Generation of convergent light beams by using surface plasmon locked Smith-Purcell radiation

Abstract

An electron bunch passing through a periodic metal grating can emit Smith-Purcell radiation (SPR). Recently, it has been found that SPR can be locked and enhanced at some emission wavelength and angle by excitation of surface plasmon (SP) on the metal substrate. In this work, the generation of a convergent light beam via using the SP-locked SPR is proposed and investigated by computer simulations. The proposed structure is composed of an insulator-metal-insulator (IMI) substrate with chirped gratings on the substrate. The chirped gratings are designed such that a convergent beam containing a single wavelength is formed directly above the gratings when an electron bunch passes beneath the substrate. The wavelength of the convergent beam changes with the refractive index of dielectric layer of the IMI structure, which is determined by the frequency of SP on the IMI substrate excited by the electron bunch. Moreover, reversing the direction of electron bunch will make the emitted light from the proposed structure to switch from a convergent beam to a divergent beam. Finally, the formation of a convergent beam containing red, green and blue lights just above the chirped gratings is also demonstrated. This work offers potential applications in the fields of optical imaging, optical beam steering, holography, microdisplay, cryptography and light source.

Spectral and spatial shaping of Smith-Purcell radiation

“…4(d) would make the experimental demonstration of its close-to-diffraction-limited behavior challenging, at least with conventional broadband imaging systems (for instance, CCD cameras). This limitation could be circumvented by designing chirped metasurfaces made of resonators with a very high spectral quality factor or plasmon-locked SPR as has been recently proposed [24]. The latter approach relies on phase matching the plasmon dispersion relation with the electron beam line ω = kv, thus preventing applications to extreme UV regimes.…”

Spectral and spatial shaping of Smith-Purcell radiation

“…Figure 4(d) shows the highly dispersive nature of a Smith-Purcell lens, which would make difficult the experimental demonstration of its close-to-diffraction-limited behavior with conventional broadband imaging systems (for instance, CCD cameras). This limitation could be circumvented by designing chirped metasurfaces made of resonators with a very high spectral quality factor or plasmon-locked SPR as has been recently proposed [23]. The latter approach relies on phase-matching the plasmon dispersion relation with the electron beam line 𝜔 = 𝑘𝑣, thus preventing applications to extreme UV regimes.…”

Electron cyclotron motion excited surface plasmon and radiation with orbital angular momentum on a semiconductor thin film

“…SPs can be excited by light with using attenuated total reflection configuration or grating structure for matching the phase velocities of light and SPs. SPs can also be excited by a relativistic electron beam with a straight motion owing that the dispersion curves of electron beam and SPs intercept with each other 19 – 21 . Furthermore, the electron straight motion (ESM) excited SPs can be further transferred into light when they pass through the periodic gratings.…”