The Research Of Random Fiber Laser Based On The Waveguide Effect

A random laser (RL) is a non-conventional laser, whose feedback mechanismis based on disorder-induced light scattering. Based on the feedback mechanisms, random lasers are classified into two categories:(1) random lasers (RLs) with incoherent (or non-resonant) feedback, also called incoherent RLs,(2) RLs with coherent (or resonant) feedback, also called coherent RLs. The nondirectional and high threshold characters of the traditional RL systems have largely limited their application. The confinement effect of optical fibers on the lasing properties of RL has obtained by introducing random scattering system into the fiber core, bringing about the birth of random fiber lasers (RFLs) with low threshold and directionality. To date, the research about RFLs most based on a distributed-feedback mechanism.This dissertation concerns the research on RFLs based on the scattering of nanoparticles. The influences of the structures of optical fibers and random systems on the threshold, directionality and mechanism of RLs have been studied. All the details are shown as follows:1. RFL is obtained by end pumping a hollow optical fiber filled with a dispersive solution of polyhedral oligomeric silsesquioxanes (POSS) nanoparticles and laser dye pyrromethene597(PM597) in carbon disulfide (CS2), in which the concentration is1.5x10-2M for PM597and18.5wt%for POSS, respectively. It is found that the pump light at the one end of the liquid core optical fiber (LCOF) can pass the whole length of LCOF because the POSS nanoparticles were dispersed in CS2at a molecular level (1-3nm) with high stability and without sedimentation. Above the threshold pump energy the RFL appears coherent and resonant feedback multimode lasing in the weakly scattering system. For the LCOF containing PM597with the same concentration and no POSS nanoparticles, there occurs only amplified spontaneous emission that can be observed under the same experimental condition.2. The RL action of the POSS/PM597medium with the extremely weakly scattering regime in the cuvette system and LCOF system were performed, respectively. Incoherent RL has been observed for the POSS/PM597medium with the extremely weakly scattering regime in a quartz cuvette. Strikingly, however, by end pumping a hollow optical fiber filled with the same solution we have achieved coherent RFLs under controlled conditions. Based on well designed control experiments combined with pertinent analyses, its working mechanism has been well elucidated; i.e., multiple scattering of nanoparticles in the LCOF is greatly enhanced by the waveguide confinement effect under the total internal reflection condition. We envision that the coherent RFL demonstrated in this work may open a window to future RL applications aiming at low threshold, directionality, and wavelength tunability.3. The disordered polymer optical fiber (POF) was fabricated using the Teflon technique. The core material of the disordered POF is PM597-doped poly(methyl methacrylate-co-benzyl methacrylate-co-methacrylisobutyl polyhedral oligomeric silsesquioxanes) copolymer. And the cladding material of the disordered POF is poly(methyl methacrylate-co-butylacrylate) copolymer. The realization of a random polymer fiber laser (RPFL) is based on laser dye Pyrromethene597-doped one-dimensional disordered POF. The stabilized coherent laser action for the disordered POF has been obtained by the weak optical multiple scattering of the POSS nanoparticles in the core of the POF in situ formed during polymerization, which was enhanced by the waveguide confinement effect. Meanwhile, the threshold of our RPFL system is almost one order of magnitude lower than that of the liquid core RFL reported previously. Meanwhile, the localized effect of the one dimensional disorder POF is also discussed in terms of the experimental results.4. The localized surface plasmon resonance (LSPR) of metal nanoparticles as scattering centers will induces selective enhancement of the photoluminescence, which is expected to decrease the threshold of random laser in the random system. In order to combine the effects of one-dimensional confinement on the lasing properties of a classical RL system with LSPR of metal nanoparticles we fabricated a hollow optical fiber filled metal nanoparticles and gain medium. The effect of LSPR of metal nanoparticles on the one-dimensional confinement of the fiber has been researched. The overlap between of the LSPR of the metal nanoparticles and the photoluminescence spectrum has been found to be a factor influencing the threshold the RL.