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SEM images of the PC layer and schematic of the TiO2 PC/LC laser device. The SEM images show the cross-section and top view of the PC layer. All scale bars are 500 nm. Transparent electrodes on both the top and bottom substrates enabled an electrical field to be applied perpendicular to the plane of the PC.
Comparison of non-patterned and nano-patterned TiO2-LC devices. (a) Fluorescence from the non-patterned TiO2 device when photo-excited along a direction normal to the plane of the device. (b) Laser emission from the nano-patterned TiO2-LC device. Δλ represents the full-width at half maximum. The cell gap in both cases was 10 μm. The insets of the figures represent the two different device structures. Note that in (b) the height of the pillars is not to scale and is simply to indicate the nano-patterned array.
Emission characteristics of the nano-patterned TiO2-LC laser device. (a) The output intensity as a function of excitation energy for the two orthogonal linear polarization states of the TiO2-LC laser when photo-excited normal to the plane of the device: parallel to the LC director (blue squares) and perpendicular to the director (orange triangles). (b) Output as a function of excitation energy for a chiral nematic LC laser with the same film thickness and dye. (c) Laser emission in the no-field state (black line) and with an applied electric field (5 kHz) with a field strength of 12 V/μm (red line). (d) Laser emission in three dimensions consisting of in-plane (x,y) and surface (z) emission.
Modification of the far-field beam profile using electric fields. No electric field: (a) illustration of the LC alignment, (b) 2D plot of the beam profile, and (c) 3D plot of the beam profile. (d), (e), and (f) are equivalent figures when the sample is subjected to an electric field (12 V/μm at 5 kHz). These results were recorded on a Spiricon Beam Profiler.
(a) and (b) Two dimensional modal analysis of a cross section of the laser device where the LC filled region is modelled as an optical uniaxial medium with optic axis parallel to the x-direction. Two modes with comparable symmetry are shown: (a) x-polarized mode, (b) z-polarized mode. ((c) light colored symbols) Band diagram obtained for the case that the LC was considered as uniaxial with optic axis parallel to the x-direction, ((c) dark colored symbols) band diagram obtained for the case that the LC was considered as uniaxial with optic axis parallel to the z-direction. ((c) inset) Electric field distribution of a selected transverse electric mode (linearly polarized) of the simulated, planar photonic crystal. For the purposes of the simulation, the region below the nano-pillars was considered to be 200 nm-thick with an effective refractive index of 2.0. In the experiment, this layer would consist of both TiO2 and ITO.
Polarization and dielectric properties of two simulated modes of a two dimensional cross section of the layered structure with nano-patterned TiO2 layer covered by a birefringent LC.
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