Role of self-focusing in laser ageing of KDP and a-LiIO3 crystals

An experimental study was made of the optical strength of KDP and a-LiIO₃ crystals irradiated periodically with nanosecond laser pulses under a variety of conditions. It was established that ageing of a-LiIO₃ was independent of the time structure of the incident radiation but was governed by its energy density, confirming the hypothesis of thermochemical nature of ageing. Damage accumulation effect in KDP crystals was observed only when they were irradiated with multifrequency radiation; this effect was interpreted as the accumulation of microdefects which appeared because of self-focusing of individual time fluctuations.