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(a) Scheme of the hot-spot. The NbN stripe is in blue (b) Dependence of normalized DE vs reduced parameter at different wavelengths. This was measured with SSPDs with width varying from 120 to 220 nm.
Hot spot diameter for a single photon of wavelength . This diameter is obtained from the largest nanowire width that gives a measurable voltage pulse under a given bias current [cf. Eq. (1)]. The line is with being the constant extracted from the data shown in Fig. 1. Inset is an example of the determination of the minimum nanowire width (≈130 nm here) for detection at a wavelength . Dotted lines are guides to the eye.
Dependence of normalized counts per second vs incoming light power. Circles (black), triangles (red) and diamond (green) symbols, respectively, correspond respectively to a linear, quadratic and cubic dependence and thus to single, two, and three-photon regime because the counts per seconds are proportional to , where is the light power and the number of photons detected.
Photon regime dependence with wavelength and nanowire width. Black circles correspond to single-photon regime, red triangles to two-photon regime and green diamonds to three-photon regime. Lines are the expected borderlines from a regime to another, with a (−1/2) slope.
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