| Nonlinear optics is an important branch of nonlinear physics,which plays an important role in wavelength conversion,high-resolution microscopy,biosensing,and photonic devices.However,nonlinear optical signals are inherently weak because they are limited by the light-matter interactions.Noble metal nanoarrays have drawn tremendous attention due to the nonlinear optical enhancement phenomenon generated by localize surface plasmon effect.Aluminum(Al).as a low-cost,earth-abundant and CMOS compatible plasmonic material exhibiting significantly larger nonlinear susceptibility and luminescence efficiencies emerges as a promising alternative to noble metals.This paper proposes a metamaterial perfect absorber structure based on metal-insulator-metal(MIM).which is mainly used to enhance optical nonlinear effects.Based on MIM perfect absorber structure,we studied the two-photon luminescence and second harmonic generation characteristics of Al nanoarrays by self-built spectral measurement system.The main innovations are as follows:1.We designed an aluminum nanoarray with a metal-insulator-metal(MIM)perfect absorber structure.At the same time,the photothermal-shaping laser processing method was used to reshape the nanoantenna,the two-photon fluorescence and the second harmonic generation signal were enhanced by dynamically adjusting the size of the nanoantenna.2.We systematically studied the two-photon luminescence characteristics,two-photon luminescence enhancement characteristics and two-photon luminescence polarization characteristics of Al nanoantenna arrays based on MIM perfect absorber structure.Firstly,we analyzed the dependence of the emission spectrum on the irradiance to reveal that the nonlinear spectrum generated by the Al nanoantenna array is derived from the in-band transition of the hot electron.Secondly,the localized field enhancement effect is theoretically verified by finite-time-difference(FDTD)mothed,and 40,000-fold enhanced up-conversion continuous light emission and 300-fold relative fluorescence enhancement are experimentally achieved.Finally,we found that the nonlinear polarizations of different sizes of aluminum nanoantennas are higher than 0.96.To the best of our knowledge,this is by far the highest linearly polarized TPL from plasmonic nanostructures,which may have important application prospects in polarization nonlinear photonic integration.3.We systematically studied the second harmonic generation characteristics,second harmonic generation enhancement characteristics and second harmonic generation polarization characteristics of Al nano-arrays based on based on MIM perfect absorber structure.Firstly,we analyzed the dependence of the second harmonic signal on the incident light to reveal that the intensity of the second harmonic generation is proportional to the quadratic of the light power.Secondly,the local field enhancement effect of the cross-nanostructure is theoretically verified by the finite-time-difference(FDTD)computational simulation,and an increase in the number of second harmonic signals is experimentally achieved.Finally,we used the method of photothermal shaping to reshape the aluminum nano-antenna,which makes the scattering of the two nano-antenna radiation signals coherent,and realized the rotation change of the polarization state of the second harmonic wave. |
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