Facility for spectral irradiance and radiance responsivity calibrations using uniform sources

Abstract

Detectors have historically been calibrated for spectral power responsivity at the National Institute of Standards and Technology by using a lamp-monochromator system to tune the wavelength of the excitation source. Silicon detectors can be calibrated in the visible spectral region with combined standard uncertainties at the 0.1% level. However, uncertainties increase dramatically when measuring an instrument's spectral irradiance or radiance responsivity. We describe what we believe to be a new laser-based facility for spectral irradiance and radiance responsivity calibrations using uniform sources (SIRCUS) that was developed to calibrate instruments directly in irradiance or radiance mode with uncertainties approaching or exceeding those available for spectral power responsivity calibrations. In SIRCUS, the emission from high-power, tunable lasers is introduced into an integrating sphere using optical fibers, producing uniform, quasi-Lambertian, high-radiant-flux sources. Reference standard irradiance detectors, calibrated directly against national primary standards for spectral power responsivity and aperture area measurement, are used to determine the irradiance at a reference plane. Knowing the measurement geometry, the source radiance can be readily determined as well. The radiometric properties of the SIRCUS source coupled with state-of-the-art transfer standard radiometers whose responses are directly traceable to primary national radiometric scales result in typical combined standard uncertainties in irradiance and radiance responsivity calibrations of less than 0.1%. The details of the facility and its effect on primary national radiometric scales are discussed.

Accurate radiometry from space: an essential tool for climate studies

“…For higher stability, stronger signal and better wavelength definition, a laser-based source can be used (figure 11). Such a source can be obtained by illuminating a small integrating sphere with a tunable laser, fed through a vibrating fibre to remove speckle [40,65]. Traceability to SI comes via the trap detector, which is itself calibrated for spectral power responsivity against the cryogenic radiometer.…”

Spectral stray light effect on high-temperature measurements using a near-infrared multi-wavelength pyrometer

“…The spectral stray light projected on the pyrometer sensor is not very intense, on the order of 10 À4 of the spectral irradiation intensity. However, the sum of the radiation reflected from all wavelengths to one wavelength, especially when the real signal is weak, can be large enough to cause large errors [27][28][29]. The multi-wavelength pyrometer is generally calibrated for the wavelength response, nonlinearity intensity response and temperature response characteristics against a standard high-temperature blackbody source and a standard HgAr lamp source before the pyrometer is used.…”

“…Spectral stray light generally originates from radiation scattered from imperfections in the dispersing grating, filter, prism and other optical elements in the system and can cause larger errors when measuring the spectral intensities of a source with a broad-band radiation distribution. The analysis of spectral stray light has been of great concern for spectrometer applications in the fields of colorimetry, photometry and optical spectroscopy with some correction methods developed to reduce the effect of the spectral stray light [27][28][29][30][31][32][33][34][35][36][37][38].…”

High Accuracy Calibration Technology of UV Standard Detector

“…In comparison with POWR, the L-1 ACR is compact and mobile, which makes it a convenient instrument to use for scale transfers. The relative combined standard uncertainty of the NIST cryogenic radiometer measurements range is from 0.01 % to 0.02 % in the visible region of the spectrum [10] . The largest components of the uncertainty are those due to the systematic correction for the Brewster angle window transmittance and the nonequivalence between electrical and optical heating.…”