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Multi-dimensional optical and laser-based diagnostics of low-temperature ionized plasma discharges

Plasma Sources Science and Technology

Barnat, Edward V.

A review of work centered on the utilization of multi-dimensional optical diagnostics to study phenomena arising in radiofrequency plasma discharges is given. The diagnostics range from passive techniques such as optical emission to more active techniques utilizing nanosecond lasers capable of both high temporal and spatial resolution. In this review, emphasis is placed on observations that would have been more difficult, if not impossible, to make without the use of such diagnostic techniques. Examples include the sheath structure around an electrode consisting of two different metals, double layers that arise in magnetized hydrogen discharges, or a large region of depleted argon 1s4 levels around a biased probe in an rf discharge. © 2011 IOP Publishing Ltd.

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TYPE Journal Article YEAR 2011
ScopusOSTIDOI

Two-dimensional mapping of electron densities and temperatures using laser-collisional induced fluorescence

Plasma Sources Science and Technology

Barnat, Edward V.; Frederickson, K.

We discuss the application of the laser-collisional induced fluorescence (LCIF) technique to produce two-dimensional maps of both electron densities and electron temperatures in a helium plasma. A collisional-radiative model (CRM) is used to describe the evolution of electronic states after laser excitation. We discuss generalizations to the time dependent results which are useful for simplifying data acquisition and analysis. LCIF measurements are performed in plasma containing densities ranging from ∼109 electrons cm -3 and approaching 1011 electrons cm-3 and comparison is made between the predictions made by the CRM and the measurements. Finally, spatial and temporal evolution of an ion sheath formed during a pulse bias is measured to demonstrate this technique. © 2010 IOP Publishing Ltd.

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TYPE Conference YEAR 2010
ScopusOSTI

New topics in coherent anti-stokes raman scattering gas-phase diagnostics : femtosecond rotational CARS and electric-field measurements

Serrano, Justin R.; Barnat, Edward V.

We discuss two recent diagnostic-development efforts in our laboratory: femtosecond pure-rotational Coherent anti-Stokes Raman scattering (CARS) for thermometry and species detection in nitrogen and air, and nanosecond vibrational CARS measurements of electric fields in air. Transient pure-rotational fs-CARS data show the evolution of the rotational Raman polarization in nitrogen and air over the first 20 ps after impulsive pump/Stokes excitation. The Raman-resonant signal strength at long time delays is large, and we additionally observe large time separation between the fs-CARS signatures of nitrogen and oxygen, so that the pure-rotational approach to fs-CARS has promise for simultaneous species and temperature measurements with suppressed nonresonant background. Nanosecond vibrational CARS of nitrogen for electric-field measurements is also demonstrated. In the presence of an electric field, a dipole is induced in the otherwise nonpolar nitrogen molecule, which can be probed with the introduction of strong collinear pump and Stokes fields, resulting in CARS signal radiation in the infrared. The electric-field diagnostic is demonstrated in air, where the strength of the coherent infrared emission and sensitivity our field measurements is quantified, and the scaling of the infrared signal with field strength is verified.

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TYPE Conference YEAR 2010
OSTI
Results 101–125 of 138
Results 101–125 of 138