Silicon chiral bump formed by optical vortex laser ablation

In this paper, a discussion of ar previous work concerning optical vortex laser ablation to form a silicon (Si) twisted bump (chiral bump) is extended. This Si chiral bump will be potentially applied to many fields, such as silicon photonics, solar-energy devices, and micro electro mechanical systems. A Q-switched, mode-locked Nd:YAG laser with a wavelength of 1064 nm, a pulse repetition rate of 10 Hz and a pulse duration of 20 ps was used. Its output pulse was converted to be an optical vortex pulse by using a spiral phase plate (SPP), azimuthally divided into 16 parts using a nπ/8 phase shifter (where n is an integer between 0 and 15). The optical vortex pulse was focused to be a ~435 μm spot on the Si target by an object lens. The pulse energy of the optical vortex output was typically 50 μJ. Experiments were also performed by involving the single-shot deposition of the optical vortex pulse at atmospheric pressure and room temperature. The proceeded surface was observed by a scanning electron microscope.