Band-edge and random lasing in paintable liquid crystal emulsions

Abstract

Lasing mechanisms within paintable dye-doped chiral liquid crystal emulsions are investigated. Evidence shows that by variation in liquid crystal droplet size, by simple control of mechanical mixing speeds, a change in the lasing mechanism from band-edge lasing (large droplets) to diffuse nonresonant random lasing (small droplets) can be facilitated. This approach represents a facile technique for the variation in lasing mechanism, within a self-organizing, flexible, and conformable system, and offers the opportunity of developing controllable linewidth laser sources.

Topological zoo of free-standing knots in confined chiral nematic fluids

“…Ensuing conformations not only depend on the anchoring, but vary continuously with the cholesteric pitch. The structures with concentric layers found in cholesteric droplets with degenerate planar anchoring have lately attracted much attention with their use in advanced soft matter photonic elements such as Bragg resonators for micro lasers [28][29][30][31][32] . The recent detailed numerical and topological study of these systems shows 27 that the degenerate boundary conditions still allow enough degrees of freedom to at least partially accommodate the requirements of the intrinsic twisting and form rather simple defect structures.…”

Wavelength-tuneable liquid crystal lasers from the visible to the near-infrared

“…Their periodic micro-molecular structure is self-organizing, allowing mirror-free lasing with low thresholds and high slope efficiencies in simple and low-cost device architectures. More recently, they have even been implemented into paintable materials, without the need for encapsulation 3,4 . Thus far, LC lasing experimentation has been restricted to wavelengths within the ultra-violet and visible regions of the spectrum, whilst longer wavelengths have only been speculated upon in theory 5 .…”

Electrically switchable random to photonic band-edge laser emission in chiral nematic liquid crystals

“…In this case, the excitation threshold is found to be approximately E th % 1.5 lJ/pulse, which is a factor of two lower than that recently observed for emulsion-based polymer dispersed LC lasers. 7 For the random laser, the slope efficiency is found to be <2% in the forward direction parallel to the normal of the glass substrates although the emission occurs over a much greater cone angle than that of the band-edge laser. The results show that, in order to observe a direct control of the emission linewidth from this laser sample, it is necessary to use excitation energies that are greater than 1.5 lJ/pulse.…”

“…However, using dyedoped LC emulsions, 9 it has recently been shown that by altering the droplet dimensions in the polymer dispersed LC, it is possible to change the feedback mechanism from one of intense multiple scattering (small droplets) to distributed feedback from a periodic macroscopic structure (large droplets). 7 The result is a system whereby the emission characteristics can be altered from a broad linewidth to a narrow linewidth by simply changing the mixing speed during the preparation of the emulsion without having to adjust the mixture composition.…”

“…Both photonic band-edge and random laser emissions have been observed in liquid crystal (LC) media in recent years. [1][2][3][4][5][6][7] Band-edge laser emission from dye-doped chiral LCs is characterized by a single-mode, narrow linewidth laser line that appears at the edge of a photonic band gap (PBG) due to enhancement in the density of the photon states. Random laser emission, on the other hand, occurs in LCs when the multiple scattering of light is combined with a component that can generate optical gain through stimulated emission.…”