Frequency characteristics of collimated blue light generated by four-wave mixing in cesium vapor

The frequency evaluation of collimated blue light (CBL) generated by parametric four-wave mixing (FWM) in hot atomic vapor is presented. The cesium (¹³³Cs) atoms are excited from the 6S_1/2 ground state to 8S_1/2 excited state with the 852 and 795 nm pump lasers, producing an optical field at 4.2 µm through an amplified spontaneous emission via population inversion on the 8S_1/2→ 7P_3/2 transition and the 456 nm CBL via FWM on the 7P_3/2→ 6S_1/2 transition. The frequency shift of 456 nm CBL has been measured by velocity-selective optical pumping spectral technique when the frequency of any one of two pumping lasers is tuned. The ratio of the frequency shift of 456 nm CBL to the two-photon frequency detuning of two pumping lasers is 0.8912, implying that the generated 4.2 µm light frequency is also correspondingly shifted.