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

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.

Approximation of a melting plateau of large area HTFP cells used for spectral irradiance realization.

This paper adopted an approximation of a melting plateau to solve the problem that temperature data cannot be monitored continuously when measuring the spectral irradiance of a large area tungsten carbide-carbon high-temperature fixed-point blackbody at each measured wavelength. Tests with fully measured curves showed that the method has a rather small deviation from the measured data of 0.017 K maximum, which corresponds to the spectral irradiance deviation of 0.005% at 500 nm. The maximum relative deviation between the Akima fitting method and the measured temperature in terms of spectral irradiance was 0.002%, which was better than -0.067% of a single temperature of 3020.11 K method and 0.026% of a linear interpolation method.

Measurement of the distance between two parallel precision apertures using time-of-flight method for cryogenic radiometry.

Time-of-flight method was adopted to measure the distance between two parallel precision apertures utilized in a vacuum chamber for cryogenic radiometry. The diameters of the apertures are 9 mm and 8 mm, respectively. A 1550-nm femtosecond pulse laser, a 70-GHz photodetector, and a 30-GHz oscilloscope were used to measure the round-trip flight time difference between the flat front surfaces of the two precision apertures. The distance between the apertures was analyzed to be 0.36423 m with a relative standard uncertainty of 0.004%. The non-contact distance measurement method is useful for applications such as low background infrared radiance measurement system based on an absolute cryogenic radiometer.

Broadband high-absorbance coating for terahertz radiometry.

We report a simple, broadband and high-absorbance coating for terahertz radiometry. The spectral properties of this coating in THz region were characterized with a home-made terahertz time-domain spectrometer. The measured spectral reflectance is less than 0.3% ranging from 0.2 THz to 0.5 THz and less than 0.1% ranging from 0.5 THz to 2.0 THz. We assembled a terahertz radiometer with this coating as absorber, and discussed its heat transfer in comparison with that of a carbon nanotube array radiometer. This coating is highly absorptive both in terahertz region and in visible light; therefore, the responsivity of this radiometer is easily traceable to National Laser Power Standards. This coating is easily fabricated. It is useful in traceability of terahertz sources and detectors to the SI units.