Fig. 1. Change of spot geometry caused by spherical aberration when laser focusing across a plane interface from air into the sample

Fig. 2. Lightpath of self-modulating femtosecond laser processing system

Fig. 3. Comparison of the process of forming microlens by wet etching. (a) Comparison of etching process between front-side processing method and self-modulating processing method; (b) confocal 3D images of the structure with regular front-side processing method when etching 0 min, 20 min, and 70 min; (c) confocal 3D images of the structure with self-modulating method when etching 0 min, 20 min, and 70 min

Fig. 4. Morphology parameters of microlenses processed by self-modulating method with different pulse energies. (a) Confocal microscope pictures of microlenses at different pulse energies; (b) cross-section profiles of microlenses prepared at different pulse energies; (c) numerical aperture and radius of curvature of the microlens vary with the pulse energy

Fig. 5. Comparison of microlens morphology parameters prepared by self-modulating processing method and regular front-side processing method when changing the defocus position. (a) Morphologies of microlenses at different defocus positions using self-modulating processing method,(i) shows the optical microscope images of microlenses with defocus positions from 1 μm to 7 μm, and (ii) shows the confocal sectional profile of microlenses with defocus position from 8 μm to 14 μm; (b) diameter and depth changed with defocus position during self-modulating processing; (c) NA changed with defocus position during self-modulating processing; (d) diameter and depth changed with defocus position during front-side processing; (e) NA changed with defocus position during front-side processing

Fig. 6. Morphological characterization and imaging results of large-area microlens arrays. (a) Optical microscope images; (b) scanning electron microscopy images; (c) imaging results tested by optical microscopy; (d) focusing results tested by optical microscopy

Fig. 7. Morphological characterization and imaging results of microlenses with different NA. (a) Optical microscopy image; (b) scanning electron microscopy image; (c) confocal microscopy image; (d) imaging results, (d1) clearest imaging position of the first row, (d2) clearest imaging position of the second row, and (d3) clearest imaging position of the third row

Table 1. NA for the microlens fabricated by self-modulating processing method and corresponding information reported in relevant references