Ultrafast local temperature measurement based on TS-DFT and tapered FBG near-field probe

In microdevices, local temperature serves as a crucial indicator of device performance. Traditional measurements often struggle to capture transient thermal events due to the small and short-lived nature of the heat generation region within the device. In this study, we use scanning probe microscopy with a fiber Bragg grating (FBG) near-field probe to identify hot spot locations precisely. We employ the time-stretched dispersive Fourier transform (TS-DFT) technique to enhance the demodulation rate, facilitating the mapping of the probe signal from the frequency domain to the time domain. Through numerical calculations of the optical pulse propagation process in a dispersive medium and conjunction with near-field temperature calibration experiments, we validate the capability of this technique to achieve the demodulation rate of 51.43 MHz. In practice, our measurements show that when subjected to an electrical excitation signal of 2 ms, the microheater leads a thermal impulse response of about 6°C, and the measurement process does not affect its regular operation.