Plasmonically enhanced random lasing and weak localization of light in powdered Nd 3+ doped lithium niobate and its spectral transformation

We report surface plasmon enhanced random lasing action and weak localization owing to charge accumulation on the grain boundaries and its spectral transformation in powdered Nd3+ doped lithium niobate (Nd: LN) specimens. Accumulative charge density resulting from screening of electric field of spontaneous polarization was estimated, proving that surface plasmons (SPs) can be excited on the grain boundaries of powdered Nd: LN. The SP based scattering is believed responsible for random lasing to occur, which was further confirmed by the estimation of the scattering mean free path and the scattering cross section and intriguing three step-like backscattering reduction observed in the process of monitoring the variation of reflection spectrum with increasing pumping power. Under a certain pumping power, the powdered Nd: LN specimen was melted locally and this resulted in great changes in random lasing wavelengths. To delve into the reason behind these changes, photoluminescence spectra of the specimens were measured before and after melting. By taking a close look at their dynamics and slopes, it was found that spectral transformation of random lasing occurred owing to the change of lattice structure in powdered Nd: LN.