<title>Growth of laser-induced damage during repetitive illumination of HfO2/SiO2 multilayer mirror and polarizer coatings</title>

Abstract

Lawrence Livermore National Laboratory, Laser Materials Department, Livermore, California 94550. ABSTRACTAs designers want to increase the peak fluence of high power laser, it becomes necessary to tolerate some damage on mirrors and polarizers. To quantify how the different types of damage morphologies initiate and grow during repetitive illumination, hafnia-silica multilayer mirror and polarizer coatings were laser damage tested. The coatings were prepared by e-beam evaporation and irradiated with a 3-ns-pulse at 1064 nm.The morphology of laser-induced damage was recorded after each shot to determine the types of damage that cause massive unstable failure and lower the optic's functional damage threshold. The results of the tests were summarized on damage stability maps plotting the average damage size as a function of the number of shots for fluences ranging from 10 to 40 J/cm The results show that the delaminate damage morphology should be prevented. This knowledge has allowed coatings development efforts to focus on eliminating the origin of such damage morphology.

Fabrication of meter-scale laser resistant mirrors for the National Ignition Facility: a fusion laser

“…14 This is important because interfacial damage such as flat-bottom pits and delamination grow at significantly lower (2-10×) fluences than nodularejection pits. 15 Attempts to deposit from silicon were less successful. 7 Good stoichiometry could only be achieved by increasing the energy of the deposition process.…”

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

“…As mentioned earlier, the study of damage growth of the various damage morphologies 16 showed that small pits and flat bottom pits as well as scalds do not usually grow upon repetitive illumination below 30 J/cm 2 . On the other hand, once formed, delaminates and large pits tend to grow very rapidly to catastrophic proportions with subsequent shots.…”

“…2,[11][12][13][14][15] The relationship between damage morphology and damage growth has also been studied in detail. 16 It is known that for hafnia-silica multilayer mirrors, four different morphologies can be found; pits, flat bottom pits, scalds and delaminates. [17][18][19][20] Other studies published in these proceedings show that the delaminate is the most unstable morphology among the four 16 and that the addition of a a) Electronic Mail: fgenin@llnl.gov thicker silica overcoat tends to eliminate such damage morphology thereby substantially improving their functional damage threshold.…”

“…16 It is known that for hafnia-silica multilayer mirrors, four different morphologies can be found; pits, flat bottom pits, scalds and delaminates. [17][18][19][20] Other studies published in these proceedings show that the delaminate is the most unstable morphology among the four 16 and that the addition of a a) Electronic Mail: fgenin@llnl.gov thicker silica overcoat tends to eliminate such damage morphology thereby substantially improving their functional damage threshold. 21 The angular dependence of damage threshold for mirrors has been studied by Newnam et al for a 351 nm, 10-ns laser.…”

Optics Performance at 1(omega), 2 (omega), and 3 (omega): Final Report on LDRD Project 03-ERD-071

“…For example, the functional damage threshold of multilayer polarizers, nodular defects in multilayer mirrors, and the effects of Pt inclusions on possible damage in Nd-doped metaphosphate amplifier slabs (laser glass) have been investigated [25][26].…”