Doppler-free spectroscopy of the Cs 6S_1/2 → 7P_3/2 atomic transition at 456 nm in a nanometric-thick vapor layer

The features of Doppler-free resonances detected by probing the 133 Cs atom 6S 1/2 → 7P 3/2 transition at 456 nm in a nanometric-thick vapor layer are investigated. The matrix element of this transition is about 11 times smaller than that of the Cs D 2 line (852 nm). When the vapor layer thickness is ℓ = λ /2 ≃ 230 nm, we observe Dicke narrowing of the lines, accompanied by a red frequency shift of the atomic transitions, which is attributed to atom–surface interactions. Realizing optical pumping with ℓ ≃ 460 nm in a single-pass configuration, we observe Doppler-free resonances with a linewidth of <20 MHz, located at the atomic transition frequencies, with a correspondence of the amplitudes to the transition intensities. These narrow resonances are of interest for high-resolution spectroscopy and instrumentation and could serve as a frequency reference.