Optics deals with the properties of light and how it behaves when interacting with matter. The ability to measure light is more important today than ever before.
Whereas the 20th century was the age of electronics, leading European experts point out that the 21st century will be the age of photonics – the century of light technology.
Light technology enables fast and precise measurements. In healthcare, for example, light is used in medical measuring equipment that provides instant test results. To ensure that decisions based on such measurements are correct, both manufacturers and users must be confident that the results are accurate. Here, the Norwegian Metrology Service plays an important role.
Light surrounds us constantly, and the right amount of light is essential for both safety and well-being. In the health sector, light is used, among other things, in the analysis of blood samples, treatment of neonatal jaundice, psoriasis, atopic eczema, and in measuring oxygen content in blood.
In products such as laser pointers, remote controls, laser speed meters and entertainment technology, it is also important to control light output to avoid harmful effects on the eyes. In transport – on roads, at sea and in the air – we depend on reliable light signals for safety. In research, for example in studies of UV radiation from sunbeds, light detection is also used.
Common to all these applications is the need for accurate measurements of optical power. This requires correct use and calibration of measuring instruments.
The Norwegian Metrology Service calibrates optical measuring instruments. Today’s calibration chain from the primary standard down to the end user can be long, and the accuracy may degrade at each stage. Calibration involves comparing an instrument with a more precise reference instrument, requiring advanced technology and expertise – often with high operating costs.
A cryogenic radiometer is the most accurate instrument for measuring optical power. It works by absorbing light radiation and measuring the resulting increase in temperature , compared with electrical heating. This method is both expensive and time-consuming, and the cost of the instrument alone often exceeds one million Norwegian kroner. Due to these limitations, specially designed silicon detectors are used as working standards in calibration laboratories.
Silicon detectors are core technology for measuring radiation within the ultraviolet, visible and near-infrared spectrum. They are inexpensive to produce, easy to use, and can achieve high quality and accuracy.
The response of silicon detectors is predictable. The Norwegian Metrology Service has completed a doctoral research project developing methods to establish a spectral responsivity scale with nearly the same accuracy as a cryogenic radiometer – but at a fraction of the cost.
This research has provided the Norwegian Metrology Service with advanced expertise in optical radiation detection and the ability to offer traceable and cost-effective measurement services. This enhances customer competitiveness and reduces costs.
The Norwegian Metrology Service’s knowledge of the properties of silicon detectors enables us to advise on their optimal use in customer-specific applications, thereby contributing to improved accuracy and safer products – to the benefit of all users.
In 2005, the Norwegian Metrology Service established a spectral responsivity scale as a result of the doctoral project. This scale has been verified through comparison with the cryogenic radiometer at the National Physical Laboratory (NPL) in the United Kingdom, showing excellent agreement.
The principle behind the Norwegian Metrology Service’s method is that silicon detectors can be manufactured with very low losses. A nearly loss-free detector can be modelled using fundamental physical constants and the wavelength of light. The losses, which mainly stem from reflection or internal absorption in the detector, can be measured and modelled accurately.
Because the losses are so small, the detector behaves almost like an ideal detector. This makes it possible to establish a primary measurement principle based on the fundamental laws of physics.
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