| The chemical properties of gold nanorods are very stable,and optical nonlinear effects are often involved in applications.Typical second harmonic are often applied to in vivo optical imaging studies due to their high sensitivity to medium and good resolution.For the epidermal tissue imaging,the second harmonic conversion efficiency of 1% can meet the requirements,but for deep tissue imaging and in order to meet the higher accuracy of the axial resolution,the second harmonic conversion efficiency needs to be improved,and the excitation wavelength It needs to be located in the near-infrared wave band of the biological transparent window.Using the local field enhancement to improve nonlinear conversion efficiency is an effective method.In order to achieve local field enhancement,common methods such as the use of composite materials and surface modification,but the complex structure will have a stronger side effect on the organism.Unlike other methods,gold nanorods could achieve local field enhancement through their own assembly to improve the efficiency of second harmonic conversion.In this paper,the near-infrared light excitation of gold nanorods generated local field enhancement in a colloidal environment,which improved the second harmonic conversion efficiency to 3.5%.This thesis theoretically simulated the field energy level distribution of gold nanorods and their assembly under specific excitation conditions,studied the preparation and assembly of gold nanorods,and experimentally verified the improvement of optical second harmonic conversion efficiency under local field enhancement conditions In the experiment,gold nanorods with absorption peaks in the near-infrared region were prepared by seed growth method,and the end-to-end assembly was realized.At the same time,the second harmonic characteristics were studied by using femtosecond laser-acting gold nanorods,and the incident optical power was mainly studied.The influence of the second harmonic signal intensity generated by the monomer and the assembly,on the premise of not decomposing the material,the intensity of the second harmonic signal also gradually increases with the increase of the incident optical power;In addition,according to the optical Kerr effect of colloidal environment,the polarization properties of the second harmonic generated by the gold nanorods were studied.In the experiment,the change of the second harmonic’s conversion efficiency were studied by changing the polarization angle of the excitation light;The application of rod second harmonic provides the basis. |
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