Ultrasensitive Terahertz Hot-Electron Mixers

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Abstract PROBER, D. E. AST-9618705 Funds will be used to develop superconductive hot-electron bolometer (HEB) mixers for heterodyne receiver application in the wavelength range from 1 mm to 0.1 mm (300 GHz - 3 THz). The bolometer mixer consists of a submicron strip of superconductor biased in the middle of its resistive transition. HEB mixers have recently shown broad IF bandwidths ( 6 GHz) and low noise along with extremely low local oscillator power requirements (TR = 650 K DSB and PLO = 15 nW at 530 GHz). Rapid thermal response and hence large IF bandwidth is achieved by out-diffusion of hot electrons. This mixer has no energy gap limitation (as for example is found in superconductive SIS mixers) and is expected to operate up to several 10's of THz. Device material, geometry, transition temperature, transition width, and sheet resistance will be investigated to optimize mixer performance for applications directly related to current and upcoming observational programs and missions. Nb bridges deposited with improved conditions, and Al and Ti bridges with very low transition temperatures will be tested to produce receivers with enhanced sensitivity.