ISO 17411:2022

Overview

ISO 17411:2022 - Optics and photonics: Test method for homogeneity of optical glasses by laser interferometry specifies laser-interferometric procedures to measure the homogeneity of the refractive index in optical glass. The standard defines test methods, measurement apparatus, preparation and operation steps, calculation and reporting to support grading systems in ISO 10110-18 and ISO 12123. It is the second edition (2022) and expands measurement options to include PHom, FT-PSI and SCI methods in addition to transmission and oil-on-plate approaches.

Key Topics and Technical Requirements

• Measurement principle: Homogeneity is obtained from the peak-to-valley (PV) of the transmitted wavefront (W) measured by a laser interferometer; PV of refractive-index variation is derived from W.
• Accepted methods:
  • Transmission method - preferred for polished, plane-parallel parts; sensitive to surface deformation.
  • PHom method - recommended for very high homogeneity (refractive index differences ≤ 2×10^-6); provides high trueness and precision.
  • Oil-on-plate method - uses index-matching liquid between test part and a reference plate; easier preparation but requires matched liquids per glass type.
  • FT-PSI and SCI methods - Fourier Transform Phase Shifting Interferometry and Spectrally Controlled Interferometry allow observation of linear-change components in refractive index.
• Apparatus requirements: laser interferometer, interferogram analysis device, thermostatic chamber (ambient 20–25 °C; spatial/time fluctuation < 0.4 °C), vibration isolation, and biaxial adjustment platform (for PHom/FT-PSI/SCI).
• Test part preparation:
  • Transmission: end surfaces polished to flatness < 32 nm PV (λ/20).
  • PHom: end-surface flatness < 1 900 nm PV (≈3 waves); small wedge angle required (example 0.10° ± 0.05° for diameters up to 350 mm).
• Measurement, calculation and reporting: Procedures cover operation, data analysis (interferogram processing to obtain W), calculation of refractive-index homogeneity and required elements of the test report.

Applications and Who Uses It

ISO 17411:2022 is used by:

• Optical glass manufacturers and suppliers for quality control and acceptance testing.
• Optical-component and lens manufacturers verifying homogeneity for high-performance optics (windows, prisms, substrates).
• Metrology laboratories and test houses performing interferometric characterization.
• R&D teams in photonics, aerospace optics, semiconductor lithography optics and precision instrumentation where refractive-index uniformity affects performance.

Keywords: ISO 17411:2022, homogeneity of optical glasses, laser interferometry, refractive index homogeneity, PHom, oil-on-plate, FT-PSI, SCI, optical materials testing.

Related Standards

• ISO 10110-18 (optical drawing/grades related to homogeneity)
• ISO 12123 (glass and glass-ceramics specifications)
• ISO 80000-1 (quantities and units)