1. theoretical background design of interference filters measurement of spectral responsivity blocking problems stability polarisation scattered light references summary Determination of spectral responsivity in radiation thermometry J. Fischer, Physikalisch-Technische Bundesanstalt, Berlin, Germany

2. Basic theory of radiation thermometry ratio Q of spectral radiance : limiting effective wavelength ( T ref  T), (Wien´s approximation) :

3. Propagation of uncertainties measurement of photocurrent ratio determination of wavelength realisation of reference temperature

4. Influence of wavelength uncertainty T ref = 1337,33 K T ref = 2300 K T ref = 1800 K = 650 nm  = 0.05 nm

5. Determination of spectral responsivity Measurement by comparison to reference detector : s ref ( ) : spectrally flat responsivity (thermopile, pyroelectric detector) s ref ( ) : calibrated responsivity (silicon photodiode, trap detector)  : monochromator with wavelength calibration, tunable laser i (  i ref (  : sensitive to out-of-band radiation, scattered light, etc.

6. Spectral comparator (IMGC)

7. Interference filters Spectral transmittance of the interference filter with effective wavelength 974 nm and halfwidth 41 nm Spectral transmittance of the interference filter with effective wavelength 653 nm and halfwidth 39 nm

8. Out-of-band error without blocking Error in silver-gold ratio of 2.1 K

9. Additional Schott glass KG3 Error in silver-gold ratio reduced to 3.9 mK

10. Confirmation by sharp-cut filter Out-of-band signal of 1.4x10 -4 measured

11. Stability, definitions

12. Stability of filter 800 nm

13. Stability of filter 900 nm

14. Measurement of filters Line above responsivity curve indicates the bandpass frequently calibrated, covering four orders of magnitude

15. Polarisation Monochromator system emits partly polarised light radiation thermometer and reference detectors sensitive to polarisation required : calibration for use at randomly polarised black body sources polariser behind exit slit, 2 measurements :

16. Scattered light in monochromator 0,996 0,997 0,998 0,999 1,000 1,001 1,002 1,003 4949992 grating integral of spectral responsivity, normalised 0° 90° with pre- disperser with pre- disperser Calculated for randomly polarised light

17. Principle of spectral comparator TUNGSTEN HALOGEN LAMPGLAN- THOMPSON PRISM GRATING MONOCHROMATOR ZEISS SPM2 (f=400 mm) TRANSLATION UNIT TRAP- DETECTOR FILTER RADIOMETER f=450 mm f=300 mm FILTER WHEEL (SUPPRESSION OF HIGHER ORDERS) SPECTRAL OR TUNGSTEN HALOGEN LAMP LEISS PRISM MONOCHROMATOR f=150 mm LIGHTTIGHT ENCLOSURE SPECTRAL LAMP

18. Example for uncertainty uncertainty contributions (k=1) for measurement of the silver-gold interval :

19. Battuello M., Girard F., Ugur S., Aytekin S.H.,. Measurements of spectral responsivity at IMGC (Italy) and UME (Turkey). a bilateral comparison, to be published in Proceedings of TEMPMEKO 2001 Battuello M., Uncertainty budgets for realisation of scales by radiation thermometry, CCT-WG5 working paper, 2001 Fischer J., Hartmann J., Calibration of tungsten strip lamps as transfer standards for temperature, In Proceedings of TEMPMEKO ‘99, edited by M. de Groot and J. Dubbeldam, Delft 1999, pp 561...566 Fischer, J., Jung, H.J., Friedrich, R., A new determination of the freezing temperature of gold relative to that of silver by radiation thermometry, Proceedings of Temperature, Its Measurements and Control in Science and Technology, Vol. 6, edited by J.F. Schooley, New York, 1992, pp 53..57 Gibson, C.E., Tsai, B.K., Parr, A.C., Radiance temperature calibrations, Natl. Inst. Stand. Technol. Spec. Pub. 250-43, 1998 Sakuma F., Kobayashi M., Interpolation equations of scales of radiation thermometers, In Proceedings of TEMPMEKO ‘96, edited by P. Marcarino, Torino 1997, pp 305...310 Saunders P., General interpolation equations for the calibration of radiation thermometers, Metrologia 1997, 34, pp 201...210 References

20. Uncertainty depends crucially on effort for calibration re-calibration interval main contributions : monochromator wavelength calibration calibration of reference detector scattered light (single/double monochromator) out-of-band blocking of filters stability of filters and detectors temperature coefficient of thermometer Conclusions