First real-time measurement of the evolving 2H/1H ratio during water evaporation from plant leaves

We have studied the temporal behaviour of the deuterium isotope ratio of water vapour emerging from a freshly cut plant leaf placed in a dry nitrogen atmosphere. The leaf material was placed directly inside the sample gas cell of the stable isotope ratio infrared spectrometer. At the reduced pressure (～40 mbar) inside the cell, the appearance of water evaporating from the leaf is easily probed by the spectrometer, as well as the evolving isotope ratios, with a precision of about 1 ‰. The demonstration experiment we describe measures the ²H/¹H isotope ratio only, but the experiment can be easily extended to include the ¹⁸O/¹⁶O and ¹⁷O/¹⁶O isotope ratios. Plant leaf water isotope ratios provide important information towards quantification of the different components in the ecosystem water and carbon dioxide exchange.     

Optical-feedback cavity-enhanced absorption spectroscopy with a quantum-cascade laser yields the lowest formaldehyde detection limit

We report on the first application of Optical Feedback-Cavity Enhanced Absorption Spectroscopy to formaldehyde trace gas analysis at mid-infrared wavelengths. A continuous-wave room-temperature, distributed-feedback quantum cascade laser emitting around 1,769 cm^?1 has been successfully coupled to an optical cavity with finesse 10,000 in an OF-CEAS spectrometer operating on the ν₂ fundamental absorption band of formaldehyde. This compact setup (easily transportable) is able to monitor H₂CO at ambient concentrations within few seconds, presently limited by the sample exchange rate. The minimum detectable absorption is 1.6 × 10^?9 cm^?1 for a single laser scan (100 ms, 100 data points), with a detectable H₂CO mixing ratio of 60 pptv at 10 Hz. The corresponding detection limit at 1 Hz is 5 × 10^?10 cm^?1, with a normalized figure of merit of 5 × 10^?11cm $^{-1}/\sqrt{\rm Hz}$ (100 data points recorded in each spectrum taken at 10 Hz rate). A preliminary Allan variance analysis shows white noise averaging down to a minimum detection limit of 5 pptv at an optimal integration time of 10 s, which is significantly better than previous results based on multi-pass or cavity-enhanced tunable QCL absorption spectroscopy.     

Sensitive detection of acrolein and acrylonitrile with a pulsed quantum-cascade laser

We report on spectroscopic measurements of acrolein and acrylonitrile at atmospheric pressure using a pulsed distributed feedback quantum-cascade laser in combination with intra- and inter-pulse techniques and compare the results. The measurements were done in the frequency region around 957 cm^?1. In the inter-pulse technique, the laser is excited with short current pulses (5–10 ns), and the pulse amplitude is modulated with an external current ramp resulting in a ～2.3 cm^?1 frequency scan. In the intra-pulse technique, a linear frequency down-chirp during the pulse is used for sweeping across the absorption line. Long current pulses up to 500 ns were used for these measurements which resulted in a spectral window of ～2.2 cm^?1 during the down-chirp. These comparatively wide spectral windows facilitated the measurements of the relatively broad absorption lines (～1 cm^?1) of acrolein and acrylonitrile. The use of a room-temperature mercury-cadmium-telluride detector resulted in a completely cryogen-free spectrometer. We demonstrate ppb level detection limits within a data acquisition time of ～10 s with these methodologies.     

Doubly radiative neutron capture by 2H, 3He, 16O and 208Pb

Cross-sections for doubly radiative thermal neutron capture on ²H, ³He, ¹⁶O and²⁰⁸Pb are calculated to be 21, 1200, 41 and 50 nb, corresponding to branching ratios of σ(n, γγ)/σ(n, γ) = 4.0 × 10^?5, ～ × 10^?2, 2.2 × 10^?4 and 1.0 × 10^?4, respectively.     

A quantum cascade laser-based optical feedback cavity-enhanced absorption spectrometer for the simultaneous measurement of CH4 and N2O in air

Optical feedback cavity-enhanced absorption spectroscopy (OF CEAS) has been demonstrated with a thermoelectrically cooled continuous wave distributed feedback quantum cascade laser (QCL) operating at wavelengths around 7.84 μm. The QCL is coupled to an optical cavity which creates an absorption pathlength greater than 1000 m. The experimental design allows optical feedback of infra-red light, resonant within the cavity, to the QCL, which initiates self-locking at each TEM₀₀ cavity mode frequency excited. The QCL linewidth is narrowed to below the mode linewidth, greatly increasing the efficiency of injection of light into the cavity. At the frequency of each longitudinal cavity mode, the absorption coefficient of an intracavity sample is obtained from the transmission at the mode maximum, measured with a thermoelectrically cooled detector: spectral line profiles of CH₄ and N₂O in ambient air were recorded simultaneously and with a resolution of 0.01386 cm^?1. A minimum detectable absorption coefficient of 5.5×10^?8 cm^?1 was demonstrated after an averaging time of 1 s for this completely thermoelectrically cooled system. The bandwidth-normalised limit for a single cavity mode is 5.6×10^?9 cm^?1?Hz^?1/2 (1σ).     

Microstructural change due to isochronal annealing in severely plastic-deformed commercial purity aluminium

Microstructural changes, such as the density of grain boundary (GB) and dislocation density, due to isochronal annealing in severely plastic-deformed commercial purity aluminium up to 523 K was evaluated using electrical resistivity measurements and scanning transmission electron microscopy. Eventually, the GB density decreases from about 7.2 × 10⁶ to about 2 × 10⁶ m^?1, whilst the dislocation density decreases from an initial value of around 1.3 × 10¹⁴ m^?2 down to around 4 × 10¹³ m^?2.     

Time resolved simultaneous detection of 14NO and 15NO via mid-infrared cavity leak-out spectroscopy

We present a ring-down absorption spectrometer based on a continuous-wave CO laser in the mid-infrared spectral region near λ?=?5 μm. Using a linear ring-down cavity (length: 0.5 m) with high reflective mirrors (R?=?99.988 %), we observed a noise-equivalent absorption coefficient of 3?×?10^?10 cm^?1Hz^?1/2. This corresponds to a noise-equivalent concentration of 800 parts per trillion (ppt) for ¹⁴NO and 40 ppt for ¹⁵NO in 1 s averaging time. We achieve a time resolution of 1 s which allows time resolved simultaneous detection of the two N isotopes. The δ¹⁵N value was obtained with a precision of ±1.2‰ in a sample with a NO fraction of 11 ppm. The simultaneous detection enables the use of ¹⁵NO as a tracer molecule for endogenous biomedical processes.     

Photoacoustic spectrometer for accurate,continuous measurements of atmospheric carbon dioxide concentration

We have developed a portable photoacoustic spectrometer that offers routine, precise and accurate measurements of the molar concentration of atmospheric carbon. The temperature-controlled spectrometer continuously samples dried atmospheric air and employs an intensity-modulated distributed feedback laser and fiber amplifier operating near 1.57 µm. For measurements of carbon dioxide in air, we demonstrate a measurement precision (60-s averaging time) of 0.15 µmol mol^?1 and achieve a standard uncertainty of 0.8 µmol mol^?1 by calibrating the analyzer response in terms of certified gas mixtures. We also investigate how water vapor affects the photoacoustic signal by promoting collisional relaxation of the carbon dioxide.     

Cavity-enhanced optical feedback-assisted photo-acoustic spectroscopy with a 10.4 μm external cavity quantum cascade laser

An ultra-sensitive photo-acoustic spectrometer using a 10.4 μm broadly tunable mid-IR external cavity quantum cascade laser (EC-QCL) coupled with optical feedback to an optical power buildup cavity with high reflectivity mirrors was developed and tested. A laser optical power buildup factor of 181 was achieved, which corresponds to an intra-cavity power of 9.6 W at a wavelength of 10.4 μm. With a photo-acoustic resonance cell placed inside the cavity this resulted in the noise-equivalent absorption coefficient of 1.9 × 10^?10 cm^?1 Hz^?1/2, and a normalized noise-equivalent absorption of 1.1 × 10^?11 cm^?1 W Hz^?1/2. A novel photo-acoustic signal normalization technique makes the photo-acoustic spectrometer’s response immune to changes and drifts in the EC-QCL excitation power, EC-QCL to cavity coupling efficiency and cavity mirrors aging and contamination. An automatic lock of the EC-QCL to the cavity and optical feedback phase optimization permitted long wavelength scans within the entire EC-QCL spectral tuning range.     

Swift heavy ion induced photoluminescence studies in Aluminum oxide

Aluminum oxide, a promising material for high temperature applications, is synthesized by combustion route and characterized by X-ray diffraction technique. Photoluminescence of aluminum oxide bombarded with 120 MeV swift Au⁹⁺ ions have been studied at room temperature. The observed PL emission with peak at ～420 nm is attributed to F-center while the two more weak emissions with peaks at ～482 and ～525 nm are attributed to aggregates of F-centers. It is found that PL intensity increases with increase in Au⁹⁺ ion fluence up to ～1×10¹³ ions cm^?2 and thereafter it reaches saturation. The Fourier transform Infrared spectroscopy results show the destruction of Al?O?H bonds whereas the XRD results indicate the surface amorphization of Al₂O₃.     

Frequency-agile,rapid scanning spectroscopy: absorption sensitivity of 2 × 10−12 cm−1 Hz−1/2 with a tunable diode laser

We present ultrasensitive measurements of molecular absorption using frequency-agile rapid scanning, cavity ring-down spectroscopy with an external-cavity diode laser. A microwave source that drives an electro-optic phase modulator with a bandwidth of 20 GHz generates pairs of sidebands on the probe laser. The optical cavity provides for high sensitivity and filters the carrier and all but a single, selected sideband. Absorption spectra were acquired by stepping the tunable sideband from mode-to-mode of the ring-down cavity at a rate that was limited only by the cavity decay time. This approach allows for scanning rates of 8 kHz per cavity resonance, a minimum detectable absorption coefficient of 1.7 × 10^?11 cm^?1 after only 20 ms of averaging, and a noise-equivalent absorption coefficient of 1.7 × 10^?12 cm^?1 Hz^?1/2. By comparison with cavity-enhanced laser absorption spectrometers reported in the literature, the present system is, to the best of our knowledge, among the most sensitive and has by far the highest spectrum scanning rate.     

Irradiation effects of 12 eV oxygen ions on polyimide and fluorinated ethylene propylene

Polyimide (PI) and Fluorinated Ethylene Propylene (FEP) samples (15 mm×15 mm×50 μm ) were exposed to atomic oxygen ions of average energy ～12 eV and flux ～5×10¹³ ions cm ^?2 s ^?1, produced in the Electron Cyclotron Resonance (ECR) plasma. The energy and the flux of the oxygen ions at different positions in the plasma were measured by a retarding field analyzer. The fluence of the oxygen ions was varied from sample to sample in the range of ～5×10¹⁶ to 2×10¹⁷ ions cm ^?2 by changing the irradiation period. The pre- and the post-irradiated samples were characterized by the weight loss, Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), and Fourier Transform Infrared (FTIR) techniques. The weight of the PI and FEP samples decreased with increasing the ion fluence. However, the erosion yield for the PI is found to be higher, by almost a factor five, when compared with that of FEP. On the surface region of irradiated samples, the concentrations of the carbon, fluorine, and oxygen and their corresponding chemical bonds have changed appreciably. Moreover, blisters and nanoglobules were also observed even at a fluence of ～10¹⁷ ions cm ^?2. This oxygen ion fluence is almost two orders of magnitude lower than that of the 5 eV atomic oxygen, which a satellite encounters in the space, at the low Earth orbit, during its mission period of about 7 years.     

Polycrystalline GaSb films prepared by the coevaporation technique

Gallium antimonide (GaSb) films were deposited onto fused silica and n-Si (100) substrates by coevaporating Ga and Sb from appropriate evaporation sources. The films were polycrystalline in nature. The size and the shape of the grains varied with the change in the substrate temperature during deposition. The average surface roughness of the films was estimated to be 10 nm. Grain boundary trap states varied between 2×10¹² and 2.2×10¹² cm^?2 while barrier height at the grain boundaries varied between 0.09 eV and 0.10 eV for films deposited at higher temperatures. Stress in the films decreased for films deposited at higher temperatures. XPS studies indicated two strong peaks located at ～543 eV and ～1121 eV for Sb 3d_3/2 and Ga 2p_3/2 core-level spectra, respectively. The PL spectra measured at 300 K was dominated by a strong peak located ～0.55 eV followed by two low intensity peaks ～0.63 eV and 0.67 eV. A typical n-Si/GaSb photovoltaic cell fabricated here indicated V _oc～311 mV and J～29.45 mA/cm², the density of donors (N _d)～3.87×10¹⁵ cm^?3, built in potential (V _bi)～0.48 V and carrier life time (τ)～28.5 ms. Impedance spectroscopy measurements indicated a dielectric relaxation time ～100 μs.     

Possibility of room-temperature multiferroism in Mg-doped ZnO

Room-temperature multiferroic properties in Mg-doped ZnO samples are reported wherein Mg replaces Zn in the ZnO matrix and retains hexagonal wurtzite structure. The saturation magnetisation is increased from ～2×10^?4 emu/g to 3×10^?4 emu/g for the dilute doping of 2 % Mg in pure ZnO and the ferroelectricity is also increased. Higher concentration of Mg does not lead to a significant enhancement in the magnetisation but improves the ferroelectric properties. An X-ray absorption spectroscopic study shows an enhancement in O vacancies with dilute doping of Mg. The origin of the multiferroic behaviour is understood based on their crystal and electronic structures.     

Investigation of the kinetics of OH∗ and CH∗ chemiluminescence in hydrocarbon oxidation behind reflected shock waves

The temporal variation of chemiluminescence emission from OH^?(A² Σ ⁺) and CH^?(A² Δ) in reacting Ar-diluted H₂/O₂/CH₄, C₂H₂/O₂ and C₂H₂/N₂O mixtures was studied in a shock tube for a wide temperature range at atmospheric pressures and various equivalence ratios. Time-resolved emission measurements were used to evaluate the relative importance of different reaction pathways. The main formation channel for OH^? in hydrocarbon combustion was studied with CH₄ as benchmark fuel. Three reaction pathways leading to CH^? were studied with C₂H₂ as fuel. Based on well-validated ground-state chemistry models from literature, sub-mechanisms for OH^? and CH^? were developed. For the main OH^?-forming reaction CH+O₂=OH^?+CO, a rate coefficient of k ₂=(8.0±2.6)×10¹⁰ cm³?mol^?1?s^?1 was determined. For CH^? formation, best agreement was achieved when incorporating reactions C₂+OH=CH^?+CO (k ₅=2.0×10¹⁴ cm³?mol^?1?s^?1) and C₂H+O=CH^?+CO (k ₆=3.6×10¹²exp(?10.9 kJ?mol^?1/RT) cm³?mol^?1?s^?1) and neglecting the C₂H+O₂=CH^?+CO₂ reaction.     

Cavity-enhanced optical frequency comb spectroscopy in the mid-infrared application to trace detection of hydrogen peroxide

We demonstrate the first cavity-enhanced optical frequency comb spectroscopy in the mid-infrared wavelength region and report the sensitive real-time trace detection of hydrogen peroxide in the presence of a large amount of water. The experimental apparatus is based on a mid-infrared optical parametric oscillator synchronously pumped by a high-power Yb:fiber laser, a high-finesse broadband cavity, and a fast-scanning Fourier transform spectrometer with autobalancing detection. The comb spectrum with a bandwidth of 200 nm centered around 3.76 μm is simultaneously coupled to the cavity and both degrees of freedom of the comb, i.e. the repetition rate and carrier envelope offset frequency, are locked to the cavity to ensure stable transmission. The autobalancing detection scheme reduces the intensity noise by a factor of 300, and a sensitivity of 5.4×10^?9 cm^?1?Hz^?1/2 with a resolution of 800 MHz is achieved (corresponding to 6.9×10^?11 cm^?1?Hz^?1/2 per spectral element for 6000 resolved elements). This yields a noise equivalent detection limit for hydrogen peroxide of 8 parts-per-billion (ppb); in the presence of 2.8 % of water the detection limit is 130 ppb. Spectra of acetylene, methane, and nitrous oxide at atmospheric pressure are also presented, and a line-shape model is developed to simulate the experimental data.     

Li+ transportation kinetics of FeF3 · 0.33H2O/C nanocomposite synthesized by one-step solid state method

A new cathode material for lithium ion battery FeF₃?·?0.33H₂O/C was synthesized successfully by a simple one-step chemico-mechanical method. It showed a noticeable initial discharge capacity of 233.9 mAh g^?1 and corresponding charge capacity of 186.4 mAh g^?1. A reversible capacity of ca.157.4 mAh g^?1 at 20 mA g^?1 can be obtained after 50 charge/discharge cycles. To elucidate the lithium ion transportation in the cathode material, the methods of electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) were applied to obtain the lithium diffusion coefficients of the material. Within the voltage level of 2.05–3.18 V, the method of EIS showed that \( {D}_{{\mathrm{Li}}^{+}} \) varied in the range of 1.2?×?10^?13?~?3.6?×?10^?14 cm² s^?1 with a maximum of 1.2?×?10^?13 cm² s^?1 at 2.5 V. The method of GITT gave a result of 8.1?×?10^?14?~?1.2?×?10^?15 cm² s^?1. The way and the range of the variation for lithium ion diffusion coefficients measured by the GITT method show close similarity with those obtained by the EIS method. Besides, they both reached their maximum at a voltage level of 2.5 V.     

Using a DS-DBR laser for widely tunable near-infrared cavity ring-down spectroscopy

Studies into the suitability of a novel, widely tunable telecom L-band (1,563–1,613 nm) digital supermode distributed Bragg reflector (DS-DBR) laser for cavity ring-down spectroscopy (CRDS) are presented. The spectrometer comprised of a 36.6?cm long linear cavity with ring-down times varying between 19–26 μs across the 50 nm DS-DBR wavelength range due to changes in the cavity mirror reflectivities with wavelength. The potential of such a broadband, high-resolution CRD spectrometer was illustrated by investigating several transitions of CO₂ in air, a 5 % calibrated mixture and breath samples. Allan variance measurements at a single wavelength indicated an optimal minimum detectable absorption coefficient (α _min) of 3 × 10^?10 cm^?1 over 20 s.     

Ultra-high-precision mid-IR spectrometer II: system description and spectroscopic performance

The development and spectroscopic performance evaluation of an ultra-sensitive, mid-IR spectrometer is reported. The laser system is based upon difference-frequency generation (DFG) at ～3.5 μm by mixing a DFB diode laser at 1562 nm and a DFB fiber laser at 1083 nm using a periodically poled LiNbO₃ crystal. DFG radiation was coupled to a 100?m optical path length astigmatic Herriott cell. Sensitive and selective spectroscopic detection of formaldehyde was performed with second-harmonic detection using Peltier-cooled HgCdTe detectors. By applying computer lock-ins, dual-beam optical noise subtraction, focus matching, thermal stabilization, active wavelength control, and advanced signal processing a sensitivity corresponding to an absorbance ～1.6×10^-7 is achieved for 260 s of averaging.     

50 MeV Li3+ ion irradiation effect on structural, electrical, and dielectric properties of PVA-based nanocomposite polymer electrolytes

Nanocomposite polymer electrolyte thin films of polyvinyl alcohol (PVA)-orthophosphoric acid (H₃PO₄)-Al₂O₃ have been prepared by solution cast technique. Films are irradiated with 50 MeV Li³⁺ ions having four different fluences viz. 5?×?10¹⁰, 1?×?10¹¹, 5?×?10¹¹, and 1?×?10¹² ions/cm². The effect of irradiation on polymeric samples has been studied and characterized. X-ray diffraction spectra reveal that percent degree of crystallinity of samples decrease with ion fluences. Glass transition and melting temperatures have been also decreased as observed in differential scanning calorimetry. A possible complexation/interaction has been shown by Fourier transform infrared spectroscopy. Temperature-dependent ionic conductivity shows an Arrhenius behavior before and after glass transition temperature. It is observed that ionic conductivity increases with ion fluences and after a critical fluence, it starts to decrease. Maximum ionic conductivity of ～2.3?×?10^?5 S/cm owing to minimum activation energy of ～0.012 eV has been observed for irradiated electrolyte sample at fluence of 5?×?10¹¹ ions/cm². The dielectric constant and dielectric loss also increase with ion fluences while they decrease with frequency. Transference number of ions shows that the samples are of purely ionic in nature before and after ion irradiation.