Abstract
A comprehensive analysis is presented that describes amplification of a seed THz pulse in a single-pass free-electron laser (FEL) driven by a photoinjector. The dynamics of the radiation pulse and the modulated electron beam are modeled using the time-dependent FEL code, GENESIS 1.3. A 10-ps (FWHM) electron beam with a peak current of 50 ‐100 A allows amplification of a � 1k Wseed pulse in the frequency range 0.5‐3 THz up to 10 ‐100 MW power in a relatively compact 2-m long planar undulator. The electron beam driving the FEL is strongly modulated, with some inhomogeneity due to the slippage effect. It is shown that THz microbunching of the electron beam is homogeneous over the entire electron pulse when saturated FEL amplification is utilized at the very entrance of an undulator. This requires seeding of a 30cm long undulator buncher with a 1‐3 MW of pump power with radiation at the resonant frequency. A narrow-band seed pulse in the THz range needed for these experiments can be generated by frequency mixing of CO2 laser lines in a GaAs nonlinear crystal. Two schemes for producing MW power pulses in seeded FELs are considered in some detail for the beam parameters achievable at the Neptune Laboratory at UCLA: the first uses a waveguide to transport radiation in the 0.5‐3 THz range through a 2-m long FEL amplifier and the second employs high-gain third harmonic generation using the FEL process at 3‐9 THz.
Highlights
Free-electron laser (FEL) interactions can be used to generate high-output power radiation or to longitudinally modulate the electron beam in the THz frequency range
The THz range of the electromagnetic spectrum can be conveniently covered by FELs because the electron beam parameters needed are relatively realized using current technology
A single-pass FEL amplifier based on selfamplified spontaneous emission of radiation (SASE) is capable of producing MW power THz pulses in a very long ( 6–10 m) undulator [1]
Summary
Free-electron laser (FEL) interactions can be used to generate high-output power radiation or to longitudinally modulate the electron beam in the THz frequency range. A single-pass FEL amplifier based on selfamplified spontaneous emission of radiation (SASE) is capable of producing MW power THz pulses in a very long ( 6–10 m) undulator [1]. In the latter case, the radiation pulse buildup from spontaneous noise makes synchronization with an external event or a laser pulse on a subpicosecond time scale extremely difficult. The second scheme is a high-gain harmonic generation (HGHG) FEL, where a short IFEL modulator seeded by a MW power pulse in the 0.5–3 THz range first bunches the beam and is followed by a second radiator-undulator tuned to the third harmonic of the fundamental frequency. The HGHG technique allows extending the spectral range of high-power radiation to 3–9 THz where the needed seed pulse is not generated in nonlinear crystals
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