Volume Modification
Highly focused ultrashort pulses enable the volume modification of transparent materials such as glass, sapphire, and other crystals. The robust control of laser parameters and the precise intra-volume positioning of the laser focal spot allow the inscription of complex structures like Bragg gratings and waveguides.
3D waveguides fabricated in fused silica.
Courtesy of Workshop of Photonics.
3D waveguides fabricated in fused silica.
Courtesy of Workshop of Photonics.
The process is typically driven by multiphoton absorption, which requires high intensities so that the material is modified only at the focal spot. The laser-induced material volume modification impacts the density of the material and subsequently, the refractive index. This is a key principle utilized in the creation of fiber Bragg gratings (FBGs), as alternating structures are written into the transparent material by inducing a refractive index change rather than optically damaging the fiber. FBGs have been demonstrated in both single-mode and dual-cladding fibers.
Furthermore, the modified material can be chemically etched away. This two-step process is called selective laser etching. After volume modification, the glass or sapphire gains different etching properties. Thus, using material-dependent etching solutions, various mechanically stable and durable structures like curved waveguides or even 3D forms can be obtained.
PHAROS and CARBIDE femtosecond lasers are widely used for all of the aforementioned volume modification applications, making a strong impact in the development of future technologies.
