Abstract
In this work, we have investigated six different in situ optical contactless temperature probing methods for cryogenic Yb:YAG systems. All the methods are based on variation of fluorescence spectra with temperature, and they either look at the width of the emission line, the ratio of the emission intensity at different wavelengths and to the overall spectral change at selected wavelength intervals. We have shown that, for Yb:YAG crystal with homogeneous temperature distribution, one can perform real-time contactless optical temperature measurements with a ± 1 K accuracy in the 78–300 K range. We have further tested the methods in measuring the average temperature of Yb:YAG rods at up to 500 W absorbed pump power level. We have seen that, a real-time temperature measurement accuracy of ± 5 K is feasible in both lasing and non-lasing situations for estimating the average temperature of crystals under nonhomogeneous thermal load. The techniques are quite valuable in evaluating the bonding quality of Yb:YAG crystals in cryogenic systems. Moreover, the real-time temperature information provides feedback on parameters like cavity alignment status and extraction efficiency to the laser engineers while optimizing the system.
Highlights
Yb-doped cryogenic solid-state lasers and amplifiers such as Yb:YAG and Yb:YLF have reached multi-100 W to kW average power levels over the last decades [1,2,3,4,5,6,7,8,9]
In this work, we have performed a set of detailed experiments, where we have comparatively investigated pros and cons of different temperature estimation methods for Yb:YAG systems operating near cryogenic temperatures
We have considered the differential luminescence thermometry (DLT) method, where we looked at the spectral changes in wider spectral intervals, focusing on the (5) 950–1060 nm and (6) 950–1025 nm regions
Summary
Yb-doped cryogenic solid-state lasers and amplifiers such as Yb:YAG and Yb:YLF have reached multi-100 W to kW average power levels over the last decades [1,2,3,4,5,6,7,8,9]. Further power scaling of these systems require detailed understanding of thermal effects and measurement/estimation of internal crystal temperatures during laser/amplifier operation [10,11,12,13,14]. While optimizing the laser/amplifier, a real-time temperature information is quite valuable for the laser engineer/scientist to pinpoint the issues in the system For both cases, a temperature estimation accuracy of at least ± 5 K is necessary. In this work, we have performed a set of detailed experiments, where we have comparatively investigated pros and cons of different temperature estimation methods for Yb:YAG systems operating near cryogenic temperatures.
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