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Laser-assisted single-step generation of elongated Au NPs is reported. Laser-generated Au NPs have some fraction of spherical NPs and elongated NPs with aspect ratio of 6 -8. The behavior of these NPs in a permanent magnetic field up to 7 Tesla is experimentally studied using in-situ optical absorption spectrometry. It is found that magnetic field causes irreversible changes in the aspect ratio of elongated Au NPs. Residence in magnetic field for time of order of tens minutes is accompanied by further elongation of Au NPs and formation of Au nanowires with aspect ratios up to 17 -18. This is corroborated with TEM images of Au NPs before and after the action of magnetic field. The results are interpreted on the basis of interaction of external magnetic field with that of electrons that take part in longitudinal plasmon oscillations in elongated Au NPs.

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Laser-assisted fragmentation is an efficient method of the nanoparticles size and morphology control. However, its exact mechanisms are still under consideration. One of the remaining problems is the plasma formation, inevitably occurring upon the high intensity laser irradiation. In this Letter, the role of the laser-induced plasma is studied via introduction of high-intensity external magnetic field (up to 7.5 T). Its presence is found to cause the plasma emission to start earlier regarding to a laser pulse, also increasing the plume luminosity. Under these conditions, the acceleration of nanoparticles fragmentation down to a few nanometers is observed. Laser-induced plasma interaction with magnetic field and consequent energy transfer from plasma to nanoparticles are discussed.