Abstract
We propose and analyze a scheme to generate enhanced narrow-band terahertz (THz) radiation through down-conversion of the frequency of optical lasers using laser-modulated electron beams. In the scheme the electron beam is first energy modulated by two lasers with wave numbers ${k}_{1}$ and ${k}_{2}$, respectively. After passing through a dispersion section, the energy modulation is converted to density modulation. Because of the nonlinear conversion process, the beam will have density modulation at wave number $k=n{k}_{1}+m{k}_{2}$, where $n$ and $m$ are positive or negative integers. By properly choosing the parameters for the lasers and dispersion section, one can generate density modulation at THz frequency in the beam using optical lasers. This density-modulated beam can be used to generate powerful narrow-band THz radiation. Since the THz radiation is in tight synchronization with the lasers, it should provide a high temporal resolution for the optical-pump THz-probe experiments. The central frequency of the THz radiation can be easily tuned by varying the wavelength of the two lasers and the energy chirp of the electron beam. The proposed scheme is in principle able to generate intense narrow-band THz radiation covering the whole THz range and offers a promising way towards the tunable intense narrow-band THz sources.
Highlights
There is growing interest in generating powerful terahertz (THz) radiation to fill the frequency gap ranging from 0.1 to 30 THz which has wide applications in nondestructive imaging and spectroscopic studies of materials and molecules
One method is to use a train of laser pulses to illuminate the photocathode to generate a train of electron beams repeated at THz frequency and the bunch trains can be used to generate narrow-band THz radiation when they are accelerated to relativistic energy [10]
We proposed and analyzed a scheme to generate enhanced narrow-band THz radiation through downconversion of the frequency of optical lasers using lasermodulated electron beams
Summary
There is growing interest in generating powerful terahertz (THz) radiation to fill the frequency gap ranging from 0.1 to 30 THz which has wide applications in nondestructive imaging and spectroscopic studies of materials and molecules (for a recent review, see Refs. [1,2,3]). The second category typically aims to provide such kinds of narrow-band THz radiation using bunched electron beam with a density modulation repeated at THz frequency [9,10]. One method is to use a train of laser pulses to illuminate the photocathode to generate a train of electron beams repeated at THz frequency and the bunch trains can be used to generate narrow-band THz radiation when they are accelerated to relativistic energy [10]. The proposed scheme is similar to that used in the echo-enabled harmonic generation freeelectron laser [12,13] except that here we only have one dispersion section and the aim is to down-convert the frequency of the lasers to generate THz modulation in the relativistic beam. In addition to generation of THz radiation, the density-modulated beam can be used to enhance the performances of infrared free-electron lasers [14] and plasma wakefield accelerators [15,16]
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