Fig. 1. Schematic of the experimental layout. BS: beam splitter; M: mirror; G1–G4: diffraction gratings; L1–L4: lenses with different focal lengths; DM: dichroic mirror; OL: objective lens; SA: sample. The dashed rectangle indicates the proposed extra-cavity pulse stretcher.

Fig. 2. (a) Numerically calculated and (e) experimentally measured laser intensity distributions at the entrance aperture of the objective lens. (b–d) Numerically calculated and (f–h) experimentally measured intensity distributions near the focus of the objective lens in XY, XZ-and YZ planes, respectively. Scale bars in (e) and (f–h) are 1 mm and 10 µm, respectively.

Fig. 3. Schematics of the fabrication procedure with the SSTF scheme along (a) x, (b) y, and (c) z directions, respectively. (d–f) Cross-sectional, (g–i) top-view, and (j–l) side-view optical micrographs of lines along different directions. The pulse energy and writing speed were 8 µJ and 200 µm/s, respectively. Scale bar: 20 µm.

Fig. 4. The influence of pulse energy and writing speed on the fabrication resolution in the SSTF scheme. Cross-sectional optical micrographs of laser-inscribed lines in the glass along (a) y and (b) x directions with different pulse energies ranging from 4.7 µJ to 11.0 µJ. (c) Lateral and longitudinal sizes of lines in XZ and YZ planes versus pulse energies. (d) A laser-written line using segmented processing with different pulse energies ranging from 11.0 µJ to 4.7 µJ at a writing speed of 5 µm/s. The insets in (d) are the corresponding cross-sectional view optical micrographs. Cross-sectional optical micrographs of several lines inscribed along (e) y and (f) x directions at different writing speeds ranging from 0.2 mm/s to 9 mm/s, pulse energy was set at 8 µJ. (g) Lateral and longitudinal resolutions versus writing speeds. Scale bars indicate 20 µm.

Fig. 5. The influence of processing depth on the fabrication resolution in the SSTF scheme. (a) Schematic of inscribing lines in glass at different depths along the X and Y directions. Cross-sectional optical micrographs of the lines written along the (b) X and (c) Y directions, respectively. (d) The lateral and longitudinal resolutions versus depth. Scale bar: 20 μm.

Fig. 6. (a) Schematic of laser-inscribed lines in the glass when the objective lens was not immersed in water. Cross-sectional optical micrographs of the lines along (b) Y and (c) X directions at different pulse energies. The pulse energies varied from 14.8 µJ to 22.8 µJ from left to right in both (b) and (c). (d) The lateral and longitudinal sizes in XZ and YZ planes versus pulse energies. Scale bar: 20 µm.

Fig. 7. (a–d) Cross-sectional view and (e–g) top-view optical micrographs of helical lines written throughout 1.6 mm thick glass at different pulse energies with the SSTF scheme. The writing speed was set at 200 μm/s, and the pulse energies from left to right were 9.5, 8.0, 7.2, and 6.2 µJ, respectively. (c) and (d) Enlarged images of (b) at different depths. (g) Enlarged image in (f). Scale bar: 100 μm.

Fig. 8. (a) Schematic of the fabrication procedure for 3D microchannel structures in glass by a combination of SSTF FLDW assisted etching, which consists of three main steps: (I) SSTF fs laser direct writing; (II) thermal annealing; (III) chemical etching. (b–d) A meandering cooling structure microchannel. Optical micrographs of the channel structure (b) after FLDW followed by thermal annealing and (c) after etching. (d) An enlarged image in (c). (e–m) A 3D multilayer microchannel network structure. Optical micrographs of the 3D network structure (e, h, k) after FLDW followed by thermal annealing and after etching in XY, XZ, and YZ planes. (g, j, m) were enlarged images in (f, i, l), respectively. (n–s) 3D helical microchannel structures. The top-view (n,o) and side-view (q,r) optical micrographs of the 3D helical lines fabricated after FLDW followed by thermal annealing and after etching. (p) and (s) are enlarged images in (o) and (r), respectively. The insets in (d, g, j, m) are photographs of the microchannel structures. Scale bar: 100 μm.