Realization of a primary spectrophotometric system

Abstract

The first step in establishing measurement uniformity in spectrophotometry is the realization of a versatile, fully evaluated and documented measurement system, which may, after metrological validation, be upheld as the primary spectrophotometric standard. In this paper, the development and realization of the spectrophotometer—primary standard in the Laboratory for Photometry of Bureau of Measures and Precious Metals—are presented. The construction of the system, as well as its metrological characterization, is shown. Evaluation of systematic errors due to various influential quantities and physical effects, such as light beam geometry effects, inter-reflections, nonlinearities and others, is presented. The results of measurements of spectral transmittance made with neutral optical filters and the evaluation of total measurement uncertainty are presented. Validation of the results was preformed according to National Institute for Standards and Technologies (NIST) certified standards of spectral transmittance.

Developement of the method for realization of spectral irradiance scale featuring system of spectral comparisons

“…Absolute calibration of the lamp was performed with the filter radiometer (V(λ )), whose absolute spectral responsivity was determined by comparison with standard detectors in the primary spectrophotometric system (figure 2), [11]. The filter radiometer was a modified LMT Photometric detector, the diffuser replaced with a precision aperture.…”

“…The measurement of absolute responsivity of the filter radiometer was performed on the primary spectrophotometric system [11], (figure 3). Detectors were automatically exchanged in the path of the light beam.…”

“…The method of mutual comparisons is based on comparison measurements between calibrated standards, where one is used as a standard and the other is used as a calibration artefact. For example, results of the comparison of two detectors is calculated as the relative deviation of the results of measurements for the second detector's responsivity, using the first one as a standard, from its values given in certificate [2]. Mutual comparisons of three standard detectors (SR1, SR2, SR3 -Hamamatsu S1337-1010BQ photodiodes) were performed by comparing each to each, in both directions (measurement sequence), meaning that six different comparisons were made.…”

“…Realization of the spectral irradiance unit is based on the comparison method [2], where the value of spectral responsivity is transferred to filter radiometers and a spectroradiometer (used as a wavelength tuneable-filter radiometer). A filter radiometer is then used for spectral irradiance unit realization, whereas a spectroradiometer is used for derivation of the relative spectral irradiance of the FEL 1000 lamp [3].…”