Laser-nanomachining by microsphere induced photonic nanojet

The photonic nanojet generated by microsphere-based modulation of incident light has attracted much research attention in recent years because its full width at half maximum (FWHM) is less than the optical diffraction limit, which enables the microsphere to serve as a superlens to achieve super-resolution imaging. In addition to its sub-diffraction limited FWHM, the intensity of the photonic nanojet is also enhanced by several times that of the incident light. Here, we report sub-micrometer features that can be fabricated on MEMS-related materials by simply using a laser-induced photonic nanojet through microspheres. The influences of the diameter of silica microspheres and the initial power of laser beams on “nano-drilling” cavities on substrates were experimentally studied. Compared to the experiments without the microspheres, the resolution of the laser-micromachined structures was markedly improved using our approach. We have shown that it is possible to use a laser beam with initial beam width of 5 μm to fabricate 250 nm diameter cavities on silica substrates. We further simulated the photonic nanojet created by silica microspheres using the finite-difference time-domain (FDTD) computational technique to gain insights into the physical mechanisms of the photonic nanojet and its influence on the final nano-drilling results. This photonic nanojet-based nano-drilling method presents new opportunities for low-cost, high-throughput fabrication of nanoscale devices in the future.