Myths about Laser Damage #2

Dense optical coatings feature the highest LIDT.

That is a common myth, which is not necessarily true.

Optical coatings can be produced by various deposition techniques: e-beam, ion-assisted deposition (IAD), ion beam sputtering (IBS), magnetron sputtering (MS), atomic layer deposition (ALD), and others. There is a common belief that only one of the procedures should be universally the best in terms of laser-induced damage threshold (LIDT) performance. Usually, dense optical coatings with stable spectral properties are assumed to have the highest LIDT values. However, the evidence shows that is not necessarily so.

A two year study was organized by Lawrence Livermore National Laboratory (LLNL) in cooperation with Lidaris. Large set of HR coatings @2ω (532nm or 515nm) were collected from various laser companies all around the world. The LIDT of these samples were tested at NS (~ 6 ns) and FS (~200 fs) regimes. The results revealed that the highest LIDT performances were observed for different coating technologies. It turned out that dense (IBS) coatings performed best at FS regime while porous coatings (e-beam) did a better job in NS regime.


[1] Negres, Raluca A., et al. “515-nm, femtosecond laser mirror thin film damage competition.” Laser-Induced Damage in Optical Materials 2021. Vol. 11910. SPIE, 2021

[2] Negres, Raluca A., et al. “532-nm, nanosecond laser mirror thin film damage competition.” Laser-induced Damage in Optical Materials 2020. Vol. 11514. International Society for Optics and Photonics, 2020.

Why is that?

It is not completely clear yet. But it is obvious that coating technology is not the only factor defining laser damage performance for all the irradiation regimes: one technology could be the best for nanosecond applications, while the other – could give the best results for femtosecond pulse regime. Also, as it was stated in myth #1, the coating is not always the main or the only limitation of LIDT.

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