A passive terahertz video camera allows for fast security screenings from distances of several meters. It avoids irradiation or the impressions of nakedness, which oftentimes cause embarrassment and trepidation of the concerned persons. This work describes the optimization of highly sensitive superconducting transition edge sensor bolometers (TES) for such a system. They enable frame rates of up to 25 Hz and have the capability to also detect non-metallic objects.Several challenges were addressed in this work:Based on a series of oxidation experiments, the sensor design could be optimized to achieve significant enhancements in long term parameter stability and reproducibility. Further measurements analyzing non-ideal behavior of the superconducting thermistor of the sensor were used to reduce excess noise and to minimize distorting influences on the low temperature readout electronics. This drastically improved the usability of the sensors for larger arrays.The chosen approach to optimize time constants while maintaining a high coupling efficiency was based on FEM models. They were used to simulate the optical coupling as well as time dependent thermal and electrical interactions, which allowed for more precise predictions of the sensor behavior compared to the common lumped model for TES. The simulation results were verified by several measurements on different designs.The applicability of these results was proven by the implementation of these sensors in a demonstrator system. Stable simultaneous operation of 64 sensors was shown and terahertz videos of 25 frames per second were achieved while attaining the same imaging quality as for lower frame rates.
|Award date||4 Sep 2014|
|Place of Publication||Enschede|
|Publication status||Published - 4 Sep 2014|