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theoretical background design of interference filters measurement of spectral responsivity

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

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theoretical background design of interference filters measurement of spectral responsivity

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

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

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

  4. Influence of wavelength uncertainty l = 650 nm Dl = 0.05 nm Tref= 1337,33 K Tref= 1800 K Tref= 2300 K

  5. Determination of spectral responsivity Measurement by comparison to reference detector : sref (l) : spectrally flat responsivity (thermopile, pyroelectric detector) sref (l) : calibrated responsivity (silicon photodiode, trap detector) l : monochromator with wavelength calibration, tunable laser i (l ) , iref (l ) : 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 653 nm and halfwidth 39 nm Spectral transmittance of the interference filter with effective wavelength 974 nm and halfwidth 41 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 1,003 1,002 0° 90° 1,001 Calculated for randomly polarised light 1,000 integral of spectral responsivity, normalised 0,999 0,998 with pre- disperser with pre- disperser 0,997 0,996 4 9 4 9 9 9 2 grating

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

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

  19. References • 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

  20. Conclusions • 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

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