Accurate measurements of laser-induced bulk damage density

Abstract

The laser damage community has long been searching for the reproducibility of damage measurements in the nanosecond (ns) regime. Here we show that laser-induced bulk damage density of frequency conversion crystals can be measured with high accuracy and repeatability in the range from 2 to 20 ns. The rasterscan test procedure (Lamaignère et al 2007 Rev. Sci. Instrum. 78 103105), previously developed in order to determine laser damage density of large aperture UV fused silica optics, has been adapted to bulk damage measurement. The large volume scanned during tests permits us to measure very low damage densities. For smaller optical components, small volumes are tested using the normalized 1/1 test procedure. Whatever test procedures, accuracy and repeatability are obtained by means of a suitable data reduction. For comparison between different procedures, the classical damage probability plot has to be converted in terms of damage density. The consideration of error bars on damage site distributions is compulsory to compare experimental data. A special emphasis is put on damage detection tools. When tests are carried out on diverse facilities, pulse duration, spatial distribution and beam overlap are the key parameters which are to be taken into account to compare experimental data. We describe the equipment, test procedures and data analysis to perform these damage tests with small beams (Gaussian beams, about 1 mm @1/e, and top-hat beams). Other tests are realized with larger beams (cm sized) which are compared with small beam results. The consistency of all the results gives confidence in the measurements. Reproducibility of measures is discussed in connection with current theoretical understanding of laser damage.

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.…”

“…For the latest, a charge-coupled device (CCD) camera is positioned at a plane optically equivalent to that of the sample (the main characteristics of the laser and measurement principles are reported in Ref. [13] E tot total energy; S pix CCD pixel area; i (x,y) pixel gray level. Due to a contrast inside the beam itself (peak to average) of about 4, a shot at a given average fluence covers a large range of local fluences (see Fig.…”

“…Values of the coefficient C are reported in the insert for each size bin. The dashed line is the standard behavior from literature [4][5][6][7][8][9][10][11][12][13][14][15][16] Refined modeling of large-beam experiments 523…”

Thermal Approaches to Interpret Laser Damage Experiments

“…Many assumptions may be done to explain these observations. Crystal inhomogeneity, tests repeatability, self-focusing, walk-off and SHG Lamaignère et al, 2009;? ) were suspected to be possible causes for these results due to their orientation dependence they may induce.…”

Correlation between laser-induced damage densities of fused silica and average incubation fluences at 1064 nm in the nanosecond regime

“…Up to now, the probabilistic aspect is dealt with statistical analysis and the laser-induced damage (LID) density is the main measurand describing a damage distribution. In most cases, damage density is obtained by means of 1-on-1 1 procedure that measures high damage densities 2,3 and/or rasterscan procedure that measures low ones. 4,5 These two procedures are complementary and permit us to compare the damage resistance of several optical components.…”