Surface Polariton Cherenkov Light Radiation Source

A physical phenomenon has been found: in a structure of nanometal film with dielectric-medium loading, the surface polaritons excited by a uniformly moving electron bunch can be transformed into Cherenkov radiation with intensity enhancement in the medium. Based on this mechanism, the surface polariton Cherenkov light radiation source is presented and explored in the Letter. The results show that surface polariton Cherenkov light radiation source can generate radiation, from visible light to the ultraviolet frequency regime and the radiation power density can reach or even exceed ${10}^8\mathrm{W}/{\mathrm{cm}}^2$ depending on the beam energy and current density. It is a tunable and miniature light radiation source promising to be integrated on a chip and built into a light radiation source array.

Figure 1

(a) A schematic of the planar structure SPCLS. Region I is a vacuum, region II is a metal film, and region III is dielectric medium. (b) Simulation results of the contour map of electrical field $E_z$ excited by an electron bunch of $d=20\mathrm{nm}$ thick silver film without dielectric-medium loading. (c) A contour map of electrical field $E_z$ excited by an electron bunch in the planar structure SPCLS (${\epsilon }_d=9$). The angle of the Cherenkov cone is $\theta$.

Figure 2

(a) Dispersion curves of $d=20\mathrm{nm}$ thick Ag film covering the dielectric medium (${\epsilon }_d=9$). The intersection is $A$ or $A^{\prime }$ for electron beam lines with energy of 100 or 400 keV. $f_{\mathrm{SP}1}$ and $f_{\mathrm{SP}2}$ are the surface plasmon frequencies at the vacuum-metal and metal-dielectric interfaces, respectively. The inset of Fig. 2a shows the calculated power spectrum. (b) Field $E_z$ of the simulation and its Fourier spectrum.

Figure 3

(a) A schematic of the circular cylindrical structure SPCLS. The radius of the dielectric medium is $r_a$, the silver film is in the region of $r_a\le r\le r_b$, and the radius of the hollow electron bunch is $r_0$. (b) Dispersion curves and beam lines in SPCLS. The dielectric cylindrical rod is covered by silver film. The green lines are the dispersion curves for the structure $r_a=100\mathrm{nm}$, $r_b=120\mathrm{nm}$, and ${\epsilon }_d=4$. The intersection points are B and C with beam energy of 100 keV. The inset is the calculated power spectrum, and the peak frequency of Cherenkov radiation is 480 THz.

Figure 4

(a) A contour map of $E_z$. (b) Simulation results of $E_z$ and its Fourier spectrum; the peak frequency is 461 THz.

Figure 5

(a) Numerical calculation results. The green dispersion curves describe the structure $r_a=100\mathrm{nm}$, $r_b=130\mathrm{nm}$, and ${\epsilon }_d=6$. The intersection points $D$ and $E$ correspond to a beam energy of 250 keV. The inset is the calculated power spectrum. (b) The Fourier spectrum of $E_z$ by computer simulation. (c) A contour map of $E_z$ for low- and high-frequency modes.