Widely tunable electron bunch trains for the generation of high-power narrowband 1–10 THz radiation

Abstract

Terahertz radiation enables coherent excitation of many fundamental modes, such as molecular rotation [1][2][3] , lattice vibration [4][5][6] and spin precession 7,8 . To excite the transient state of matter far out of equilibrium, high-power and tunable narrow-band THz radiation source has been in great demand for years. However, with such fertile spectrum resources waiting for exploitation, the currently available THz sources cannot satisfy the demands on the tunability and the power level, leaving a large scientific gap scarcely explored. Here, we convert the energy modulation exerted by the nonlinear longitudinal space charge force to density modulation, and for the first time experimentally demonstrate the generation of widely tunable electron bunch trains with modulation frequency adjustable between 1-10 THz. The electron bunch trains can be directly used to produce tunable high-power narrow-band THz radiation fully covering the long-standing 'THz gap', which will open up much more possibilities in THz science.Searching for high-intensity and tunable narrow-band terahertz (THz) source is motivated by broad scientific and industrial applications, such as the transient state control of materials 1-8 , imaging for security or medical applications 9, 10 , and time-domain spectroscopy 11,12 . Although various THz sources have been developed during the past decades, the high-peak-power narrowband THz source tunable from 1 to 10 THz is still scarce. Electron-accelerator-based THz sources stand out due to their exceptional high peak or average power and wide tunability. However, the peak power decreases rapidly as the radiation frequency increases due to the deteriorating longitudinal coherence 13 . Much work has devoted to overcome this obstacle. The common workaround adopts elaborate arrangements for bunch compression, but it is increasingly difficult to compress the beam even shorter with large beam charge 14 . Another approach commonly used in present THz free electron laser (FEL) is to utilize an optical resonator to accumulate the extracted radiation energy in the low-gain regime, but it requires high repetition rate and multiple separate beamlines to cover the whole 'THz gap' 15 , which leads to a sophisticated design and high maintenance cost.Recently, THz electron bunch trains consisting of multiple equally spaced micro-bunches with

THz SASE FEL at PITZ: lasing at a wavelength of 100 μm

“…For such sources, afterburner option is often considered when short beams are used after they are radiated at a shorter wavelength. Narrowband THz radiation can be generated by short or modulated beams in suitable undulators or by the CTR/CDR effect with modulated beams [2,6,7,8,9]. This work employs a different approach and idea of applying the same mechanism of radiation that is used to generate X-ray pulses in XFELs, namely, the Self Amplified Spontaneous Emission (SASE), where a microbunching is achieved by a single pass of high-current electron beam with a length much longer than the radiation wavelength through an undulator.…”

A strong-field THz light source based on coherent transition radiation at the Shanghai soft x-ray free-electron laser facility

“…Due to the nonlinear effects of space charge force, it is difficult to compress the root-mean-square (RMS) length of the electron beam below 100 fs. Through electron gun by direct laser pulse stacking 15 , transverse and longitudinal phase space exchange 16 , dielectric tube wakefield modulation 17 , space charge oscillation modulation or other methods 18 , the electron bunch train with THz information above 10 THz can be obtained. However, these methods have certain difficulties in achieving large-scale continuous frequency tuning, and the longitudinal structures of the generated electron bunch train are easily erased by effects such as space charge force.…”

Nonreciprocal Terahertz Beam Steering Manipulated by Magnetic Weyl Semimetal Metasurface Based on Universal Chirality‐ Wavevector‐ Magnetic Field Relation

“…[ 1–4 ] With the growing demand for THz technology, plenty of THz sources and functional devices are developed. [ 5–9 ] Unfortunately, unlike the microwave and communication band, the functional materials are severely lacking for active manipulation of the wavefront and polarizations which is essential in applications such as radar, communication, and imaging. [ 10 ] Recently, topological photonics has become a hot topic due to its special properties in the photonic energy band.…”