Intracavity ultraviolet second-harmonic generation scheme (335-nm) combined with an actively mode-locked AlGaInP laser diode fundamental light source

Abstract

We propose an advanced LD-based UV-SHG scheme, where the external cavity active mode-locking and the intracavity SHG configurations are combined to increase the averaged fundamental power (P/sub av//sup /spl omega// and to shorten the pulses, both of which are expected to lead to higher UV output. We used a 670 nm AlGaInP LD. The laser was driven by an RF sinusoidal signal with a DC bias current. The external cavity was set by a mirror with its reflectivity of 0.97. The length of the external cavity was approximately 69-cm-long, which corresponds to the roundtrip frequency of 217 MHz. In order to increase (P/sub av//sup /spl omega//, the pulse repetition frequency was set around second or fourth harmonics of the roundtrip frequencies (434 or 870 MHz). A 5-mm-long LiIO/sub 3/ crystal, which was cut for type-I phase-matching at 690 nm, was inserted between the laser and the mirror. The generated UV light was taken out of the cavity by a dichroic mirror inside the cavity.