Bulletin of the American Physical Society
75th Annual Gaseous Electronics Conference
Volume 67, Number 9
Monday–Friday, October 3–7, 2022;
Sendai International Center, Sendai, Japan
The session times in this program are intended for Japan Standard Time zone in Tokyo, Japan (GMT+9)
Session DF2: Laser Diagnostics II |
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Chair: Uwe Czarnetzki, Ruhr University Bochum, Germany Room: Sendai International Center Tachibana |
Friday, October 7, 2022 10:00AM - 10:15AM |
DF2.00001: Low temperature plasma diagnostics using Brewster angle-cavity ringdown spectroscopy Rongrong Wu, Chuji Wang We report on the development of a Brewster angle-cavity ringdown spectroscopy (BA-CRDS) system for low temperature plasma diagnostics. The system can measure gaseous species in solutions, with a detection limit of 1.2×10-5 (the minimum detectable absorbance), which is equivalent to a detection limit of 6 ppb for measuring OH radicals in water at 308 nm. In the initial test, we measured the absorption cross section of HgBr2 in aqueous phase to be (1.8±0.1)×10-18 cm2, consistent with the reported data in gas phase (1.4 ×10-18 cm2). We also used the system to characterize the temporal behavior of a helium plasma jet treated distilled water at different plasma power and gas flow rates. Some reaction pathways leading to the removal of HgBr2 by OH radical and formation of H2O2 in the solutions are proposed. Results demonstrate that the BA-CRDS system is a powerful tool for quantification of reactive plasma species in multiphase systems or other complex settings, with high detection sensitivity. |
Friday, October 7, 2022 10:15AM - 10:30AM |
DF2.00002: Optical trapping and manipulation of single particles in dusty plasma Pubuduni AK Ekanayaka MEW, Chuji Wang, Saikat Chakraborty Thakur, Edward Thomas Current methods of laser manipulation in dusty plasma mostly focus on manipulating groups of particles suspended in the plasma sheath to probe collective dust-dust interactions. In this work, we report on single particle trapping and manipulations in a rf dusty plasma using the optical trapping technology. A recently-developed universal optical trap (UOT) is integrated with a rf Argon or Argon/air plasma that operates in the pressure range of tens – hundreds of millitorr, at 1-10 W. Single wall carbon nanotube particles, for the initial technology demonstration, are introduced individually into the plasma and becomes trapped by the balance of the optical force, the Coulomb force, and the gravitational force. Results show that the UOT can not only trap a single particle, but also walk the trapped particle to different locations in the dusty plasma, becoming an effective probe of both sheath and plasma properties. The particle's trapping status such as its steady state and motion dynamics is monitored in real time by an embedded imaging system. Optical configurations and plasma operating conditions, which affect the particle trapping and manipulations, are also explored. |
Friday, October 7, 2022 10:30AM - 11:00AM |
DF2.00003: Plasma sheath diagnostic using microscpic particle probes manipulated in laser tweezers Invited Speaker: Holger Kersten Low-temperature plasmas are important tools in industrial applications as well as in many basic research fields. Important plasma parameters such as density, temperature or composition are diagnosed using various established methods [1]. However, it is difficult to probe the extremely important sheath region, which is only a few millimeters thick and, thus, not accessible with macroscopic methods, as they themselves change the plasma. In recent years, microparticles have been used as probes for non-conventional plasma diagnostic purposes. Due to their size and behavior in the plasma, they are well suited for increasing the spatial resolution and, thus, providing information in addition to common diagnostics [2]. |
Friday, October 7, 2022 11:00AM - 11:15AM |
DF2.00004: Probing plasma-chemistry interactions through novel ultrafast nonlinear laser diagnostics Christopher J Kliewer, Madeline Vorenkamp, Scott Steinmetz, Timothy Chen, Yiguang Ju, Peter Bruggeman The field of plasma-assisted chemistry is inducing a paradigm shift in optimizing chemical reactions for desired outcomes. In-situ diagnostics are critical to understanding and optimizing plasma induced molecular effects. Ultrafast nonlinear laser spectroscopies can provide non-perturbative, in-operando, probes with time resolution in the picosecond regime. In this talk we discuss recent results from two sets of experiments. First, the opportunity for enhanced control of detonation transitions through plasma treatment of the reactive mixture was studied. Ultrafast coherent Raman scattering and electric field-induced second-harmonic generation for the direct measurement of time-resolved chemical speciation, electric field, and nonequilibrium ro-vibrational molecular energy distributions during plasma-assisted combustion will be discussed. Second, surface sum-frequency generation (SFG) vibrational spectroscopy results on the interfacial structure of water during plasma-water interactions will be presented. Polarization-resolved SFG provides a glimpse of the interfacial molecular response induced by the plasma-water interaction. |
Friday, October 7, 2022 11:15AM - 11:30AM |
DF2.00005: Investigation of the early-stage dynamics of laser-produced plasma using collective Thomson scattering Yiming Pan, Kentaro Tomita, Atsushi Sunahara, Katsunobu Nishihara Plasma temperature, density and flow velocity are the critical physical properties of Laser produced plasmas (LPP) to reveal the ablation mechanism, energy transport and hydrodynamic evolution. In the time window during and just after the ablation irradiation, experimental data are very scarce so that many theoretical models remain untested. In this study, we give a concise evolution history of LPP expansion within 0 to 14 ns after the ablation peak. Electron density (ne) , temperature (Te) and drift velocity (Vd) in LPPs are measured using ion feature of collective Thomson scattering (CTS). |
Friday, October 7, 2022 11:30AM - 11:45AM |
DF2.00006: Time resolved CO2 ro-vibrational excitation in a nanosecond discharge measured with quantum cascade laser absorption spectroscopy Dirk Luggenhölscher, Yanjun Du, Tsanko V Tsankov, Uwe Czarnetzki CO2 conversion is of growing interest and non-thermal plasmas are promising to be efficient in this regard due to their unique parameters (electron, vibrational, rotational, and gas temperatures). On the short time scale of a nanosecond pulsed discharge, energetic electrons lead to vibrational excitation instead of gas heating. Ladder-climbing population of higher vibrational levels due to the small energy difference (∼0.3 eV) is a more efficient dissociation pathway. Temporally resolved measurement of the ro-vibrational excitation is important to gain insight into the excitation and relaxation processes and to validate detailed kinetic models of CO2 dissociation. Measurements are performed in a nanosecond pulsed discharge at 150 mbar CO2 (10 %) in He (90 %). A quantum cascade laser and a fast detector are used for measuring the absorption with down to 8 ns temporal resolution. The tuning range of the laser allows for simultaneous measurement of rotational and vibrational temperature for the symmetric and asymmetric modes. In order to obtain the multiple temperatures (Trot, Tv1, Tv2 and Tv3) and the CO2 concentration, spectra as a function of the temperatures are fitted to the measured ones. The evolution of the rotational and vibrational temperatures of CO2 within the nanosecond discharge pulse of 150 ns length is obtained and analyzed. |
Friday, October 7, 2022 11:45AM - 12:00PM |
DF2.00007: Ro-vibrational kinetics in CO2-N2 ns pulsed discharge Yanjun Du, Tsanko Vaskov Tsankov, Jan Kuhfeld, Nikita D Lepikhin, Dirk Luggenhölscher, Uwe Czarnetzki The vibrational kinetics of the molecules in discharges in pure CO2 gas and its mixtures with other gases are of particular interest for a number of fields. Understanding the processes involving excited molecules is a challenging task due to the complex reaction pathways that often cannot be separated. Repetitively pulsed ns discharges offer unique possibility to introduce the high degree of vibrational excitation provided by the plasma electrons while keeping the reactions due to electron impact and molecular collisions apart through the separation of time scales. This advantage is used for studying the ro-vibrational kinetics of the CO2 molecules in a mixture with N2 at a pressure of 150 mbar. The temporal evolution of selected ro-vibrational states of CO2 are obtained via ns-resolved tunable laser absorption in the mid-infrared region. The information on the temperatures for the various vibrational and the rotation modes is combined with measurements of the discharge current, voltage and electric field to provide information on the excitation behaviour of the CO2 molecules. The efforts are supported by analytical models that provide explanations for the observed trends with varying mixture ratios of the CO2 gas into the N2. |
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