Amplification of the Fluorescence Propagating in the Waveguide Regime in a Planar Layer of NLC
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Amplification of the Fluorescence Propagating in the Waveguide Regime in a Planar Layer of NLC N. M. Shtykova,*, S. P. Paltoa, B. A. Umanskiia, D. O. Rybakova, and I. V. Simdyankina a
Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,” Russian Academy of Sciences, Moscow, 119333 Russia *e-mail: [email protected] Received April 12, 2018; revised April 28, 2018; accepted May 7, 2018
Abstract—The amplification of spontaneous fluorescence in a planar layer of nematic liquid crystal doped with DCM dye in the mode of waveguide light propagation has been studied. The gain reaches the value α = 0.0014 μm–1 at a pump radiation intensity of 1.38 MW/cm2. Numerical simulation of the structure imitating the experimental cell showed qualitative agreement of the calculation results with the experimental data. DOI: 10.1134/S1063774519020275
INTRODUCTION The study of lasing in liquid crystals (LCs) is one of the newest lines of fundamental research, which has been intensively developing in recent years all over the world [1]. The idea of implementing lasing under conditions where the feedback is formed by not external mirrors, as in traditional laser schemes, but the spatial periodicity of the dielectric permittivity or gain of a medium was proposed in [2]. This concept of distributed feedback (DFB) has been implemented for LCs in different versions. Most studies were devoted to light lasing in cholesteric liquid crystals (ChLCs), which have an internal spatially periodic (helical) structure [3–6]. Here, we are speaking of lasing at the photonic band boundaries (selective reflection region), associated with Bragg modes propagating along the helical structure axis, which is oriented perpendicular to the ChLC layer plane. Lasing was experimentally obtained for the first time in this scheme in 1980 [3]. In this version, the first order of the Bragg diffraction of radiation from the structure with a period of half helix pitch served as DFB. The second version of DFB is associated with the use of spatially periodic structures (micro-gratings) at the LC layer boundary, similar to that proposed [7] for plane waveguides with one of the surfaces corrugated. The distributed feedback is implemented when the Bragg conditions are satisfied, i.e., the inhomogeneity period Λ is equal to the integer number of half-waves of generated light: Λ = m λ , where m is the diffraction 2n order (an integer number), λ is the light wavelength in vacuum, and n is the refractive index of the medium. In solid-state waveguides, these DFB scheme was
implemented in the 6th, 12th, and 25th [8, 9] Bragg diffraction orders. The implementation of this idea in the case of LCs is based on the use of an interdigitated electrode system (IES) on the surface of one of the LC cell substrates. In [10], opaque electrodes with a period of 15 μm pursued a dual objective. First, they, being an opaque mask, provided spatial modulation of the gain of the medium. Second, the electrodes were used to change the effec
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