Growth of laser-initiated damage in fused silica at 351 nm

Abstract

The effective lifetime of optics in the UV is limited both by laser induced damage and the subsequent growth of laser initiated damage sites. We have measured the growth rate of laser induced damage in fused silica in both air and vacuum. The data shows exponential growth in the lateral size of the damage site with shot number above threshold fluence. The concurrent growth in depth follows a linear dependence with shot number. The size of the initial damage influences the threshold for growth; the morphology of the initial site depends strongly on the initiating fluence. We have found only a weak dependence on pulse length for growth rate. Low fluence conditioning in air may delay the onset of growth. Most of the work has been on bare substrates but the presence of a sol-gel AR coating has no significant effect.

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

“…Bold squares represent the experimental averages of all coefficients inside fluence bins. In this graph, the dashed line represents values commonly reported in literature [4]. 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.…”

“…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.…”

“…Indeed, front surface growth rate is limited and characterized by a linear growth shot after shot [3]. Observations on the Beamlet laser and the first experimentations on the OSL facility at Livermore [4] revealed the fundamental aspect from an operational point of view: the exponential nature of the growth shot after shot for exit surface damage. This behavior is observed for many sites, but depending on the morphology, some damage sites do not evolve and remain stable up to large fluence.…”

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

“…The initial damage threshold and damage growth are typically used to estimate the properties of optical damage [6][7][8][9] . The morphology of damage sites is of great importance in investigating damage mechanisms [10,11] .…”