Tm:YAG is used as an efficient means to generate high power 2.01 micron laser emission from the ³F₄ - ³H₆ transition, for surgical cutting and coagulation applications due to the high water absorption at this wavelength [1]. Diode pumping is commonly employed into the 785nm ³H₆-³H₄ absorption feature. Of interest in Tm³⁺ activated systems is the increased quantum efficiency obtained thru Tm-Tm ion cross relaxation; a non-radiative process where an excited Thulium in the ³H₄ state (energy level around 12900 cm −1 ) decays to the ³F₄ state (energy level around 6000 cm −1 ) and a nearest neighbor ground-state Thulium ion is promoted to the ³F₄ level, along with phonon byproduct to satisfy energy conservation [2]. Thus, in appropriate concentrations, a single Thulium ion excited to the ³H₄ level generates two Thulium ions in the ³F₄ upper laser level.
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