Correction of femtosecond laser asymmetric spot size for achieving uniform axial intensity in Bessel beam propagation via GPM

A compact phase-engineering method for generating zero-order Bessel beams with uniform on-axis intensity from femtosecond lasers exhibiting asymmetric Gaussian inputs (w_x ≠ w_y) is presented. An axicon phase combined with Gaussian phase modulation (GPM) was encoded on a spatial light modulator (SLM) to correct beam ellipticity and axial decay. Analytical expressions derived using the stationary-phase method reveal the effects of asymmetry, while numerical GPM tuning ensures axial uniformity. Theoretical, simulated, and experimental results at 1030 nm show strong agreement, even for a small asymmetry (<i>δ</i>_w= w_y/w_x ≈ 0.95-1.05). The technique provides a simple and practical route to high-fidelity Bessel beams for ultrafast laser microfabrication.