## 2 Materials and Methods  
Laser Processing. All experiments were performed using Foturan PG (commercially available from Schott). Foturan is a photo-structurable lithium alumino-silicate glass that accommodates small amounts of Ag2O (0.05-0.15%) and Ce2O3 (0.01-0.04%), primarily designed for the UV light-induced selective microstructuring. The protocol for obtaining free-form shaped microstructures in Foturan glass using PLAE is schematically depicted in Figure 1. LDW was carried out using a ps laser source (Coherent, model Lumera HyperRapid 50), delivering pulses of about 10-ps duration at 500-kHz repetition rate. The large-scale area microfluidic structures and PG molds were fabricated using visible (VIS--532 nm) ps laser, which proved to be more appropriate for a precise and controlled volume processing, while UV (355 nm) laser pulses were employed for fabrication of photo-masks, since it was experimentally found that the ps laser was more adequate for efficient and rapid formation of through-holes in bulk glass. Laser power was adjusted between 30-50 mW in case of UV and 500-600 mW for VIS laser pulses. The laser beam was focused onto the sample surface using an aspheric lens of 15-mm focal length and 0.5 numerical aperture to generate a circular spot of about 4 \(\upmu\)m in diameter (calculated by \(\mathrm{w}=2\mathrm{f}\mathrm{M}^{2}/\upmu\mathrm{T}\), where \(\mathrm{w}\) is the minimum beam waist radius, \(\mathrm{f}\) is a focal distance of the focusing lens, \(\mathrm{M}\) is a quality beam factor, \(\mathrm{D}\) is a laser beam diameter, and \(\mathrm{\lambda}\) is the wavelength of the laser used [43]). The writing speed was varied from 0.1 to 1 mm/s depending on the pattern dimensions and geometrical features. The samples were placed on a customized LDW processing platform consisting of motorized translation stages (PlanarDL Aerotech), providing a spatial resolution of a few tens of nanometers (Figure 1a). The experiments were carried out in a clean room, in air, at atmospheric pressure, and were in-situ monitored with a charge-coupled device (CCD) camera (Thorlabs). In a subsequent step (Figure 1b), the laser-exposed glass samples were annealed in a programmable furnace (Carbolite, model MTF M1238-250). First, controlled heating with a slope of 5 \({}^{\circ}\)C/min up to 500 \({}^{\circ}\)C was performed. Then the temperature was kept constant for 1 h in order to cause diffusion of precipitated Ag atoms to grow Ag nanoclusters. Next, the temperature was increased again with a slope of 3 \({}^{\circ}\)C/min up to 605 \({}^{\circ}\)C and kept constant for another hour to induce the formation of crystalline lithium metasilicate phase around the grown Ag nanoclusters, which acted as nuclei. The latent image formed during the laser direct writing process was then developed by the thermal treatment to be  
Figure 1: Schematic of the PLAE (picosecond laser-assisted etching) process: (**a**) laser direct writing followed by (**b**) thermal treatment and (**c**) chemical etching in HF (hydrofluoric acid). visible. By changing the laser fluence and scanning speed one may thus modify the glass and evaluate tracing line thicknesses (Figure 2). The pulse overlap for all cases can be estimated to more than 99.9%. This evaluation allows choosing further laser parameters for the glass processing for specific needs, e.g., thinner lines for higher-resolution processing or thicker lines for larger-area modification. In our case we found threshold line widths of about 4 \(\upmu\)m in case of UV laser pulses and of 5.5 \(\upmu\)m in case of VIS, which can increase with increasing laser fluence and decreasing scanning speed (Figure 2b,d). In the last step, the glass samples were submitted to chemical etching in an 8% HF solution under the ultrasonic condition (Figure 1c).