<title>Effect of electric field distribution on the morphologies of laser-induced damage in hafnia-silica multilayer polarizers</title>

Abstract

Hafnia-silica multilayer polarizers were deposited by e-beam evaporation onto BK7 glass substrates. The polarizers were designed to operate at a wavelength of 1064 nm at Brewster's angle (56°). The polarizers were tested with a 3-ns laser pulse at 45°, 56°, and 65° incidence angle in order to vary the electric field distribution in the multilayer, study their effects on the damage morphology, and investigate the possible advantages of off-use angle laser conditioning. The morphology of the laser-induced damage was characterized by optical and scanning electron microscopy. Four distinct damage morphologies (pit, flat bottom pit, scald, and outer layer delamination) were observed.These damage morphologies were found to depend strongly on the angle of incidence of the laser beam. In particular, massive delamination observed at 45° and 56° incidence, did not occur at 65°. Instead, large and deep pits were found at 65°. The electric field distribution, the temperature rise and the change in stress in the multilayer were calculated to attempt to better understand the relationship between damage morphology, electric field peak locations, and maximum thermal stress gradients. The calculations showed a two-fold increase in stress change in the hafnia top layers depending on the incidence angle. The stress gradient in the first hafnia-silica interface was found to be highest for 45°, 56°, and 65°, respectively. Finally, the maximum stress was deeper in the multilayer at 65°. Although the limitations of such simple thermal mechanical model are obvious, the results can explain that outer layer delamination is more likely at 45° and 56° than 65° and that damage sites are expected to be deeper at 65°.

Investigation of laser-induced damage threshold of hafnia/silica high reflectors at 1064 nm

“…It is known that in case of irradiating coatings the optical resistance of the coatings mainly depends on deposition methods [9] and many parameters such as contamination, thin film materials, coating designs, laser wavelength, fluence, film thickness, laser pulse repetition rate and pulse length [10][11][12] . So in the aim of producing high laser damage threshold coatings, we proposed in the paper to make a comparative study of the laser damage resistance of high reflectors deposited through various deposition techniques.…”