DIN EN ISO 21254-1:2011-10

Optical components can be damaged by laser irradiation of sufficiently high energy or power. At any specified laser irradiation level and operation mode of the laser source, the probability for laser damage is usually higher for the surface of a component than for the bulk. Thus, the limiting value of an optical component is frequently given by the damage threshold of its surface which might be coated to influence the optical properties. Bulk damage is observed if the electrical field strength in the bulk of the component is enhanced by self-focusing, interference, scattering or other effects. Also, imperfections, such as inclusions, dislocations, colour centres or inhomogeneities, can reduce the power-handling capability in the bulk of an optical component. Damage by single laser pulses is often induced by defects or mechanical stress in the coating, contamination of the surface, or optical absorption, leading to catastrophic heating of the surface. For multiplepulse operation, not only reversible mechanisms induced by thermal heating and distortion but also irreversible damage mechanisms induced by ageing, microdamage, moisture damage and generation or migration of defects are observed. The various parts of this International Standard are concerned with the determination of irreversible damage of the optical surfaces and the bulk of an optical component under the influence of a laser beam. Depending on the environmental conditions, damage is a function of the material properties and the laser parameters, in particular wavelength, spot size and irradiation duration. This part of ISO 21254 is dedicated to the fundamentals and general principles of the measurement of laserinduced damage thresholds (LIDTs). On the basis of the apparatus and measurement protocols described in ISO 21254-1, ISO 21254-2 and ISO 21254-3, this part of ISO 21254 outlines procedures for damage testing under different conditions. The protocols for the determination of the 1-on-1 and S-on-1 damage thresholds are described in ISO 21254-2. The 1-on-1 test is a damage threshold measurement procedure that uses one shot of laser radiation on each unexposed site on the specimen surface. In contrast to this, the S-on-1 measurement programme is based on a series of pulses with constant energy density applied to each unexposed site of the specimen surface. This test reflects the operational conditions of the sample in typical applications but, compared to the 1-on-1 measurement protocol, the experimental effort necessary for S-on-1 tests is significantly higher. ISO 21254-3 concentrates on the assurance of the power or energy density handling capability of optical surfaces, leaving samples that pass the test undamaged. ISO/TR 21254-4, which considers damage detection methods and the inspection of tested surfaces, is a Technical Report which complements ISO 21254-1. The Committee responsible for this standard is NA 027-01-18 AA "Laser" ("Laser") of the Optics and Precision Mechanics Standards Committee at DIN.