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Title:Spatially Enhanced Electric Field Induced Second Harmonic (seefish) Generation For Measurements Of Electric Field Distributions In Gases And Plasmas
Author(s):Raskar, Sai
Contributor(s):Adamovich, Igor V.; Orr, Keegan
Subject(s):Instrument/Technique Demonstration
Abstract: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 compared to that in the collinear phase matching. The resulting SEEFISH signal is spatially isolated from the “conventional” EFISH signal and measured by a photomultiplier detector. 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 well 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. The estimated spatial resolution of the SEEFISH diagnostic is approximately 1 mm, in the direction of the laser beam. The SEEFISH spatial resolution can be improved further, potentially to $\sim$ 0.1 mm, by using two independently focused, crossed laser beams. However, this would result in a further reduction of the signal, which may necessitate the use of a fs pump laser. SEEFISH measurements of the electric field distribution in an atmospheric pressure argon plasma jet are underway.
Issue Date:2021-06-23
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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