In Situ 3-D Temperature Mapping of High Average Power Cryogenic Laser Amplifiers

Error analysis of contactless optical temperature probing methods for cryogenic Yb:YAG

“…Hence, for these methods, accurate temperature estimation is only feasible in the 78-200 K interval, as we will see in upcoming section as well. Note that, as an example, our measured temperature variation of 1022/1027 nm intensity ratio is similar but different than earlier reports [10,19]. This again shows the need to take these calibration data carefully in a setting similar to the intended usage of the Yb:YAG sample (so universal calibration data are not feasible).…”

“…As a result, besides the directly emitted light from the excited volume of interest, scattered light from other regions could still reach the spectrometer and this reduces the spatial resolution of temperature measurement. More advanced techniques such as confocal laser scanning microscopy geometry could ideally be adopted for 3-D temperature mapping of the crystal with high spatial resolution (~ 100-200 µm) at the expense of increased complexity [10]. In this work, we focused our attention on analyzing the accuracy of different temperature estimation methods, and knowledge of crystal average temperature is sufficient for determining crystal bonding quality or for analyzing laser/amplifier performance for our case.…”

“…This shows that, from one perspective, the FWHM of the emission is not a strong function of system conditions (doping level of crystal, measurement conditions, etc.…), and hence, unlike the intensity peak ratios, once a calibration curve is taken, it can potentially be used in different configurations. On the other hand, lasing and gain narrowing occurring in this line will certainly become an issue limiting wider usability of this method [10]. As usual, to achieve the minimum error bar in temperature estimation, the reference data should be repeated for different cases.…”

“…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]. Infrared thermal cameras that could effectively provide temperature information for room-temperature systems [15] are not effective at cryogenic temperatures.…”

“…Fruse et al [19,20] demonstrated that the fluorescence intensity ratio of Yb:YAG at 1022 nm and 1027 nm could be used for estimation of temperature in the 77-200 K area. Chi et al [10,21] used the fluorescence spectra of Yb:YAG in the 1015-1029 nm interval for estimating temperatures in the 50-140 K range using neural network functions. The variation of pump absorption at 1030 nm with temperature was employed in estimating Yb:YAG thin-disk temperatures in the 40-300 K range by Petrov et al [22].…”