Research Of FWHM And Focal Length on Photonic Nanojet Generated by Microsphere

Photonic nanojet (PNJ) is generated on the shadow side of the microspheres, and various potential characteristics of PNJ are widely used in various fields such as medicine, nanomanufacturing, super-resolution imaging. Therefore, it is of great value to study the properties of PNJ. In this paper, the influence of internal and external factors on the distance between the maximum intensity point formed by PNJ and the surface of the microsphere (viewed as focal length) and the full width at half maxima (FWHM) with the method of finite difference time domain (FDTD) have been studied. The internal factors include the refractive index and radius of the microsphere. As the refractive index and radius increase, the focal length and FWHM will both be reduced with the increase of refractive index while opposite characteristics are featured with the change of radius of microspheres. The external factors include the wavelength and polarization direction of the incident plane wave. With the increase of the wavelength, the distance and FWHM have the opposite trend, and the distance decreases while the FWHM increases. By changing the polarization direction of the light, it is found that the focal length and FWHM also have significant changes. The research will build a good theoretical foundation for the application of PNJ in photoelectric field and other related fields.