“…For example, it was experimentally proved that S/F hybrids are optimal systems to be used as ultrafast superconducting optical detectors and eventually even as single photon detectors, due to the small value of the penetration length of the superconducting correlations in the F layer, ξ F 6 nm, which determines better performance in terms of both photoresponse signal detection and sensitivity [3][4][5]. In fact, in these devices the light probes a distance α (the material optical penetration depth), which is typically smaller than 50 nm in the 400-900 nm visible light wavelength range [3,4]. If S/N hybrids were to be used (here N stands for normal metal), due to the value of the penetration length of the Cooper pairs in the N layer, ξ N , which at low temperatures can be of the order of hundreds of nanometers, a thin N layer would not be an effective perturbation to the S layer to detect effects induced by the proximity effect.…”