Objective In order to realize ultrafast laser microdevice processing with high efficiency and flexibly adjustable processing accuracy, an ultrafast laser processing method based on tunable Bessel beam is proposed in this paper. This method achieves flexible adjustment of the central lobe radius and maximum nondiffracting propagation distance of the ultrafast laser Bessel beam by adjusting the compression ratios of the double telecentric optical system that can compress the primary Bessel beam, in which the double telecentric optical system with different compression ratios is realized by the control of the high-resolution displacement voice coil actuator with a closed-loop feedback control. Theoretical analyses and experimental tests confirm that the central main lobe radius and the maximum nondiffracting propagation distance of ultrafast laser Bessel beams are 3.73 μm and 5.28 mm, 1.86 μm and 1.32 mm, 0.93 μm and 0.33 mm, respectively, with the cooperation of a axicon lens (base angle of 2°) and a double telecentric optics system (f₁ = 250 mm, f₂ = 36 mm, 18 mm, and 9 mm). Meanwhile, a Bessel beam detection system is designed to realize the accurate measurement of the tunable Bessel beams designed above.

Methods The flexible adjustment of Bessel beam parameters can be realized by combining the axicon lens with a double telecentric optical system with different beam compression ratios. This adjustment is controlled by the high-resolution displacement voice coil actuator with a closed-loop feedback control. Meanwhile, theoretical calculation and numerical simulation are carried out to get the Bessel spatial light distribution of the Gaussian beam passing through the axicon lens and the double telecentric optical system with different beam compression ratios. In addition, a Bessel beam monitoring optical system was constructed by using a beam quality analyzer and a motion guide, and the above adjustable Bessel beam was tested.

Results and Discussions The simulation analysis and experimental results indicate that the incident Gaussian beam passing through an axicon lens (base angle of 2°) and a double telecentric optical system (f₁ = 250 mm, f₂ = 36 mm, 18 mm, and 9 mm) results in a Bessel beam, with respective the central main lobe radius and maximum nondiffracting propagation distance denoted as 3.73 μm and 5.28 mm, 1.86 μm and 1.32 mm, 0.93 μm and 0.33 mm, respectively. The double telecentric optical system with different compression ratios is realized by the control of the high-resolution displacement voice coil actuator with a closed-loop feedback control.

Conclusions In this paper, a tunable ultrafast laser Bessel beam processing system is designed and constructed. The theoretical analysis and simulation of the spatial light field propagation characteristics of the Bessel beam generated by the ultrafast laser through the axicon lens and different double telecentric optical systems are performed, and comparative analyses are carried out, in which different compression ratios of the double telecentric optical system are controlled by the high-resolution displacement voice coil actuator with a closed-loop feedback control. The designed Bessel processing system can be flexibly switched according to the characteristics of the samples. Then, the central main lobe radius and maximum nondiffracting propagation distance of the Bessel beam are experimentally tested using the self-constructed beam detection device, and the experimental results are consistent with the theoretical design. Finally, perforation experiments were carried out on fused silica samples with a thickness of 1 mm, and the results show that the system can realize the ultrafast laser microdevice processing with high precision, high efficiency and flexible adjustment of processing accuracy.