Optical fatigue investigation with in situ time resolved digital holography

Abstract

So called “optical fatigue effect” of transparent optical materials is triggered by repetitive laser pulses. It first appears in form of gradual modification of optical properties of the element (change in refractive index or absorption) and eventually leads to formation of catastrophic damage. As this phenomenon can be governed by distinct underlying physical processes it is also sensitive to laser irradiation conditions, intrinsic material and environmental properties, thus it is not always deterministic and therefore hardly predictable. There exist models of optical fatigue that relate absorbed pulse energy, dynamics of lattice deformation, reduced mechanical strength and heat accumulation to predict optical damage, however many quantitative features of such materials as well as scaling laws of irradiation for such models remain unknown. In order to address this issue appropriate set of experimental data is needed. Thus, well known transparent material - fused quartz - was investigated in bulk by using in situ quantitative tool, namely time-resolved digital holographic microscopy. Optical materials response was investigated by optically probing excited material at different time delays. Various dependencies were investigated by changing pump irradiation conditions as a function of incident laser pulses.