Frontier femtosecond mid-infrared pump-probe and 2DIR techniques: Advances in experimental methodologies

Mid-infrared (MIR) spectroscopy has emerged as a pivotal tool for studying molecular dynamics with ultrafast time resolution, allowing precise investigations into structural changes, chemical reactions, and energy transfer processes. This review explores the transformative capabilities of femtosecond MIR spectroscopy techniques such as pump-probe (PP) and two-dimensional infrared (2DIR) spectroscopy, which offer unparalleled specificity in probing molecular vibrations and exploring complicated energy landscapes across diverse scientific fields. Advanced laser technologies, including pulse shapers and asynchronous optical sampling (ASOPS), have significantly enhanced the precision and efficiency of MIR spectroscopic methods. ASOPS, in particular, has revolutionized time-resolved studies by mitigating traditional mechanical delay stage limitations, enabling robust femtosecond-to-nanosecond dynamics investigations with enhanced noise reduction and long-term stability. This review provides a comprehensive overview of the evolution and strengths of MIR-based PP and 2DIR spectroscopy, emphasizing the pivotal role of ASOPS in overcoming technical challenges. By delineating current methodologies, this review aims to guide researchers in selecting and optimizing experimental configurations tailored to their scientific inquiries.