Scientific Results

Experimental study on the performances of
second-harmonic dispersion interferometers at
10.6 μm and 1064 nm for plasma density
measurements

Year: 2020

Authors: Brandi F., Frank Wessel, Christopher M. Lohff, James R. Duff,
Zachary O. Haralson

Autors Affiliation: L-Egant Solutions, LLC, 22 Santa Eugenia, Irvine, California 92606, USA

Istituto Nazionale di Ottica (CNR-INO), S.S. Pisa, Via Moruzzi 1, 56124 Pisa, Italy

Lockheed Martin Aeronautics Co., 1011 Lockheed Way Palmdale, California 93599, USA

Abstract: Two common-path interferometers based on CO 2 and Nd:Y 3 Al 5 O 12 (Nd:YAG) lasers are benchmarked with a
two-arm microwave interferometer on a hydrogen plasma produced by an RF discharge and injected into a large
magnetic-confinement vessel. The ∼10 19 m −2 line-integrated electron density is clearly measured in agreement
by the interferometers. The frequency spectrum of the measured data is analyzed on the 20 kHz range for all inter-
ferometers and up to 600 kHz for the Nd:YAG laser-based interferometer. Mechanical vibration measurements
performed on the components of the two common-path interferometers result in a peak-to-peak displacement
up to about one and twenty wavelengths for the CO 2 and Nd:YAG laser-based interferometers, respectively. Such
results set for the first time, to the best of our knowledge, a quantitative limit for the displacement that the two
second-harmonic dispersion interferometers can sustain while still providing a high sensitivity for accurate plasma
density measurements.

Journal/Review: APPLIED OPTICS

Volume: 59      Pages from: 8486  to: 8493

KeyWords: plasma diagnostics, interferometry
DOI: https://doi.org/10.1364/AO.399551