A permanent magnet undulator has been built and installed on the ACO Storage Ring. The undulator design, the spontaneous emission and gain of the system, as well as the laser induced bunch lengthening of the electron bunch, are presented. A low-loss optical cavity has been also recently built and operated on the ring. Its performance and the degradation problems of the mirrors are discussed. Amplification of the spontaneous emission stored in the optical cavity has been observed. Also, preliminary results on the operation of an optical klystron are reported and interpreted