Femtosecond laser processing with aberration correction based on Shack-Hartmann wavefront sensor

• Aberrations measurement in femtosecond laser processing by direct wavefront sensing. • Using plasma excited by femtosecond laser as a guiding star for wavefront detection. • The characteristics of supercontinuum excited by femtosecond laser were measured. • The experimental results demonstrate the accuracy of aberrations measurement. Optical aberrations are critical for high-precision and large-depth fabrication of femtosecond lasers in transparent media. Some approaches have been demonstrated to correct these aberrations, such as calculated formulas, iterative algorithms for phase retrieval, and neural networks. However, these approaches have a few drawbacks, such as insufficient aberration correction and a lack of real-time operation, limiting the processing depth and performance of the device. Thus, this study demonstrated an aberration correction scheme with direct wavefront sensing. The aberrations during processing at different depths, from 100 to 600 μm, were measured using a Shack-Hartmann wavefront sensor. As a guide star, this sensor used the supercontinuum emitted by the plasma, which is generated by multiphoton absorption and avalanche effects in the focal region. A liquid-crystal spatial light modulator (SLM) effectively compensated the aberrations. Voxels with a constant aspect ratio of 2.82–2.91 were fabricated in different depths, significantly lower than the aspect ratio of 4.46–19.5 with uncorrected aberrations. This technology allows the precise fabrication of three-dimensional photonic devices consisting of curved waveguides at continuously different depths and improves the throughput of laser processing.