We have investigated two alternative laser systems for the Laser Interferometer Space Antenna (LISA). One consisted of the laser of LISA's technology precursor LISA Path nder and a ber ampli er originally designed for a laser communication terminal onboard TerraSar-X. The other consisted of a commercial ber distributed feedback (DFB) laser seeding a ber ampli er. We have shown that the TerraSar-X ampli er can emit more than 1 W without the onset of stimulated Brillouin scattering as required by LISA. We have measured power noise and frequency noise of the LISA Path nder laser (LPL) and the ber laser. The ber laser shows comparable or even lower power noise than the LPL. LISA will use electro-optical modulators (EOMs) between seed laser and ampli er for clock noise comparison between spacecraft. This scheme requires that the excess noise added by the ampli ers be negligible. We have investigated the phase characteristics of two ber ampli ers emitting 1 W and found them to be compatible with the LISA requirement on amplifier differential phase noise.