Characterization of picosecond-scale response time of superconducting NbN hot electron bolometric mixers

A superconducting hot electron bolometer (HEB) mixer is an ultra-sensitive detector widely used for heterodyne detection of electromagnetic radiation, particularly at terahertz (THz) and submillimeter wavelengths. The response time of an HEB mixer is a critical parameter that defines its dynamic properties. In this work, we employ a pump–probe optical technique to investigate how the response time varies with temperature and bias voltage. Our measurements, conducted at 7 K under bias voltages of 1 mV and 2 mV, reveal a response time of approximately 40 ps. The pump–probe method was introduced to measure the HEB response time for the first time, overcoming conventional electronic bandwidth limitations and achieving picosecond-scale temporal resolution to characterize its ultrafast dynamics in the time domain. Additionally, the results not only reflect the intermediate-frequency noise bandwidth performance of the device but also provide direct guidance for material and fabrication process verification.