Origin of light scattering in dye doped polymeric waveguides and the dependence of excitation geometry on coherent random lasing. (7th April 2020)

• Record Type: Journal Article
• Authors: Choubey, Priyanka S; Ojha N N, Subhashree; Ghosh, Subhabrata; Varshney, Shailendra K; Bhaktha B N, Shivakiran
• Is Part Of: Journal of physics. Volume 53:Number 24(2020)
• Publication Date: 2020-04-07
• Subjects: random lasing -- polymeric waveguide -- amplified spontaneous emission; Physics -- Periodicals; 530
• DOI: 10.1088/1361-6463/ab8039
• Languages: English
• ISSNs: 0022-3727

Abstract

Abstract: We present an experimental investigation on the origin of coherent random laser (RL) emission from 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminos-tyryl)-4H-pyran (DCM) doped polyvinyl alcohol (PVA) thin film (DCM-PVA) planar waveguide using various characterization techniques. Absorption and fluorescence spectra of the DCM-PVA thin film confirm the presence of aggregates at dye concentrations greater than 0.08 wt. %. Time correlated single photon counting measurements were perfomed to confirm the presence of dye aggregates in PVA matrix. x-ray diffraction studies reveal the semi-crystalline nature of the DCM-PVA thin film. The optical gain coefficient was determined by the variable stripe length method under 532 nm pulsed laser excitation and was found to be 2.1 cm −1 using the one-dimensional amplifier model for the 0.08 wt. % thin film. The RL emission of the planar waveguide depends on the geometry of the excitation spot. The emission spectrum consists of randomly positioned narrow spectral lines under stripe excitation geometry whereas, a smooth spectrum lacking the narrow peaks is observed under circular spot excitation, both above the lasing thresholds. The origin of weak scattering in DCM-PVA waveguide is attributed to the formation of dye aggregates and inhomogeneities created by the semi-crystalline nature of the film. The RL threshold decreases with an increase of the stripe length due to weak waveguiding in the planar film under stripe excitation. The high optical gain and low lasing thresholds attainable in DCM-PVA waveguides make them a promising candidate for the fabrication of polymer waveguide based photonic devices.