研究目的
To compute the field in the near and far zones and analyze how it depends on electron beam parameters, and to demonstrate the excitation of internal resonances useful for nanoscale non-invasive beam position monitors.
研究成果
The research demonstrates that nanowires act as open resonators, enhancing radiated power near natural-mode wavelengths. For dielectric nanowires, in-resonance fields form rotating cylindrical waves due to beam field asymmetry and mode degeneracy. For silver nanowires, both radiated and absorbed powers are enhanced near plasmon resonance wavelengths, with an 'invisibility' effect observed at wavelengths where metal becomes optically transparent. These findings are useful for monitoring beam parameters in non-invasive diagnostics.
研究不足
The study is based on a two-dimensional formulation, which may not fully capture three-dimensional effects. It assumes the fixed-current approximation, neglecting the action of the field on electrons, and uses idealized models for materials (e.g., lossless silicon and silver with interpolated permittivity). The numerical truncation of series may introduce approximations, and the results are specific to circular nanowires of 50 nm radius.
1：Experimental Design and Method Selection:
The study uses a two-dimensional formulation to investigate optical diffraction radiation from dielectric and silver nanowires excited by a modulated electron beam. The method of separation of variables is employed, expanding field functions in Fourier series in the angular coordinate, and solving the Helmholtz equation with boundary conditions.
2：Sample Selection and Data Sources:
The scatterers are circular nanowires with a radius of 50 nm; dielectric nanowire has relative dielectric constant ε = 12 (silicon), and metal nanowire uses silver with complex permittivity from Johnson and Christy (1972). The electron beam is modeled as a modulated sheet current.
3：2). The electron beam is modeled as a modulated sheet current. List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: No specific experimental equipment is mentioned; the work is theoretical and computational, involving numerical calculations based on derived analytical equations.
4：Experimental Procedures and Operational Workflow:
The incident field of the electron beam is defined, and the scattered field is expressed using Bessel and Hankel functions. Coefficients are found analytically, and numerical computations are performed for total scattering cross-section (TSCS) and absorption cross-section (ACS) as functions of wavelength and beam velocity.
5：Data Analysis Methods:
Data is analyzed by plotting normalized TSCS and ACS versus wavelength, computing complex eigenvalues for resonance modes, and visualizing near and far field patterns.
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