We elaborate a quadratic nonlinear theory of plural interactions of growing space charge wave （SCW） harmonics during the development of the two-stream instability in helical relativistic electron beams. It is found ...We elaborate a quadratic nonlinear theory of plural interactions of growing space charge wave （SCW） harmonics during the development of the two-stream instability in helical relativistic electron beams. It is found that in helical two-stream electron beams the growth rate of the two-stream instability increases with the beam entrance angle. An SCW with the broad frequency spectrum, in which higher harmonics have higher amplitudes, forms when the frequency of the first SCW harmonic is much less than the critical frequency of the two-stream instability. For helical electron beams the spectrum expands with the increase of the beam entrance angle. Moreover, we obtain that utilizing helical electron beams in multiharmonic two-stream superheterodyne free-electron lasers leads to the improvement of their amplification characteristics, the frequency spectrum broadening in multiharmonic signal generation mode, and the reduction of the overall system dimensions.展开更多
In this Letter,we propose a scheme to generate helical optical fields with multi-freedom controllable features.High-quality helical lobes with adjustable radii,chirality,and lobe numbers can be generated by tuning the...In this Letter,we propose a scheme to generate helical optical fields with multi-freedom controllable features.High-quality helical lobes with adjustable radii,chirality,and lobe numbers can be generated by tuning the phase term of two paired highorder Bessel beams.Furthermore,the pitch of the helical beam can be controlled by combining another rotational phase term.The validity of our scheme is demonstrated in both simulations and experiments.Our scheme is promising to facilitate the rapid fabrication of helical structures with diverse parameters,which are critical in various applications,such as optical metamaterials,biology,and particle transport.展开更多
基金Supported by the Ministry of Education and Science of Ukraine under Grant No 0117U002253
文摘We elaborate a quadratic nonlinear theory of plural interactions of growing space charge wave （SCW） harmonics during the development of the two-stream instability in helical relativistic electron beams. It is found that in helical two-stream electron beams the growth rate of the two-stream instability increases with the beam entrance angle. An SCW with the broad frequency spectrum, in which higher harmonics have higher amplitudes, forms when the frequency of the first SCW harmonic is much less than the critical frequency of the two-stream instability. For helical electron beams the spectrum expands with the increase of the beam entrance angle. Moreover, we obtain that utilizing helical electron beams in multiharmonic two-stream superheterodyne free-electron lasers leads to the improvement of their amplification characteristics, the frequency spectrum broadening in multiharmonic signal generation mode, and the reduction of the overall system dimensions.
基金supported by the National Natural Science Foundation of China(Nos.62275191 and 62227821).
文摘In this Letter,we propose a scheme to generate helical optical fields with multi-freedom controllable features.High-quality helical lobes with adjustable radii,chirality,and lobe numbers can be generated by tuning the phase term of two paired highorder Bessel beams.Furthermore,the pitch of the helical beam can be controlled by combining another rotational phase term.The validity of our scheme is demonstrated in both simulations and experiments.Our scheme is promising to facilitate the rapid fabrication of helical structures with diverse parameters,which are critical in various applications,such as optical metamaterials,biology,and particle transport.
