Search

We measured the refractive index of germanium and gold prisms at 1.7 MeV to explore if there are refractive index enhancements to 6th power of atomic number due to high order nonlinear process of Delbruck scattering in quantum electrodynamics. We measured the deflection by prisms using imaging plates and laser Compton scattering γ -rays with linear and random polarization. We used crystal and polycrystalline prisms for Au. The measured upper limit of the refractive index, δ , for crystal Ge, crystal Au, or polycrystal Au prisms is 4.0 × 10 − 8 , 2.9 × 10 − 7 , or 2.4 × 10 − 7 . We could not find any signature for high order nonlinear process. This result does not support the hypothesis suggested by Habs et al. (2012) [3] .

Publisher Summary This chapter discusses phase shift induced by a free-electron laser (FEL) interaction. An FEL interaction with unbunched electrons at resonant energy induces a positive phase shift of the FEL field relative to the input phase. The positive phase shift corresponds to giving electrons positive energy detuning and results in the FEL amplification. The positive phase shift connects the zero small signal gain in low gain regime for resonant electrons to the exponential growth in high gain regime. The interaction between unbunched electrons and the FEL field with uniform amplitude and phase is considered in the time domain. The positive phase shift corresponds to giving positive detuning to the electron energy, and the FEL field is amplified regardless of the dimensionless current when the initial electron energy is resonant. The present amplification mechanism has been known as the collective instability. The diffraction effect or the frequency shift appears as a result of the phase shift but is much smaller than the phase shift effect.

The free-electron laser (FEL) linac has been modified to the energy recovery linac (ERL) at the Japan Atomic Energy Research Institute (JAERI) to achieve the higher power FEL of the next stage of 5-10kW. We review transverse instabilities and present experimental data on transverse beam breakup (BBU) obtained at the JAERI ERL-FEL. We compare measurement with simulation.

An infrared FEL project is carried out using an rf linear accelerator at UT/NERL. Characteristics of projected FEL performance are presented, as well as modifications to the accelerator to improve electron beam quality. Also, features of higher harmonics generation are discussed using multi-mode analysis.

A multi-mode free-electron laser simulation has been made to estimate the spectrum of long-pulsed free-electron lasers. It was found that mode selectivity is deteriorated in deep-saturated region.