During the past decades, the femtosecond lasers become a unique tool for 3D structures fabrication in different optical materials. Femtosecond lasers can space-selectively induce local modifications in any transparent materials due the strong nonlinear absorption. These internal modifications in fused silica cause the structural and chemical changes that can be selectively removed by immersing the samples to aqueous solutions of etchant such as hydrofluoric acid (HF) or potassium hydroxide (KOH) resulting in direct fabrication of the true 3D micro-devices inside transparent materials. The transparent materials plays crucial role due the ability of confined internal modifications and selective modified zone removing by chemical etching.
The processing of transparent materials such as fused silica or sapphire with conventional fabrication techniques or direct laser ablation have a limitation due the structure size and material thickness. The taper is involved and surface chipping due the accumulated stresses limits the quality of the final sample. The technology combining femtosecond lasers with chemical etching (Selective Laser Etching SLE) involves avoiding all mentioned drawbacks during the fabrication of high resolution structures in transparent materials. The etching selectivity from 100:1 to 10000:1 can be achieved depending on the transparent material and etchant used. That involves formation of high aspect ratio (>50:1) taper less holes, 2D free shape structures according the imported CAD drawing and embedded 3D microsystems involving optical, mechanical and fluid transportation properties in the single device.