Large bandwidth and low noise in a diffusion-cooled hot-electron bolometer mixer

Abstract

Heterodyne measurements have been made at 533 GHz using a novel superconducting hot-electron bolometer in a waveguide mixer. The bolometer is a 0.3 m long niobium microbridge with a superconducting transition temperature of 5 K. The short length ensures that electron diffusion dominates over electron-phonon interactions as the electron cooling mechanism, which should allow heterodyne detection with intermediate frequencies ͑if͒ of several GHz. A Y-factor response of 1.15 dB has been obtained at an if of 1.4 GHz with 77 and 295 K loads, indicating a receiver noise temperature of 650 K DSB. The Ϫ3 dB rolloff in the if response occurs at 1.7 GHz.

Appropriate microwave frequency selection for biasing superconducting hot electron bolometers as terahertz direct detectors

“…In order to evaluate the performance of the NbN HEB, we measured its T N at the LO frequency of 0.65 THz and bath temperature of 4.2 K. The improved Y-factor method [11] is used to measure the T N for avoidance of the direct detection effect. The IF output power, P hot and P cold , corresponding to the hot and cold loads, are measured at the same bias voltage to getY=P hot /P cold .…”

Low-noise heterodyne mixing with NbN microbolometers at 800 GHz

“…They extend to both sides on top of the Au pads which significantly reduces alignment problems that might occur for previously reported process sequences. 8,9 Subsequently, the NbN layer is removed by CF 4 reactive ion etching. After etching, the Al lines can be easily removed in a basic solution revealing the NbN microbridges.…”

Optical and terahertz power limits in the low-temperature-grown GaAs photomixers

“…Anticipated uses for the photomixer include a tunable coherent source for high-resolution molecular spectroscopy, 4 an optical-heterodyne converter for frequency metrology of visible and near-infrared lasers, 5 and a local oscillator for terahertz receivers based on superconducting bolometric mixers. [6][7][8] An important and challenging technical problem is to increase the available output power of the photomixer for frequencies above ϳ1 THz. The output power is limited by the maximum optical power that these devices can withstand before failure.…”