Femtosecond laser direct writing provides a means to fabricate 3D microstructures within transparent media such as volumetric Fresnel zone plates and embedded microfluidic channels. To characterize these buried structures, we need not only destructive imaging technique such as electron microscopy but also nondestructive means enabling in-depth visualization. Optical microscope is a conventionally used non-destructive imaging tool. However, Figure 5 shows a side view of laser-written voids in fused silica. The sample was grinded and polished to reveal the structures near the surface of the side wall.
Optical coherence microscopy (OCM) is widely used non-destructive imaging technique which deserves high depth resolution by a use of broadband source giving short coherence length. 3D visualization of embedded laser-written structure is achievable by rendering scanned images in 2D. Figure 6 shows 3D OCM images of Figure 5. The images were obtained without any post processing and/or grinding/polishing.