What is ISO 17901‑2 for Holograms? Measurement of Recording Characteristics
ISO 17901‑2:2015 – Optics and photonics – Holography – Part 2: Methods for measurement of hologram recording characteristics is an international standard that specifies methods for measuring key parameters related to how a hologram is recorded, particularly when created by double‑beam laser interference. While ISO 17901‑1 focuses on measuring the resulting optical properties (diffraction efficiency, angular/wavelength selectivity), Part 2 provides a framework for evaluating the recording process itself – parameters such as the exposure characteristic curve, exposure at half‑maximum, R‑value, and amplitude of refractive index modulation. These measurements help hologram origination laboratories optimise their recording setups (e.g., photoresist or photopolymer materials) to achieve consistent, high‑brightness holograms with minimal batch‑to‑batch variation. The standard does not restrict the materials used (glass, plastic, or other substrates) nor prescribe a specific manufacturing process, making it universally applicable to research labs, security hologram manufacturers, and quality control departments. By adhering to ISO 17901‑2, hologram producers can ensure that their master plates are recorded under controlled, repeatable conditions – directly impacting the brightness, sharpness, and security feature fidelity of the final embossed holograms.
🔬 Scope of ISO 17901‑2
ISO 17901‑2 is specifically concerned with exposure characteristics of holograms created by double‑beam interference – the most common method for origination of security holograms (2D, 2D/3D, and some DOVIDs). The standard defines:
- Terms and definitions – establishing a common language for describing recording parameters.
- Measurement methods – detailed procedures for quantifying exposure characteristics using standardised optical setups.
- Data analysis – how to derive key parameters from measurement data (e.g., exposure characteristic curve, half‑maximum exposure, R‑value, refractive index modulation).
Importantly, the standard is material‑agnostic and process‑neutral – it applies to any hologram recorded by double‑beam interference, regardless of the photoresist, photopolymer, or other recording medium used. It also does not restrict the manufacturing process, allowing flexibility while ensuring that measurements are comparable across different laboratories and production environments.
⚙️ Key Measurement Parameters in ISO 17901‑2
1. Exposure Characteristic Curve
A graph plotting diffracted light intensity against exposure energy (mJ/cm²). This curve reveals the recording material’s sensitivity and linearity. An ideal hologram recording material should have a steep, linear region where small changes in exposure produce predictable changes in diffraction efficiency.
2. Exposure at Half‑Maximum
The exposure energy required to reach 50% of the maximum achievable diffraction efficiency. This value helps set the optimal exposure level for the hologram master. Too low exposure results in dim holograms; too high exposure can saturate or over‑modulate the recording.
3. R‑Value (Recording Sensitivity)
A dimensionless metric indicating how efficiently the recording material converts exposure energy into refractive index modulation. Higher R‑values mean the material is more sensitive, allowing shorter exposure times and more consistent results.
4. Amplitude of Refractive Index Modulation (Δn)
The peak‑to‑peak variation in refractive index within the recorded interference pattern. This is the fundamental physical quantity that determines the hologram’s diffraction efficiency. A larger Δn means a brighter, more distinct hologram. ISO 17901‑2 provides a method to calculate Δn from measured diffraction efficiency and material thickness.
🛡️ How ISO 17901‑2 Relates to ISO 17901‑1 (Diffraction Efficiency)
- ISO 17901‑1:2015 – Focuses on measuring the optical performance of finished holograms: diffraction efficiency, angular selectivity, and wavelength selectivity. These are the “output” characteristics that determine how bright and angle‑sensitive a hologram appears to the human eye or a scanner.
- ISO 17901‑2:2015 – Focuses on the recording process itself: exposure sensitivity, refractive index modulation, and recording material characterisation. These are the “input” characteristics that ensure the master plate is recorded correctly.
Together, the two parts of ISO 17901 provide a complete quality control loop: Part 2 ensures the recording process is optimised and consistent; Part 1 validates that the final hologram meets brightness and angular performance specifications. Security hologram manufacturers that adhere to both standards can deliver products with predictable, batch‑to‑batch consistency – critical for banknotes, passports, and high‑security labels.
🔐 Why ISO 17901‑2 Matters for Security Holograms
- Consistent brightness – By controlling exposure and refractive index modulation, manufacturers ensure that every batch of holograms has the same vivid rainbow effect. Without such control, some labels might look dull, reducing their deterrent value.
- Reproducible security features – Microtext, kinetic effects, and DOVID switching angles depend on precise grating depth and refractive index. ISO 17901‑2 helps maintain these parameters.
- Reduced waste – By characterising the recording material’s sensitivity curve, labs can dial in the optimal exposure, reducing failed master plates and saving time and materials.
- Scientific basis for quality control – The standard provides a quantitative, objective method for evaluating recording quality, replacing subjective “looks good” assessments.
📦 Implementation in Hologram Origination Labs
A typical application of ISO 17901‑2 might involve:
- Setting up the double‑beam interference optical bench – with a laser, beam splitter, mirrors, and a photoresist plate holder.
- Preparing test exposures – A series of exposures with increasing energy (e.g., from 0.1 mJ/cm² to 10 mJ/cm²) on the same photoresist plate.
- Developing and measuring – The plate is developed, and the diffracted intensity of each test area is measured with a photodetector.
- Plotting the exposure characteristic curve – Diffracted intensity vs. exposure energy. From this, half‑maximum exposure and Δn are calculated.
- Optimising production exposure – The lab sets the production exposure energy to the point on the curve that yields maximum contrast and linearity.
This process is typically performed when a new batch of photoresist is received, when a new laser is installed, or periodically to verify process stability.
🌍 Holoseal’s Alignment with International Standards
While Holoseal is a hologram supplier (not a manufacturer), we work exclusively with origination laboratories and embossing facilities that adhere to rigorous quality management systems. Our partners follow international standards such as:
- ISO 17901‑1 and ISO 17901‑2 – for measurement and control of hologram recording and performance.
- ISO 14298 – for management of security printing processes (access control, material traceability, secure destruction).
- ISO 9001 – for general quality management.
When you order hologram labels through Holoseal, you benefit from our commitment to quality and standardisation. We can provide measurement reports (e.g., diffraction efficiency, exposure parameters) upon request, ensuring that your security holograms meet the highest international benchmarks.
❓ Frequently Asked Questions About ISO 17901‑2
What is the difference between ISO 17901‑1 and ISO 17901‑2?
ISO 17901‑1 measures the optical performance of the finished hologram (diffraction efficiency, angular/wavelength selectivity). ISO 17901‑2 measures the recording process characteristics (exposure curve, refractive index modulation). Think of Part 1 as the product quality test and Part 2 as the process control test.
Is ISO 17901‑2 required for all hologram manufacturers?
No – it is not mandatory. However, high‑security hologram suppliers (e.g., those serving central banks, passport printers, or pharmaceutical companies) often adopt it as part of their quality management system to demonstrate process control and reproducibility.
Can ISO 17901‑2 be applied to dot matrix or e‑beam holograms?
The standard is written for holograms recorded by double‑beam interference (the classical method for 2D and 2D/3D masters). Dot matrix and e‑beam holograms use different writing methods. However, the principles of exposure control and refractive index modulation still apply, though specific measurement techniques may differ. Some labs adapt the standard’s concepts to those technologies.
Does ISO 17901‑2 apply to embossed holograms on PET film?
Indirectly – the standard applies to the master recording process (on glass photoresist). Once the master is optimised, the embossing process transfers that pattern to PET. The quality of the embossed hologram depends on the master quality, so ISO 17901‑2 is a foundational standard.
How does ISO 17901‑2 help in anti‑counterfeiting?
Consistent, high‑brightness holograms are more effective as anti‑counterfeit devices. Moreover, the ability to measure and control recording parameters ensures that security features (microtext, DOVIDs) are reproduced faithfully across millions of labels. Any deviation could indicate a security breach or unauthorised production.
How does Holoseal ensure compliance with ISO 17901‑2?
We partner with origination laboratories that follow ISO 17901‑2 principles. For high‑security projects, we can request measurement reports and validate that the recording parameters meet specifications. Contact us to discuss your quality requirements.
