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**Optical radiation

Works that have been launched by the NMIs (LNE-INM and LNE/CMSI) are covering the national references as well as the means for transfer towards the users (calibrating benches).

Projects involving the references, consist in maintaining them at the highest metrology level and in comparing them with the other national references as part of the international comparisons. This is the basic mission assigned to the NMIs. Moreover, it is often necessary to make the references progress by improving them (means and uncertainties) or by developing fresh references (new types, fresh methods).

Projects relating to the means for transfer, generally involve maintaining the calibrating means at the highest metrology level, from the national reference up to the users references, adapting means to the new instruments or references of the users, and developing new benches to widen the calibration possibilities (new ranges of measurements or new instruments).

Photometry

The candela has been materialised by standard lamps of luminous intensity. But over these last years, standard photometers were realised to materialise the candela. These are instruments made up of a detector calibrated to a cryogenic radiometer, filters that mimic the V(λ) curve and diaphragms. It could thus be two complementary methods to maintain the candela based on the lamps and the detectors. Nevertheless, this will imply monitoring the long-term stability of the photometers realised, and these works are under way. In addition, in order to improve the calibration uncertainty of the photometers to the cryogenic radiometer, the LNE-INM are studying the realization of new photometers by using trap detectors and not plane detectors as is currently the case. A group of standard lamps will then be formed for the luminous flux.

Detector radiometry

To calibrate the detectors, meaning to measure their spectral responsivity, the current national reference is the cryogenic radiometer. To achieve this purpose, several measuring benches are available for measurements over a large spectral band running from ultraviolet (200 nm) to infrared (14 µm).

Spectral responsivity of detector

Cryogenic radiometer allows calibrating the detectors at some wavelengths in the visible range. But the available laser sources are ranging from UV to the near IR. In order to improve the measurement uncertainties, the current studies are aimed at extending the use of the cryogenic radiometer in the ultraviolet and near infrared. The detectors that have been directly calibrated against this reference are then used as secondary references or transfer references on the other measuring benches. And these are, as often as possible, trap detectors or detectors exhibiting the best possible characteristics (stability, spatial homogeneity, linearity...).

Components of trap detector.
Components of trap detector.

In order to transfer the references having the best uncertainties using the transfer detectors, a specific study has been launched on the characterisation of these transfer detectors, notably in the UV and IR ranges. Different detectors (Si, InGaAs, GaAsP, ...) are characterised then assembled in trap fashion.

Irradiance

This is about realising new references for spectral irradiance traceable to the cryogenic radiometer to improve the current stability and increase the number of measurement wavelength. These references are filter radiometers.

The transfer means towards the users (calibration of the radiometers and spectroradiometers) are under consolidation in the UV range where improvement in the uncertainties was especially required.

Calibration of radiometers used for the heat sources

These detectors (called "fluxmeters") are used by laboratories carrying out fire tests to measure the emitted heat flux. The LNE/CMSI holds three benches (reference and transfer) for the calibration of Gardon or Schmidt-Boelter type sensors.
The purpose of the current study is to improve the measurement methods using reference sources and reduce the calibration uncertainties of the IR radiometers that are used. The sources are blackbodies working in vacuum (minimizing convection), that allows absolute calibrating of the fluxmeters, or atmospheric pressure cavity for relative calibration.
Additionally, the expansion of the calibration capabilities to other types of fluxmeters is under study.

New reference bench for the fluxmeters calibration.
New reference bench for the fluxmeters calibration.

Source radiometry

Utilization of new sources with the cryogenic radiometer

In order to extend the use of the cryogenic radiometer in the ultraviolet and infrared ranges as well as increase the wavelengths available for the characterisation of detectors or radiometers, the LNE-INM have acquired a tunable titanium:sapphire laser which, associated to different OPO, will be made useable over the full usual spectral range in radiometry.

Photometry on LED-type sources

The objective of this project that was launched in 2006, is to study the characteristics of the electroluminescent diodes, in intensity, in flux and spectral distribution, to be able to turn them into reference sources and use them to answer the industrial problems raised by security and colour appearance of the objects illuminated by such sources.

White LEDs
White LEDs

Sources spectroradiometry

A new calibrating bench for sources ranging from 200 nm to 1 000 nm is under finalization. This bench will allow, according to its configuration, the calibration of the detectors, or sources calibration.

Calibration bench for sources and detectors.
Calibration bench for sources and detectors.

Infrared sources radiometry

The goal of this project is to reduce the uncertainties in metrology measurement of sources, from 1 µm to 14 µm, through the implementation of a system of radiometers and detectors fitted with spectral analysis tools to cover the full spectral range. These measurement means will be characterised in front of blackbody sources or laser sources via comparison against references.

Optical properties of materials measurement

The LNE/CMSI keeps different measurement means in transmittance and in reflectance

Improvement of the spectrophotometric measurements

In order to have references for the reflectance measurements using the LNE’s different spectrophotometers, the laboratory is developing one absolute measuring bench of the directional hemispheric reflectance.

Bench for absolute measurement of reflectance.
Bench for absolute measurement of reflectance.

Refractive index for materials

The purpose is to develop the means for absolute measurement of glass plate in order to have one reference of glass refraction in the laboratory. This reference will then be used for standardised measurement of brightness.

Fibre optics

Study of photon components

The objective of this study is the realisation of one measuring bench for the photon characteristics and components including spatial resolution in the magnitude of one millimeter. Measurements are made on the optical low coherence reflectometer (OLCR). The measuring methods and signal processing obtained are developed on the basis of typical components: photo-inscribed Bragg gratings fibres, photon crystal fibres, high order mode fibres.

ESM photography of one micro-structured fibre.
ESM photography of one micro-structured fibre.