Use of Al2O3 layers for higher laser damage threshold at 22.5 degrees incidence, S polarization of a 527 nm/1054 nm dichroic coating

We have designed and reported on a dichroic beam combiner coating consisting of HfO2/SiO2 layer pairs to provide high transmission at 527 nm and high reflection at 1054 nm for 22.5 degrees angle of incidence (AOI) in S polarization (Spol). The laser-induced damage threshold (LIDT) of this first coating at the use AOI and polarization with 3.5 nanosecond (ns) pulses at 532 nm is 7 J/cm(2), and only marginally adequate for our beam combining application. In this paper, we describe the use of a combination of Al2O3 and HfO2 high index layers to modify the first as well as a second dichroic coating in two different ways, which results in a higher LIDT of 10 J/cm(2) for 3.5 ns pulses at 532 nm and 22.5 degrees AOI, Spol for the second dichroic coating, and in the same 7 J/cm(2) LIDT for the first dichroic coating.