 Crystal

An erbium-doped Lu3Ga5O12(LuGG) single crystal was grown by the Czochralski method. The crystalline phase in the grown crystal was analyzed by powder X-ray diffraction. The erbium-ion emission spectra of the crystal were acquired. The erbium-ion emission cross-section (ECS) spectrum was computed from the acquired emission spectrum. The erbium-ion absorption cross-section (ACS) spectrum was computed using the McCumber relationship. The results are discussed in contrast to those computed from the acquired absorption spectrum, and the comparison shows that both methods give consistent results. The temporal characteristics of the emissions were also studied based on 0.98 μm pulse pumping. The study shows that the infrared emissions at 1.0, 1.5, and 2.8 μm show mono-exponentially temporal behavior. Instead, the decays of two visible emissions at 0.56 and 0.67 μm show considerable non-exponential features; each trace can be fitted double-exponentially. The non-exponential behavior is associated with those erbium ions that are present in the form of clusters, which enables non-radiative upconversion depopulation and hence additional contribution to the decay through cross relaxation between the erbium ions in clusters. The study also shows that about half of the erbium ions are present in the cluster state in the studied crystal.

Comparing two-photon absorption of chalcone, dibenzylideneacetone and thiosemicarbazone derivatives

We compared the experimental nonlinear optical responses (NLO) of one chalcone (BCH-1), two dibenzylideneacetone (BCH-2 and BCH-3), and two thiosemicarbazones dibenzylideneacetone (TSCD-1 and -2). The compounds were synthesized by the Claisen-Schmidt reaction and characterized using NMR, FTIR, and UV–Vis. The Z-scan technique, using femtosecond pulses, obtained two-photon absorption cross-section (σ2PA) spectra of the investigated compounds, which presented moderate values of σ2PA, ranging from 28 GM to 69 GM. Such σ2PA difference in the NLO response is usually associated with the length of the conjugated chain and the different functional groups used. For example, increasing the conjugated π-chain and peripherals groups from BCH-1 to BCH-2 led to a doubling effect on the magnitude of the NLO (σBCH−12PA=28GM, σBCH−22PA=64GM). A noticeable drop in the NLO response is observed from σBCH−22PA=64GM to σBCH−32PA=39GM due to the replacement of the 3,4,5 tri-methoxyphenyl by the thiophene aromatic peripheral group, respectively. The higher NLO response is attributed to compounds TSCD-1 and -2, with values of about 69 GM and 66 GM, respectively, indicating that bromo- and chloro-substituents do not influence the NLO response. According to the obtained results and considering the investigated compounds' short π-chain, we could claim that these classes of organic molecules are promising NLO materials.

Influence of Er3+ concentration in Er:GGAG crystal on spectroscopic and laser properties

Detail spectroscopy study of erbium-doped active media is crucial for understanding of the behavior of erbium-based lasers. In this paper, for the first time, detailed study of the concentration dependence of Er3+ in garnet-based active media is presented. Wide range of novel samples Er:GGAG (26 in total) with various Er3+ concentration (0.5–38 at%), were investigated for the first time. The complete spectroscopy (absorption and emission cross-section, Raman, mid- and far-infrared transmission spectra, decay times at 4I11∕2 and 4I13∕2) together with Judd-Ofelt analysis and laser characteristics were measured at room temperature. Results shows strong dependence of the first excited state (4I13∕2) on concentration, on the other hand, the 4I11∕2 level is completely independent of the erbium doping level. The Judd-Ofelt analysis show that erbium doping has minimal effect on the structural properties of Er:GGAG. Also it is shown that Er:GGAG laser has a slope efficiency of 15.3 % (almost half of the theoretical limit) and generated maximal output power of 350 mW.

Cross-section spectra and transient characteristics of Er3+ emissions in Gd3(Al, Ga)5O12 garnet single crystal

We measured fluorescence spectra of visible and infrared electronic transitions at 530 (2H11/2 → 4I15/2), 560 (4S3/2 → 4I15/2), 670 (4F9/2 → 4I15/2), 980 (4I11/2 → 4I15/2), 1530 (4I13/2 → 4I15/2) and 2700 nm (4I11/2 → 4I13/2) of Er3+ in Gd3(Al0.4Ga0.6)5O12 garnet single-crystal excited at the wavelength 520 nm (for the 980 nm emission) or 980 nm (for other emissions). From measured fluorescence spectrum, Er3+ emission cross-section spectrum was calibrated for each transition. Absorption cross-section spectra were further derived on the basis of McCumber equation, and compared with those spectra obtained from measured absorption spectrum on the basis of the Beer-Lambert law. The comparison showed that the results given by two methods can be regarded as same within the error. The transient features of visible and infrared emissions were also studied under pulse excitation. The results showed that, while the three IR emissions at 980, 1530 and 2700 nm all follow a mono-exponential function, both green and red 980-nm-upconverted emissions at 560 and 670 nm exhibit non-mono-exponentially decaying feature, and each decaying trace can be fitted by a sum of two exponential functions. The non-mono-exponential feature is related to cross relaxation caused by non-radiative short-distance energy transfer between clustered Er3+ sites.

Study of optical absorption cross-section spectra and high-order harmonic generation of thymine, thymine glycol, and thymine dimer molecules.

The last two decades have witnessed advances in femtosecond and sub-femtosecond physics which have made accessible the study of phenomena with atomic and subatomic resolution. In particular, developments in laser physics and high-order harmonic generation have enabled tracking and investigating molecular reaction dynamics and the actual dynamics of electrons in chemical reactions, as well as investigating the structure of molecules. High-order harmonic generation has proved to be an ideal means for generating autosecond pulses. Time-dependent density functional theory provides an invaluable tool for the theoretical study of high-order harmonic generation. In this article, an exact study of the optical absorption cross-section spectra and high-order harmonic generation of thymine and its damage forms (thymine glycol and thymine dimer) has been performed using the time dependent density functional theory via the octopus code. The spectra have been characterized with the aim of distinguishing thymine from its damaged forms. The discrepancies in the optical absorption spectra of thymine and its damaged forms have been elucidated. The effects of laser pulse intensity and pulse profile on the high-order harmonic spectra of these molecules has been investigated, showing the possibility to distinguish between thymine and its damaged forms using high-order harmonic generation. In particular, it is demonstrated that high-order harmonic generation corresponding to a laser pulse with a cosinusoidal envelope and intensity [Formula: see text] clearly differentiates thymine from its damaged forms. This laser could potentially be applied to discern damage in more complex DNA material.

Diode-pumped continuous-wave laser of a self-frequency-doubling Yb:La2CaB10O19 crystal.

We report the first, to the best of our knowledge, laser operation of acentric Yb3+-doped La2CaB10O19 (Yb:LCB) crystal since its discovery in 1998. The polarized absorption and emission cross-section spectra of Yb:LCB were calculated at room temperature. Using a fiber-coupled 976 nm laser diode (LD) as the pump source, we realized effective dual-wavelength laser generation at around 1030 and 1040 nm. The highest slope efficiency of 50.1% was obtained in the Y-cut Yb:LCB crystal. In addition, via resonant cavity design on a phase-matching crystal, a compact self-frequency-doubling (SFD) green laser at 521 nm was also realized in a single Yb:LCB crystal with an output power of 152 mW. These results promote Yb:LCB as a competitive multifunctional laser crystal, especially for highly integrated microchip laser devices ranging from the visible to the near-infrared regime.

Investigating the structure-sensitive factors relevant to cryogenic laser operation of Yb3+ ions in oxide crystals

Optical absorption and luminescence spectra of Yb3+ ions in Gd3(Al0.5Ga0.5)5O12, (Lu0.3Gd0.7)2SiO5 and YAl3(BO3)4 hosts crystals were examined as a function of temperature between 80 and 300 K. The analysis of obtained data provided detailed information on the thermally induced change of intensities, wavelengths and bandwidths of Yb3+ transitions that governs the temperature dependence of absorption and emission cross section spectra. This information, combined with structural peculiarities of the systems studied made it possible to propose generalizations regarding the importance of the structural disorder in the Yb3+-doped laser crystals operating at cryogenic temperatures.

Growth and Spectroscopy of Yb:YMgB5O10 Crystal

A transparent Yb:YMgB5O10 single crystal with dimensions up to 25 × 23 × 25 mm and weight 10.337 g was grown using a high-temperature solution growth on dipped seeds technique with a K2Mo3O10 solvent. The Yb3+ concentration was calculated to be 4.7 at.% (NYb = 3.71 × 1020 atoms/cm3) with a distribution coefficient Kd of 0.59. The grown crystal was characterized by means of PXRD, TGA-DSC and ATR-FTIR techniques. The spectroscopic characteristics of the Yb:YMgB5O10 crystal were demonstrated. Absorption cross-section spectra were produced. The luminescence spectra of the Yb:YMgB5O10 crystal were measured in the spectral range of 950–1100 nm. The luminescence kinetics of the 2F5/2 energy level were investigated and the lifetime was determined.

Infrared absorption cross section and radiative forcing efficiency features of four hydrofluoropolyethers: Performance of some DFT functionals

The present work aimed to investigate the infrared absorption cross section spectra using a series of eight DFT methods including DSD-PBEP86, B2PLYP, B3LYP, BLYP, G96LYP, M06-L, PBEPBE, and TPSSTPSS with basis sets Def2-TZV and Def2-TZVP. These were assigned to a series of four H-Galdens noted HG-00, HG-10, HG-01, and HG-11. The experimental infrared spectra of these gases provided by Myhre et al. [Atmos. Environ. 33 (1999) 4447] are well reproduced using the method M06-L/Def2-TZVP over the frequency range 0–3200 cm−1. The radiative forcing efficiency, descriptor of climate effect, was estimated using the narrow band model and corrected with a lifetime factor for different computational methods. The double hybrid functionals yield accurate results compared to experiment in the range 0–2500 cm−1 for HG-00, HG-10, and HG-01, and in the range 600–1600 cm−1 for HG-11. The other functionals are in good agreement over the specific frequency ranges.

The Optical Response of Metallic Spherical Core-Shell Nanoparticles

The optical response of spherical nanoparticles was studied based on the quasi-static approximation of classical electrodynamics. The simple Drude model was used to calculate the complex dielectric function of the metal. We investigated the behavior of the absorption cross-section spectra of metallic spherical core–shell (including dielectric-metal and metal-dielectric) nanoparticles numerically. We found that the number of resonance peaks in the absorption cross-section spectra depends on the number of metal-dielectric interfaces of the nanostructure, as predicted by plasmonic hybridization theory. Furthermore, the absorption cross-section spectra can be precisely controlled by changing the thickness of the shell and the dielectric constant of the medium.

Effect of peripherical groups on the two-photon brightness of (E)-3-benzyl-6-bromo-2-styryl-3H-imidazo[4,5-b]pyridine derivatives

Here, a study of the effect of several electron-withdrawing (F, Br, CF3, Cl) and electron-donating (OMe, OTBDMS, CH3, S) on the two-photon brightness (2 PB) of nine imidazo[4,5-b]pyridine derivatives was developed. The two-photon absorption cross-section (2PACS) spectra were acquired by the tunable femtosecond Z-scan technique from 470 nm up to 700 nm, and hence the 2 PB was evaluated at the 2PACS peak (around 540 nm) and 700 nm. Transition dipole moment, the difference of state dipole moments, anisotropy coefficient, and fluorescence lifetime were figured out as a result of the Gaussian decomposition of one-photon absorption spectra, solvatochromism, fluorescence anisotropy, and Strickler Berg equation, respectively. Besides the photophysical analysis, the photophysical parameters were used as input parameters to phenomenologically model the 2PACS applying the Sum-Over-States approach regarding a three-level energy system. Results have shown a 2PACS peak of around 130 GM for all imidazo[4,5-b]pyridine derivatives, and values of 2PACS at 700 nm ranged from 4 up to 14 GM. Results show that for Br-π-electron withdrawing (Br-π-EW) molecular arrangement, higher values of 2 PB can be reached, mainly through the control of ϕ, which demonstrated to be more sensible than the 2PACS to the addition of different peripherical groups.

Synthesis and Laser-Related Spectroscopy of Er:Y2O3 Optical Ceramics as a Gain Medium for In-Band-Pumped 1.6 µm Lasers

In this paper, Er:Y2O3 optical ceramics were fabricated and details of the synthesis were presented. The spectral–luminescent properties of Er3+:Y2O3 optical ceramics were investigated. The absorption and emission cross-section spectra were determined. The luminescence kinetics at near 1.6 µm was single exponential and the lifetime of erbium 4I13/2 energy level was determined. In the frame of the conventional Judd–Ofelt theory, the emission properties of the energy levels of erbium 4I13/2 and 4I11/2 involved in laser operation at near 1.6 µm were calculated. The gain coefficient curves for typical values of the relative population of the upper laser level 4I13/2 were presented. The composition and structure were studied using the SEM, XRD, FTIR spectroscopy, and X-ray computer tomography techniques.

Resonantly enhanced absorption in bifurcation plasmonic nanostructure for refractive index sensing

By changing or fine-tuning the surface structure of the metal, the characteristics of surface plasmon – especially the interaction with light – can be customized. In this work, we numerically design a plasmonic nanostructure composed of a pair of symmetrical bifurcation nanostructures. An underlying optical property of the observed scattering and absorption cross section spectra and physical mechanism is illustrated by analyzing spatial distributions of the magnetic field, electric field, and surface current component at resonant wavelengths. Moreover, the extremely intense and highly confined electromagnetic fields induced in the bifurcation plasmonic nanostructure provide a sensitive environment to probe minor changes in the dielectric environment. Such high-performance composite nanostructure provides great potential for the application of sensing.

Influence of electron-withdrawing groups in two-photon absorption of imidazopyridines derivatives

This work investigates the influence of different electron-withdrawing groups (Cl, Br, fluorobenzonitrile), on the two-photon absorption cross-section of six imidazo[4,5-b]pyridine derivatives. The two-photon absorption cross-section spectra were obtained by ultra-fast Z-scan technique from 470 nm up to 700 nm. The Sum-Over-States approach was applied to model the two-photon absorption spectra, using a three-level energy system. Photophysical properties, such as transition dipole moment, the difference of permanent dipole moments, and anisotropy coefficient were determined through the analysis of one-photon absorption spectra, solvatochromism, and fluorescence anisotropy, respectively. Besides, the excited state absorption spectra were measured through ultra-fast transient absorption, allowing the excited state lifetime and spectral position determination. Two-photon absorption cross-sections of about 160 GM were observed when two electron-withdrawing groups are linked to the imidazo[4,5-b]pyridine core, elucidating a path to achieve high optical nonlinearities in imidazopyridine derivatives. Furthermore, a increase in the two-photon cross-section was observed when chloride is linked at the C-6 position (90 GM) instead of the C-5 position (50 GM), which is related to the proximity of a higher excited state.