Currently two options are being considered as the light source for LISA. Each type is a variation of a diode pumped solid-state laser. This figure shows a schematic of both laser types. Both the Non-Planar Ring Oscillator (NPRO - top) and Master Oscillator with Power Amplifier (MOPA - bottom) laser configurations are currently available in non-space modified versions.
From LISA TRIP review (2002) (Fig F-11)