Subsurface defects of fused silica optics and laser induced damage at 351 nm

Abstract

Many kinds of subsurface defects are always present together in the subsurface of fused silica optics. It is imperfect that only one kind of defects is isolated to investigate its impact on laser damage. Therefore it is necessary to investigate the impact of subsurface defects on laser induced damage of fused silica optics with a comprehensive vision. In this work, we choose the fused silica samples manufactured by different vendors to characterize subsurface defects and measure laser induced damage. Contamination defects, subsurface damage (SSD), optical-thermal absorption and hardness of fused silica surface are characterized with time-of-flight secondary ion mass spectrometry (TOF-SIMS), fluorescence microscopy, photo-thermal common-path interferometer and fully automatic micro-hardness tester respectively. Laser induced damage threshold and damage density are measured by 351 nm nanosecond pulse laser. The correlations existing between defects and laser induced damage are analyzed. The results show that Cerium element and SSD both have a good correlation with laser-induced damage thresholds and damage density. Research results evaluate process technology of fused silica optics in China at present. Furthermore, the results can provide technique support for improving laser induced damage performance of fused silica.

Analysis of the beam-pointing stability in the high power laser system

“…This laser system is ideally suited for a wide variety of high-energy-density scientific experiments, including laser-induced damage mechanism for UV optics research [20][21][22], stimulated Brillouin scattering (SBS) [23][24][25][26][27] and stimulated Raman scattering (SRS) [28,29]. To obtain one beam with an aperture of 60-mm-diameter, the whole size of the laser system is designed to be about 7 m length, 2 m height and 1.5 m width.…”

Investigation of surface characteristics evolution and laser damage performance of fused silica during ion-beam sputtering

“…The Ce element, which has strong absorbency to UV laser, is almost undetectable [4]. Other impurity elements, such as Al, Fe and Mg were monitored for maybe leading to strong absorption in the UV [20]. And their concentration has greatly reduced at least 91% of the original surface after sputtering.…”

Interaction of laser pulse with confined plasma during exit surface nanosecond laser damage

“…Specifically, we will discuss experiments [4], where damage was induced by 8 nsec pulses of 355 nm light with fluence ~50 J/cm 2 The calculations demonstrate almost complete absorption of laser radiation by plasma for 355 nm laser light [5]. We approximate the motion of the material and the associated pressure fronts along the axial direction (normal to the surface) as initially one-dimensional when the laser spot size is much larger then the absorption length, which is the case in our experiments.…”

“…The pressure on the thin layer between the plasma and free surface causes the bulging up to about 25 ns delay and break up and particle ejection at delays longer than about 35 ns as shown in Fig 2. The velocity V of this layer with thickness d can be expressed as (2) When the layer starts to move, the plasma expands, and the pressure drops from the value given by Eq(1) and the acceleration stops. This moment is determined by the time needed by the rarefaction wave reflected by the free surface to return to the plasma region.…”

“…The optical damage induced by a high-power ICF class laser systems is initiated by small defects localized within a few microns below the surface [1][2][3]. Recently, the processes accompanying the damage event were observed with high spatial and temporal resolution [4].…”