450nm Laser diode beam shaping in engraving process

Abstract

Laser applications in manufacturing processes such as cutting, welding, and engraving processes are become more popular nowadays. High-power and pulsed lasers such as CO2 and Nd:YAG gas lasers are commonly used in applications of metal cutting and welding. Meanwhile, for engraving process laser diode is more preferred due to its properties of compact shape, easy to operate, low power and high efficiency in comparison to CO2 and Nd:YAG laser gas. Owing to the rectangle resonator, the diode laser beam has some inevitable property disadvantages, such as wide-angle divergence, astigmatism and beam profile which has non-ideal elliptical beam shape. These deficiencies lead to a poor quality of beam profile. In order to obtain a high-quality engraving process, two things have to be considered. The first one is a significant requirement of a good beam quality, which is ideally a round beam shape and the second is characterization of burning time and laser intensity for each specific material object. The beam profile quality can be improved by several optical process steps, which finally end up to a perfect Gaussian round beam shape profile. The beam quality improvement can be done by using several-lens structures, for instances: (1) a combination of two sequential cylindrical lenses; (2) the use of two serial anamorphic prisms; (3) cylindrical micro lenses structure and (4) the usage of a single mode optical fiber. In this paper, we design a combination of two sequential cylindrical lenses to reshape a non-ideal beam shape (ellipse) generated from 450-nm laser diode to be more ideal round beam shape, which reduces the divergence angle of the fast axis. Based on the technical experience and consideration the uses of two cylindrical lenses are the most common, low cost and simple method. We analyze the quality of the beam profile by observing the laser-diode burned footprint on the material object. The round beam shape is the best shape and appropriate for engraving process. Moreover, in order to obtain a perfect engraving result, we are also conducting and reporting the burning time and laser intensity characterization.