Observation of the interplay between seeded and self-seeded nondegenerate four-wave mixing in cesium vapor

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 6S1/2 ground state to 8S1/2 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 8S1/2 → 7P3/2 transition and the 456 nm CBL via FWM on the 7P3/2 → 6S1/2 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.

Polychromatic and collimated lights generated by nondegenerate four-wave mixing in cesium vapor

We demonstrate the generation of polychromatic and collimated lights at 456 nm, 459 nm, and 761 nm based on cesium (133Cs) 6S1/2 - 6P3/2 - 8S1/2 - 7P3/2, 7P1/2, 6P1/2 - 6S1/2 multi-diamond-type atomic system via two-photon excitation with two IR pump lasers at 852 nm and 795 nm. The 456 nm, 459 nm (7P3/2, 7P1/2 → 6S1/2) collimated blue lights result from the self-seeded four-wave mixing process (FWM), and the 761 nm coherent light (8S1/2 → 6P1/2) is from a seeded FWM process with the injection of a third laser at 895 nm. We measure the dependency of generated polychromatic fields on the temperature of 133Cs vapor cell and the powers of input lasers, clearly demonstrating the competition between the self-seeded FWM and seeded FWM, as they share the same excitation path. This work is helpful to further produce entangled multi-color photons for quantum communication.

Theoretical and experimental study of the 6S-8S two-photon absorption cross-section in cesium atoms

The probability of a two-photon absorption (TPA) process is quantified by means of the TPA cross-section. In this work the TPA cross-section for the 6S1/2 → 8S1/2 transition in cesium (Cs) atoms is obtained from a theoretical and experimental approach. It is calculated using second order perturbation theory including hyperfine structure and Doppler broadening for a thermal atomic vapor. The theoretical values for the TPA cross-sections of the two allowed hyperfine transitions are σ~3,3=3.10×10-24 cm4/W and σ~4,4=3.65×10-24 cm4/W. An experiment is set up to measure these cross-sections based on the quadratic dependence between the TPA transition rate and the intensity of the laser light. Values of σ~3,3=(3.6±1.1)×10-24 cm4/W and σ~4,4=(4.6±1.1)×10-24 cm4/W are obtained from the measurements. The results show an agreement between theory and experiment. To the best of our knowledge, this is the first time that these cross-sections are reported.

Spatial mapping of the polarization-resolved spectrum based on vector-beam-assisted nondegenerate four-wave mixing

The introduction of vector beams (VBs), with space-variant polarization, into the polarization-resolved spectrum, provides a convenient and rapid pathway for revealing micro-structure. Here, we realize the spatial mapping of the polarization-resolved spectrum based on VB-assisted nondegenerate four-wave mixing (FWM) in a diamond atomic system of ⁸⁵Rb. The 780 nm radial VB and 776 nm linearly polarized Gaussian beam serve as the probe and pump beams in the FWM process, respectively. The generated 420 nm coherent blue light (CBL) possesses a space-variant intensity profile due to the spatially polarized atomic medium. Accordingly, the polarization-resolved spectrum can be directly mapped from a single CBL profile and the polarization information of the input 776 nm beam can be accurately extracted. In particular, such nondegenerate FWM based on VB provides a proof of principle for rapid and visual polarization-related detection by converting to a frequency domain where efficient detectors are readily available.

Experimental realization of wavelength multiplexed nonlinear upconversion in cesium atoms

Blue-violet wavelength multiplexing offers the capability to enhance the operational capacity and efficiency in optical information processing, underwater communications, biology, and medicine. Here we present a specially designed atomic scheme of cesium for simultaneously generating two blue-violet lasers at 456 and 459 nm via four-wave-mixing (FWM)-based upconversion processes. We experimentally and theoretically show that a double-diamond-type coherent system pumped with 852 and 921 nm lasers is responsible for the efficient generation of the two blue-violet lasers. In this system, the large population inversions lead to self-amplified spontaneous emissions at 15.6 and 12.1µm, which, in turn, serve as the seeds for enhanced double FWM processes with dual-wavelength upconversions.