Multispectral sparkling of microbubbles with focused femtosecond las

Nonlinear interactions of focused femtosecond laser with water can provide interesting optical phenomena. We observed intense scattered lights with multi colors at the surface of microbubbles formed by focused femtosecond laser inside the water. This optical scattering phenomena is found for the first time since the invention of femtosecond laser. The bubbles are formed rapidly before the emissions of colorful sparkling lights at a back-side point of water-vapor interface of the microbubbles. Analysis of the nonlinear optical processes, particularly spectral blueshift and broadening with filamentation hot spots in the water explains the effect of multispectral scattering. This work may provide a new method for visualizing the filamentation hot spots and the corresponding frequency components in the focusing region by making use of the strong scattering at the water-vapor interface of the microbubbles.