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| Author |
Bulaevskii, L. N.; Graf, Matthias J.; Kogan, V. G. |
| Title |
Vortex-assisted photon counts and their magnetic field dependence in single-photon superconducting detectors |
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Journal Article |
| Year |
2012 |
Publication |
Phys. Rev. B |
Abbreviated Journal |
Phys. Rev. B |
| Volume |
85 |
Issue |
1 |
Pages |
9 |
| Keywords |
SSPD; SNSPD; single-vortex crossing; normal-state belt |
| Abstract |
We argue that photon counts in a superconducting nanowire single-photon detector (SNSPD) are caused by the transition from a current-biased metastable superconducting state to the normal state. Such a transition is triggered by vortices crossing the thin and narrow superconducting strip from one edge to another due to the Lorentz force. Detector counts in SNSPDs may be caused by three processes: (a) a single incident photon with sufficient energy to break enough Cooper pairs to create a normal-state belt across the entire width of the strip (direct photon count), (b) thermally induced single-vortex crossing in the absence of photons (dark count), which at high-bias currents releases the energy sufficient to trigger the transition to the normal state in a belt across the whole width of the strip, and (c) a single incident photon of insufficient energy to create a normal-state belt but initiating a subsequent single-vortex crossing, which provides the rest of the energy needed to create the normal-state belt (vortex-assisted single-photon count). We derive the current dependence of the rate of vortex-assisted photon counts. The resulting photon count rate has a plateau at high currents close to the critical current and drops as a power law with high exponent at lower currents. While the magnetic field perpendicular to the film plane does not affect the formation of hot spots by photons, it causes the rate of vortex crossings (with or without photons) to increase. We show that by applying a magnetic field one may characterize the energy barrier for vortex crossings and identify the origin of dark counts and vortex-assisted photon counts. |
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RPLAB @ gujma @ |
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Alda, Javier; Rico-García, José M.; López-Alonso, José M.; Boreman, G. |
| Title |
Optical antennas for nano-photonic applications |
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Journal Article |
| Year |
2005 |
Publication |
Nanotechnology |
Abbreviated Journal |
Nanotech. |
| Volume |
16 |
Issue |
5 |
Pages |
S230-S234 |
| Keywords |
optical antennas |
| Abstract |
Antenna-coupled optical detectors, also named optical antennas, are being developed and proposed as alternative detection devices for the millimetre, infrared, and visible spectra. Optical and infrared antennas represent a class of optical components that couple electromagnetic radiation in the visible and infrared wavelengths in the same way as radioelectric antennas do at the corresponding wavelengths. The size of optical antennas is in the range of the detected wavelength and they involve fabrication techniques with nanoscale spatial resolution. Optical antennas have already proved and potential advantages in the detection of light showing polarization dependence, tuneability, and rapid time response. They also can be considered as point detectors and directionally sensitive elements. So far, these detectors have been thoroughly tested in the mid-infrared with some positive results in the visible. The measurement and characterization of optical antennas requires the use of an experimental set-up with nanometric resolution. On the other hand, a computation simulation of the interaction between the material structures and the incoming electromagnetic radiation is needed to explore alternative designs of practical devices. |
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RPLAB @ gujma @ |
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734 |
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Boreman, Glenn D. |
| Title |
A Users guide to IR detectors |
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Conference Article |
| Year |
2001 |
Publication |
Proc. SPIE |
Abbreviated Journal |
Proc. SPIE |
| Volume |
4420 |
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79-90 |
| Keywords |
optical antennas |
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This paper will guide the first-time user toward proper selection and use of IR detectors for applications in industrial inspection, process control, and laser measurements. |
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RPLAB @ gujma @ |
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735 |
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Brown, E. R.; Lee, A. W. M.; Navi, B. S.; Bjarnason, J. E. |
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Characterization of a planar self-complementary square-spiral antenna in the THz region |
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Journal Article |
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2006 |
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Microwave and Optical Technology Letters |
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Microwave Opt Technol Lett |
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48 |
Issue |
3 |
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524-529 |
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optical antennas; square spiral antenna; self complementary THz; photomixing; lens; method of moments; geometric optics; physical optics |
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This paper describes a compact, self-complementary square-spiral antenna on a GaAs substrate with a broadside high-directivity (~9 dB) frequency-independent pattern when coupled through a silicon hyperhemisphere. The driving-point resistance undulates between ~00 and 300Ω from 200 GHz to 1 THz—much higher than the 72Ω value from Booker's modified formula, but quite beneficial for coupling to high-impedance broadband devices |
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RPLAB @ gujma @ |
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736 |
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| Author |
Bryant, Garnett W.; García de Abajo, F. Javier; Aizpurua, Javier |
| Title |
Mapping the Plasmon Resonances of Metallic Nanoantennas |
Type |
Journal Article |
| Year |
2008 |
Publication |
Nano Letters |
Abbreviated Journal |
Nano Lett. |
| Volume |
5 |
Issue |
2 |
Pages |
631-636 |
| Keywords |
optical antennas |
| Abstract |
We study the light scattering and surface plasmon resonances of Au nanorods that are commonly used as optical nanoantennas in analogy to dipole radio antennas for chemical and biodetection field-enhanced spectroscopies and scanned-probe microscopies. With the use of the boundary element method, we calculate the nanorod near-field and far-field response to show how the nanorod shape and dimensions determine its optical response. A full mapping of the size (length and radius) dependence for Au nanorods is obtained. The dipolar plasmon resonance wavelength λ shows a nearly linear dependence on total rod length L out to the largest lengths that we study. However, L is always substantially less than λ/2, indicating the difference between optical nanoantennas and long-wavelength traditional λ/2 antennas. Although it is often assumed that the plasmon wavelength scales with the nanorod aspect ratio, we find that this scaling does not apply except in the extreme limit of very small, spherical nanoparticles. The plasmon response depends critically on both the rod length and radius. Large (500 nm) differences in resonance wavelength are found for structures with different sizes but with the same aspect ratio. In addition, the plasmon resonance deduced from the near-field enhancement can be significantly red-shifted due to retardation from the resonance in far-field scattering. Large differences in near-field and far-field response, together with the breakdown of the simple scaling law must be accounted for in the choice and design of metallic λ/2 nanoantennas. We provide a general, practical map of the resonances for use in locating the desired response for gold nanoantennas. |
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RPLAB @ gujma @ |
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737 |
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