3RD-HARMONIC GENERATION IN POSITIVELY DISPERSIVE GASES WITH A NOVEL CELL

The generation of UV third-harmonic radiation by a focused laser beam in a positively dispersive gaseous medium is investigated. The nonline ar gas is confined to a focal half-space by using a differentially pum ped gas cell. The resulting density gradient along the beam axis is sh own to provide an efficient frequency conversion in spectral regions o f positive dispersion. Experimental results obtained in argon at lambd a approximately 197 nm, which compare favorably with theory, are prese nted.