Production of high brightness<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>γ</mml:mi></mml:math>rays through backscattering of laser photons on high-energy electrons

Based on the requirements from a conceptual design of a polarized positron beam for future linear colliders, we constructed a special collision system with a short focal length of 150 mm of the laser beams so as to produce $\ensuremath{\gamma}$ rays through inverse Compton scattering. In order to achieve efficient laser-electron collisions, we created a special optics to produce very small ${e}^{\ensuremath{-}}$-beam sizes of ${\ensuremath{\sigma}}_{{e}_{x0}}=7.6\text{ }\ensuremath{\mu}\mathrm{m}$ and ${\ensuremath{\sigma}}_{{e}_{y0}}=5.4\text{ }\ensuremath{\mu}\mathrm{m}$ in the horizontal and vertical directions at the collision point. Using laser light with a wavelength of 532 nm and an ${e}^{\ensuremath{-}}$ beam of 1.28 GeV, provided from the ATF-damping ring at KEK, we generated $2\ifmmode\times\else\texttimes\fi{}{10}^{5}$ $\ensuremath{\gamma}$ rays with a time duration of 26 ps in rms, leading to a peak brightness of $1.7\ifmmode\times\else\texttimes\fi{}{10}^{18}/({\mathrm{mrad}}^{2}\text{ }{\mathrm{mm}}^{2}\text{ }0.1%\mathrm{bandwidth}\text{ }\mathrm{s}$) near to the maximum energy of 56 MeV.