Lasing in Dye‐Doped Cholesteric Liquid Crystals: Two New Tuning Strategies

Abstract

tial for applications such as anisotropic building blocks for the preparation of colloidal crystals and photonic materials of unusual symmetry, colloidal liquid crystals, and biosensors.In summary, we have used a gel trapping technique as a generic method for preparing Janus particles by templating of particle monolayers at air±water or oil±water interfaces, followed by lifting off the particles with PDMS and subsequent deposition of gold. By replication of colloidal monolayers of repulsive particles at liquid surfaces we have also fabricated microporous surfaces and composite supraparticles. ExperimentalIn a typical procedure for the preparation of microporous surfaces or Janus particles, 30 lL of a latex particle suspension/isopropanol solution (50:50) was injected at the interface between a hot Gellan solution at 50 C (prepared by hydration of 2 % Gellan (Kelcogel, CPKelco, UK) in water at 95 C for 10 min) and a pre-warmed decane phase. After setting the gel at 25 C, the decane phase was replaced with PDMS (Sylgard 184, Dow Corning) and cured for 48 h. Then the solid elastomer was peeled off the gel and washed in hot water (95 C) for 10 min to remove Gellan residues from the surfaces. To fabricate PDMS with a microporous surface, the particles were removed by stretching the elastomer and collecting the released particles with a metal blade from the surface in the presence of a surfactant solution (1 mM C 12 E 5 ). Janus particles were produced by gold sputtering (NanoTech Seprep II Sputter coater) on the partially embedded particle monolayer on PDMS and subsequent mechanical removal of the particles from the interface.

Optically pumped mirrorless lasing. A Review. Part II. Lasing in photonic crystals and microcavities

“…If the twisting power of a chiral dopant is sensitive to the optical (e.g., UV) irradiation, the pitch and therefore the lasing can be phototunable [52,83,84]. It is worth noticing that a chiral dopant ZLI-811 (also known as S811) undergoes a photo-transformation under UV irradiation with the wavelengths shorter than 300 nm [83], which leads to decreasing twisting power and thus moving the PhBG towards the longer wavelengths. Spatial tuning of the lasing may be implemented if a gradient of the pitch is formed in a dye-doped ChLC sample, moving the spot of the pumping light along the pitch gradient direction.…”

“…Spatial tuning of the lasing may be implemented if a gradient of the pitch is formed in a dye-doped ChLC sample, moving the spot of the pumping light along the pitch gradient direction. The pitch gradient can be produced via placing in contact two ChLC mixtures with different concentrations of the chiral agent [83], by photo-patterning [85], or through a temperature dependence of solubility of the chiral agent [86]. A position-sensitive dye-doped ChLC laser covering a whole visible range has been fabricated by the authors of Ref.…”

Dielectric and Electro-Optical Properties of Ceramic Nanoparticles Doped Liquid Crystals

“…If the helical pitch is comparable to the wavelength of light a distributed optical feedback results in selective light reflection and giant optical activity. Effective control of the helical pitch value by external fields makes chiral nematics extremely promising for uses in photonic and electro-optic devices, such as photonic crystals [56], light shutters and switches [57], and adaptive laser optics and lasing [58].…”

Different Approaches of Employing Cholesteric Liquid Crystals in Dye Lasers

“…An alternative approach to the generation of laser radiation tunable over a wide range of wavelengths in DD CLCs based on preparation a cell with gradient of the helical pitch was proposed in [39]. The pitch gradient was produced by filling of the cell with a cholesteric liquid-crystal mixture having a concentration gradient of chiral dopants.…”