Using simplified two-dimensional finite element method (FEM) modeling we study such structures where the triangular dielectric prism is used for producing nano-jets. The soda-lime glass (n=1.46), polystyrene (n=1.56), polyester (n=1.59), barium titanate (n=1.8) is considered as material of the prism. The width of the triangular prism base is fixed at 60 um while the height is varied to obtain optimal focal spot parameters such as maximum intensity, full width and depth at half-maximum of intensity. The linear polarized Gaussian beam with a wavelength of 4 um and the waist width of 80 um is taken as the input radiation. All numerical simulations were carried out by COMSOL Multiphysics which used irregular grids with variable steps for FEM. The small step equal to 0.1 um was used in regions which are close to the interface between two media, while the other area is described by grids with steps of 0.2 um. Comparison of simulation results for dielectric triangular prism and simulation results for dielectric circular cylinder shows that prism can produce the narrower focal spot. It can be also noticed that there are resonance modes similar to the whispering gallery modes are formed inside the triangular dielectric prism. The influence of these modes on light focusing is also studied.