Manx Publishes Ground-Breaking White Paper about LIDT
Ryan J. McGuigan and Helmut Kessler of Manx Precision Optics have written a ground-breaking white paper. This paper, entitled “Thermal Laser Induced Damage in Optical Coatings Due to An Incident Pulse Train,” originally appeared in the Electro Optics magazine.
Here is an excerpt from the Introduction of this paper:
“Laser Induced Damage Threshold (LIDT) of an optical component defines the maximum intensity the component can resist before the onset of laser damage and as a result is a critical parameter for any modern laser system, with the LIDT defining the maximum possible intensity. However laser damage is a multi-faceted and complex problem with multiple theoretical mechanisms depending on pulse duration, optical coating quality and the manufacturing process of the component. As multi-Petawatt systems become commonplace and laser intensities approach the scale of 1024 Wcm-2, experimentally verified theories and models of laser damage as well as scaling laws become ever more important. Traditionally, LIDT in the nano-second pulse duration regime has long been thought to be due to intrinsic defects within thin film interference coatings, arising as a result of the optical coating deposition process. These defects act as highly absorbing spots, heating the surrounding coating material to its softening or melting point….
Despite decades of research however laser damage remains as something of a theoretical unknown as LIDT values are notoriously unreliable or at times contradict common expectation. In this article the results of a thermal theory of laser damage presented at the SPIE Laser Damage Conference (2021) are explored.
Previous thermal models focused on the role of individual intrinsic, microscopic defects absorbing energy from single pulses of sufficient intensity. The model discussed here is instead macroscopic in nature, accounting for the geometry and dimensions of the optic and beam. There is a greater emphasis on the heat diffusion capabilities of the film and substrate, the former of which may play a larger role due to the thermal conductivity of thin film coatings sometimes being orders of magnitude lower than that of the bulk material. We focus primarily on the effects of long term bulk heating rather than damage due to singular pulses and account for the impact of repletion rate on LIDT.”
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