Lasing towards the VUV in the NIJI-IV FEL

The lasing wavelength in the NIJI-IV free electron laser (FEL) reached 212 nm in the deep ultraviolet (UV) range. Adoption of Al2O3/SiO2 multilayer mi rrors to the laser cavity, whose light absorption loss is sufficiently smal l even below 220 nm, compared with HfO2/SiO2 usually used in the UV, was es sential to shorten the wavelength in the deep UV range. The laser gain was estimated to be similar to 2% around 214 nm with a peak beam current of sim ilar to 4A (average beam current of similar to 20 mA) from the measured los s of the cavity degraded after the lasing experiments which agreed well wit h an analytic gain calculation. Lasing in the vacuum ultraviolet (VUV) rang e is also expected even on the compact storage ring NIJI-IV with possible e nhancement of the laser gain. (C) 2000 Elsevier Science B.V. All rights res erved.