Study On The Influence Of Micro-Nano Superficial Deficiency On KDP Crystal' Laser Damage Threshold

As a kind of inorganic nonlinear optical materials with good properties, KDP crystals has widespread applications in technological areas such as laser inertial confinement fusion and laser communication. The damage of KDP crystal is the key technique of the ICF optical manufacturing. The number of KDP crystal laser damage threshold has the direct influence on the laser output energy-flux density and the life of KDP crystal itself. At the moment, the actual laser damage threshold of KDP crystals is far below the theory laser damage threshold, researches on laser damage threshold are mainly centralized on stationary-state and transient-state deficiency inside the crystals, while researches on influences of machined micro-nano superficial layer are less. So, deep research on influences of micro-nano superficial layer deficiency on laser damage threshold will disclosure laser damage mechanisms of crystal materials further, provide the correlative theoretical foundation of increasing laser damage threshold, also provide theoretical foundation and parameter basis to obtain ultra-smooth surfaces.Firstly, based on finite element analysis software ANSYS, applied with temperature field and thermal stress field theory of KDP crystals surface irradiated by laser, the distribution of temperature field and thermal stress field of surface-uncoated, ideal KDP crystals surfaces is researched in laser irradiation.Secondly, in terms of such characters disadvantageous for optical machining as soft, easily deliquescent, very brittle, sensible to temperature and easy to crack, influences of various micro-nano superficial layer deficiency of KDP crystals are analyzed individually, which includes residual internal stress, micro-crack, micro-pore and concave etc. It is discovered through analysis that the deficiency of crystal micro-nano machined superficial layer all affects the distribution of temperature field and thermal stress field of crystal surfaces, which makes injected laser centralize inside a small area around deficiency resulting in temperature lifting intensively around the deficiency, cause partial melting phenomena, damage of KDP crystals and lowering of KDP crystals laser damage threshold.Finally, based on the temperature field and thermal stress field theory around inclusions of KDP crystals, the distribution of crystal temperature field and thermal stress field is analyzed under the influence of micro-nano machined superficial layer inclusions. It is found that ions of inclusions make great absorbing of injected laser leading to crystal damages. Inclusions'great absorbing of laser is the main factors causing crystal damages, as well as the main factor influencing KDP crystals laser damage threshold. Also the radius of adverse inclusion is obtained, which makes the energy inclusions absorb highest as well as the temperature. In addition, different kinds and different contents of inclusions also affect the crystal laser damage threshold.