光子纳米射流是一种高强度，极窄的亚波长电磁场区域，它是由介电微球或微柱体的Mie散射对电磁场的聚焦作用产生的。光子纳米射流广泛应用于激光加工、纳米光刻、光学高密度存储以及超分辨率显微镜。从径向偏振光的角度出发，使用一种介电圆环结构对光束进行聚焦，由于径向偏振光在焦点区域可以产生较强的纵向场，通过优化圆环的尺寸、折射率以及与物镜焦点的相对位置，可以得到超过90%光束质量的纵向光子纳米射流，而且强度相比于未使用圆环时可以提高约一个数量级，并在高折射率下可以获得半高全宽小于衍射极限尺寸的光斑，因此该结构预计可以在粒子加速、光镊以及拉曼光谱学中有所应用。

The photonic nanojet is a high-intensity, extremely narrow sub-wavelength electromagnetic field region, which is generated by the focusing effect of Mie scattering from dielectric microspheres or micro-columns on the electromagnetic field. Because of these characteristics, it is widely used in laser processing, nanolithography, optical high-density storage, and super-resolution microscopy. From the perspective of radially polarized light, a donut-shaped dielectric micro-body is used to focus the beam. Since radially polarized light can produce a strong longitudinal field in the focusing region, by optimizing the donut size, refractive indexes, and the relative position between the donut and the focal point of the objective lens, a longitudinal photonic nanojet with more than 90% of the beam quality can be obtained, and its intensity is increased by about an order of magnitude compared to that without the donut. Moreover, the full width at half-maximum of focal spot is below diffraction limit under high refractive index. Therefore, this structure is expected to have applications in particle acceleration, optical tweezers, and Raman spectroscopy.