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The NIJI-IV free electron laser (FEL) is being developed as a compact light source with very good optical quality and ultra-wideband tunability from the VUV to the IR. To obtain lasing at shorter wavelengths in the VUV region, continuous efforts to improve the cavity-mirror performance have been made. As a result, the original loss of Al2O3/SiO2 multilayer mirrors was recently decreased by 30% around 195nm, compared with that of previous ones. A new optical cavity system, composed of two sets of a heavy granite base and a stable mirror manipulator holding two in-vacuum interchangeable mirrors, was installed to stabilize the lasing and also to extend the tuning range. This will enable us to carry out reproducible FEL application experiments, such as real-time observation of surface chemical reactions. As for the IR FEL, modification of the beam transport system to make space for installation of the optical cavity was completed. Here we report recent progress in the NIJI-IV FEL.
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