Low NEP pyroelectric radiometer standards

Abstract

Verification of the low measurement uncertainty of a group of eight newly developed pyroelectric detectors at the output of a traditional monochromator is described. The frequency compensated hybrid detector-amplifier packages have fixed 1010 Ω feedback resistors. The characterizations verified that the 3 dB upper roll-off frequencies of the signal-gain curves are close to 100 Hz and the temperature coefficient of responsivity is 0.14 %/oC. The hybrid packages were tested for noise performance in the f/8 beam of a grating monochromator between 900 nm and 2.7 μm. The monochromator output beam-power, the output signal, and the output noise of the hybrid packages were measured and compared. The NEPs were between 3.3 nW/Hz1/2 and 10 nW/Hz1/2. The relative standard uncertainty of the noise measurements was 20 % (k=1). The noise tests were utilized to select hybrid packages with NEPs that are one order of magnitude lower than that of traditional pyroelectric detectors and current-amplifiers. The power responsivity of one hybrid was calibrated against an absolute cryogenic radiometer. With this detector, the measured signal-to-noise ratios were higher than 400 between 1.1 μm and 2.1 μm and 250 at 2.5 μm using a lock-in integrating time-constant of 1 s. The noise test results show that using a hybrid detector with an NEP equal to the group average of about 6 nW/Hz1/2, spectral responsivity measurements with a relative standard uncertainty of 0.2 % to 0.4 % (k=1) can be achieved.