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Single photon counting detector for THz r adioastronomy .

MSPU. D . Morozov 1,2 , M . Tarkhov 1 , P . Mauskopf 2 , N . Kaurova 1 , O . Minaeva 1 , V . Seleznev 1 , B . Voronov 1 and Gregory Gol’tsman 1 1 Department of Physics, Moscow State Pedagogical University, Moscow 119992, Russia 2 Cardiff University, Cardiff, CF24 3YB, Wales, UK.

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Single photon counting detector for THz r adioastronomy .

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  1. MSPU D.Morozov1,2, M.Tarkhov1, P.Mauskopf2, N.Kaurova1, O.Minaeva1, V.Seleznev1, B.Voronov1 and Gregory Gol’tsman1 1Department of Physics, Moscow State Pedagogical University, Moscow 119992, Russia 2Cardiff University, Cardiff, CF24 3YB, Wales, UK Single photon counting detector for THz radioastronomy. Outline Introduction and motivation Operation mechanisms of superconducting single-photon detectors (SSPD) Performance and experimental results for NbN SSPD Prospective Superconducting material for terahertz single-photon detector

  2. Infrared single-photon detector comparison table

  3. Terahertz Receivers

  4. Energy Relaxation Process Schematic description of relaxation process in an optically excited superconducting thin film.

  5. Mechanism of SSPD Photon Detection G. Gol'tsmanet al, Applied Physics Letters 79 (2001): 705-707 A. Semenov et al, Physica C, 352 (2001) pp. 349-356

  6. IV-curves of the 4-nm thick film devices at 4.2 K

  7. Mechanism of elliptic spot formation Consider an average quasi-particles (qps) energy ε: T<ε<Δ(T). In the absence of j they would be trapped due to Andreev reflection. Existence of j flowing around the spot makes the gap spatially nonuniform. j=0 => gap equals Δ>ε => qps diffusion is blocked by Andreev reflection j~jc => minimal gap equals Δ-pFvs<ε => qps diffuse in that regions vw vw |vw|>|vL| vL Schematic gap profile across the spot

  8. Scanning electron microscope image of one of the current SSPDs • Fabrication: • DC reactive magnetron sputtering of 4-nm-thick NbN film • Patterning of meander-shaped structure by direct e-beam lithography. • Formation of Au contacts with optical lithography. Korneev A. et al, Appl. Phys. Lett. 84 (2004) 5338

  9. Image of new SSPD design(in electron resist before etching process) 120 nm 52 nm Stripe width 68 nm, spacing 120 nm

  10. Image of new SSPD design (in electron resist before etching process) • Narrower stripe • Narrower spacing • We expect: • - better light coupling • higher QE Wider wavelength range 41 nm Stripe width: 54 nm Spacing: 41 nm

  11. Resistance vs Temperature Curves for Sputtered NbN Film 4 nm Thick and for SSPD Device Direct electron beam lithography and reactive ion etching process

  12. Experimental quantum efficiency and dark counts rate vs. normalized bias current at 2 K

  13. Experimental data for QE (open symbols) and the dark count rate (closed symbols) vs. the bias current measured for 1.55-μm photons and different temperatures

  14. Experimental set-up for measurements of QE in the IR in free-space optic

  15. NbN SSPD spectral sensitivity at 3 K temperature Ic =29.7A at 3 K

  16. Spectral dependences of QE for normalized bias currents Ib/Ic>0.9 measured at 4.9 K and 2.9 K T=4.9K

  17. Experimental data for count per second vs. the temperature measured for 3-μm photons and constant normalized bias current.

  18. 1.7 K insert for liquid helium storage dewar

  19. Experimental data for QE vs. the bias current measured for 5-μm photons and different temperatures

  20. Experimental data for QE vs. the temperature measured for 5-μm photons and different normalized current.

  21. NbN SSPD noise equivalent power (NEP) at different radiation wavelengths at 1.7K temperature

  22. SSPD integrated with optical cavities The design of advanced SSPD structure consists of a quarter-wave dielectric layer, combined with a metallic mirror.

  23. Spectral sensitivity of SSPD integrated with optical cavities Tests performed on relatively low-QE devices integrated with microcavities, showed that the QE value at the resonator maximum was of the factor up to 2-3 higher than that for a nonresonant SSPD.

  24. Thickness of the film 2 nm 3 nm 4 nm Тс (К) 4.2 – 5.2 4.4-6.53 5.17-7.22 Tc (К) ~0.1 ~0.1 ~0.1 R300/R20 1,2 1.38-1.49 Rs (Ω/□) 120-190 77-117 52-69 µΩ*cm 24-38 23-35 21-28 Ic (µА) 170 – 125 jc (А/cm2) (1-5)*106 D (cm2/s) 1.72 Prospective materials for superconducting single-photon detector: MoRe on sapphire substrate Width=200 nm Length=10 mm

  25. Conclusions • Our best NbN SSPD exhibit at 1.7 K temperature: • - QE~30% at near infrared (1.3-1.55 mm) • - QE~0.25% at 5 mm • - extremely low dark counts rate provides NEP about 5x10-21 W/Hz1/2 at near infrared and ~10-19 W/Hz1/2 at 5 mm. • MoRe Prospective material for THz SSPD are: • 200-nm-wide and 10- mm-long bridge made from 4-nm-thick MoRe film exhibited single-photon counting capability

  26. Experimental Setup 300mK

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