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Temperature evolution in a pulsed CO<sub>2</sub>-N<sub>2</sub> glow discharge measured using quantum cascade laser absorption spectroscopy
摘要： This work uses in situ narrowband Quantum Cascade Laser (QCL) absorption spectroscopy to study the effect of N2 on the time evolution of gas temperature, rotational temperature and the vibrational temperatures of CO2 and CO in a pulsed glow discharge. Three colinear QCLs are used to scan three regions of about 1 cm?1 between 2179.20 and 2253.51 cm?1, including (v1, vl2 2 , v3 + 1) → (v1, vl2 2 , v3) CO2 transitions up to the asymmetric stretch level v3 = 6, as well as (vCO) → (vCO +1) CO transitions up to vCO = 1. A fitting routine is used to extract temperatures from the measured absorption spectra. The time resolved measurements are performed in CO2, admixed with up to 90% N2, with the plasma operated with a 5-10 ms on-off cycle, a discharge current of 50 mA and a pressure of around 6.7 mbar. The time evolution of the gas temperature has been measured and agrees well with the time evolution of the rotational temperature. The asymmetric stretch vibrational temperature T3 of CO2 reaches a maximum of 1060 K at 0.7 ms for pure CO2, while T3 goes up to 2250 K for a N2 content of 90% and stays constant until the plasma is switched off. Both T3 and the vibrational temperature of CO TCO show a clear non-equilibrium with respect to the rotational temperature Trot. Both do not equilibrate with the rotational temperature Trot between consecutive plasma cycles for a N2 content above 70%, although T3 and TCO always equilibrate with each other in the afterglow. The symmetric stretch and bending mode temperature T12 is elevated more with respect to the rotational temperature for increasing N2 content, while the maximum of the rotational temperature decreases for increasing N2 admixtures, which might be attributed to the energy stored in the vibrational modes of N2, CO2 and CO. Additionally, an indication of an increase in the total pressure during the plasma on-time due to heating and a subsequent decrease in the afterglow due to cooling was found for a pure CO2 plasma.
关键词： glow discharge,carbon dioxide plasma,vibrational temperature,gas temperature,quantum cascade laser
更新于2025-09-23 15:21:01
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Spectroscopic diagnostics of continuous and transient microplasma formed in a millimeter wave photonic crystal
摘要： We present spectroscopic measurements of a microplasma formed within a photonic crystal (PhC) at argon gas pressures up to 750 Torr. Continuous and pulsed millimeter waves (MMW) generate plasma at a vacancy defect within the crystal. Rotational gas temperatures of 300-1050 K and electron densities of 0.5-2×1020 m-3 are obtained from the CH rotational emission spectrum and from Stark broadening of the ???? atomic transition. Electron density is found to be weakly dependent on MMW power because the plasma expands within the defect volume at higher power. Pulsed MMWs slightly increase the peak electron density compared to continuous waves with the same peak power. With MMW pulses, a rapid decrease of wave transmission through the PhC is observed at the beginning of plasma formation. During plasma ignition two distinct plasmas are formed, one on the conducting wall of the PhC near the optical access port and a second within the center of the PhC defect. With longer periods between pulses, the weak wall plasma is observed to form before the principal plasma in the defect, which aids in initiating the main plasma.
关键词： photonic crystal,millimeter waves,electron density,spectroscopic diagnostics,microplasma,gas temperature
更新于2025-09-23 15:19:57
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Luminescence interference to two-colour toluene laser-induced fluorescence thermometry in a particle-laden flow
摘要： We present the use of two-colour toluene planar laser-induced fluorescence (LIF) to obtain spatially resolved measurements of the gas temperature ( T g ) in a particle-laden turbulent flow under sufficiently dense particle loading that the interference from laser interactions with the particles is significant. The effect of the ratio of volumetric flow rates of the particle phase to the gas phase ( ?? ) on the accuracy and precision of two-colour toluene LIF thermometry was systematically investigated for three particle materials, alumina, zinc activated zinc oxide (ZnO:Zn) and polymethyl methacrylate (PMMA), each of which has differing interactions with the excitation laser. The PMMA particles were spherical and mono-disperse with diameters of 6 to 40 μm , while the alumina and ZnO:Zn particles had diameters in the range 1–40? μm and 2–200?μm, respectively. The results show that the accuracy of the gas temperature measurement is insensitive to particle size for the PMMA particles, but dependent on the instantaneous particle loading. Importantly, reliable measurements can be performed in the dense two-way coupling regime, with the measurement being accurate to within 5?°C for ???<?2.5 × 10?4 for the PMMA particles and for ?? < 7.6 × 10?4 for the alumina and ZnO:Zn particles.
关键词： volumetric flow rates,gas temperature measurement,particle-laden flow,two-colour toluene LIF,particle materials
更新于2025-09-23 15:19:57
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Study on the maximum electric power supplied to copper bromide vapor lasers
摘要： Copper and copper-compound vapor lasers are most powerful in the visible spectrum with output power over 100 W. They offer unique properties including a laser beam with high coherence and convergence and high average output powers with relatively small dimensions. Recently, these lasers, and in particular the copper bromide (CuBr) laser, have been widely used as radiation sources and vapor brightness amplifiers in a new type of laser active optical systems, designed for the visual monitoring and control of fast processes shielded by intense background lighting. However, new problems arise with the development of such optical systems, related to the laser technology and the optimization of their operating parameters. Important operating characteristics of copper lasers include the input electric power and the gas temperature of the discharge. The upper limit of the laser power that can be supplied to the gas discharge is studied herein by considering the permissible thermal population thresholds of the lower level of the λ = 510.6 nm laser line. The application of enhanced analytical models based on a steady-state heat conduction equation and computer simulations enables the development of a methodology to determine the maximum possible electric power that can be supplied to the gas discharge, taking into account its radial distribution across the tube cross-section. This methodology is then applied to the case of an actual small-bore CuBr laser used as a brightness amplifier.
关键词： Copper vapor laser,Gas temperature,Copper bromide (CuBr) laser,Computer simulation,Laser active optical system,Heat conduction
更新于2025-09-19 17:13:59
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Simultaneous measurements of fuel concentration and temperature in gas jets by laser induced breakdown spectroscopy
摘要： Laser induced breakdown spectroscopy (LIBS) enables quantitative measurements of the equivalence ratio in flames, spray and gas jets. Although there are always considerable temperature differences between the calibrations and the LIBS measurements in flames and fuel jets, the temperature effects on LIBS were rarely mentioned and not corrected in the previous LIBS measurements. In this study, a novel method to simultaneously measure the equivalence ratio and the gas temperature by LIBS in a single laser shot is proposed. This method can correct the temperature effects based on the linear correlation between the peak intensity ratio (PIR) of atomic lines and the gas temperature. The PIR of H656/N746 and the full width at half maximum (FWHM) of H656 are employed to establish calibration curves with the equivalence ratio and the gas temperature, respectively, and both of calibrations show high coefficients of determination (R2). Then, the measurement accuracy and precision of the proposed method are discussed in detail. The total uncertainties in measurements of equivalence ratio and gas temperature are estimated by 5.6% and 5.8%, respectively. Finally, the simultaneous measurements of equivalence ratios and gas temperatures in methane jets at different positions and at different injection pressures are conducted. The comparison of equivalence ratios before and after correction of the temperature effects indicates that the accuracy of the fuel concentration measurements by LIBS would be remarkably degraded if the temperature variations were neglected.
关键词： Measurement uncertainties,Laser-induced breakdown spectroscopy (LIBS),Equivalence ratio,Gas temperature,Full width at the half maximum (FWHM)
更新于2025-09-12 10:27:22
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Experimental investigations of temperature distribution in non-premixed flames with different gas compositions by large lateral shearing interferometry
摘要： The gas temperature fields of axisymmetric co-annular laminar diffusion ethylene flame jets in air and oxygen-enriched atmospheres were measured and visualized using large lateral shearing interferometry. The relationship between the refractive index and the temperature is obtained using a state equation and the Gladstone–Dale relation. Considering the unknown local gas composition can be a potential source of error, local gas compositions provided by corresponding numerical simulations were employed. The spatial resolution of the temperature fields was 0.1 mm/pixel. The temperature results obtained using hot air assumption and simulated local composition indicate that deviations of up to 400 K occur at the bottom part on the centerline, whereas at larger axial or radial positions, the deviations could be less than 50 K. The results are also validated by comparison with CARS. In addition, compared with flames under air atmosphere, significant deviations occurred in a greater region of oxygen-enriched flames.
关键词： gas temperature,diffusion flame,lateral shearing interferometry,oxygen-enriched
更新于2025-09-09 09:28:46