Recent Developments in Dual-Laser Digital Holography for Plasma-Facing Surface Characterization

• Published in: IEEE transactions on plasma science Vol. 48; no. 6; pp. 1655 - 1660
• Main Authors: Smith, Cary D., Biewer, Theodore M., Ren, Xi, Thomas, C. E., Gebhart, Trey, Zhang, Zhili
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Correlation analysis; Diagnostic systems; Digital holography (DH); Holography; Laser beams; Laser modes; Laser tuning; Lasers; Measurement by laser beam; Nuclear fusion; plasma diagnostic; Plasma measurements; plasma-facing component (PFC); plasma-material interaction (PMI); Research facilities; Rough surfaces; Stainless steels; Surface properties; Surface roughness
• ISSN: 0093-3813; 1939-9375
• DOI: 10.1109/TPS.2019.2943739

A digital holography device is currently undergoing development at the Oak Ridge National Laboratory for the purpose of measuring surface topography, with the goal of deployment as a real-time plasma-facing component diagnostic for the study of materials that could be utilized in a nuclear fusion device. The holography system utilizes one or two lasers depending on the scale of surface features under measurement. Measurements of surface roughness were performed in a single-laser mode and compared with the data from profilometry, with a linear correlation of increased holographic measurement fidelity as surfaces became smoother. Characterization of the dual-laser operating mode has been performed via surface measurement of stainless steel targets with "stair-step" features in various sizes. Results demonstrated that surface features with known sizes as small as <inline-formula> <tex-math notation="LaTeX">25.4~\mu \text{m} </tex-math></inline-formula> could be resolved. Measurements were within <inline-formula> <tex-math notation="LaTeX">\sim 55~\mu \text{m} </tex-math></inline-formula> or less deviation from the actual sizes, and measurement accuracy was improved as feature size was increased, corresponding to the effect of noise becoming less pronounced. A target exposed to plasma generated by an electrothermal (ET) arc source was analyzed with flat-field correction and averaging of sequential image frames to demonstrate the improved measurement quality in preparation for future use of holography on ET arc-exposed targets.