A Measurement of Modal Gain Profile and Its Effect on the Lasing Performance in Vertical-External-Cavity Surface-Emitting Lasers

We investigate the effect of relative wavelength difference between material gain and resonance peaks on lasing performance in vertical-external-cavity surface- emitting lasers ( VECSELs ). We propose a measurement method of the wavelength-dependent modal gain profiles by inserting a birefringent filter inside a cavity in order to modulate the optical loss according to the wavelength. With knowledge of the detailed gain profiles, we achieve a stable green output power of 3.3 W and a power conversion efficiency ( $=$ green output power/pump input power) of 17% in VECSEL with a LiB$_{3}$ O$_{5}$ crystal as an intracavity frequency doubler.