Rear-surface laser damage on 355-nm silica optics owing to Fresnel diffraction on front-surface contamination particles

Abstract

Light intensity modulations caused by opaque obstacles (e.g., dust) on silica lenses in high-power lasers often enhance the potential for laser-induced damage. To study this effect, particles (10-250 mum) with various shapes were sputter deposited on the input surface and irradiated with a 3-ns laser beam at 355 nm. Although a clean silica surface damages at fluences above 15 J/cm(2), a surface contaminated with particles can damage below 11.5 J/cm(2). A pattern that conforms to the shape of the input surface particle is printed on the output surface. Repetitive illumination resulted in catastrophic drilling of the optic. The damage pattern correlated with an interference image of the particle before irradiation. The image shows that the incident beam undergoes phase (and amplitude) modulations after it passes around the particle. We modeled the experiments by calculating the light intensity distribution behind an obscuration by use of Fresnel diffraction theory. The comparison between calculated light intensity distribution and the output surface damage pattern showed good agreement. The model was then used to predict the increased damage vulnerability that results from intensity modulations as a function of particle size, shape, and lens thickness. The predictions provide the basis for optics cleanliness specifications on the National Ignition Facility to reduce the likelihood of optical damage.

Design and optimization of a highly efficient optical multipass system forγ-ray beam production from electron laser beam Compton scattering

“…In particular, severe conditions have to be respected for the cleanliness of the manufacturing process, during installation and during operation. In fact similar to the conditions to be respected for the National Ignition Facility and for Laser MegaJoule [53][54][55].…”

Influence of oil contamination on the optical performance and laser induced damage of fused silica

“…The influence of particulate contaminants such as dust, aerosol, metal flakes and cloth threads on the optical performance and LIDTs of optical components have been widely studied [6][7][8][9].…”

“…In most cases, the damage mechanism is usually attributed to thermo-mechanical rupture or laser intensity modulation [6,7]. For organic contaminant, it often exists as gaseous molecules or nonvolatile residues (NVRs).…”

Optimizing the cleanliness in multi-segment disk amplifiers based on vector flow schemes

“…Due to the increase in laser energy and the expansions of the laser driver's scale, the cleanliness of the working environment with numerous optical elements has greatly affected the construction cycle and operating life of the high power solid-state laser driver [1][2][3][4] . Recent studies have shown that flashlamp illumination is a major factor causing damage to the lasing media (slab or disk) when the contaminant particles deposit onto the surface of the optical element in a multi-segment Nd:glass disk laser amplifier [5][6][7][8] . Because the full fluence of the flashlamp illumination in SG-II can reach 10 J/cm 2 , most contaminant particles on the surface of the lasing media will be melted or decomposed.…”