Overview
ISO 23701:2023 - "Optics and photonics - Laser and laser-related equipment - Photothermal technique for absorption measurement and mapping of optical laser components" defines standardized procedures for using photothermal techniques to measure and map absorption (and, after calibration, absolute absorptance) of optical laser components. The standard targets high spatial-resolution two-dimensional and three-dimensional absorption mapping, and is optimized for components used in high-power / high-energy laser systems where localized absorbing defects and non-uniform absorption can limit performance.
Key benefits emphasized in the standard:
- High sensitivity to weak absorptance
- High spatial resolution for defect detection
- Capability to handle large-sized optics that traditional laser calorimetry struggles with
Key Topics and Requirements
ISO 23701:2023 specifies methods, equipment and reporting elements, including:
- Test principles: Photothermal detection based on induced temperature rises, surface displacement and refractive-index gradients. Main techniques described are photothermal lensing (TL) and photothermal deflection (PTD).
- Detection schemes: Both reflected and transmitted probe-beam detection options and guidance on selecting the appropriate scheme.
- Measurement arrangement and equipment:
- Pump laser (excitation source) and probe laser (detection)
- Translation stage for spatial mapping
- Detection unit, data acquisition and processing
- Environmental and cleanroom considerations
- Test procedure: Preparation of test samples, measurement of photothermal amplitude and phase, creation of 2D/3D absorption maps, and calibration steps to determine absolute absorptance.
- Evaluation and reporting: Converting photothermal signals to absorption/absorptance values, mapping area and spatial resolution guidance, and required contents of the test report.
- Informative annexes: Guidance on calibration theory/practice and on separating surface vs. bulk absorption.
Practical Applications and Who Uses It
ISO 23701:2023 is intended for organizations and professionals concerned with laser optics quality, reliability and performance, such as:
- Optical manufacturers and coating houses (quality control and process optimization)
- Laser system integrators and R&D teams for high-power / high-energy lasers
- Metrology and calibration laboratories measuring absorptance and mapping defects
- Defense, fusion, and industrial laser facilities where laser-induced damage threshold (LIDT) and thermal distortion are critical
- Researchers studying thermo-physical properties of optical materials (using photothermal phase mapping)
Practical outcomes include detecting absorbing defects, improving fabrication/coating processes, measuring absorptance of large optics, and reducing thermal distortion in high-power laser systems.
Related Standards
- ISO 11145 (vocabulary and symbols for lasers)
- ISO 80000-7 (quantities and units - light and radiation)
- ISO 14644-1 (cleanroom classifications)
- Complementary: ISO 11551 (laser calorimetry for absorptance - limited for large optics)
Keywords: ISO 23701:2023, photothermal technique, absorption measurement, absorption mapping, absorptance, photothermal lensing, photothermal deflection, laser optics, high-power laser systems, optical component metrology.