Suppression of nano-absorbing precursors and damage mechanism in optical coatings for 3ω mirrors

Abstract

Damage precursors in the 3ω (351 nm) mirror for a high-power laser system are investigated as well as the relevant damage mechanisms. The precursors are classified into two ensembles according to the different laser resistance and damage features. The former is nano-absorbing precursors, which are sensitive to the standing wave electric field and vulnerable to the laser irradiation. The latter is submicrometer nodular defects, which have higher laser resistance and are sensitive to the adhesion strength between the fluoride coatings and oxide coatings. The damage due to nano-absorbing precursors is efficiently suppressed with the double stack design that screens the electric field in the oxides. Currently, the nodular seed is major originating from the Al2O3/SiO2 stack. Even for the same defect type and mirror, the final damage features are dependent on the local mechanical properties at the irradiation location. The investigations of the damage mechanisms provide a direction to further improve the laser-induced damage threshold of the 3ω mirror.

SiO2/HfO2 Laser Film with Enhanced Protection and Antireflection for Sapphire Infrared Windows at High Temperatures

“…The poor interfacial adhesion and the large stress mismatch are believed to have adverse impacts on laser-damage resistance. Hence, the lower residual stress and higher adhesion strength endow the HfO 2 /SiO 2 film with a higher LIDT. , It should be noted that the introduction of the HfO 2 interlayer is expected to further increase LIDT. However, the defects of the HfO 2 interlayer, as shown in Figure e, weaken the resistance toward laser damage.…”

The characterization of laser-induced thermal damage mechanism of mid-infrared optical coatings with surface contaminants

“…Under the irradiation of high power continuous wave (CW) laser, the thermal effect is the main origin of the damage when the laser interaction occupies for a long time [2,3]. There are many factors causing the thermal damage of the optical coatings, such as substrate flaw, coating defect and surface contaminant [4][5][6]. Among them, surface contaminant has the major effect for thermal damage which could lead to a serious absorptivity peak.…”

On-line detection method based on optimal modified lateral shearing interferometry for evaluating the damage growth characteristics

“…[1][2][3] The growth in lateral size and depth of initial damage sites under successive irradiation will decrease the laser-induced damage resistance of optical components and thus limit the reliable and cost-effective operation of high power laser systems. [4][5][6][7] The optical function of damaged components is also degraded severely because of the increase of initial damage sites. Moreover, optical modulation effects on the transmitted laser beam may induce the damage of downstream components.…”

“…At the present time, some high-precision and high-resolution techniques, such as atomic force microscope, optical surface profiler, scanning electron microscope, are applied to detect vertical and horizontal cross sections of damage sites for estimating the damage growth behavior. [6][7][8][9][10] Thus, the lateral size and the depth of damage sites are measured accurately. However, these techniques have limitations to be inserted into the laser damage experimental setup and detect on-line the lateral size and depth of damage sites because of complex configurations.…”