Showing papers in "Applied Physics B in 2008"
TL;DR: In this article, the authors present results from field trials by Pennsylvania State University and the National Oceanographic and Atmospheric Administration (NOAA) of a newly available analyzer, based on cavity ring-down spectroscopy (CRDS), capable of measuring the concentrations of carbon dioxide (CO2) and water vapor (H2O).
Abstract: Researchers investigating global climate change need measurements of greenhouse gases with extreme precision and accuracy to enable the development and benchmarking of better climate models. Existing atmospheric monitors based on non-dispersive infrared (NDIR) sensors have known problems – they are non-linear, sensitive to water vapor concentration, and susceptible to drift. Many cannot easily be simultaneously calibrated across different sites to the level of accuracy required for use in atmospheric studies. We present results from field trials by Pennsylvania State University and the National Oceanographic and Atmospheric Administration (NOAA) of a newly available analyzer, based on cavity ring-down spectroscopy (CRDS), capable of measuring the concentrations of carbon dioxide (CO2) and water vapor (H2O). In addition, we present data from a new analyzer which measures CO2, methane (CH4), and H2O.
530 citations
TL;DR: In this paper, the authors explored the use of several methods for carrying out absorption spectroscopy with mid-infrared quantum cascade sources, which include multipass absorption spectrography, cavity ring down spectrograms (CRDS), ICOS, and quartz-enhanced photoacoustic spectrogram (QEPAS).
Abstract: Quantum cascade (QC) lasers are virtually ideal mid-infrared sources for trace gas monitoring. They can be fabricated to operate at any of a very wide range of wavelengths from ∼ 3 μm to ∼ 24 μm. Seizing the opportunity presented by mid-infrared QC lasers, several groups world-wide are actively applying them to trace gas sensing. Real world applications include environmental monitoring, industrial process control and biomedical diagnostics. In our laboratory we have explored the use of several methods for carrying out absorption spectroscopy with these sources, which include multipass absorption spectroscopy, cavity ring down spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS), and quartz-enhanced photoacoustic spectroscopy (QEPAS).
346 citations
TL;DR: In this paper, the dispersion equations were derived from quasi-phase-matched nonlinear interactions with these two crystal compositions in the near and mid-infrared, and the results show a good agreement with previously published frequency conversion experiments.
Abstract: We present wavelength- and temperature-dependent refractive index equations for 5% MgO-doped congruent PPLN and for 1% MgO-doped stoichiometric PPLN crystals valid for a wide spectral and temperature range. The dispersion equations were derived from quasi-phase-matched nonlinear interactions with these two crystal compositions in the near and mid-infrared. The results show a good agreement with previously published frequency conversion experiments.
304 citations
TL;DR: In this article, the authors investigate potential sources of measurement errors and compare them with the scientific requirements for a direct detection CO2 system operating at 1.6μm, 0.4% for CO2 at 2.1μm and 0.3% for CH4 at 3.9μm.
Abstract: CO2, CH4, and N2O are recognised as the most important greenhouse gases, the concentrations of which increase rapidly through human activities. Space-borne integrated path differential absorption lidar allows global observations at day and night over land and water surfaces in all climates. In this study we investigate potential sources of measurement errors and compare them with the scientific requirements. Our simulations reveal that moderate-size instruments in terms of telescope aperture (0.5–1.5 m) and laser average power (0.4–4 W) potentially have a low random error of the greenhouse gas column which is 0.2% for CO2 and 0.4% for CH4 for soundings at 1.6 μm, 0.4% for CO2 at 2.1 μm, 0.6% for CH4 at 2.3 μm, and 0.3% for N2O at 3.9 μm. Coherent detection instruments are generally limited by speckle noise, while direct detection instruments suffer from high detector noise using current technology. The wavelength selection in the vicinity of the absorption line is critical as it controls the height region of highest sensitivity, the temperature cross-sensitivity, and the demands on frequency stability. For CO2, an error budget of 0.08% is derived from our analysis of the sources of systematic errors. Among them, the frequency stability of ± 0.3 MHz for the laser transmitter and spectral purity of 99.9% in conjunction with a narrow-band spectral filter of 1 GHz (FWHM) are identified to be challenging instrument requirements for a direct detection CO2 system operating at 1.6 μm.
303 citations
TL;DR: Quasi-three-level solid state solid-state lasers using trivalent rare earth ions are efficient sources in the near and mid-infrared spectral regions as mentioned in this paper, and their unique properties arise from special energy level structures in different host materials and highly efficient laser operation became possible with the availability of highly efficient high-brightness pump sources like laser diodes.
Abstract: Quasi-three-level solid-state lasers using trivalent rare earth ions are efficient sources in the near- and mid-infrared spectral regions. Their unique properties arise from special energy level structures in different host materials and highly efficient laser operation became possible with the availability of highly efficient high-brightness pump sources like laser diodes. This work will give an overview of quasi-three-level solid-state lasers emitting in the wavelength range 1–5 μm. Recent research and advances in spectroscopic and laser results will be presented. In comparison to four-level lasers such as e.g. Nd3+ lasers at 1.06 μm, quasi-three-level lasers show a much stronger influence of temperature on laser performance, mainly due to the thermally induced changes in the spectroscopic properties of the laser medium. Nevertheless, highly efficient lasers can be realized by direct diode pumping with high spatial and spectral brightness laser diodes. The population dynamics in the manifolds also play an important role and ion concentrations are used to minimize or maximize energy-transfer effects. These general topics will be addressed in Sect. 1, in which basic aspects of quasi-three-level lasers and their description are discussed. Section 2 deals with the general energy-level structure of trivalent rare earths in hosts, from which the most interesting ions and their transitions can be derived. These ions, Nd3+, Yb3+, Er3+, Tm3+ and Ho3+, are investigated in detail in Sect. 3 in order of their emission wavelengths, focusing on their spectral properties and laser results in different laser architectures and host media. In Sect. 4 the work is finally summarized.
276 citations
TL;DR: In this article, a detailed analysis of the most relevant sources of phase noise in an atomic interferometer is carried out, both theoretically and experimentally, and a simple and robust technique of vibration compensation is described, which is based on correcting the inter-ferometer signal by using the ac acceleration signal measured by a low-noise seismometer.
Abstract: A detailed analysis of the most relevant sources of phase noise in an atomic interferometer is carried out, both theoretically and experimentally. Even a short interrogation time of 100 ms allows our cold atom gravimeter to reach an excellent short term sensitivity to acceleration of 1.4×10-8g at 1 s. This result relies on the combination of a low phase noise laser system, efficient detection scheme and good shielding from vibrations. In particular, we describe a simple and robust technique of vibration compensation, which is based on correcting the interferometer signal by using the ac acceleration signal measured by a low noise seismometer.
245 citations
TL;DR: In this article, the authors reported a single mode tuning range of 155 cm-1 (∼ 8% of the center wavelength) with a maximum power of 11.1mW and 182 cm −1 ( ∼ 15% of center wavelength).
Abstract: Recent progress in the development of room temperature, continuous wave, widely tunable, mode-hop-free mid-infrared external cavity quantum cascade laser (EC-QCL) spectroscopic sources is reported. A single mode tuning range of 155 cm-1 (∼ 8% of the center wavelength) with a maximum power of 11.1 mW and 182 cm-1 (∼ 15% of the center wavelength) with a maximum power of 50 mW was obtained for 5.3 and 8.4 μm EC-QCLs respectively. This technology is particularly suitable for high resolution spectroscopic applications, multi species trace-gas detection and spectroscopic measurements of broadband absorbers. Several examples of spectroscopic measurements performed using EC-QCL based spectrometers are demonstrated.
214 citations
TL;DR: In this paper, the authors focus on the use of supercontinuum sources to construct novel instrumentation for chemical sensing and provide an outlook and a summary of where and how the field may develop over coming years.
Abstract: The advent of compact, high brightness supercontinuum radiation sources employing solid core photonic crystal fibres is beginning to make an impact across the field of applied spectroscopy research In this article we focus on the use of supercontinuum sources to construct novel instrumentation for chemical sensing A brief overview is given on the mechanisms of supercontinuum generation in solid core photonic crystal fibres, and then we review recent, and present new, results from our own research We present examples on gas phase sensing applications, permitting wide bandwidth molecular spectra to be gathered at ultrahigh speed Furthermore we demonstrate the design and construction of a wide bandwidth microscope for wavelength flexible hyperspectral confocal imaging We conclude with an outlook and a summary of where and how we think the field may develop over coming years
208 citations
TL;DR: In this article, the success of laser-based trace gas sensing techniques crucially depends on the availability and performance of tunable laser sources combined with appropriate detection schemes, which are based on sensitive absorption measurements and comprise direct absorption in multi-pass cells as well as photoacoustic and cavity ringdown techniques.
Abstract: The success of laser-based trace gas sensing techniques crucially depends on the availability and performance of tunable laser sources combined with appropriate detection schemes. Besides near-infrared diode lasers, continuously tunable midinfrared quantum cascade lasers and nonlinear optical laser sources are preferentially employed today. Detection schemes are based on sensitive absorption measurements and comprise direct absorption in multi-pass cells as well as photoacoustic and cavity ringdown techniques in various configurations. We illustrate the performance of several systems implemented in our laboratory. These include time-resolved multicomponent traffic emission measurements with a mobile CO2-laser photoacoustic system, a diode-laser based cavity ringdown device for measurements of impurities in industrial process control, isotope ratio measurements with a difference frequency (DFG) laser source combined with balanced path length detection, detection of methylamines for breath analysis with both a near-IR diode laser and a DFG source, and finally, acetone measurements with a heatable multipass cell intended for vapor phase studies on doping agents in urine samples.
188 citations
TL;DR: The cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) as discussed by the authors was proposed to provide ultra-sensitive absorption measurements simultaneously over a wide spectral range and with acquisition times shorter than a second.
Abstract: In less than fifteen years since the development of the first optical frequency comb (OFC), the device has revolutionized numerous research fields. In spectroscopy, the unique properties of the OFC spectrum enable simultaneous acquisition of broadband spectra while also providing high spectral resolution. Due to the regular structure of its spectrum, an OFC can be efficiently coupled to an optical enhancement cavity, resulting in vastly increased effective interaction length with the sample and absorption sensitivities as low as 1.3×10−11 cm−1 Hz−1/2 per spectral element. This technique, called cavity-enhanced direct frequency comb spectroscopy (CE-DFCS), provides ultra-sensitive absorption measurements simultaneously over a wide spectral range and with acquisition times shorter than a second.
179 citations
TL;DR: In this paper, an extension of spectral precision distance microscopy/spectral position determination microscopy (SPDM) was presented, exploiting the novel spectral signature offered by reversible photobleaching of fluorescent proteins.
Abstract: Far-field fluorescence techniques based on the precise determination of object positions have the potential to circumvent the optical resolution limit of direct imaging given by diffraction theory. In order to use localization to obtain structural information far below the diffraction limit, the ‘point-like’ components of the structure have to be detected independently, even if their distance is lower than the conventional optical resolution limit. This goal can be achieved by exploiting various photo-physical properties of the fluorescence labeling (‘spectral signatures’). In first experiments, spectral precision distance microscopy/spectral position determination microscopy (SPDM) was limited to a relatively small number of components to be resolved within the observation volume. Recently, the introduction of photoconvertable molecules has dramatically increased the number of components which can be independently localized. Here, we present an extension of the SPDM concept, exploiting the novel spectral signature offered by reversible photobleaching of fluorescent proteins. In combination with spatially modulated illumination (SMI) microscopy, at the present stage, we have achieved an estimated effective optical resolution of approximately 20 nm in the lateral and 50 nm in the axial direction, or about 1/25th–1/10th of the exciting wavelength.
TL;DR: In this paper, simultaneous PIV and OH-PLIF measurements were conducted in an enclosed gas turbine model combustor for investigating the influence of turbulence on local flame characteristics, revealing the formation of reaction zones at regions where hot burned gas from the recirculation zones mixes with the fresh fuel/air mixture at the nozzle exit.
Abstract: In highly turbulent environments, combustion is strongly influenced by the effects of turbulence chemistry interactions. Simultaneous measurement of the flow field and flame is, therefore, obligatory for a clear understanding of the underlying mechanisms. In the current studies simultaneous PIV and OH-PLIF measurements were conducted in an enclosed gas turbine model combustor for investigating the influence of turbulence on local flame characteristics. The swirling CH4/air flame that was investigated had a thermal power of 10.3 kW with an overall equivalence ratio of ϕ=0.75 and exhibited strong thermoacoustic oscillations at a frequency of approximately 295 Hz. The measurements reveal the formation of reaction zones at regions where hot burned gas from the recirculation zones mixes with the fresh fuel/air mixture at the nozzle exit. However, this does not seem to be a steady phenomenon as there always exist regions where the mixture has failed to ignite, possibly due to the high local strain rates present, resulting in small residence time available for a successful kinetic runaway to take place. The time averaged PIV images showed flow fields typical of enclosed swirl burners, namely a big inner recirculation zone and a small outer recirculation zone. However, the instantaneous images show the existence of small vortical structures close to the shear layers. These small vortical structures are seen playing a vital role in the formation and destruction of reaction zone structures. One does not see a smooth laminar flame front in the instantaneous OH-PLIF images, instead isolated regions of ignition and extinction highlighting the strong interplay between turbulence and chemical reactions.
TL;DR: In this article, a new attosecond FROG algorithm optimized for the characterization of sub-100 as pulses from streaked electron spectra was proposed, and the effects of the approximations that must be made in order to apply the generalized projections scheme were investigated.
Abstract: We describe a new attosecond FROG algorithm optimized for the characterization of sub-100 as pulses from streaked electron spectra. We make improvements upon the treatment of the attosecond streaking spectrogram, and show that these are necessary in order to accurately characterize shorter pulses with ever larger bandwidths. We investigate the effects of the approximations that must be made in order to apply the generalized projections scheme.
TL;DR: In this article, three types of trace gas detection systems based on CO2 laser and continuous wave (cw) optical parametric oscillator (OPO) in combination with photoacoustic spectroscopy and cw quantum cascade laser (QCL).
Abstract: Infrared gas phase spectroscopy is becoming very common in many life science applications. Here we present three types of trace gas detection systems based on CO2 laser and continuous wave (cw) optical parametric oscillator (OPO) in combination with photoacoustic spectroscopy and cw quantum cascade laser (QCL) in combination with wavelength modulation spectroscopy. Examples are included to illustrate the suitability of CO2 laser system to monitor in real time ethylene emission from various dynamic processes in plants and microorganisms as well as from car exhausts. The versatility of an OPO-based detector is demonstrated by simultaneous detection of 13C-methane and 12C-methane (at 3240 nm) at similar detection limits of 0.1 parts per billion by volume. Recent progress on a QCL-based spectrometer using a continuous wave QCL (output power 25 mW, tuning range of 1891–1908 cm-1) is presented and a comparison is made to a standard chemiluminescence instrument for analysis of NO in exhaled breath.
TL;DR: In this article, it is shown that using the Drude critical points model rather than the widely used Drude-Lorentz model can increase the accuracy of gold and silver permittivity description.
Abstract: We show that it is possible to increase the accuracy of gold and silver permittivity description by using the Drude–critical points model rather than the widely used Drude–Lorentz model. We also show the effect of this improvement on the extinction efficiency and near-field intensity precision.
TL;DR: In this article, an experimental setup of an integrated path differential absorption lidar (IPDA) is presented, operating at 1.57 μm using direct detection, an injection seeded KTP-OPO system pumped by a Nd:YAG laser serves as the transmitter, and the seed laser is actively stabilized by means of a CO2 reference cell.
Abstract: Active remote sensing is a promising technique to close the gaps that exist in global measurement of atmospheric carbon dioxide sources, sinks and fluxes. Several approaches are currently under development. Here, an experimental setup of an integrated path differential absorption lidar (IPDA) is presented, operating at 1.57 μm using direct detection. An injection seeded KTP-OPO system pumped by a Nd:YAG laser serves as the transmitter. The seed laser is actively stabilized by means of a CO2 reference cell. The line-narrowed OPO radiation yields a high spectral purity, which is measured by means of a long path absorption cell. First measurements of diurnal variations of the atmospheric CO2 mixing ratio using a topographic target were performed and show good agreement compared to simultaneously taken measurements of an in situ device. A further result is that the required power reference measurement of each laser pulse in combination with the spatial beam quality is a critical point of this method. The system described can serve as a testbed for further investigations of special features of the IPDA technique.
TL;DR: As a result of a combination of an external cavity and modulation techniques, noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is one of the most sensitive absorpt...
Abstract: As a result of a combination of an external cavity and modulation techniques, noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is one of the most sensitive absorpt ...
TL;DR: In this paper, the authors discuss the current status and new frontiers of research on high-sensitivity and high-precision laser spectroscopy for isotope ratio analyses in molecules of environmental importance.
Abstract: Small molecules exhibit characteristic ro-vibrational transitions in the near- and mid-infrared spectral regions, which are strongly influenced by isotopic substitution. This gift of nature has made it possible to use laser spectroscopy for the accurate analysis of the isotopic composition of gaseous samples. Nowadays, laser spectroscopy is clearly recognized as a valid alternative to isotope ratio mass spectrometry. Laser-based instruments are leaving the research laboratory stage and are being used by a growing number of isotope researchers for significant advances in their own field of research. In this review article, we discuss the current status and new frontiers of research on high-sensitivity and high-precision laser spectroscopy for isotope ratio analyses. Although many of our comments will be generally applicable to laser isotope ratio analyses in molecules of environmental importance, this paper concerns itself primarily with water and carbon dioxide, two molecules that were studied extensively in our respective laboratories. A complete coverage of the field is practically not feasible in the space constraints of this issue, and in any case doomed to fail, considering the large body of work that has appeared ever since the review by Kerstel in 2004 (Handbook of Stable Isotope Analytical Techniques, Chapt. 34, pp. 759–787).
TL;DR: In this paper, the plasmon hybridization of the individual nanorod dimers was used to investigate the plasmons of the nanorhod dimers in axial and parallel orientations.
Abstract: Using the plasmon hybridization method we investigate the plasmon modes of nanorod dimers in axial and parallel orientations. We show that the plasmon modes of the system can be viewed as bonding and anti-bonding modes resulting from the hybridization of the plasmon modes of the individual nanorods. The dimer plasmon modes are found to depend sensitively on separation between the nanorods and on their relative spatial orientation. The calculated optical properties agree quantitatively with results from the numerical finite-difference time-domain method. The electric field enhancements are found to depend strongly on aspect ratio defined as the ratio of the major and minor radii, and on the relative orientation of the nanorods. For a nanorod dimer of fixed overall length, the maximum field enhancements are lower than those induced in a solid sphere dimer.
TL;DR: In this article, a tunable diode-laser sensor based on CO2 absorption near 2.7 μm was developed for high-resolution absorption measurements of CO2 concentration and temperature.
Abstract: A new tunable diode-laser sensor based on CO2 absorption near 2.7 μm is developed for high-resolution absorption measurements of CO2 concentration and temperature. The sensor probes the R(28) and P(70) transitions of the ν1+ν3 combination band of CO2 that has stronger absorption line-strengths than the bands near 1.5 μm and 2.0 μm used previously to sense CO2 in combustion gases. The increased absorption strength of transitions in this new wavelength range provides greatly enhanced sensitivity and the potential for accurate measurements in combustion gases with short optical path lengths. Simulated high-temperature spectra are surveyed to find candidate CO2 transitions isolated from water vapor interference. Measurements of line-strength, line position, and collisional broadening parameters are carried out for candidate CO2 transitions in a heated static cell as a function of temperature and compared to literature values. The accuracy of a fixed-wavelength CO2 absorption sensor is determined via measurement of known temperature and CO2 mole fraction in a static cell and shock-tube. Absorption measurements of CO2 are then made in a laboratory flat-flame burner and in ignition experiments of shock-heated n-heptane/O2/argon mixtures to illustrate the potential of this sensor for combustion and reacting-flow applications.
TL;DR: Far-field subdiffraction-resolution fluorescence imaging based on photoswitching of individual standard fluorophores in air-saturated solution based on light-induced switching of organic fluorophore into long-lived metastable dark states and spontaneous repopulation of the fluorescent state is introduced.
Abstract: We introduce far-field subdiffraction-resolution fluorescence imaging based on photoswitching of individual standard fluorophores in air-saturated solution. Here, photoswitching microscopy relies on the light-induced switching of organic fluorophores (ATTO 655 and ATTO 680) into long-lived metastable dark states and spontaneous repopulation of the fluorescent state. In the presence of low concentrations (2–10 mM) of reducing, thiol-containing compounds such as s-mercaptoethylamine or glutathione, the density of fluorescent molecules can be adjusted to enable multiple localizations of individual fluorophores with an experimental accuracy of ∼20 nm. The method requires wide-field illumination with only a single laser beam for readout and photoswitching and provides superresolution fluorescence images of intracellular structures under live cell compatible conditions.
TL;DR: In this paper, the authors present a detailed theoretical investigation of how the particle size influences the relationship between LII signal and soot volume fraction for different experimental conditions, and they are able to understand how experimental conditions should be chosen in order to minimize the errors introduced when assuming a linear dependence between the signal and volume fraction.
Abstract: “The laser-induced incandescence (LII) signal is proportional to soot volume fraction” is an often used statement in scientific papers, and it has – within experimental uncertainties – been validated in comparisons with other diagnostic techniques in several investigations. In 1984 it was shown theoretically in a paper by Melton that there is a deviation from this statement in that the presence of larger particles leads to some overestimation of soot volume fractions. In the present paper we present a detailed theoretical investigation of how the soot particle size influences the relationship between LII signal and soot volume fraction for different experimental conditions. Several parameters have been varied; detection wavelength, time and delay of detection gate, ambient gas temperature and pressure, laser fluence, level of aggregation and spatial profile. Based on these results we are able, firstly, to understand how experimental conditions should be chosen in order to minimize the errors introduced when assuming a linear dependence between the signal and volume fraction and secondly, to obtain knowledge on how to use this information to obtain more accurate soot volume fraction data if the particle size is known.
TL;DR: In this paper, a near-room-temperature pulsed quantum cascade laser and a spectral ratio method based upon dual multiple pass absorption cells were used to measure stable isotopic ratios of carbon dioxide.
Abstract: We present a new approach to the measurement of stable isotopic ratios of carbon dioxide using a near-room-temperature pulsed quantum cascade laser and a spectral ratio method based upon dual multiple pass absorption cells. The spectral ratio method improves precision and accuracy by reducing sensitivity to variations in the laser tuning rate, power and line width. The laser is scanned across three spectral lines (near 2310 cm-1) quantifying three CO2 isotopologues: 12C16O2, 13C16O2 and 12C16O18O. Isotopic ratios are determined simultaneously with a precision of 0.2δ for each ratio with a one-second measurement. Signal averaging for 400 s improves the precision to better than 0.03δ for both isotopic ratios (13
R and 18
R). Long-term accuracy of 0.2 to 0.3δ is demonstrated with replicate measurements of the same sample over a one-month period. The fast time response of this instrument is suitable for eddy flux measurements.
TL;DR: The sensitivity of several OA-ICOS instruments with differing design parameters are compared, how comparisons are hindered by differing definitions of instrument performance metrics are shown, and a common metric of MDAmeas is suggested, the fractional absorption equivalent to 1σ uncertainty in an actual measurement, normalized to 1 s integration.
Abstract: Off-axis integrated cavity output spectroscopy (OA-ICOS) has generated much interest because it potentially allows highly sensitive field measurements with robust optical alignment. We discuss here design choices involved in design of an OA-ICOS instrument and how these choices impact instrument sensitivity, using as our example the design of the Harvard ICOS isotope instrument, which demonstrates the highest reported sensitivity for mid-IR OA-ICOS (2.4×10-11 cm-1Hz-1/2 at 6.7 μm, obtained during measurements of water vapor isotopologues H2O, HDO, and H2
18O in the laboratory and onboard NASA’s WB-57 high-altitude research aircraft). We compare the sensitivity of several OA-ICOS instruments with differing design parameters, show how comparisons are hindered by differing definitions of instrument performance metrics, and suggest a common metric of MDAmeas, the fractional absorption equivalent to 1σ uncertainty in an actual measurement, normalized to 1 s integration. We also note that despite an emphasis on sensitivity in the literature, in the Harvard ICOS isotope instrument and likely also similar instruments, systematic errors associated with fitting of the baseline laser power are of equal importance to total measurement uncertainty.
TL;DR: In this paper, a new approach for simultaneous 2D velocity and temperature measurements using phosphoric particles is presented, where the temperature sensitive particles respond to temperature changes in the flow while acting as tracers for velocity mapping.
Abstract: In this paper a new approach for simultaneous 2D velocity and temperature measurements using phosphoric particles is presented. The phosphoric particles respond to the temperature changes in the flow while acting as tracers for velocity mapping. The temperature sensitive particles were seeded into a heated flow and were excited by a pulsed UV laser. The subsequent red shifted emission was detected and analyzed to infer temperature using calibration procedures for lifetime and emission spectra against temperature. The diameter of the temperature sensitive particles, usually in the range of 1-10 mu m, makes them useful for velocity measurements using particle image velocimetry (PIV). As such, simultaneous measurement of temperature and flow velocity of a gaseous flow were performed and presented. (Less)
TL;DR: In this paper, the authors developed a compact instrument for sensitive, rapid and continuous measurement of trace gases in air, with results presented here for methane (CH4), nitric oxide (NO), nitrous oxide (N2O) and ammonia (NH3).
Abstract: We have developed a compact instrument for sensitive, rapid and continuous measurement of trace gases in air, with results presented here for methane (CH4), nitric oxide (NO), nitrous oxide (N2O) and ammonia (NH3). This instrument takes advantage of recent technology in quantum cascade (QC) lasers and infrared detectors, which allows high sensitivity without cryogenic liquids, e.g., 0.2 ppb (0.2×10-9) of NH3 in air in 1 s. One may substitute a QC laser operating at a different wavelength to measure other gases. The instrument operates continuously, requiring little operator attention, and web-based remote access is provided for instrument control, calibration and data retrieval. The instrument design includes a thermoelectrically (TE) cooled pulsed distributed feedback (DFB) QC laser, a low volume (0.5 l) multipass cell offering 76 m absorption path length and a TE cooled detector. Integrated software for laser control and data analysis using direct absorption provides quantitative trace gas measurements without calibration gases. The instrument may be applied to field measurements of gases of environmental concern.
TL;DR: In this paper, a single-laser single-camera imaging technique was demonstrated for in-cylinder temperature distribution measurements in a direct-injection internal combustion engine with homogeneous charge and yielded temperature images with a single shot precision of approximately ± 6%.
Abstract: A single-laser single-camera imaging technique was demonstrated for in-cylinder temperature distribution measurements in a direct-injection internal combustion engine. The single excitation wavelength two-color detection technique is based on toluene laser-induced fluorescence (LIF). Toluene-LIF emission spectra show a red-shift with increasing temperature. Temperature can thus be determined from the ratio of the signal measured in two separate wavelength ranges independent of the local tracer concentration, laser pulse energy, and the intensity distribution. An image doubling and filtering system is used for the simultaneous imaging of two wavelength ranges of toluene LIF onto the chip of a single camera upon excitation at 248 nm. The measurements were performed in a spark-ignition engine with homogeneous charge and yielded temperature images with a single-shot precision of approximately ± 6%.
TL;DR: Single mode laser action in a diode-pumped gain-guided, index- antiguided Nd3+-doped phosphate glass fiber having a 200-μm-diameter core is demonstrated, indicating robust lowest order mode oscillation.
Abstract: Single mode laser action in a diode-pumped gain-guided, index- antiguided Nd3+-doped phosphate glass fiber having a 200-μm-diameter core is demonstrated. Near-Gaussian beam quality was maintained, even when pumped up to four times the threshold pump power, indicating robust lowest order mode oscillation. Subtle differences associated with the effectiveness of diode pumping gain-guided, index-antiguided fibers are discussed.
TL;DR: In this paper, a quantum cascade laser based absorption spectrometer (QCLAS) was proposed for in situ, continuous and high precision isotope ratio measurements of atmospheric CO2.
Abstract: The present paper describes a compact and cryogen-free, quantum cascade laser based absorption spectrometer (QCLAS) designed for in situ, continuous and high precision isotope ratio measurements of atmospheric CO2. The mobile instrument incorporates several new features including a novel astigmatic multi-pass cell assembly, a quasi-room temperature quantum cascade laser, thermoelectrically cooled detectors as well as a new retrieval approach. The combination of these features now makes it possible to measure isotope ratios of ambient CO2 with a precision of 0.03 and 0.05‰ for δ13C and δ18O, respectively, using a 100 s integration time. A robust and optimized calibration procedure was developed to bring the retrieved isotope ratios on an absolute scale. This assures an accuracy better than 0.1‰ under laboratory conditions. The instrument performance was also assessed in a field campaign in which the spectrometer operated autonomously and provided mixing ratio values for the main three CO2 isotopologues at one second time resolution. An accuracy of 0.2‰ was routinely obtained for both isotope ratios during the entire period. The results were in excellent agreement with the standard laboratory-based isotope ratio mass spectrometer measurements made on field-collected flask samples. A few illustrative examples are used to depict the potential of this optical method in atmosphere–biosphere research.
TL;DR: In this article, double-perovskite-type phosphors Ba2-zSrzCa080Eu010Li010Mo1-yWyO6 were synthesized by solid state reactions to understand photoluminescence properties and the energy transfer process in the phosphors well.
Abstract: Series double-perovskite-type phosphors Ba2-zSrzCa080Eu010Li010Mo1-yWyO6 were synthesized by solid state reactions To understand photoluminescence properties and the energy transfer process in the phosphors well, Raman spectra were collected and the first-principle calculations on the band structures were conducted for some selected samples The series phosphors present relatively effective excitation bands in near UV range (370–400 nm), which originates from the charge transfer state of MoO6, and perform orange-reddish luminescence (595 nm) arising from the 5D0→7F1 transition of Eu3+ In Mo-rich phosphors, the luminescence of Eu3+ is weak, because the energy transferred among MoO6 groups along (MoCa)O6 framework is concentration quenched and less energy transfers to Eu3+ WO6 groups introduced into the lattice act as energy obstacles to block the energy transfer among MoO6 groups, which results in that more energy is transferred from MoO6 to Eu3+ Sr-rich phosphors in the series Ba2-zSrzCa080Eu010Li010Mo010W090O6 have better luminescence than Ba-rich phosphors Possibly because in the former, the links among MO6 (M = Mo, W and Ca) octahedra are distorted and the possibility of the energy transfer among MoO6 groups is reduced, which leads to more energy trapped by Eu3+ The phosphors may be suitable for applications in white light ultraviolet light-emitting-diodes