The role of excited-state absorption in tunable solid-state lasers

The lasing properties of tunable solid state lasers can be strongly influenced by Excited State Absorption (ESA). It is shown that the tuning behaviour of Cr:GSGG and Cr:LLGG is limited at short wavelengths due to the ESA transitions²E ²T₂ (b),²T₁ (b) and⁴T₂ ⁴T₁ (b), respectively. At long wavelengths the⁴T₂ ⁴T₁ (a) ESA transition narrows the tuning range largely. The reason is that both levels are Jahn-Teller split due to the centric chromium site resulting in a very broad ESA band. In Ti: YAIO₃ strong ESA of the pumping wavelength into a charge transfer band occurs, which is caused by a Ti³⁺/Fe³⁺ complex centre. By this transition the pumping efficiency is diminished largely. It is believed that the lasing behaviour of Ti: YAIO₃ can be improved considerably by growing of highest iron-free crystals.