Standards Development

Scope

This International Standard specifies procedures for the absorption measurement and high spatialresolution absorption mapping of optical laser components, and upon calibration, the measurement of absolute absorptance of large-sized laser optics. The methods given in this International Standard are intended to be used for the absorption mapping of optical laser components, that is, measurement of absorption as a function of position, as well as absorption/absorptance measurement and mapping of large-sized laser optics used in high-power /high-energy laser systems.

Purpose

With the rapid development of high-power/energy laser technology, laser systems with output power/energy exceeding 1 MW/1 MJ have been developed in the past few years. Laser systems with output power/energy exceeding 1 kW/1 J are routinely available and widely used in various applications. In such high-power/energy laser systems, the laser-induced damage to optical laser components and laser-induced thermal distortion in the laser components are the most important limiting factors for the operation and applications of these laser systems. Normally, the laser-induced damages to optical laser components are caused by absorbing defects on the surface or within the laser components which result in thermal stress or melting of the laser components and lead to damage. The thermal distortions, which induce wavefront distortions and therefore beam quality deteriorations to the laser beam, are caused by non-uniform thermal expansion and refractive index changes due to absorption irregularities inside the laser components. To improve the laser-induced damage threshold and reduce the laser-induced thermal distortion of laser components used in highpower/ energy laser systems, there are needs to not only measure precisely the absorptance of the laser components, but also to detect various absorbing defects on/within the laser components, therefore to improve the performance of these laser components via optimizing fabrication/coating processes. The defect detections can be fulfilled via absorption mapping. On the other hand, there is also a need to measure the absolute absorptance of large-sized optical (laser) components actually used in high-power/energy laser systems.

Currently, the ISO 11551 standardized testing method - laser calorimetry for absorptance measurements of optical laser components can only measure test samples with small sizes (normally less than 50mm in diameter and 10mm in thickness. For coating laser components normally witness samples during coating deposition processes are used as test samples) and have almost no capability to measure the absorptance of large-sized laser components (100mm in diameter and over) widely used in high-power/high-energy laser systems. In addition, laser calorimetry has only limited capability to map the absorptance distribution of an optical laser component.