tailieunhanh - Handbook of High Temperature Superconductor Electronics Part 12

Tham khảo tài liệu 'handbook of high temperature superconductor electronics part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 11 High-Temperature Superconducting IR Detectors John C. Brasunas NASA s Goddard Space Flight Center Greenbelt Maryland . INTRODUCTION It is already over 10 years since the discovery of high-temperature superconductor HTS materials with transition temperatures Tc in excess of the liquid nitrogen LN2 temperature 77 K at 1 atm . In addition to the continuing mystery of what exactly accounts for their high-Tc the relative ease of LN2 cooling versus liquid helium LHe cooling promises to make a number of engineering applications practical ranging from magnetically levitated trains to microelectronics such as SQUID superconducting quantum interference devices -based medical imaging devices. In this chapter we will present an overview of employing HTS materials in thin-film 1 m form for the direct detection of infrared IR radiation spanning the approximate wavelength range of m to 1 mm. Some of the examples particularly for fast picosecond response will be for HeNe laser sources m . Excluded are heterodyne applications where the HTS material serves the role of mixer for instance as a so-called hot electron bolometer 1 producing a difference frequency between a radio-frequency input and a local oscillator. Also excluded are SQUID approaches in general as the SQUID is covered in a companion chapter. An excellent review of the detector situation as of 1994 may be found in Ref. 2. Copyright 2003 by Marcel Dekker Inc. All Rights Reserved. Figure High-temperature superconductor resistive transition. A typical resistance curve for an HTS material is shown in Figure Typical Tcs include 90 K for YBCO yttrium barium copper oxide 110 K for BSCCO bismuth Strontium calcium copper oxide and 125 K for TBCCO thallium barium calcium copper oxide . Direct detection falls into two main categories thermal and nonthermal or quantum. In the thermal approach incoming radiant power W causes a temperature rise in the HTS lattice phonons are the dominant heat-capacity