Research On The Characteristics Of Optics And Magneto-optical Effects In Periodical Magnetoplasmonic Nanostructures

Magnetoplasmonic nanostructures with combined magnetic and plasmonic functionalities have in recent years become an active topic of research.By an adequate internal architecture of the constituting components,the magneto-optical activity of these structures can be greatly increased due to the electromagnetic field enhancement associated with the plasmon resonance.Simultaneously,the magnetic functionality permits the control of the plasmonic properties by an external magnetic field,which allows the development of active plasmonic devices.These materials find applications in,for example,biosensing and chemical sensing areas,all-optical magnetic data storage,optical isolators and modulators,and in integrated photonic devices for telecommunications,etc.Although a lot of research on obtaining simultaneously excellent properties of optics and magneto-optical activity in the magnetoplasmonic nanostructures has been studied.Nevertheless,significant challenges still remain because of the difficulty in the design of availably tunable systems exhibiting novel plasmonic and magneto-optical reponses simultaneously.In this research work,we firstly succeeded in extending the finite difference time domain(FDTD)method so as to study the optical and magneto-optical properties of the structures comprising layers of anisotropic magnetic materials.We built the 1D and 2D periodical magnetoplasmonic crystal nanostructures,the characteristics of the optical and magneto-optical effects of the magnetoplasmonic crystal nanostructures were investigated by using the extended finite difference time domain(EFDTD)method.It was most noteworthy that the strongly enhanced Faraday rotation accompanied by high transmittance can be achieved simultaneously by optimizing the geometrical parameters of the magnetoplasmonic crystal nanostructures in a broad spectrum spanning visible to near-infrared frequencies,and the physical mechanism of the physical phenomenon observed in this paper had been explained in detail.To verify the validity and reliability of the theory in this research work,we presented an experimental study of the properties of the optical and magneto-optical effects of the magnetoplasmonic nanostructures,which were prepared by means of the laser-interference lithography and magnetron sputtering technology in the experiment.The closely correlation between the surface plasmons and the enhancement of the magneto-optical effects has been discussed in detail.The detailed research work of this paper has three aspects as follows.1.We studied the optical and magneto-optical characteristics of the magnetoplasmonic crystal nanostructures comprising a bilayer and/or monolayer metallic grating and magnetic transparent medium by using the EFDTD method.By systematically optimizing the parameters of our designed system,we obtained two pairs of enhanced Faraday rotation angles whose signs are opposite,and a high transmittance of 57%accompanied by the enhancement of Faraday rotation by 44 times,which is of very important practical applications in designing novel optical and magneto-optical devices.The influence of the incident angle,the refractive index of the dielectric between the upper and lower grating,and the period of structure on the optical and magneto-optical characteristics of the magnetoplasmonic crystal nanostructures was discussed in detail.It showed that the optical and magneto-optical characteristics of the nanostructures can be simply tailored by the geometric parameters,such as the refractive index,period and incident angle.Meanwhile,the characteristics of the optics and magneto-optical effects of the monolayer metallic grating was also studied.Comparing with them,we found that the characteristics of the optics and magneto-optical effects of the bilayer metallic grating has some advantages over that of the monolayer metallic grating.Moreover,we deeply discussed the implied physical mechanism of the resonant transmission peaks and valleys,the enhancement and the reversal sign of Faraday rotation,and the enhancement of the optical and magneto-optical effects of the bilayer metallic grating compared with that of the monolayer metallic grating.The research results showed that the resonant peaks and dips are determined by different hybrid modes of surface plasmon polariton mode and waveguide resonance mode,and the efficient conversion of the TM-and TE-mode and the increase of the effective propagation length of light in the magnetic dielectric layer mostly governs the enhancement of the Faraday rotation.2.The phenomenon of the extraordinary light transmission(EOT)and enhancement of the magneto-optical Faraday effects of the magnetoplasmonic crystal nanostructures comprising an improved plasmonic nanohole arrays blocked by gold mushroom caps and/or a subwavelength rectangular annular arrays was investigated by using the EFDTD method.It was most striking that the strongly enhanced Faraday rotation accompanied by high transmittance in two kinds of magnetoplasmonic crystal nanostructures can be achieved simultaneously by optimizing the geometrical parameters of the magnetoplasmonic crystal nanostructures in a broad spectrum spanning visible to near-infrared frequencies,and the physical mechanism of the physical phenomenon observed had been explained in detail by investigating the electromagnetic field distributions at the location of resonance.The research results showed that the transmission resonance peak is largely due to the coupling of the LSPR mode,SPP mode and waveguide mode,and the increase of Faraday rotation is mostly related to the efficient conversion of the TM-and TE-mode and the increase of the effective propagation length of light in the magnetic dielectric layer.3.We provided an experimental investigate on the properties of the optics and transverse magneto-optical Kerr effect(TMOKE)of 1D periodical magnetoplasmonic nanostructures combining noble metal with magnetic metals.Firstly,we detailedly analyzed the inherent feature of the excitation of TMOKE and the SPP-assisted enhancement of TMOKE.Secondly,we fabricated the multilayer magnetoplasmonic nanostructures comprising metal and oxide medium,then investigated the reflectance and the values of TMOKE as a function of the incident wavelength under different conditions,discussed the influence of non-magnetic oxide medium on the optical and magneto-optical characteristics of the magnetoplasmonic nanostructures.Finally,we gave a reasonable physical interpretation on the physical phenomenon observed in the experiment.It is important that the experimental results in this part can confirm the validity and reliability of the theory above.