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Optics Express

Radiometric calibration of a multiphoton microscope capable of measuring absolute photon flux of single photon sources

Yangting Fu, Xiangliang Liu, Yingwei He, Yingce Wang, Yandong Lin, Haiyong Gan

Published Jun 3, 2022• 0 citations
Publisher

Abstract

Precise photon flux measurement of single photon sources (SPSs) is essential to the successful application of SPSs. In this work, a novel method, to our knowledge, was proposed for direct measurement of the absolute photon flux of single photon sources with a femtosecond laser multiphoton microscope. A secondary 2-mm-diameter aperture was installed under the microscope objective to define the numerical aperture (NA) of the microscope. The defined NA was precisely measured to be 0.447. An LED-based miniaturized integrating sphere light source (LED-ISLS) was used as a standard radiance source to calibrate the photon flux responsivity of the multiphoton microscope, with the defined NA. The combined standard uncertainty of the measured photon flux responsivity was 1.97%. Absolute photon flux from a quantum-dot based emitter was measured by the multiphoton microscope. The uncertainty of the photon flux was evaluated to be 2.1%. This work offers a new, to our knowledge, radiometric method for fast calibration of photon flux responsivity of microscopes, and absolute photon flux calibration of single photon sources.

DOI
10.1364/oe.458745

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Abstract The traceability of measurements of the parameters characterizing single-photon sources, such as photon flux and optical power, paves the way towards their reliable comparison and quantitative evaluation. In this paper, we present an absolute measurement of the optical power of a single-photon source based on an InGaAs quantum dot under pulsed excitation with a calibrated single-photon avalanche diode (SPAD) detector. For this purpose, a single excitonic line of the quantum dot emission with a bandwidth below 0.1 nm was spectrally filtered by using two tilted interference filters. Since high count rates are essential for many metrological applications, we optimized the setup efficiency by combining high overall transmission of the optical components with a geometrical enhancement of the extraction efficiency of a single quantum dot by a monolithic microlens to reach photon fluxes up to 3.7 ⋅ 10 5 photons per second at the SPADs. A relative calibration of two SPAD detectors with a relative standard uncertainty of 0.7% was carried out and verified by the standard calibration method using an attenuated laser. Finally, an Allan deviation analysis was performed giving an optimal averaging time of 92 s for the photon flux.
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Abstract We present the metrological characterization of a single-photon source based on a germanium-vacancy center in diamond under a solid immersion lens in a confocal microscope setup at room temperature. It was characterized in terms of the emission’s spectral distribution, single-photon purity, temporal stability and the emitter’s excited state lifetime and saturation behavior. An Allan deviation analysis was performed on the emission of the single-photon source to determine the optimal averaging time of the photon flux. The single-photon source was used for the relative calibration of the detection efficiency of two single-photon avalanche diode detectors. The results were compared with measurements using attenuated laser light for the calibration of the detectors.
Single-photon detectors are of great importance in spectroscopy, laser ranging, astronomy and wherever weak light detection is required, so a precise knowledge of their quantum efficiency is essential, but their calibration is by no means trivial. Traditional methods need a black body radiation source or a highly attenuated laser beam as a reference standard, or an already calibrated reference detector. It is well known that absolute measurement of the quantum efficiency, absolute in the sense that the calibration is independent of any radiometric standard or the properties of another detector, can be performed using entangled twin photons generated in optical spontaneous parametric down-conversion together with a reference detector. We have performed the first proof-of-principle experiment to determine the quantum efficiency by which no second detector or reference standard is required. This absolute self-calibration method is also based on the time correlation of photons emitted in parametric down-conversion, but with the introduction of a suitable time delay between the arrival times of the twin photons. Furthermore, we describe a scheme for absolute self-calibration of the quantum efficiency at different wavelengths by means of a pulsed source of nondegenerate down-converted photons. This method should have even greater potential for applications.
A widespread use of various relative calibration techniques is established in order to realize reliable and low uncertainty measurements of the detection efficiency, which is one key parameter characterizing single photon detectors. In the following paper we will present an approach to evaluate the relative detection efficiency of single photon avalanche photo diode (SPAD) detectors compared to a standard detector. This calibration technique is based upon the fiber-coupled relative efficiency calibration of analogue detectors, used in fiber-optic communication. For the first time, to our knowledge, an intrinsic single photon source based on the nitrogen-vacancy center in diamond was used for this purpose. Furthermore, the possible influence of different photon statistics, arising from different irradiation sources like thermal sources or lasers on the calibration results for the fiber exchange method has been theoretically studied.