Lasing in bulk liquid crystal structures has been well studied in the last decades but light propagation in liquid crystal boundaries, disclinations and droplets has only recently gained attention. One way to introduce a wave guide in liquid crystals is by introducing disclination lines in an otherwise homogeneous liquid crystal medium. Due to the disclination there is locally a higher refractive index which confines the light. This leads to three-dimensional configurations. The disclinations can be generated in a controlled way by introducing geometrical structures on the surface of the substrate or by optical trapping.
A uniform liquid crystal cell may exhibit domains after application of a voltage when different kinds of switching are energetically equivalent, as for example in a pi-cell in which the liquid crystal aligned in a parallel way. At the domain boundaries, the liquid crystal director has a different orientation and may support optical waveguiding. The domain boundaries can be attached to geometrical imperfections at the substrates, such as spacer balls or polymer structures.
Besides light propagation in disclinations and domain boundaries, lasing in LC droplets also offers very promising perspectives. These droplets can be easily produced and give rise to low threshold 3D lasing. Depending on the students interest, this system can be further elaborated on.
In this topic the student will investigate new lasing structures in liquid crystals and depending on his/her interest the focus can be shifted to one of the systems. The student will have the change to investigate how wave guide geometries, such as closed rings or long lines, and 3D microdroplets can be used to obtain low threshold lasing.
The project consists of a fabrication part and an experimental part. The processing will mainly be done in the clean room in Zwijnaarde while the fabricated cells will be characterized in the labs at the Technicum.