Abstract
The feasibility of the idea of double stack HR coating was discussed in this paper both in theory and experiment. The theoretical simulation was made by employing optical coating design software. The analysis results showed that the design of double stack HR coating was feasible, which made the HR coating have ascendancy not only at reflectance but also at laser damage resistance. Then, the LaF 3/MgF 2 HR coating, the HfO 2/SiO 2 HR coating and the double stack HR coating were prepared for comparison, respectively. Transmittance spectra, surface morphologies and damage morphologies of these coatings were measured. Measurement of laser-induced damage threshold (LIDT) of S polarized light of the samples was performed at 355 nm, 45° incidence. The measurement results showed that the LIDT value of the LaF 3/MgF 2 HR coating with 30 layers was very high, but the reflectance was low. When the layer number was increased up to 36, lots of cracks appeared on the surface of the LaF 3/MgF 2 HR coating, with the LIDT badly declining. It was thought that the residual stress resulted in the cracks and the decline of the LIDT. The spectra measurement showed the double stack HR coatings could provide higher reflectance and wider reflection band than LaF 3/MgF 2 HR coating with less layer pairs. Any crack was also not found on the surface of the double stack coatings. Meanwhile, the double stack HR coatings possessed greater laser damage resistances than the HfO 2/SiO 2 HR coating. The damage morphologies showed that the damage of the double stack coating was even milder than that of the HfO 2/SiO 2 coating. Therefore, the double stack design was effective to gain high reflectance and great UV laser radiation resistance simultaneously.
Published Version
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