Overview
ISO 11146-2:2021 specifies standardized test methods for measuring laser beam widths (diameter), divergence angles and beam propagation ratios for general astigmatic beams or beams of unknown type. Unlike methods that rely directly on beam diameters, this part of ISO 11146 uses the second order moments of the Wigner distribution to describe beam properties. Physical quantities (beam width, divergence, waist location, etc.) are closely related to these moments; formulae to convert moments into physical parameters are given in ISO/TR 11146-3. This standard is valid within the paraxial approximation.
Key topics and technical requirements
- Second order moments (Wigner distribution): Measurement and use of ten independent second order moments to fully characterize a general astigmatic beam (spatial and angular moments and cross-terms).
- Derived invariants: Definitions and procedures to determine the effective beam propagation ratio (Meff), intrinsic astigmatism (a), and twist parameter (t) - invariants important for beam focusability and phase characteristics.
- Measurement arrangement and equipment: Requirements for measurement setup, environmental control, detector systems, beam-forming optics and attenuators, and preparation steps to ensure repeatable results.
- Measurement procedures: Methods for measuring spatial second order moments from power (or energy) density distributions, and for obtaining all ten second order moments of the Wigner distribution.
- Data processing and reporting: Procedures for background subtraction, offset correction (see ISO/TR 11146-3), and the required content of the test report.
- Applicability: Intended for general astigmatic or unknown beams; for stigmatic and simple astigmatic beams, ISO 11146-1 applies.
Practical applications
- Quality control and acceptance testing of industrial and scientific lasers.
- Optical system and resonator design validation where beam astigmatism, focusability and twist affect performance (e.g., material processing, fiber coupling, microscopy).
- Metrology and calibration laboratories that measure and certify beam propagation ratio and divergence.
- R&D teams working on laser sources with complex phase or astigmatic properties, and system integrators verifying beam delivery performance.
- Safety and compliance testing that requires standardized beam characterization.
Who should use this standard
- Laser manufacturers and OEMs
- Test and calibration laboratories
- Optical designers, systems integrators and metrology engineers
- Regulatory and conformity assessment bodies
Related standards
- ISO 11146-1 - Stigmatic and simple astigmatic beams
- ISO/TR 11146-3 - Technical Report with formulae and alternative measurement methods (variable aperture, knife-edge, moving slit)
- ISO 11145 - Vocabulary and symbols
- EN 61040 - Power and energy measuring detectors for laser radiation
Keywords naturally included: ISO 11146-2, laser beam measurement, beam widths, divergence angles, beam propagation ratio, astigmatic beams, Wigner distribution, second order moments, Meff, intrinsic astigmatism.