We have measured the quantum efficiency (QE), GHz counting rate, jitter, and noise-equivalent power (NEP) of nanostructured NbN superconducting single-photon detectors (SSPDs) in the visible to infrared radiation range. Our 3.5-nm-thick and 100- to 200-nm-wide meander-type devices (total area 10×10μm2), operating at 4.2K, exhibit an experimental QE of up to 20% in the visible range and ∼10% at 1.3 to 1.55μm wavelength and are potentially sensitive up to midinfrared (∼10μm) radiation. The SSPD counting rate was measured to be above 2GHz with jitter <18ps, independent of the wavelength. The devices’ NEP varies from ∼10−17W∕Hz1∕2 for 1.55μm photons to ∼10−20W∕Hz1∕2 for visible radiation. Lowering the SSPD operating temperature to 2.3K significantly enhanced its performance, by increasing the QE to ∼20% and lowering the NEP level to ∼3×10−22W∕Hz1∕2, both measured at 1.26μm wavelength.
A novel superconducting single-photon detector ͑SSPD͒, intrinsically capable of high quantum efficiency ͑up to 20%͒ over a wide spectral range ͑ultraviolet to infrared͒, with low dark counts ͑Ͻ1 cps͒, and fast ͑Ͻ40 ps͒ timing resolution, is described. This SSPD has been used to perform timing measurements on complementary metal-oxide-semiconductor integrated circuits ͑ICs͒ by detecting the infrared light emission from switching transistors. Measurements performed from the backside of a 0.13 m geometry flip-chip IC are presented. Other potential applications for this detector are in telecommunications, quantum cryptography, biofluorescence, and chemical kinetics.
We describe two- and three-dimensional imaging of a flip-chip silicon integrated circuit using backside optical probing and femtosecond two-photon excitation at a laser wavelength of 1.275 μm. Using a ×50 microscope objective, we typically achieved micron resolutions or better in both lateral and axial directions. Using axial scanning and a peak-detection algorithm we have demonstrated optical depth profiling across components on the chip.
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