A Study of the Position-Dependent Response of Thermal Kinetic Inductance Detectors Through the Use of Cryogenic Beam Steering

There are a number of considerations when de signing a low temperature detector for the best possible energy resolution. One that has been particularly challenging for thermal kinetic inductance detectors (TKIDs) is ensuring that the detector's response to deposited energy is constant across the active area of a single pixel. In this manuscript, we directly probe the position-dependent response of our TKID devices at 100-μm-scale resolution through the use of a pulsed laser beam steered with a cryogenic micro-electromechanical system mirror. We observe position-dependent response that could limit the energy resolution of our current devices to the part per ten scale. We find that the position-dependent response is strongly correlated with the local current density in the TKID inductor, although the thermal physics and geometry associated with the micromachined absorber also likely have a non-negligible effect. Finally, we suggest analysis methods and design considerations that could reduce the severity of this position dependence, and we argue that there is significant potential for further improvement.