Characteristics of the NIJI-IV UV-VUV FEL system—toward lasing down to 150 nm using a compact storage ring

Improvement of the NIJI-IV free electron laser (FEL) system is in progress. Recent gain enhancement made the lasing more stable in the wavelength range from 216 to 211 nm. The temporal lasing characteristics were studied with a dual sweep streak camera and a relatively stable cw lasing with a short micro-pulse width of ∼14 ps (FWHM) was observed at 214 nm. Numerical calculation for the bunch lengthening and the laser gain revealed that full operation of our new RF cavity and installation of low impedance ring chambers will drastically increase the laser gain up to 20% at 200 nm and 12% at 150 nm. We can expect FEL lasing below 200 nm and even at wavelengths down to 150 nm using the compact storage ring NIJI-IV.