Electrical thermography via centimetre-scale fiber-based distributed temperature sensing

We present a Raman-based Distributed Temperature Sensor (RDTS) with centimetre-scale resolution for thermographic analysis of electronic circuits. Temperature is measured along a single-mode fiber routed across a custom printed circuit board (PCB) with 1 cm$^2$ heating elements, using optical time-domain reflectometry of Raman signals detected by superconducting nanowire single-photon detectors (SNSPDs). This approach enables two-dimensional thermal mapping of the PCB under heating configurations with multiple hotspots. A spatial resolution of 3 cm and a temperature accuracy of 2 {\deg}C are achieved with an integration time of 5 minutes. Thermography can be performed down to 77 K, revealing that the PCB thermal resistance decreases by nearly an order of magnitude compared to room temperature, due to enhanced convective cooling in liquid nitrogen. These results establish centimetre-scale RDTS as a robust technique for real-time, spatially resolved thermography of electronic circuits, particularly in regimes where infrared imaging is ineffective, such as at low temperatures or within volumetric electronic architectures.