title: Multi-photon excited coherent random laser emission in ZnO powders.
abstract: We report the observation and analysis of anti-Stokes coherent random laser (RL) emission from zinc oxide (ZnO) powders excited by one-, two- or three-photon femtosecond laser radiation. The ZnO powders were produced via a novel proteic sol-gel, low-cost and environmentally friendly route using coconut water in the polymerization step of the metal precursor. One- and two-photon excitation at 354 nm and 710 nm, respectively, generated single-band emissions centred at about 387 nm. For three-photon excitation, the emission spectra showed a strong ultraviolet (UV) band (380-396 nm) attributed to direct three-photon absorption from the valence band to the conduction band. The presence of an intensity threshold and a bandwidth narrowing of the UV band from about 20 to 4 nm are clear evidence of RL action. The observation of multiple sub-nanometre narrow peaks in the emission spectra for excitation above the RL threshold is consistent with random lasing by coherent feedback.
authors.affiliation: Departamento de Física, Universidade Federal de Pernambuco, Recife, PE 50670-901, Brazil. anderson@df.ufpe.br.
authors.forename: Christian
authors.initials: C
authors.lastname: Tolentino Dominguez
authors.forename: Maria de A
authors.initials: Mde A
authors.lastname: Gomes
authors.forename: Zélia S
authors.initials: ZS
authors.lastname: Macedo
authors.forename: Cid B
authors.initials: CB
authors.lastname: de Araújo
authors.forename: Anderson S L
authors.initials: AS
authors.lastname: Gomes