Abstract
The phase spectrum encodes spatial translations of fine structural features in images, offering unique physical insights distinct from conventional amplitude-based measurements. Here, we propose a novel technique, transient image phase spectroscopy (TIPS), integrating phase-resolved image analysis with ultrafast spectroscopy to extract carrier diffusion coefficients by tracking phase evolution across a time series of images. Unlike amplitude spectrum, the phase spectra of the time-resolved carrier dynamic images exhibit intrinsic immunity to overall intensity change arising from carrier recombination. Moreover, the dynamic features of the phase spectrum can be leveraged to effectively distinguish and suppress system noise. These 2 types of fundamental robustness enable reliable diffusion characterization under low signal-to-noise conditions where traditional amplitude-based methods fail. Through numerical simulations and experimental validation, we demonstrate the superior performance of TIPS, including the successful determination of high hot-carrier diffusion coefficients (~130 cm
2
s
−1
) in a rough-surface boron arsenide (BAs). For TIPS decouples spatial dynamics from amplitude decay and fluctuations, we anticipate that this phase-based paradigm will advance innovation in optical and optoelectronic measurement.