Figure 4
From: Fabricating THz spiral zone plate by high throughput femtosecond laser air filament direct writing
Estimation of the maximal direct writing range. (a) Optical image of the laser filament taken by a CCD camera; (b) schematic diagram of the laser filament direct writing range (gray area is the area covered by the filament when it is scanned by the galvanometer); (c) burn pattern on a thermal paper caused by the laser filament used in the fabrication process.
