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Detector Based Traceability Chain Established at the UME
F.Sametoglu * , O.Bazkir, O.Celikel
TUBITAK-Ulusal Metroloji Enstitusu (UME),
Gebze, 41470, Kocaeli, Turkey
Abstract. In UME, detector based traceability chain for
radiometry and photometry was established in 2003, which
is presented.
1. Introduction
The concept of traceability to a national laboratory is
fundamental to a unified system of metrology. Metrology
institutions establish their own traceability chains and
cross-linkings in measurements depending on primary and
secondary standards. In optical metrology this type of chain
can be established either with source or detectors based
standards. We developed detector-based radiometric and
photometric scales and established traceability chain in
measurements, which is given in Figure 1.
Calibration, Fl
Radiometers
Power Meters
Cryogenic
Radiometer
Absolute Optical Power
Sphere
Radiometer
Absolute Responsivity
Pyroelectrical Radiometer Trap Detector Filter Radiometer
Optical Power
Absolute Responsivity Absolute Responsivity
Spectral Responsivity
Calibration, Rl
Radiometers
Detectors
Meters
Calibration, EV
Photometers
Luxmeters
Si Detectors
Spectral Responsivity
Calibration, IV
Light Sources
Illuminance
Relative Responsivity
Luminous Responsivity
Calibration, RI
Retroreflectors
Cat Eyes
Luminous Intensity
Luminous Intensity
Coefficient
Figure 1. Traceability chain for radiometry and photometry
established at the UME.
2. Absolute Optical power Scale
Filter Radiometer
Spectral Irradiance
Goniometer
Luminous Flux
Integrating Sphere
Luminous Flux
Retroreflection
Coefficient
Luminance
Calibration, RA
Retroreflectors
Cat Eyes
Calibration, Rl
Fiber Optic
Power Meters
Calibration, El
Radiometers
Light Sources
Calibration, FV
Light Sources
Calibration, LV
Luminance Sources
Luminance Meters
Top of chain constitutes the absolute measurement of
optical power (W) measured by using a helium-cooled
electrical-substitution cryogenic radiometer (ESCR).
Intensity stabilized and vertically polarized lasers (He-Ne,
Ar + and Nd:YAG) are used for the realization. The
measurement of optical power at each laser wavelength
was performed using static substitution method by which
optical temperature induced by optical heating is
sandwiched between two electrical temperatures, which are
slightly above and blow the optical temperature, obtained
by electrical heating. Then optical power was obtained by
equating it to the electrical power calculated by
interpolation of an optical and two electrical temperatures
and two electrical powers. Effects of all the parameters like
scattering, window transmittance and imperfect cavity
absorbance on the optical power were examined and the
optical power scale was realized with an expanded
uncertainty of a few parts of 10 4 .
3. Responsivity Scale
Absolute responsivity scale is based on calibration of
homemade reflection type trap detectors, which consist of
three Hamamatsu S1337-11 windowless silicon
photodiodes, against ESCR. The absolute spectral
responsivity scales for optically characterized each trap
detectors were obtained at two steps. In the first step, the
absolute spectral responsivities at the mentioned discrete
laser wavelengths were measured. Then in the second step,
developing the interpolation and extrapolation models for
the internal quantum efficiency and reflectance of detectors
the scale was expanded to 350 - 850 nm wavelength range
with an expanded uncertainty of 0.05 %.
The relative optical power and spectral responsivity
scales from 250 nm to 350 and 850 nm to 2500 nm
wavelength ranges were realized by calibrating the
detectors against another transfer standard called as
electrically calibrated pyroelectric radiometer (ECPR). The
ECPR has flat response pyroelectric detector made from
lithium tantalite crystal, which has permanent dipole
moment. The pyroelectric detector was calibrated against
ESCR and the responsivity scale was realized between 250
and 2500 nm wavelength range with an expanded
uncertainty of 1.74 % by using the spectral reflectance of
coating of pyroelectric detector.
3. Spectral Irradiance Scale
Temperature-controlled home-made filter radiometers
were used in order to realize spectral irradiance scale
between 286 nm and 901 nm wavelength range. Filter
radiometer consists of three element silicon trap detector,
band-pass filters and precision aperture. The temperature
of each radiometer housing including, aperture and filter
can be adjusted from 18 °C to 35 °C range with stability of
better than 0.05 °C using circular thermo-electric Peltier
element. The irradiance scale was realized using the
measurements of aperture area, transmittance of filters and
* Corresponding author. Phone: +902626795000; Fax: +902626795001
E-mail address: ferhat.sametoglu@ume.tubitak.gov.tr
Proceedings NEWRAD, 17-19 October 2005, Davos, Switzerland 331