CLIC is a linear e+e- (gamma-gamma) collider project which uses a drive beam to accelerate the main beam. Various portions of the drive beam provide RF power for corresponding units of the main linac through energy extracting RF structures. CLIC can operate over a wide range of center-of-mass energies, from 150 GeV to 3 TeV. The present paper describes the optimization of a Free-Electron-Laser (FEL) mode of operation for CLIC, where some additional bunches of the CLIC drive beam produce polarized FEL radiation while passing through an appropriate wiggler-magnet section close to the collision point, and then presents the luminosity spectrum of such gamma gamma collider, for a center-of-mass energy of Ecm=0.5 TeV. The FEL radiation is converted to a polarized high-energy gamma beam by Compton backscattering off main-linac high-energy low-emittance electron (or positron) bunches at the Conversion Point (CP). The Compton-scattered gamma rays inherit the strong focusing of their parent main linac bunches and collide in a nm-size transverse area at the CLIC primary electron-positron interaction point (IP). In this paper we show that the CLIC drive beam parameters satisfy the requirements of the FEL mode of operation. The FEL scheme holds the promise to solve two main problems of gamma gamma collider which are high peak power and repetition frequency. Additionally essential wiggler parameters are also defined. With optimized beam parameters, a gamma gamma luminosity above 10^34 cm^-2s^-1 can be achieved in this machine.