Overview
ISO 13142:2021 - Optics and photonics: Cavity ring‑down method for high‑reflectance and high‑transmittance measurements - defines standardized measurement procedures for precisely determining very high reflectance or transmittance (>99%) of optical laser components. The standard specifies cavity ring‑down (CRD) techniques (pulsed, continuous‑wave and feedback variants) to measure decay times of optical cavities and derive mirror reflectance or sample transmittance with high accuracy, repeatability and immunity to source power fluctuations.
Key topics and technical requirements
- Cavity ring‑down (CRD) principle: measurement of optical decay time (τ) of a ring‑down cavity to infer losses due to mirror reflectance or sample transmittance rather than relying on absolute power measurements.
- Initial and test cavity procedures: measure decay time of the empty (initial) cavity to determine mirror reflectance, then insert the test sample (reflective or transmissive) and measure the altered decay time to compute the sample’s reflectance/transmittance.
- Measurement variants: pulsed‑CRD, cw‑CRD (square‑wave switching), and optical‑feedback CRD techniques are described for different instrumentation and sensitivity needs.
- Instrumentation and setup: guidance on test sample preparation, laser source selection, mode matching, ring‑down cavity configuration (concave/plane mirrors, accounting for curvature/focal length when measuring lenses), detectors, data acquisition and processing.
- Environmental and cleanliness controls: references to cleanroom considerations (ISO 14644‑1) and refractive index/air effects.
- Error sources and uncertainty: discussion of instrumental response time, data fitting and truncation strategies, cavity length and decay time measurement errors, and recommended assessments and reporting.
- Reporting: content and format expectations for a comprehensive test report (including reliability checks and uncertainty statements).
Applications and users
ISO 13142:2021 is intended for:
- Optical component manufacturers (high‑reflectance mirrors, anti‑reflection coatings, AR windows)
- Coating and thin‑film laboratories performing QC and R&D
- Metrology and calibration labs needing sub‑0.1% accuracy at >99% reflectance/transmittance
- Laser system integrators for high‑power lasers, interferometers, laser gyroscopes and cavity‑enhanced spectroscopy setups
- Research facilities (e.g., gravitational‑wave detectors) where ultra‑high reflectance/transmittance measurement is critical
Practical value: improves measurement accuracy where spectrophotometry/laser ratiometry are not precise enough (ISO 15368 methods typically reach ±0.3% and are not suitable for measurements beyond ~99.9%).
Related standards
- ISO 15368 - Reflectance and transmittance by spectrophotometry (complementary; broader range but lower precision at extreme values)
- ISO 11145 - Vocabulary and symbols for lasers and optics
- ISO 14644‑1 - Cleanrooms and air‑cleanliness classification
- ISO 80000‑7 - Quantities and units for light and radiation
Keywords: ISO 13142:2021, cavity ring‑down, CRD, high reflectance, high transmittance, optics and photonics, laser component metrology.