Femtosecond Bessel laser beam generated directly from a mode-locked solid-state oscillator with axicon output couplers.

Ultrafast Bessel beams have shown great potential in scientific research and industrial applications, particularly in laser material processing. However, traditional methods for generating Bessel beams typically rely on external phase elements, which increase the complexity and reduce the efficiency of the laser system. Here, we report a compact Kerr-lens mode-locked Yb:KGW laser oscillator that can directly generate ultrafast Bessel beams using coated axicons as intracavity output couplers. Femtosecond Bessel beams with average power exceeding 1 W, a repetition rate of 69.3 MHz, and tunable diffraction-free distances were produced at three different base angles, and the shortest pulse duration was 105 fs. This approach eliminates the requirement for external optics, significantly simplifying system setup and improving stability. The proposed laser oscillator provides a practical solution for high-precision laser material processing and other advanced ultrafast beam applications.