Damage threshold prediction of crystal materials irradiated by femtosecond lasers based on ionization model and two-temperature model

Crystal materials may be damaged irradiated by high-power femtosecond laser pulse during terahertz radiation generation in optical rectification, limiting the further increase of the intensity and the conversion efficiency of the generated terahertz radiation. It remains a big challenge to predict the damage threshold of crystal materials by femtosecond lasers. In this paper, the interaction mechanism between the femtosecond laser pulse and the crystal material has been analyzed and the related theoretical model has been built up. Consequently, two types of models for the damage threshold prediction of crystal materials based on the ionization model and the two-temperature model have been proposed. On the basis, the evolution of free electron in crystals and the temperature variation of electron and lattice have been discussed in detail. The influence of the major parameters of femtosecond laser pulses on the damage threshold has also been analyzed quantitatively. The results show that, the actual damage threshold of the crystal material may be between the calculated values based on the ionization model and the two-temperature model. For the incident femtosecond laser pulse with larger central wavelength, the damage threshold of crystal materials becomes relatively larger.