Overview
EN ISO 11146-2:2021 - “Lasers and laser-related equipment - Test methods for laser beam widths, divergence angles and beam propagation ratios - Part 2: General astigmatic beams” - specifies standardized measurement methods for laser beam widths (diameters), divergence angles and beam propagation ratios for general astigmatic beams or beams of unknown type. Adopted by CEN and superseding the 2005 edition, this part uses the second order moments of the Wigner distribution as the basis for beam description, from which common physical quantities (e.g., beam widths, divergence, M²) are derived. The methods are valid within the paraxial approximation.
Key topics and technical requirements
- Second order moments (Wigner distribution): Primary descriptive quantities used to characterize beam propagation and geometry.
- Derived physical quantities: Beam diameter, divergence angle and effective beam propagation ratio (M²) are obtained from these moments; calculation guidance is provided in ISO/TR 11146-3.
- Measurement procedures: Requirements for measurement arrangement, detector systems, beam-forming optics, optical attenuators, background subtraction and offset correction.
- Practical measurement steps: Determination of all relevant second order moments across cross-sections, integration range considerations, and procedures to obtain effective M², intrinsic astigmatism and the twist parameter.
- Environmental and equipment control: Guidance on preparation and control of measurement environment and detector calibration (including power/energy detectors).
- Alternative methods (correlation): ISO/TR 11146-3 documents how variable aperture, moving knife-edge and moving slit methods relate to the second-moment approach.
- Reporting: Required test-report content to ensure traceability and reproducibility of beam characterization.
Applications and practical value
- Beam quality assessment: Standardized determination of beam propagation ratio (M²) and divergence for R&D and production verification.
- Laser product specifications: Defining and verifying manufacturer claims for beam width, divergence and beam quality.
- Optical system design & alignment: Accurate characterization of astigmatic or unknown beams for lens selection, focusing, and imaging systems.
- Metrology and certification: Test labs and quality assurance functions use the standard for consistent, comparable measurements.
- Safety & regulatory compliance: Supporting documentation for laser classification and safe system integration.
Who uses this standard
- Laser manufacturers and optical component suppliers
- Photonics R&D teams and system integrators
- Calibration and testing laboratories (metrology labs)
- Quality assurance, compliance and certification bodies
- Academic and industrial researchers working with complex/astigmatic beams
Related standards
- ISO 11146-1 - Stigmatic and simple astigmatic beams
- ISO/TR 11146-3 - Formulas and guidance to calculate physical beam parameters from second order moments
- ISO 11145 - Vocabulary and symbols for lasers and photonics
- EN 61040 - Power and energy measuring detectors for laser radiation
Keywords: EN ISO 11146-2:2021, laser beam widths, divergence angles, beam propagation ratio, general astigmatic beams, Wigner distribution, second order moments, beam characterization, M² measurement.
