Fig. 1. Femtosecond laser digital projection lithography system. (a) Optical path diagram of femtosecond laser digital projection lithography system; (b) femtosecond laser photoreduction of precursor solution to form metal nanoparticles; (c) optical micrograph of printed metallic sliver pattern; (d) scanning electron microscope image of printed metallic sliver pattern

Fig. 2. Principle of femtosecond laser photoreduction. (a) Reduction process of silver precursor solution; (b) reduction process of gold precursor solution

Fig. 3. Sliver structures under different parameters and elemental analysis results. (a) Relationship between sliver pattern thickness and printing time; (b) relationship between time required to process silver structure with maximum thickness and laser power; (c) SEM image of sliver Taiji pattern with imported picture in DMD shown in inset; (d) SEM image of sliver nucleus pattern with corresponding optical micrograph shown in inset; (e) element mapping in sliver structure; (f) element composition

Fig. 4. Gold structures under different parameters and elemental analysis results. (a) Relationship between gold pattern thickness and printing time; (b) relationship between time required to process gold structure with maximum thickness and laser power; (c) SEM image of gold “USTC” pattern with imported picture in DMD shown in inset; (d) SEM image of gold snowflake pattern with corresponding optical micrograph shown in inset; (e) element mapping in gold structure; (f) element composition

Fig. 5. Processing resolution and time comparison. (a) Effects of laser power on processing resolutions of gold and silver; (b)‒(e) processing resolutions of silver under different laser powers; (f) material processing time under different processing methods

Fig. 6. Surface topography analysis results of silver patterns. (a) SEM image of sliver heart-shaped pattern; (b) local magnification of Fig.6(a); (c) AFM image of silver pattern surface; (d) AFM line scanning result