Recent progress of a soft X-ray generation system based on inverse Compton scattering at Waseda University

At Waseda University, we are developing a table-top size soft X-ray source based on inverse Compton scattering between a high quality electron beam and a high power laser. Using 1047 nm laser beam (Nd:YLF) and 4.6 MeV electron beam generated from a photo-cathode rf-gun, we had already succeeded in generating inverse Compton X-rays. The energies are within the “water window” region (250–500 eV) which can be applied to biological studies. For good signal to noise ratio (S/N) and a larger number of photons, we remodeled our collision chamber and laser amplifier system. S/N is defined by the X-ray photon signal over all other noises and backgrounds such as a bremsstrahlung X-rays from a lost electron beam and an electric noises caused by a radiation and rf power source. With these modifications, the X-ray photons detected by a micro channel plate (MCP) have increased 10-fold to reach 312 ph/pulse. Total generated photons were estimated to be 3.3×104. Further, we succeeded in generating stable soft X-rays for more than 12 h. Good S/N ratio, stable X-rays have made it possible to observe the beam–laser interaction very precisely. By using this technique, we have measured the electron beam size at the collision point as 251 μm (σx)×56 μm (σy).