Gain dynamics in a highly ytterbium-doped potassium double tungstate thin-film amplifier

Yean-Sheng Yong; Shanmugam Aravazhi; Sergio A. Vázquez-Córdova; Jennifer L. Herek; Sonia M. García-Blanco; Markus Pollnau

doi:10.1117/12.2514806

7 March 2019 Gain dynamics in a highly ytterbium-doped potassium double tungstate thin-film amplifier

Yean-Sheng Yong, Shanmugam Aravazhi, Sergio A. Vázquez-Córdova, Jennifer L. Herek, Sonia M. García-Blanco, Markus Pollnau

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Proceedings Volume 10896, Solid State Lasers XXVIII: Technology and Devices; 108961G (2019) https://doi.org/10.1117/12.2514806
Event: SPIE LASE, 2019, San Francisco, California, United States

Abstract

Active media with high rare-earth concentrations are essential for small-footprint waveguide amplifiers. When operating at high population inversion, such devices are often affected by undesired energy-transfer processes and thermal effects. In this work, we study a 32-μm-thick epitaxial layer of potassium gadolinium ytterbium double tungstate with a high Yb content of 57at.%, representing an Yb³⁺ concentration of ~3.8 × 10²¹ per cubic centimeter, grown onto an un-doped KY(WO₄)₂ substrate. The pump absorption, luminescence decay, and small-signal gain are investigated under intense pumping conditions. Spectroscopic signatures of an energy-transfer process and of quenched ions, as well as thermal effects are observed. We present a gain model which takes into account excessive heat generated due to the abovementioned experimental observations. Based on finite-element calculations, we find that the net gain is significantly reduced due to, firstly, a fraction of Yb³⁺ ions not contributing to stimulated emission, secondly, a reduction of population inversion owing to a parasitic energy-transfer process and, thirdly, degradation of the effective transition cross-sections owing to device heating. Nevertheless, a signal enhancement of 8.1 dB was measured from the sample at 981 nm wavelength when pumping at 932 nm. The corresponding signal net gain of ~800 dB/cm, which was achieved without thermal management, is promising for waveguide amplifier operating without active cooling.

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Yean-Sheng Yong, Shanmugam Aravazhi, Sergio A. Vázquez-Córdova, Jennifer L. Herek, Sonia M. García-Blanco, and Markus Pollnau "Gain dynamics in a highly ytterbium-doped potassium double tungstate thin-film amplifier", Proc. SPIE 10896, Solid State Lasers XXVIII: Technology and Devices, 108961G (7 March 2019); https://doi.org/10.1117/12.2514806

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KEYWORDS

Ions

Ytterbium

Absorption

Optical amplifiers

Thermal effects

Luminescence

Crystals

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