Multiphoton lithography

To enable 3D structuring, the light source must be adequately adapted to the liquid photoresin in that single-photon absorption is highly suppressed.

Concretely, those regions of the laser beam which exceed a given exposure threshold of the photosensitive medium define the basic building block, the so-called voxel.

Other parameters which influence the actual shape of the voxel are the laser mode and the refractive-index mismatch between the resist and the immersion system leading to spherical aberration.

It was found that polarization effects in laser 3D nanolithography can be employed to fine-tune the feature sizes (and corresponding aspect ratio) in the structuring of photoresists.

This proves polarization to be a variable parameter next to laser power (intensity), scanning speed (exposure duration), accumulated dose, etc.

Inorganic glass and ceramics have better thermal and chemical stabilities than photopolymers do, and they also offer improved durability due to their high resistance to corrosion, degradation, and wear.

[12] Nowadays there are several application fields for microstructured devices, made by multiphoton polymerization, such as: regenerative medicine, biomedical engineering, micromechanic, microfluidic, atomic force microscopy, optics and telecommunication science.

They vary in key parameters as geometry, porosity and dimension to control and condition, in a mechanical and chemical fashion, fundamental cues in in vitro cell cultures: migration, adhesion, proliferation and differentiation.

The multiphoton polymerization can be suitable to realize microsized active (as pumps) or passive (as filters) devices that can be combined with Lab-on-a-chip.

First, the 3D filter has increased mechanical resistance to shear stresses, enabling a higher void ratio and hence more efficient operation.

Considering the integrated micropumps, they can be polymerized as two-lobed independent rotors, confined into the channel by their own shaft, to avoid unwanted rotations.

[7] To date, atomic force microscopy microtips are realized with standard photolithographic techniques on hard materials, such as gold, silicon, and its derivatives.

Nonetheless, the mechanical properties of such materials require time-consuming and expensive production processes to create or bend the tips.