Design of an adjustable working distance Bessel lens for femtosecond laser cutting

An adjustable working distance Bessel lens for high-precision femtosecond laser cutting is designed. The system is composed of an axicon and a bi-telecentric optical system. By adjusting the distance between the axicon and the bitelecentric optical system, a zero-order Bessel beam with continuously adjustable working distance within a certain range can be obtained. Compared with the traditional Gaussian beam, when the central core diameter of the Bessel beam and the beam width of the Gaussian beam are the same, the non-diffracting propagation distance of the Bessel beam is much larger than the Rayleigh length of the Gaussian beam. The focusing accuracy can be effectively reduced, and a larger processing dynamic range can be achieved in laser processing. Ultra-short pulse Bessel beam generated by this method in laser cutting has longer laser focal field length and smaller light field axial intensity distribution gradient, which can provide a high-quality light source for laser cutting. In this paper, the spatial intensity distribution of Bessel beam is simulated by MatLab software. The simulation results show that, by the incidence of a femtosecond pulsed Gaussian beam whose central wavelength is 1030 nm with a certain diameter on the Bessel lens, a Bessel beam with a central core diameter of 6.7 μm, a non-diffracting propagation distance of 3.40 mm, and a continuously variable working distance from 18 mm to 21 mm can be obtained.