Bulletin of the American Physical Society
74th Annual Gaseous Electronics Conference
Volume 66, Number 7
Monday–Friday, October 4–8, 2021;
Virtual: GEC Platform
Time Zone: Central Daylight Time, USA
Session JW62: Plasma Diagnostics: Laser Diagnostics II |
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Chair: Ben Yee, Lam Research Room: Virtual GEC platform |
Wednesday, October 6, 2021 2:00PM - 2:15PM |
JW62.00001: Spatially Enhancing Resolution of Electric Field Induced Second Harmonic (SEEFISH) Generation Measurements Sai Raskar, Keegan Orr, Igor V Adamovich The spatial resolution of the ps Electric Field Induced Second Harmonic (EFISH) generation has been enhanced by using a non-collinear laser beam phase matching geometry. This approach is similar to the one used in Unstable Resonator – Enhanced Detection Coherent Anti-Stokes Raman Scattering (USED CARS). Briefly, the pump laser beam (1064 nm, pulse duration 150 ps, pulse energy 20-35 mJ) is separated into two coaxial beams before the focusing lens. The two beams, with the combined pulse energy of 10-18 mJ, overlap only near the focal point, generating the Spatially Enhanced EFISH (SEEFISH) signal over a significantly shorter region. Blocking of either of the two beams results in a complete suppression of the signal, demonstrating that it is generated by the superposition of the two beams overlapping near the focal point. Measurements of a known Laplacian field generated between two parallel cylinder electrodes in ambient air demonstrated that SEEFISH improves the spatial resolution of the measurements by over a factor of 2. The spatial resolution is improved further by reducing the focal distance of the lens. As expected, the magnitude of the SEEFISH signal is lower compared to that of the “conventional” EFISH, by a factor of 2-10, depending on the lens focal distance. |
Wednesday, October 6, 2021 2:15PM - 2:30PM |
JW62.00002: Characterization of plasma in RF jet interacting with water: Thomson scattering versus Spectral line broadening Shurik Yatom, Trey Oldham, Elijah J Thimsen, Yevgeny Raitses This work reports on comparison of plasma characteristics measured by means of Thomson scattering and spectral line analysis. Both measurements were performed on RF powered plasma jet, running at 20% duty cycle, with Ar as a carrier gas. The plasma was impinging on a water surface located 1 cm away from the powered needle electrode. To support the plasma analysis, we also have performed gas temperature measurement by means of laser Rayleigh scattering and detailed time-resolved imaging of the plasma filament. The difference between the plasma parameters measured by the two methods is discussed and analyzed. The main observed difference is in the re-ignition of the jet following the voltage switch-off. |
Wednesday, October 6, 2021 2:30PM - 2:45PM |
JW62.00003: Diagnostics of neutral particles in a low pressure DC glow discharge using single shot coherent Rayleigh-Brillouin scattering Robert Randolph, Junhwi Bak, Alexandros Gerakis Single shot coherent Rayleigh-Brillouin scattering (CRBS), a non-linear, four-wave mixing laser diagnostic technique, is applied to measure the translational temperature and density of neutral species in a low pressure, xenon, DC glow discharge. The single shot CRBS configuration scans the entire velocity distribution function of the neutral species in the medium in the duration of a single laser shot (approximately 150 ns), allowing for rapid spectral acquisition. To enable a stronger signal at low pressures (here ~15 Torr), the system used employs a dual color configuration with the pump beams operating at 1064 nm and the probe beam at 532 nm; all three beams having the same pulse duration. CRBS spectra of neutral species are obtained radially across the xenon glow discharge, mapping horizontal temperature and density profiles. Experimentally obtained spectral lineshapes show good agreement when compared to simulated ones. Single shot CRBS exhibits the significant advantages of being able to measure at both low densities and optically noisy environments. The CRBS measurements within a glow discharge presented here can lead to diagnostics of neutral species in similar environments such as arc discharges, flames, plasma torches, etc. |
Wednesday, October 6, 2021 2:45PM - 3:00PM |
JW62.00004: Single-Shot Ptychography as a Diagnostic Imaging Technique for Studying Electro-Static Discharge Jonathan Barolak, Claudia A Schrama, Charles G Durfee, Daniel Adams Recent advances in computational imaging are paving the path towards next generation plasma |
Wednesday, October 6, 2021 3:00PM - 3:15PM |
JW62.00005: Understanding the Accuracy of Electric Field Induced Second Harmonic Generation (E-FISH) Measurements in Fast Ionization Waves Tat Loon L Chng, David Pai, Olivier Guaitella, Svetlana Starikovskaia, Anne Bourdon E-FISH has shown significant potential for measuring electric fields in non-equilibrium plasmas, especially for its high sensitivity and temporal resolution. Yet, a recent study has shown that the E-FISH signal is a function of the entire electric field profile that overlaps with the laser beam path. This raises the possibility that measured field strengths could be in error if the electric field profiles in the plasma are not well matched with that of the calibration. To assess the accuracy of such measurements, we utilize field profiles from numerical simulations to theoretically predict the results of an E-FISH experiment. We apply this approach to analyzing the electric field evolution in a fast ionization wave for a diffuse, atmospheric pressure, nanosecond discharge in a pin-plane geometry. We find that the discharge development is characterized by three distinct phases: an initial phase before the arrival of the front, a second phase after the passage of the front, and a final conduction phase when the interelectrode gap is closed. Each of these phases has an associated field shape that produces a different signal response. Our results suggest that measurements in phase 1 and 3 are likelier to be more accurate, and supports the continued use of E-FISH in these regimes. |
Wednesday, October 6, 2021 3:15PM - 3:30PM |
JW62.00006: 1D profile diagnostics of neutral species with singleshot coherent Rayleigh-Brillouin scattering. Alexandros Gerakis Temperature and density gradients of neutral species are important quantities to be experimentally estimated in low temperature plasmas, allowing for the validation of developed simulation codes and the better understanding of plasma processes. It is of importance that these diagnostics are performed non-perturbatively, fast, and simultaneously across the length of the plasma. Single shot coherent Rayleigh-Brillouin scattering (CRBS), a non-linear, non-resonant four-wave mixing laser diagnostic technique, has been demonstrated recently as an effective, non-perturbative, single laser shot diagnostic technique for nanoparticles produced in an arc discharge and for the temperature and density measurement of neutral species in glow discharges, among other studies. As is the case with four-wave mixing techniques, the current state-of-the-art CRBS implementations only allow for point measurements in the medium of interest, where the spatial resolution is dictated by the implemented laser beam geometry. Here, we report on the progress toward the implementation of a novel 1D single shot CRBS scheme, which will enable the simultaneous, single shot measurement (~150 ns) of quantities of interest across line profiles of extended dimensions in a variety of low temperature plasmas. |
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