TECH FOCUS SINGLE PHOTON COUNTING
Sponsored by
said NIST group leader Alan Migdall. ‘Combining that ultimate sensitivity with the ability to achieve the counting of photons at high rates has been a long-standing challenge. We are pushing both performance limits all in the same device.’ The NIST innovation entails
a redesign of the control electronics system surrounding a workhorse detector called a single photon avalanche diode (Spad), in which an incoming photon triggers a tiny but measurable burst of current across a semiconductor. A voltage is applied across
“Combining that ultimate sensitivity with the ability to achieve the counting of photons at high rates has been a long-standing challenge”
the semiconductor. When a photon hits the detector, its absorbed energy kicks an electron off an atom in the semiconductor – the same photoelectric effect that generates electricity in solar panels. That loose electron is
accelerated by the applied voltage, and causes a sort of chain reaction in which large numbers of adjacent atoms release an ‘avalanche’ of electrons just as a small added stress can prompt an entire mountainside of snow to collapse. That avalanche current is the output signal. Finally, the device is reset by quenching the current with a counter-voltage and restoring the initial applied voltage. Because the avalanche involves such a large number of electrons, getting the entire system back to a quiet state where it is ready to detect another photon is challenging. A conventional Spad can
detect from 1 million to 10 million photons per second,
g
NIREOS FEATURED PRODUCT
Photonic Solutions Ltd in partnership with Nireos
GEMINI Interferometer A novel device for measuring the light spectrum via a Fourier- transform approach
Nireos is an official spin-off company from Politecnico di Milano University, based in Milan (Italy), that develops and provides innovative devices for spectroscopy applications.
The Gemini is a robust common-path and ultra- stable interferometer, which enables the measurement of the light spectrum via a Fourier-Transform (FT) method. The Gemini unlocks all the advantages of the FT approach down to the UV-visible and near infrared spectral region. Also, thanks to its 10mm clear aperture and the absence of entrance slits or gratings, it overcomes the
main drawbacks of grating- based devices, providing a high throughput, a variable spectral resolution, and a broad spectral coverage. The Gemini is provided
with plug and play software, and it can be easily integrated in already existing setups to spectrally resolve the light, either coherent (i.e. a laser) or incoherent (i.e. a lamp or a fluorescence signal).
The Gemini is now used
in a wealth of scientific applications, such as static and time-resolved fluorescence, broadband pump-probe and coherent Raman spectroscopy.
Find out more at:
www.photonicsolutions.co.uk/ product-detail.php?prod=6773 Available through Photonic Solutions in the UK and Ireland
www.electrooptics.com | @electrooptics
July 2021 Electro Optics 33
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