The shape of manufactured microtubes is one of the most important properties in their numerous emerging applications areas, like drug delivery, microfluidics, and cell biology. However, making non-cylindrical microtubes with 3D features in a reproducible and single-step fashion, and meanwhile, with the ability of remote control has remained challenging. In this study, we demonstrate the controlled synthesis of highly curved 3D microtubes by two-photon polymerization with single exposure of structured optical vortices, which is generated by phase modulation with a liquid crystal spatial light modulator (SLM). We exploit the tight focusing property of the optical vortices along the light path to create 3D microtubes. By modulating the topological charge and symmetry of the optical vortices, the size and geometry of fabricated microtubes can be well controlled. Finally, we combine these two ideas with the use of magnetic nanoparticles doped resist to fabricate 3D microtubes with elaborate features and remote controllability. Precise rotation and motion of the microtubes are realized by external magnetic field. With the fabricated functional mocrotubes, elaborate capture, delivery, and realease of microparticles are demonstrated. The technology we introduce is simple, stable and achieves a high production rate to make a wide variety of functional 3D microtubes, which have broad applications in cargo transportation, drug delivery, biosensing, microfluidics, and targeted cell therapy.
The residual stress field of fused silica induced by continuous wave CO2 laser irradiation is investigated with specific photoelastic methods. Both hoop stress and axial stress in the irradiated zone are measured quantitatively. For the hoop stress along the radial direction, the maximum phase retardance of 30 nm appears at the boundary of the laser distorted zone (680-μm distance to center), and the phase retardance decreases rapidly and linearly inward, and decreases slowly and exponentially outward. For the axial stress, tensile stress lies in a thin surface layer (<280 μm) and compressive stress lies just below the tensile region. Both tensile and compressive stresses increase first and then decrease along the depth direction. The maximum phase retardance induced by axial tensile stress is 150 nm, and the maximum phase retardance caused by axial compression stress is about 75 nm. In addition, the relationship between the maximum axial stress and the deformation height of the laser irradiated zone is also discussed.
The laser-induced bulk damage and stress behaviors of fused silica are studied by using a neodymium-doped yttrium aluminum garnet laser operated at 1064 nm with pulse width of 11.7 ns. Three zones of bulk damage are defined: columned cavity zone, compacted zone, and crack zone. The damage morphology and stress distribution are characterized by a three-dimensional digital microscope and a polarizer stress analyzer. The results show that the stress in the columned cavity zone and compacted zone is approximately zero. From the laser beam center to fringe, both tensile and compressive stresses in the crack zone increase abruptly and linearly and then decrease exponentially. Thermal annealing is used to prove the phase retardation caused by the residual stress. The formation mechanism of bulk damage is also discussed.
Two-photon polymerization is a powerful technique in the area of functional micro/nano device fabrication. The greatest limiting factor in widespread use of this technique is the low efficiency because the structure is fabricated by point-by-point scanning. In recent years, computer generated hologram is used for parallel fabrication via multi foci. In this paper, we proposed a new rapid fabrication method which use desirable multi-focus pattern as scanning cell instead of single focus point or foci array to polymerize. We establish a femtosecond laser experimental setup involved in a liquid crystal spatial light modulator. The computer generated hologram pattern on spatial light modulator is used to produce desirable foci array. The position and intensity of each focus in the pattern can be controlled well by optimal design. We use multi foci in a line as scanning cell to fabricate some revolving structure and the Fresnel lens can be expected. This work provides a new method to greatly improve the efficiency of two-photon polymerization production in fabricating revolving structures.