Enhanced detection stability in femtosecond time resolution transient absorption system from a tight-focusing filamentation

Abstract

Femtosecond time resolution transient absorption spectroscopy (FTRTAS) is a powerful tool to obtain ultrafast photoexcitation dynamics of matter. The rapid development of photosensitive materials such as bioprotein and advanced photoelectric nanocrystal put forward higher stability requirements for the technique of FTRTAS. In this paper, we propose a strategy to establish a tight-focusing stable femtosecond laser filamentation system to optimize the stability of probe pulses, and finally achieve highly sensitive detection of weak signals. It is found that intense geometric focusing with short-focus lens can effectively reduce the self-focusing effect and plasma defocusing effect in the process of filamentation, avoid multiple filamentation, and promote a stable and tight femtosecond laser filamentation in the crystal. The results indicate that the supercontinuum white light (WL) pulse generated from 50 mm lens tight-focusing filamentation displays a comprehensive high detection ability with an enhanced stability and appropriate power and width, which improves the performance of the FTRTAS system and increases the detection sensitivity from conventional mode of 0.75 mOD to 0.3 mOD. The optimized FTRTAS system shows a great performance in detecting weak signals and tracking carrier evolution of perovskite and carotenoid after photoexcitation. These results demonstrate that the optimization of the femtosecond laser filamentation system can effectively improve the signal-to-noise ratio, and provide a valuable strategy for optimizing the FTRTAS system.