Electrically controllable liquid crystal random lasers below the Fréedericksz transition threshold

Abstract

This investigation elucidates for the first time electrically controllable random lasers below the threshold voltage in dye-doped liquid crystal (DDLC) cells with and without adding an azo-dye. Experimental results show that the lasing intensities and the energy thresholds of the random lasers can be decreased and increased, respectively, by increasing the applied voltage below the Fréedericksz transition threshold. The below-threshold-electric-controllability of the random lasers is attributable to the effective decrease of the spatial fluctuation of the orientational order and thus of the dielectric tensor of LCs by increasing the electric-field-aligned order of LCs below the threshold, thereby increasing the diffusion constant and decreasing the scattering strength of the fluorescence photons in their recurrent multiple scattering. This can result in the decrease in the lasing intensity of the random lasers and the increase in their energy thresholds. Furthermore, the addition of an azo-dye in DDLC cell can induce the range of the working voltage below the threshold for the control of the random laser to reduce.

Soliton-assisted random lasing in optically-pumped liquid crystals

“…In recent years they have attracted a great deal of attention, mainly due to the versatility stemming from cavity-less geometries and the ease of realization [1][2][3][4][5][6][7][8][9]. In liquid crystals, suitable dopants can provide the gain action through optical pumping, while optical birefringence in conjunction with intense fluctuations of the dielectric tensor yield the required recurrent multiple scattering for random resonances to occur [10][11][12][13][14][15][16][17]. In the nematic phase, moreover, liquid crystals are positive uniaxial materials subject to optic axis reorientation under the action of electric fields, either at low or optical frequencies [18].…”

Lowering the excitation threshold of a random laser using the dynamic scattering states of an organosiloxane smectic A liquid crystal

“…7 The most extensively studied LC phase for random lasers, however, is the nematic phase. [8][9][10][11][12][13] In random lasers, an important parameter is the transport mean free path l, which is defined as the distance a photon travels before its direction is randomized, because it influences the excitation threshold for laser emission. This property, which is also inversely proportional to the scattering cross-section, is sensitive to external fields in nematic LCs.…”

“…This property, which is also inversely proportional to the scattering cross-section, is sensitive to external fields in nematic LCs. Consequently, reports have typically focused on thermally, [8][9][10] optically, 12 and electrically 13 driven changes in the scattering properties and the subsequent effect they have on the laser characteristics. There have also been studies carried out on the statistical properties of the emission from dye-doped nematic random lasers.…”

Random laser emission in a sphere-phase liquid crystal

“…7,11 Liquid crystal is the ideal host media for random lasing due to its large birefringence and linear or nonlinear light-scattering ability, coupled with the large susceptibility of crystalline reorientation or disorder induced by an external field. 4,5,12-17 To date, random lasing has been observed in different phases of liquid crystal, including nematic, 18 smectic, 19 chiral nematic, 20,21 and blue phases (BP). 4, 13 Recently, a self-assembly liquid crystal phase denoted sphere phase (SP) has been observed between isotropic and blue phases as well as isotropic and chiral nematic phases.…”