Optical strength of YAG and LiNbO3crystals irradiated with giant pulses from a YAG:Er3+laser (λ= 2.94μ)

Measurements were made of the bulk damage threshold I d of yttrium aluminum garnet (YAG) crystals, either free of deliberately introduced impurities or activated with Er 3+ ions in different concentrations (up to 80 wt. % ), and also of LiNbO 3 crystals. This threshold was determined using giant pulses from a YAG:Er 3+ laser emitting at λ = 2.94 μ ; the energy per pulse was 70 mj and the pulse duration was 120nsec. In the case of YAG crystals it was found that Id varied considerably from sample to sample in the range I d = (1.5–18) × 10 10 W/cm 2 , which was not associated with the presence of Er3+ but was clearly due to the presence of some accidental impurities. A considerable increase in I d was observed for YAG:Er 3+ samples characterized by low damage thresholds when these samples were annealed in air. In the case of LiNbO 3 , a typical value of the damage threshold was I d ≈ 10 11 W/cm 2 . The results obtained indicated a sufficiently high optical strength of YAG:Er 3+ and LiNbO 3 crystals, used respectively as the active and modulating elements in YAG:Er 3+ lasers.