Laser-microdroplet interactions influence the quality of nanoparticle deposition on a substrate. When a microdroplet and its impinging spot are heated, the microdroplet can either evaporate gently, boil immediately after impingement or bounces back inhibiting the deposition process.  The interaction between a laser and droplets carrying semiconductor and metal nanoparticles is studied for different laser powers.

Microdroplets ranging from an original pre-impact diameter of 10 to 70 µm are generated using an electrospray method and guided by electric and gravity forces toward a hollow conical laser beam.  Eventually the droplets interact with the laser slightly above or at the substrate surface. In the focal volume, the conical beam forms a Bessel beam irradiation distribution that is used to heat the microdroplet and the impinging spot. Thermography, high speed imaging and image processing are used to analyze the thermal response of the microdroplets to laser heating when the laser power is increased. The results indicate that the laser is refocused by the droplets, and deposition of nanoparticles and formation of nanofeatures are achieved under certain conditions. On the other hand, when the laser power exceeds a critical value of approximately 20 W in this study, all microdroplets bounce back from the substrate and subwavelength features such as nanoholes are not observed.