Mechanism and Experimental Study of Femtosecond-Laser Super-Resolution Processing Based on Beam Shaping Technology

Abstract

The three-dimensional microsolid can be fabricated by scanning point-by-point inside the polymer material according to the predetermined trajectory in femtosecond-laser two-photon direct writing mode. In the process of machining, the shape and intensity distribution of focus spot are changed by some processing parameters, which affect the processing accuracy and surface quality. Based on Fresnel diffraction theory and the intensity distribution function of focal spot, the focal spot shape is simulated and the main factors affecting the light intensity distribution are analyzed theoretically and simulated numerically. We propose a shaping method to improve the asymmetric shape of the facula by adding a prefocusing lens. According to the mechanism of femtosecond-laser super-resolution processing, we propose a beam shaping method using four-ring complex transmittance phase plate to achieve super-resolution processing. The phase plate was optimized on the global optimization algorithm and genetic algorithm. The validation experiment was carried out by scanning the photochromic material film with pulsed laser and reading the fluorescence signal of the photochromic point with single photon confocal. The experimental results show that the facula distribution is approximately symmetrical, and the size of facula is decreased obviously. The compression ratio is basically consistent with the theoretical calculation results. Therefore, super-resolution processing can be achieved by adding pre-focusing lens and phase plate to shaping the laser beam. The results of theoretical and experimental studies provide sufficient basis for improving the machining accuracy and surface quality of microdevices.