LIDT

LIDT stands for Laser-Induced Damage Threshold. It is a measure of the maximum laser energy density or power that a material or optical component can tolerate without sustaining damage when exposed to a laser under specified conditions. LIDT is a property of the particular material or coating, and it depends on factors such as wavelength, pulse duration, pulse shape, beam size, polarization, and environment.

In practice, LIDT is reported in terms of fluence (Joules per square centimeter) for pulsed lasers or irradiance (Watts per square centimeter) for continuous-wave lasers. Measurements typically involve exposing a representative set of test sites to increasing laser fluences or irradiances and recording the onset of damage. For pulsed sources, common test protocols assess multiple shots (for example, S-on-1 or S-on-2 sequences) to estimate a damage probability at each fluence. The resulting threshold is often expressed with a statistical confidence level.

Standards and methods exist to standardize LIDT testing and reporting. International guidelines, such as ISO-related documents, describe how to perform damage testing on optical coatings and materials, specify test durations, beam characteristics, and how to derive a threshold value with defined confidence. The exact LIDT value depends on the test setup and conditions, so comparisons should be made only between tests performed under the same conditions.

LIDT is essential in the design and qualification of optical components for high-power laser systems, space instrumentation, and safety-critical optics. It highlights the need to consider material quality, coating deposition, cleanliness, and conditioning, as well as potential aging effects.