Design and Fabrication of Innovative Optical Head for Picosecond Laser Machining Applied on LED Sapphire Subtract Ablation

We proposed a new method based on illuminating picosecond laser source through a sub-wavelength annular aperture (SAA) on metallic film so as to produce Bessel-like beam of sub-wavelength spot size while maintaining large depth of focus. To further advance the ease of use in our proposed design, producing sub-wavelength annular aperture with sub-wavelength focusing ability is detailed. It is shown that this method can be applied in the LED sapphire subtract machining with an emphasis to produce high aspect ratio structure (1:5) for laser sawing. More specifically, the ablation property of picosecond laser (1030nm) was utilized to eliminate the laser melting induced residue deposition problem associated with the traditional laser machining. Throughout the research, we have the parameters associated with the optimized SAA structure for 1030 nm wavelength of the picosecond laser obtained by the finite difference time domain (FDTD) simulations method. A lateral microscope system modified from traditional microscope was developed to facilitate the optical energy distribution of the emitted light beam to be used for machining. Finally, the design of SAA device was successfully integrated with the picosecond laser to perform the intended laser micromachining.