Abstract
Mid-infrared free electron laser (MIR-FEL) is an attractive light source for laser isotope separation because of its wavelength tunability and high output pulse energy. Several demonstrations have already done in the world FEL facilities. In this review, the recent results of isotope separation by use of MIR-FEL are described with our experimental result of silicon isotope separation by use of phenyltrifluorosilane.