Rafeeq Syed will present his thesis topic, “The tale of the tailless frog pulse: Challenges and innovations in ultrafast laser pulse characterization: A study on two-photon absorption and fourth-order dispersion.” in-person.

Abstract: This thesis delves into advancements and limitations in ultrafast laser optics, particularly focusing on novel methodologies for measuring pulse duration in femtosecond lasers. Initially, the fundamental principles of Chirped Pulse Amplification (CPA) lasers are elaborated, laying the groundwork for the advanced techniques that follow. The primary contribution is a new method of pulse duration measurement that employs two-photon absorption in a liquid medium, coupled with fluorescent dye solution. This technique offers a broad range of applications in near-infrared wavelengths and showcases improved accuracy over conventional methods like Frequency-Resolved Optical Gating (FROG). A brief discussion on FROG’s setup and algorithmic workings. The research also uncovers previously unobserved limitations in FROG due to hardware constraints, particularly its inability to account for fourth-order dispersion (FOD). Further, the study dives into the complex realm of optical vortex propagation in liquid mediums. By using mathematical models rooted in 2D harmonic oscillators and perturbation theory, the work explores how nonlinear phenomena can be treated as perturbations, enriching the understanding of optical vortex behavior. A mathematical model based on symmetries and Bloch theorem is introduced, explaining generation of multiple optical vortex orders through single fork grating. The thesis concludes by offering computational tools for simulating the effects of perturbation theory on optical vortex propagation and showing nonlinear effects of Self-Focusing or Self-Trapping using the new simulation method, thereby setting the stage for ongoing research in this ever-evolving field.