Controlling the parameters of photon nanojets of composite microspheres

We consider the spatial and amplitude characteristics of PNJ forming in the neighborhood of the shadow surface of micron-sized composite particles consisting of a nucleus and a shell with various refraction indices when laser radiation scatters on them. We study the longitudinal and transverse dimensions of a photon flux and its peak intensity depending on the microparticle shell thickness. We show that a certain choice of the refraction index of the shell relative to the nucleus in two-layer composite spherical microparticles can significantly lengthen the forming PNJ or increase their peak intensity. The width of the photon flux during this changes insignificantly.