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Single photon detection efficiency calibration setup based on the correlated photon approach.

qutools’ quEff is a complete system for absolute efficiency calibration of photon counting detectors. Designed for simple and user-friendly operation the measurements can be performed within a few minutes. Contrary to all conventional calibration techniques, the measurements using quEff are self-referenced and do not require comparison to any external radiometric standards.

At the heart of quEff is the photon pair source based on a nonlinear optical process called spontaneous parametric down-conversion. Since the photons are always emitted from the source in pairs, the detection of one photon at the trigger detector (TRIG) heralds the existence of the other. The energy and momentum conservation in the down-conversion process allows one to accurately determine not only the existence, but also the wavelength and the propagation direction of the other photon from a pair, which is incident on the device under test (DUT). The fraction of trigger detections, for which the other photon from a pair is registered in a coincidence at the DUT, defines the efficiency of this detectors. The correlated-photon calibration method is self-referenced and absolute because it is independent of any radiometric standard or the properties of another detector.

The quEff includes all the necessary equipment to readily accomplish the efficiency measurement of a single photon detector. The wavelength of the photons arriving at the DUT can be chosen over a wide range (roughly 0.6 μm to 1.5 μm). Using the same setup one can additionally measure the timing jitter of the DUT*.

*: Additional analysis tools are required for some of the applications.

Key Features

  • Absolute efficiency measurements of single photon detectors without reference to externally calibrated standards
  • Wide wavelength range (0.6 μm … 1.5 μm)
  • Compact and easy-to-use
  • Complete system: Measurement completed within a minimum of time


  • Absolute detector efficiency measurement
  • Spatial detection uniformity characterization
  • Detector timing jitter and dead time analysis

System Includes

  • Source of correlated photon pairs
  • Fibre-coupled single photon trigger detector
  • Alignment facilities for quick positioning of the detector under test
  • Three-channel counter with integrated coincidence logic
  • Control and read-out unit


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