Beam Conditioning and Collimation
The laser exits the fiber like a firework and must first be conditioned. A collimating mirror compresses the beam’s divergence to below 0.1 mrad. A mere 0.01 mm depression on this mirror will translate into a 0.25 mm positional error on the steel sheet, instantly eroding micron-level accuracy.
Focus Formation and Lens Alignment
The conditioned beam then passes through two ZnSe lenses that shrink it to a 25 µm focus. The center-to-center spacing of these lenses is locked to ±2 µm with a laser interferometer; every 1 µm deviation shifts the focal plane by 4 µm, so mechanical tolerances are controlled at the sub-micron scale.
Thermal Compensation and Real-Time Correction
During high-power cutting the lenses absorb heat, changing their refractive index and defocusing the beam. A motorized compensator lens, driven by temperature feedback, moves ±50 µm in <1 ms to restore the focal position, ensuring that the kerf remains within ±10 µm even at traverse speeds exceeding 10 m min⁻¹.
