Dopplerless spectroscopy of 6S/sub 1/2/-8P/sub 1/2,3/2/ transitions of cold atomic caesium

Summary form only given. The 6S/sub 1/2/-8P caesium transition at 389 nm might be a favourable candidate to provide a new secondary standard in the near UV. Moreover, high resolution spectroscopy has impressively benefited from the reduction of thermal motion by laser cooling techniques. We report on the Dopplerless spectroscopic investigation of the 6S/sub 1/2/-8P/sub 1/2,3/2/ transitions of cold caesium atoms in a vapour cell magneto-optical trap. The ultraviolet light is generated by frequency doubling the output of a Ti:sapphire laser at 778 nm in a LBO crystal. The cold atom cloud is periodically released and recaptured by switching rapidly off and on the trapping laser beams and the magnetic field gradient. The gated detection of the fluorescence light at 450 nm (7P-6S cascading transition) using a photon counting device allows the observation of unperturbed atoms. The hyperfine structure of the 8P/sub 1/2/ level. The recorded linewidth is about 800 kHz and is yet larger than the expected purely radiative one i e. 480 kHz. The influence of the magnetic field gradient and AC Stark effect on the recorded spectra have been also studied.