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Author |
Lobanov, Y.; Tong, C.; Blundell, R.; Gol'tsman, G. |
Title |
A study of direct detection effect on the linearity of hot electron bolometer mixers |
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Conference Article |
Year |
2009 |
Publication |
Proc. 20th Int. Symp. Space Terahertz Technol. |
Abbreviated Journal |
Proc. 20th ISSTT |
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282-287 |
Keywords |
HEB mixer, direct detection effect |
Abstract |
We have performed a study of how direct detection affects the linearity and hence the calibration of an HEB mixer. Two types of waveguide HEB devices have been used: a 0.8 THz HEB mixer and a 1.0 THz HEB mixer which is ~5 times smaller than the former. Two independent experimental approaches were used. In the ΔG/G method, the conversion gain of the HEB mixer is first measured as a function of the bias current for a number of bias voltages. At each bias setting, we carefully measure the change in the operating current when the input loads are switched. From the measured data, we can derive the expected difference in gain between the hot and cold loads. In the second method (injection method [1]), the linearity of the HEB mixer is independently measured by injecting a modulated signal for different input load temperatures. The results of both approaches confirm that there is gain compression in the operation of HEB mixers. Based on the results of our measurements, we discuss the impact of direct detection effects on the operation of HEB mixers. |
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RPLAB @ gujma @ |
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724 |
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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 |
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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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733 |
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Boreman, Glenn D. |
Title |
A Users guide to IR detectors |
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Conference Article |
Year |
2001 |
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Proc. SPIE |
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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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Hu, Xiaolong; Dauler, Eric A.; Kerman, Andrew J.; Yang, Joel K. W.; White, James E.; Herder, Charles H.; Berggren, Karl K. |
Title |
Using surface plasmons to enhance the speed and efficiency of superconducting nanowire single-photon detectors |
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Conference Article |
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2009 |
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Proceedings of the Conference on Lasers and Electro-Optics, 2009 and 2009 Conference on Quantum electronics and Laser Science Conference |
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Proc of Conf. on Lasers and El.-Opt. |
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1-2 |
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optical antennas |
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We report our design and fabrication of superconducting nanowire single-photon detectors integrated with gold plasmonic nanostructures, which can enhance the absorption of TM-polarized light, and can enlarge the effective area without sacrificing detector speed. |
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RPLAB @ gujma @ |
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744 |
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Author |
Novotny, Lukas |
Title |
Effective wavelength scaling for optical antennas |
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Journal Article |
Year |
2007 |
Publication |
Phys. Rev. Lett. |
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Phys. Rev. Lett. |
Volume |
98 |
Issue |
26 |
Pages |
266802(1-4) |
Keywords |
optical antennas |
Abstract |
In antenna theory, antenna parameters are directly related to the wavelength λ of incident radiation, but this scaling fails at optical frequencies where metals behave as strongly coupled plasmas. In this Letter we show that antenna designs can be transferred to the optical frequency regime by replacing λ by a linearly scaled effective wavelength λeff=n1+n2λ/λp, with λp being the plasma wavelength and n1, n2 being coefficients that depend on geometry and material properties. It is assumed that the antenna is made of linear segments with radii Râ‰<aa>λ. Optical antennas hold great promise for increasing the efficiency of photovoltaics, light-emitting devices, and optical sensors. |
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RPLAB @ gujma @ |
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749 |
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