Linac-based Laser Compton Scattering X-ray and Gamma-ray Sources

Laser Compton scattering (LCS) light sources can provide high-energy photons from keV to MeV range. Many research and development projects of linac-based LCS sources are carried on. For the photon energies of tens keV, linac-based LCS sources realize laboratory-size X-ray sources, of which performance is potentially comparable to 2 generation synchrotron light sources. Linac-based LCS also realizes unparalleled γ-ray sources of high-brightness and narrow bandwidth. In the present paper, status and perspectives of linac-based LCS X-ray and γ-ray sources are reviewed. LASER COMPTON SCATTERED PHOTON SOURCES The combination of a high-energy electron accelerator and a laser realizes high-energy photon sources based on laser Compton scattering (LCS) [1]. Figure 1: Laser Compton scattering. Figure 1 shows a schematic representation of laser Compton scattering, where a high-energy photon (X-ray or γ-ray) is generated via the Compton back-scattering of an incident laser photon with a relativistic electron. The energy of the scattered photon, Ex, is a function of the incident photon energy, EL = hc/λ, electron energy Ee = γmc2, and scattering geometry, and approximated for a head-on collision: E x≈ 4γ 2 EL 1+(γ θ )+4γ E L /(mc ) (1) The above equation shows that the LCS photon energy is tunable by changing electron beam energy, laser wavelength or collision angle. The LCS photon energy also has a correlation to the scattered angle. Therefore, monochromatic photon beam can be obtained by putting a collimator to restrict the LCS beam divergence at the downstream. We can produce linearand circularpolarized high-energy photons by using polarized lasers. The electron energy necessary for generation of hard Xray (20 keV, for example) is only 30 MeV, which is much smaller than the electron energy to produce hard X-ray via synchrotron radiation. Owing to the above features of LCS photon source, energy tunability, monochromatic and polarized photon generation, compactness, LCS sources have been developed by using various types of accelerators such as storage rings, linacs and microtron [2-6]. In the present review, we focus on linac-based LCS photon sources in X-ray and γ-ray energies. A photon flux from laser Compton scattering at an ideal head-on geometry integrated over the entire scattering angle is given by F total= 16 3 N e N L f r 0 2