Absorption and oscillation characteristics of a pulsed Cr4+ :YAG laser investigated by a double-pulse pumping technique

Because of the low Cr⁴⁺ concentration in Cr⁴⁺: YAG crystals, the output energy of the Cr⁴⁺:YAG laser is limited by the ground-state depletion of Cr ⁴⁺ when pumped by a Q-switched Nd:YAG laser. We propose and demonstrate a double-pulse pumping technique to improve the output power and energy, by which a Cr⁴⁺ ion that returns to the ground state during lasing is repumped by the second pump pulse and can immediately contribute to lasing. The output power and energy were increased by factors of 5 and 4, respectively, from those in conventional single-pulse pumping. These enhancement factors were limited by the relaxation time from the higher excited state following excited-state absorption to the upper laser level. In addition to the fast relaxation reported so far, we found that there is a slow relaxation channel with a time constant of approximately 100 ns, which was also explored by using the double-pulse pumping technique