LAUSR

Ultrashort pulse Bessel beams have gained attention for their ability to process high aspect ratio structures with precision drilling and cutting. However, focusing the beam inside transparent materials can lead to local stretching or compression due to material-air interface mismatch and nonlinear absorption, causing issues with uniformity of focus and processing depth. In this study, we propose a nonlinear compensation scheme for femtosecond pulsed Bessel beam stretching that modulates the optical phase of the pulse beam ring, achieving high-uniformity longitudinal distribution. This scheme enabled the creation of a highly uniform damaged structure measuring $540 \mu \text{m}$ in length and with a width standard deviation of only 145 nm inside fused silica. Our findings offer a new solution for ultrashort pulse laser applications in high aspect ratio drilling and fast precision cutting of transparent materials.