Low noise lasers in the UV spectrum (355 nm) are important for many applications like spectroscopy, confocal microscopy, flow cytometry, cell sorting, CD mastering, semiconductor inspection and reprographics. The UV CW laser sources currently commercially available, are restricted to excimers lasers, gas ions lasers which suffer from low power efficiency (0.01% or less), high electrical consumption and bulky dimensions. These products, which are expensive, are still waiting for practical replacements. To our best knowledge, we report in this paper the first efficient low noise diode-pumped neodymium doped solid-state laser operating at 355 nm by intra-cavity third harmonic generation (THG). The fundamental infrared laser light is generated by a diode-pumped Nd:YVO4 crystal optically contacted with others components of the laser cavity. Intra-cavity SHG and THG are achieved with a KTP and LBO respectively. Several configurations have led to low noise 355 nm single-frequency operation at a power exceeding 10 mW. We believe that this power can still be improved.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.