Abstract
Optical coatings with the highest laser damage thresholds rely on clean conditions in the vacuum chamber during the coating deposition process. A low-base pressure in the coating chamber, as well as the ability of the vacuum system to maintain the required pressure during deposition, are important aspects of limiting the amount of defects in an optical coating that could induce laser damage. Our large optics coating chamber at Sandia National Laboratories normally relies on three cryo pumps to maintain low pressures for e-beam coating processes. However, on occasion, one or more of the cryo pumps have been out of commission. In light of this circumstance, we explored how deposition under compromised vacuum conditions resulting from the use of only one or two cryo pumps affects the laser-induced damage thresholds of optical coatings. The coatings of this study consist of HfO2 and SiO2 layer materials and include antireflection coatings for 527 nm at normal incidence and high-reflection coatings for 527 nm at 45-deg angle of incidence in P-polarization.
Highlights
The large optics coating system at Sandia NationalLaboratories uses e-beam evaporation to produce optical coatings with high resistance to laser damage for the kJclass Z-Backlighter laser system.[1,2] Since 2005, the coating system has been in operation for the production of antireflection (AR), high reflection, polarizer, and dichroic coatings on meter-class optics, materials.[3,4,5,6,7] using mainly HfO2 and SiO2 coatingOptics with high resistance to laser damage are essential for operating high-power laser systems such as the Z-Backlighter lasers
This study addresses whether high laser-induced damage threshold (LIDT) optical coatings for large laser systems can be produced with reduced vacuum pumping capability in a coating chamber
In the case of both AR and HR coatings for 527 nm, reducing the number of cryo pumps in our coating chamber had a negative effect on the LIDT of the coatings, highlighting the importance of adequate vacuum pumping speeds to reduce damage-initiating defects in the coatings
Summary
The large optics coating system at Sandia NationalLaboratories uses e-beam evaporation to produce optical coatings with high resistance to laser damage for the kJclass Z-Backlighter laser system.[1,2] Since 2005, the coating system has been in operation for the production of antireflection (AR), high reflection, polarizer, and dichroic coatings on meter-class optics, materials.[3,4,5,6,7] using mainly HfO2 and SiO2 coatingOptics with high resistance to laser damage are essential for operating high-power laser systems such as the Z-Backlighter lasers. Laboratories uses e-beam evaporation to produce optical coatings with high resistance to laser damage for the kJclass Z-Backlighter laser system.[1,2] Since 2005, the coating system has been in operation for the production of antireflection (AR), high reflection, polarizer, and dichroic coatings on meter-class optics, materials.[3,4,5,6,7] using mainly HfO2 and SiO2 coating. Producing an optical coating with a low number of defects and a high LIDT involves many variables, including the substrate preparation,[8,9,10] coating material selections,[5,6,11] deposition method,[12] and the pressures maintained during deposition. Pressure is important because it must be low enough, with a vacuum pumping capability sufficiently high enough, to remove possible gas-phase contaminants from the coating chamber before they can attach to the coating and serve as defects that could increase laser damage. This study concerns pressure, the consequences of losing some vacuum pumping capability during a coating deposition
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