Low-Threshold and High Intensity Random Lasing Enhanced by MnCl₂.

Energy transfer is known to have a significant influence on random lasers. However, the study about the effect of energy transfer between metallic salt and dye molecules on random lasers is still lacking at present. Here, we investigate random lasing actions in Pyrromethene-597 (PM597), PM597-doped MnCl₂ (manganese (II) chloride), PM597-doped polymer-dispersed liquid crystal (PDLC) and PM597-doped PDLC with MnCl₂ capillary systems. We find that random lasing of the systems with MnCl₂ exhibits lower threshold, higher intensity, sharper peak and variable resonance wavelength in comparison with the systems without MnCl₂. This behavior is closely related to the decrease of fluorescence quenching effect and the enhancement of local field induced by energy transfer between MnCl₂ and PM597. Red-shift of wavelength is observed with increasing dosage concentration of MnCl₂ in the PM597-doped PDLC with MnCl₂ system. Through the analysis of single-shot emission spectra of PM597-doped PDLC without and with MnCl₂ systems, the role of MnCl₂ in the coupling of lasing modes is confirmed. Lengths of laser oscillation cavities of the PM597-doped PDLC without and with MnCl₂ systems are calculated by a power Fourier transform (PFT) analysis of their emission spectra. It well accounts for the effect of MnCl₂ on the variation of the oscillation cavity.