The quantum efficiency of photon counters can be measured with standard uncertainty below 1% level using correlated photon pairs generated through spontaneous parametric down-conversion process. Normally a laser in UV, blue or green wavelength range with sufficient photon energy is applied to produce energy and momentum conserved photon pairs in two channels with desired wavelengths for calibration. One channel is used as the heralding trigger, and the other is used for the calibration of the detector under test. A superconducting nanowire single photon detector with advantages such as high photon counting speed (<20 MHz), low dark count rate (<50 counts per second), and wideband responsivity (UV to near infrared) is used as the trigger detector, enabling correlated photons calibration capabilities into shortwave visible range. For a 355nm single longitudinal mode pump laser, when a superconducting nanowire single photon detector is used as the trigger detector at 1064nm and 1560nm in the near infrared range, the photon counting efficiency calibration capabilities can be realized at 532nm and 460nm. The quantum efficiency measurement on photon counters such as photomultiplier tubes and avalanche photodiodes can be then further extended in a wide wavelength range (e.g. 400-1000nm) using a flat spectral photon flux source to meet the calibration demands in cutting edge low light applications such as time resolved fluorescence and nonlinear optical spectroscopy, super resolution microscopy, deep space observation, and so on.
The instrument for spectral diffuse reflectance and color coordinate measurement has to be calibrated by a spectral
reflectance standard, so as to obtain an absolute value. Normally, the value is traced to the primary color standard or
diffuse reflectance standard. The integration sphere is one of the key components in the primary color standard of China,
and the reflectance nouniformity of the sphere is the biggest systematic error source of the absolute measurement result.
A novel uniformity analysis method is developed basing on scanning technique with CCD array spectrometer for
reducing the effect of uniformity to the primary color standard measurement. The preliminary experiment shows that the
effect of sphere nouniformity can be corrected basing on the scanning data of uniformity distribution.
A reflectance colorimetry measurement system is constructed using scanning spectrometer with array detector, and the
color measurement can be achieved under 45:0 and 0:45 geometry conditions. Typically, there are two types of
spectrometer for colorimetry measurement: the scanning spectrometer with single-channel detector requires
point-by-point spectral reading, and the measurement is time consuming; array sensor spectrometer (multichannel
spectrometer) can completes the measurement in a few milliseconds, but its spectral resolution and range are limited by
the array sensor and the optical elements. This colorimetry measurement system is designed for color calibration service,
it using a scanning spectrometer with array detector, which divides the board spectral measurement range into sections,
and uses the array detector to measure each section respectively, thus achieving the rapid measurement of spectral data
with high resolution and wide wavelength range, so as to realized fast color measurement with high precision. The array
sensor of the system using a photo diode array (PDA) with 1024 pixel, having a larger dynamic range and better linearity
compared to CCD. The grating is rotated with a precision rotation stage, and the rotation angle is calculated basing the
parameters of grating and collimator lens, so as to stitch the spectral data of each measurement section., the measurement
signal is mutated at the junction point between measurement sections, due to the rotation angle and the shape of grating
efficiency curve. The theoretical analysis and experiment shows that the signal mutation at the junction point can be
eliminated by comparison measurement of reflectance.