Thermal lensing impact on the focal shift and optical deformation in the cutting head of 1064nm fiber lasers 1–6 kW

Thermal lensing is an unavoidable phenomenon in optical systems utilizing high-power lasers, including laser cutting heads, due to energy absorption-induced thermal and optical variations. This study analyzes its effects on a 1064 nm laser system (1–6 kW) using two fused silica plano-convex lenses, with focusing lens focal lengths of 125–300 mm. Simulations indicate a peak lens temperature of 952 K at 6 kW, driving focal shifts up to Δf = −45.4 mm (300 mm focal length) and relative refractive index changes of 74.5–114%. Spot diagram analysis at the focal plane indicates severe beam spreading and optical distortion when the laser power exceeds 4 kW. Proposed solutions include thermally stable materials, enhanced anti-reflective coatings, and real-time focal adjustments to optimize cutting precision.