Growth behavior of laser-induced damage on fused silica optics under UV, ns laser irradiation

Abstract

The growth behavior of laser-induced damage sites is affected by a large number of laser parameters as well as site morphology. Here we investigate the effects of pulse duration on the growth rate of damage sites located on the exit surface of fused silica optics. Results demonstrate a significant dependence of the growth parameters on laser pulse duration at 351 nm from 1 ns to 15 ns, including the observation of a dominant exponential versus linear, multiple-shot growth behavior for long and short pulses, respectively. These salient behaviors are tied to the damage morphology and suggest a shift in the fundamental growth mechanisms for pulses in the 1-5 ns range.

Damage growth in fused silica optics at 351 nm: refined modeling of large-beam experiments

“…Bold squares are very close to this line, meaning that the growth behavior can be described in average by a unique value at a given fluence. A growth threshold around 5 J/cm 2 is deduced from this experiment; it corresponds to the threshold previously reported by several authors [4][5][6][7][8][9][10][11][12][13][14][15][16]. Shot after shot, damage sites are bigger and bigger, but for a given laser energy deposition, the stresses developed by the pressure pulse remain equal for longer circumferential and radial cracks that are more numerous too.…”

“…In this figure, a change in the slope in this semilogarithmic representation is perceptible too (dashed areas are just a guide for eye), meaning that other parameters are involved in the description of the growth. It is commonly admitted that the rear growth phenomenon is well characterized by an exponential behavior [4][5][6][7] except for shorter pulse duration where a linear growth is sometimes observed [6]. On this basis, we consider the singleshot growth rate coefficient k defined in Eq.…”

“…The plasma is formed before the peak of the pump pulse, and then for shorter pulses, the energy deposition process is shortened, and then the length of cracks formed is reduced. At the opposite, for longer pulses the amount of cracks and their size increase leading to a rate increase by which the damage site grows characterized by the exponential growth reported in literature [6]. From these observations, the exponential growth behavior is deeply linked to the size of the ''core'' region and the space with the cracks on the edges; in other words, the damage size has to be considered.…”

“…This standard approach of the growth is referred as the linear model in this paper. Recent papers showed that these two coefficients depend slightly on pulse duration [6]. Up to a recent study, the growth phenomena were considered as independent of the damage size, meaning that the growth coefficients are the same whatever the sizes and the morphologies of damage sites.…”

Laser-induced damage tests based on a marker-based watershed algorithm with gray control

“…The difference possibly results from the site morphologies tested and the local fluence. Numerous researchers [9,13,18,19] have demonstrated that the complex damage growth process is affected not only by the various laser parameters but also the intrinsic structural features of the optical components. In general, there are various precursors on the optical surface that induce damage sites with different morphologies.…”