Intense terahertz pulses from SLAC electron beams using coherent transition radiation

Abstract

SLAC has two electron accelerators, the Linac Coherent Light Source (LCLS) and the Facility for Advanced Accelerator Experimental Tests (FACET), providing high-charge, high-peak-current, femtosecond electron bunches. These characteristics are ideal for generating intense broadband terahertz (THz) pulses via coherent transition radiation. For LCLS and FACET respectively, the THz pulse duration is typically 20 and 80 fs RMS and can be tuned via the electron bunch duration; emission spectra span 3-30 THz and 0.5 THz-5 THz; and the energy in a quasi-half-cycle THz pulse is 0.2 and 0.6 mJ. The peak electric field at a THz focus has reached 4.4 GV/m (0.44 V/Å) at LCLS. This paper presents measurements of the terahertz pulses and preliminary observations of nonlinear materials response.

High-field half-cycle terahertz radiation from relativistic laser interaction with thin solid targets

“…Via coherent transition radiation (CTR), high field THz radiation with ultrashort electron bunches from Linac has been reported [9,10,11]. In principle, the ultrashort intense laser pulses can also generate ultrashort electron bunches, which can be used to produce intense THz emission through CTR.…”

Below gap optical absorption in GaAs driven by intense, single-cycle coherent transition radiation

“…As each bunch passes through a thin metal foil, the discontinuity in dielectric constant leads to emission of broadband radiation at frequencies related to the temporal charge distribution of the bunch [31]. The short duration of the bunch leads to coherent enhancement of the emitted radiation in the THz regime with peak frequencies centered near 10 THz (30 μm) and a quasi-half-cycle pulse shape of duration ~100 fs [13,24]. The radiated spectrum extends to higher frequencies through the visible range, with some optical frequencies also experiencing coherent enhancement due to microbunching in the electron beam [32].…”

“…Nevertheless, many field-driven processes remain out of reach at these field strengths, and accelerator based sources, based on coherent radiation from relativistic electron beams, represent an alternative pathway towards the generation of extreme fields, reaching sizable fractions of interatomic fields in matter [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Previously, we have reported the measurement of quasi-half cycle pulses with peak fields exceeding 20 MV/cm at a center frequency of 10 THz via coherent transition radiation (CTR) at the Linac Coherent Light Source (LCLS) free-electron laser [13,24]. Here, we present first pump-probe, time-resolved measurements of dynamics induced by a CTR-based source.…”

Tailoring of Highly Intense THz Radiation Through High Brightness Electron Beams Longitudinal Manipulation

“…THz-based technologies and research applications have seen a rapid increment in the last years due to the development of new radiation sources based both on femtosecond lasers and sub-picosecond electron bunches [1,2].…”