High-resolution femtosecond laser 3D micromachining using low-NA focusing systems

Low-NA focusing systems can offer longer working distances than the high-NA ones, thereby enabling fabrication of 3D structures of great heights/thicknesses. However, degradation of the longitudinal resolution occurs at low NAs as a consequence of diffraction of the light waves. Here, we report on high-resolution laser printing of three dimensional (3D) structures of heights up to a few centimeters with a sub-10 mu m longitudinal resolution by incorporating a simultaneous spatiotemporal focusing (SSTF) scheme into the femtosecond laser direct writing. Remarkably, the SSTF can ensure generation of symmetric focal spots (i.e., spherical focal spots) of comparable sizes along both the horizontal and vertical directions. The resolutions are tunable in real time by dynamically varying the power of the writing laser beam. The ability to simultaneous achieving the large heights and high longitudinal resolutions in femtosecond laser 3D micromachining is of great use for applications ranging from microfluidics to infrared and THz photonics.