A homogeneous focusing system for diode lasers and its applications in metal surface modification

Abstract

High power diode lasers are applied in many different areas, including surface modification, welding and cutting. It is an important technical trend in laser processing of metals in the future. This paper aims to analyze the impact of the shape and homogeneity of the focal spot of the diode laser on surface modification. A focusing system using the triplet lenses for a direct output diode laser which can be used to eliminate coma aberrations is studied. A rectangular stripe with an aspect ratio from 8:1 to 25:1 is obtained, in which the power is homogeneously distributed along the fast axis, the power is 1117.6 W and the peak power intensity is 1.1587 × 106 W/cm2. This paper also presents a homogeneous focusing system by use of a Fresnel lens, in which the incident beam size is 40 × 40 mm2, the focal length is 380 mm, and the dimension of the obtained focal spot is 2 × 10 mm2. When the divergence angle of the incident light is in the range of 12.5–20 mrad and the pitch is 1 mm, the obtained homogeneity in the focal spot is the optimum (about 95.22%). Experimental results show that the measured focal spot size is 2.04 × 10.39 mm2. This research presents a novel design of homogeneous focusing systems for high power diode lasers.