Overview
ISO 11455:1995 - Raw optical glass - Determination of birefringence describes a standard, repeatable stress-optical method for measuring birefringence in raw optical glass (bulk and preshaped forms). The method, based on the de Senarmont / Friedel compensation technique, uses polarized light and interference optics to quantify optical path difference caused by manufacturing, thermal or mechanical stresses. Results are reported as birefringence (Δn) in nanometres per centimetre (nm/cm) and are applicable in quality control and photo-elasticity testing.
Key topics and requirements
- Scope: Measurement of birefringence in optically homogeneous, isotropic glasses under stress; applicable to simple geometrical shapes (plates, disks, rods, blocks).
- Principle: Measure optical path difference (Δs) between orthogonal polarization components and compute birefringence Δn = Δs / a, where a is the light path (thickness) in cm.
- Wavelengths: Typical monochromatic filters near maximum eye sensitivity - 546 nm or 589 nm - are recommended.
- Apparatus:
- Polarimeter with compensator (de Senarmont / Friedel type)
- Collimated light source, diffuser, polarizer and analyser
- Quarter-wave plate (rotatable); optional full-wave plate (≈565 nm) for white-light colour checks
- Telescope for parallax-free viewing; immersion cell for non‑parallel or rough surfaces
- Thickness measurement to ±1%
- Procedure:
- Orient sample so principal stress directions are at 45° to the polarizer
- Measure thickness at each point (≈5% from edge for plate samples)
- Rotate analyser to compensate optical path difference; use white light to count interference orders if Δs > one wavelength
- Report Δn rounded to nearest 1 nm/cm
- Limits & interpretation:
- Compensation method effectively covers retardations up to one wavelength; for larger retardations count interference fringes
- Determination of stress sign (tension/compression) using full-wave plate and colour sequence; converting Δn to mechanical stress (elastic calculation) is outside this standard
Applications and users
ISO 11455:1995 is practical for:
- Optical glass manufacturers and suppliers - in-process and final quality control
- Metrology and test laboratories performing birefringence audits
- Optical engineers specifying raw glass for lenses, prisms and precision components
- Materials scientists and researchers using photo-elasticity to map stress distributions
- Process engineers monitoring annealing and forming operations
Keywords: ISO 11455:1995, birefringence measurement, raw optical glass, stress optical method, polarimeter, de Senarmont, photo-elasticity.
Related standards
- ISO 9802 - Raw optical glass - Vocabulary (definitions)
- ISO 10110-2 - Optics drawings - Material imperfections, stress birefringence
For routine testing, follow ISO 11455:1995’s apparatus, sample preparation and compensation procedure to obtain consistent, comparable birefringence data for quality assurance and research.
