Adaptive Chirped Pulse Shaping for Laser-Driven Droplet Generation in Microfluidic Systems

This work introduces an adaptive chirped pulse shaping (ACPS) framework to precisely control the temporal intensity and spatial energy deposition of femtosecond laser pulses for generating monodisperse droplets in microfluidic systems.

Details

Microfluidic technologies enable microliter or nanoliter sample handling, with droplet generation being a key operation. Traditional methods like electro- or pneumatically actuated valves suffer from limited speed and high fabrication complexity. Recent advances in ultrafast laser science suggest an all-optical route, where femtosecond laser pulses can impart controllable momentum to a fluid surface to generate micro-jets that disrupt into droplets. However, deterministic control of droplet size and formation timing remains elusive due to nonlinear laser-matter interactions, pulse-duration variability, and the sensitivity of fluid dynamics to laser parameters. This work introduces an adaptive chirped pulse shaping (ACPS) framework that modulates the spectral phase and amplitude of each femtosecond pulse to precisely control the temporal intensity envelope and spatial energy deposition. By integrating ACPS with a microfluidic chip, the technique produces laser-driven droplets with monodisperse volumes ranging from 0.5 to 5 μL at kilohertz repetition rates. The approach is built on existing, readily commercialized components, ensuring near-term market readiness.