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11 September 2019 Fiber-based optical thermocouples for fast temperature sensing in extreme environments
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We have developed fiber-based optical thermocouples (OTCs) for fast temperature sensing in extreme environments. Our OTCs consist of a thin film of dysprosium-doped yttrium aluminum garnet (Dy:YAG)—a well-known two-color thermometry phosphor—deposited on the end of a sapphire fiber using pulsed laser deposition. Temperature sensing is achieved by comparing the relative intensities of photoluminescence arising from two closely spaced Dy3  +   excited states. Using a combination of time-gated detection and blackbody background subtraction, we are able to measure Dy:YAG’s photoluminescence up to 2033 K, which is one of the highest temperatures obtained in literature. However, we are only able to use the photoluminescence spectra for temperature sensing up to 1773 K due to poor signal-to-noise ratio for higher temperatures. These results suggest the possibility of measuring higher temperatures with time-gated detectors designed for low-light levels. After characterizing the fiber-based OTCs’ temperature response, we next demonstrate their functionality using subsecond pulsed CO2 laser heating using both intensified charge-coupled device detection and a photodiode-based software time-gating technique. In the lab, we have utilized this technique to measure temperatures at rates up to 80 kHz. In addition, we comment on the applicability of OTCs to fast temperature sensing in turbulent flows and estimate rise times on the order of several hundred microseconds for a 1-μm OTC film.

© 2019 Society of Photo-Optical Instrumentation Engineers (SPIE) 0091-3286/2019/$28.00 © 2019 SPIE
Benjamin R. Anderson, Steven Livers, Ray Gunawidjaja, and Hergen Eilers "Fiber-based optical thermocouples for fast temperature sensing in extreme environments," Optical Engineering 58(9), 097105 (11 September 2019).
Received: 21 February 2019; Accepted: 14 August 2019; Published: 11 September 2019

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