Ultrafast Optical Properties Of Gold Nanospheres

Metal nanomaterials have excellent optical properties and are widely used in physics,chemistry,biology and other fields.Gold nanoparticles show a strong surface plasmon resonance(SPR)effect in the visible region of the spectrum,which greatly enhances the local electromagnetic field on the particle surface,and makes the corresponding material have a large optical nonlinearity near the resonance wavelength and super fast response time.In this paper,the optical properties of spherical gold nanoparticles are first studied theoretically,and then the nonlinear optical absorption characteristics and ultrafast dynamics of gold nanoparticles are experimentally studied.The specific work is as follows:The optical properties of single gold nanospheres were first studied by using finite difference time domain(FDTD)method,and the size of single gold nanospheres was increased.It was found that the SPR peak position appeared red-shifted in a small size range,but the peak position and peak width did not match.There is no obvious change,and multi-level resonance occurs when the size exceeds 70 nm.The optical properties of symmetrical and asymmetric dimer gold nanospheres were studied,and it was found that the absorption peak position appeared blue-shifted when the spacing was increased,and the peak value decreased,and the peak width did not change significantly,This is caused by the decrease of the coupling effect due to the increase of the spacing.The nanosecond aperture Z-scan technology was used to study the nonlinear absorption characteristics of gold nanospheres with two sizes of 5 nm and 20 nm under different energies and different excitation wavelengths.They found their broadband saturated absorption in the visible light band and the strong dependence of the incident wavelength,explained their physical mechanism through ground state bleaching,and theoretically analyzed the data to obtain the relevant parameters of the non-linear absorption of the gold nanospheres.It is found that the corresponding relationship between saturated light intensity and wavelength,at the absorption peak,has the largest saturated light intensity.The femtosecond laser pumped detection technology is used to study the ultra-fast dynamics of the two-size gold nanospheres in the resonance and non-resonance regions.The study found that relaxation includes two processes: fast and slow.Theoretical analysis has obtained the plasma bleaching process and the initial fast relaxation time.Because the decay time is related to the intensity of the pump laser,the thermal effect generated with the increase of the light intensity increases the decay time.The relevant life parameters of the fast relaxation time are obtained by fitting.