In photometry, the main quantities measured are luminous
intensity and luminous flux. Those measured in radiometry include everything
from luminance to irradiance of sources to the spectral responsivity
of detectors as well as the transmission of filters.
One aim of our present studies is to bridge the gap
between radiometry and pyrometry via the determination of the thermodynamic
temperature of a black body. This is to be achieved using radiometric
methods anchored to the cryogenic radiometer.
Research activities:
The following studies and research activities undertaken
in the radiometry-photometry laboratories of the BNM-INM/CNAM have been
selected by the scientific committee of the BNM, based on their importance
in metrology and impact upon industry :
-
The cryogenic radiometer:
The cryogenic radiometer is the current reference for measurement
of optical radiation at the BNM. This high technology instrument,
equipped with an electrical substitution detector, enables one
to measure radiation originating from power controlled laser beams
and of appropriate geometry with an uncertainty of a few times
10-4. The BNM-INM has designed and built an experimental set-up
allowing the comparison of transfer standard detectors with the
cryogenic radiometer for wavelengths ranging from the near ultra-violet
to the near infra-red
-
Transfer detectors:
The use of the cryogenic radiometer is a somewhat delicate operation
and is thus reserved for only the highest level calibrations.
Consequently, the BNM-INM continues to study transfer standards.
This involves first building multi-photodiode "trap"
detectors, starting from commercially available photodiodes. The
metrological characteristics, stability and spectral responsivity
of these devices are then established.
- Standard sources (lamps)
Two quantities are linked to radiant sources, the radiance, i.e. the
intrinsic characteristic of a source and the irradiance. The latter
is more generally used, but here the distance and orientation of measurement
must be accurately defined.
The spectral range, from 300 nm to 2500 nm, includes the major part
of the radiant power for the usual sources to be measured, natural
or artificial ones. The reference is built from a detector calibrated
against a cryogenic radiometer and a black body whose temperature
is measured by comparison with the 1990 International Temperature
Scale (ITS 90). The uncertainty is better than 1% over a large part
of the spectrum.
-
Measurements of irradiance in the UV region:
UV irradiance are measured using radiometers with filters. These
devices, comprised of a photodiode detector, an interference filter
of bandwidth 10 nm and a calibrated diaphragm, are linked to the
cryogenic radiometer.
- Parametric down-conversion applied to radiometry
-
Photometry:
The realisation of the unit of luminous intensity, candela, is
based on the use of standard photometers linked to the cryogenic
radiometer. The realisation of the unit of luminous flux, the
lumen, uses a goniophotometer calibrated with lamps of luminous
intensity.
-
Measurement of the transmittance of optical filters:
Regular transmittance measurements of optical filters are carried
out using a reference laboratory set-up that allows one to determine
with precision and minimise every contribution to the uncertainty.
- Spectral radiance and thermodynamic temperature
Calibrations and traceability:
As a NML (National Measurement Laboratory) , the BNM-INM/CNAM
is capable of providing links to national references.
- Sources : Luminous intensity, luminous flux, illuminance, spectral
radiance, spectral irradiance
- Detectors : Spectral responsivity, linearity.
- Materials : Regular transmission of optical filters.
The laboratories concerned by these calibrations are:
- the other NMLs that have no reference of their own,
- the laboratories of the GIP-BNM*
- accredited laboratories for which a need for a link to national
references is stipulated.
Calibration laboratories and people from industry should get in touch
with one of the accredited laboratories of which a list is available
from the COFRAC (Comité français d’accréditation
= French national accreditation committee).
* GIP-BNM groupement d’intérêt public
BNM = the public sector umbrella group of laboratories and ministries
that make up the BNM
International Collaborations:
The "Radiometry - Photometry" group at BNM-INM
is involved in several international collaboration either as steering
laboratory or mere participant.
- CCPR-K1.a Spectral irradiance (VIS-IR)
- CCPR-K1.b Spectral irradiance (UV)
- CCPR-K2.a Spectral responsivity of detectors (IR)
- CCPR-K2.b Spectral responsivity of detectors (VIS)
- CCPR-K2.c Spectral reponsivity of detectors (UV)
- CCPR-K3.a Luminous intensity · CCPR-K3.b Illuminance
- CCPR-K4 Luminous flux· CCPR-K6 Regular transmittance
- CCPR-S1 Spectral radiance· CCPR-S2 Aperture area
- CCPR-S3 Cryogenic radiometers
- EUROMET.PR.K3a Luminous intensity
- EUROMET.PR.K4 Luminous flux
- EUROMET.PR.K6 Regular transmittance
Contacts:
- Jean BASTIE research scientist, head of group bastie
- Jeanne-Marie COUTIN research scientist coutin
- Bernard ROUGIE research scientist rougie
- Annick RAZET lecturer razet
- Stephan BRIAUDEAU lecturer briaudeau
- Aurélie STEPNIK research scientist aurelie.stepnik
- Fatima TAYEB-CHANDOUL research assistant tayeb
- Arnaud RICHARD technician arnaud.richard
- Christelle VELLY engineering diploma student christelle.velly
- Laura-Patricia GONZALES doctoral student laura-patricia.gonzalez
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