LDT values are relevant to both transmissive and reflective optical elements and in applications where the laser induced modification or destruction of a material is the intended outcome.
At a certain point, there can be sufficient localized heating to either affect the material properties or induce thermal shock.
Although this concept is more common in the context of DC and relatively low frequency AC electrical engineering the electromagnetic fields from a pulsed laser can be sufficient to induce this effect, causing damaging structural and chemical changes to the optic.
This plasma readily absorbs the laser energy, leading to the liberation of more electrons and a run-away "avalanche" effect, capable of causing significant damage to the optic.
Some applications make use of laser breakdown directly, necessitating knowledge of the materials' LDT properties.