Gain dynamics of Tm:Ho:YAG pumped in near infrared

Abstract

This paper reports time-resolved spectroscopic studies of mid infrared (IR) gain in Tm:Ho:YAG. The gain was populated through an excitation of the 3H4 states of Tm3+ ions. The excitation was at 0.78 μm and was followed by the energy transport from Tm3+ ions to the 5I7 states of Ho3+. We measured the rise and the relaxation characteristics of the mid-IR gain of Ho3+. The results demonstrated Stokes energy shifts and a strongly inhomogeneous broadening of the Stark components of the Ho3+ spectrum. The gain dynamics demonstrated negligible interaction between the Stark components. The interaction between the center and the wings of inhomogeneously broadened energy levels was also weak. The studies also demonstrated a two-step excitation process (involving 3H4 states of Tm3+ and 5I7 states of Ho3+ ions) which populates the 5I7 states of Ho3+. The Stark splitting of the states, the energy level inhomogeneity, and the two-step excitation will limit the narrow-band gain extraction efficiency.