Unveiling Molecular Structure, Interactions, and Synergism in Solutions with Novel Femtosecond Laser Spectroscopy

Femtosecond laser pulses differ fundamentally from continuous-wave lasers by delivering brief, high-intensity pulses separated by long intervals without illumination, producing highly intermittent dynamics that significantly alter molecular behavior and, in turn, can serve as an effective probe of molecular structure, interactions, and even synergistic behavior. We have also shown that femtosecond optical tweezers differ fundamentally from continuous-wave trapping by delivering brief, high-intensity pulses separated by long periods without illumination, resulting in highly intermittent dynamics that significantly alter particle behavior. Leveraging this framework, the study uses femtosecond trapping to probe microscopic thermodynamics in liquid mixtures, revealing how molecular structure governs nonlinear solvent response, viscosity, and Gibbs free energy through intermolecular interactions. In parallel, thermal lensing analysis shows that femtosecond pulses act as impulsive heat sources, with the resulting refractive response determined by total absorbed energy rather than pulse duration, enabling consistent comparison with longer-timescale behavior. Building on these insights, our work develops a rigorous time-domain theory of femtosecond trapping that captures transient forces, demonstrating that shorter pulse widths enhance trapping stability and providing a quantitative design framework for next-generation optical tweezers. Short bio: Debabrata Goswami is a physical chemist and Professor at the Indian Institute of Technology Kanpur, recognized for pioneering contributions to ultrafast laser science, nonlinear spectroscopy, and coherent control. His work spans femtosecond pulse shaping, quantum information, and bioimaging, with over 200 publications. He is a Fellow of multiple scientific societies and a recipient of honors including the Galileo Galilei Medal and India’s Shanti Swarup Bhatnagar Prize.