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Upconversion-induced heat generation and thermal lensing in Nd:YLF and Nd:YAG

Upconversion-induced heat generation and thermal lensing in Nd:YLF and Nd:YAG
Upconversion-induced heat generation and thermal lensing in Nd:YLF and Nd:YAG
We investigate the influence of interionic upconversion between neighboring ions in the upper laser level of Nd:YLF and Nd:YAG on population dynamics, heat generation, and thermal lensing under lasing and non-lasing conditions. It is shown that cascaded multiphonon relaxations following each upconversion process generate significant extra heat dissipation in the crystal under non-lasing compared to lasing conditions. Owing to the unfavorable temperature dependence of thermal and thermo-optical parameters, this leads, firstly, to a significant temperature increase in the rod, secondly, to strong thermal lensing with pronounced spherical aberrations and, ultimately, to rod fracture in a high-power end-pumped system. In a three-dimensional finite-element calculation, excitation densities, upconversion rates, heat generation temperature profiles, and thermal lensing are calculated. Differences in thermal lens power between non-lasing and lasing conditions up to a factor of six in Nd:YLF and up to a factor of two in Nd:YAG are experimentally observed and explained by the calculation. This results in a strong deterioration in performance when operating these systems in a Q-switched regime, as an amplifier, or on a low-gain transition. Methods to decrease the influence of interionic upconversion are discussed. It is shown that tuning of the pump wavelength can significantly alter the rod temperature.
1550-235X
16076-16092
Pollnau, M.
1094856b-791a-4050-98d9-c07777d5f0f5
Hardman, P.J.
2b18897a-de16-4a46-9e91-0b27f905a120
Kern, M.A.
c9295821-16f6-4a6c-981b-a6fe8994f4e3
Clarkson, W.A.
3b060f63-a303-4fa5-ad50-95f166df1ba2
Hanna, D.C.
3da5a5b4-71c2-4441-bb67-21f0d28a187d
Pollnau, M.
1094856b-791a-4050-98d9-c07777d5f0f5
Hardman, P.J.
2b18897a-de16-4a46-9e91-0b27f905a120
Kern, M.A.
c9295821-16f6-4a6c-981b-a6fe8994f4e3
Clarkson, W.A.
3b060f63-a303-4fa5-ad50-95f166df1ba2
Hanna, D.C.
3da5a5b4-71c2-4441-bb67-21f0d28a187d

Pollnau, M., Hardman, P.J., Kern, M.A., Clarkson, W.A. and Hanna, D.C. (1998) Upconversion-induced heat generation and thermal lensing in Nd:YLF and Nd:YAG. Physical Review B, 58 (24), 16076-16092. (doi:10.1103/PhysRevB.58.16076).

Record type: Article

Abstract

We investigate the influence of interionic upconversion between neighboring ions in the upper laser level of Nd:YLF and Nd:YAG on population dynamics, heat generation, and thermal lensing under lasing and non-lasing conditions. It is shown that cascaded multiphonon relaxations following each upconversion process generate significant extra heat dissipation in the crystal under non-lasing compared to lasing conditions. Owing to the unfavorable temperature dependence of thermal and thermo-optical parameters, this leads, firstly, to a significant temperature increase in the rod, secondly, to strong thermal lensing with pronounced spherical aberrations and, ultimately, to rod fracture in a high-power end-pumped system. In a three-dimensional finite-element calculation, excitation densities, upconversion rates, heat generation temperature profiles, and thermal lensing are calculated. Differences in thermal lens power between non-lasing and lasing conditions up to a factor of six in Nd:YLF and up to a factor of two in Nd:YAG are experimentally observed and explained by the calculation. This results in a strong deterioration in performance when operating these systems in a Q-switched regime, as an amplifier, or on a low-gain transition. Methods to decrease the influence of interionic upconversion are discussed. It is shown that tuning of the pump wavelength can significantly alter the rod temperature.

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Published date: December 1998

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Local EPrints ID: 77860
URI: https://eprints.soton.ac.uk/id/eprint/77860
ISSN: 1550-235X
PURE UUID: 7bd3fe59-921c-4817-adbe-06b96941bf54

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Date deposited: 11 Mar 2010
Last modified: 04 Nov 2019 21:06

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