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Frontiers of Physics

Generation of coherent blue light via bichromatic pumping in cesium vapor

Guiyuan Ge, Tian Li, Guoqing Zhang, Ningxuan Zheng, Wenliang Liu, V. B. Sovkov, Jizhou Wu, Yuqing Li, Yongming Fu, Peng Li, Jie Ma, Liantuan Xiao, Suotang Jia

Published Mar 6, 2023• 7 citations
Publisher

Abstract

Diode-pumped alkali lasers, possessing high efficiency and narrow linewidth, can provide feasible solutions for wavelength ranges difficult to reach by commercial lasers. In this study, we investigate a generation of coherent blue light (CBL) via four-wave mixing (FWM)-based up-conversion processes in cesium (Cs) vapor. A bichromatic pumping scheme with 852- and 917-nm lasers drives the Cs atoms to the 6 D 5/2 excited level, followed by cascaded decay of 6 D 5/2 → 7 P 3/2 → 6 S 1/2 , producing 456-nm CBL under phase matching conditions. The fluorescence in multiple bands from blue to near- and far-infrared in the FWM process is demonstrated under different experimental conditions. To optimize the experimental parameters, we investigate the dependence of 456-nm CBL on the vapor temperature, frequency, and intensity of the two pump lasers. A maximum power of 2.94 mW is achieved with pump powers of 430 mW (for 852 nm) and 470 mW (for 917 nm). The corresponding conversion efficiency is 1.5%/W, three-fold higher than those in previous studies. Our results can contribute to fundamental research on atom—photon interactions and quantum metrology.

DOI
10.1007/s11467-022-1255-1

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Optics Express•Mar 25, 2022•18 citations
Diode-pumped alkali lasers, possessing high efficiency and narrow linewidth, can provide feasible solutions for wavelength ranges difficult to reach by commercial lasers. In this study, we investigate a generation of coherent blue light (CBL) via four-wave mixing (FWM)-based up-conversion processes in cesium (Cs) vapor. A bichromatic pumping scheme with 852- and 917-nm lasers drives the Cs atoms to the 6 D 5/2 excited level, followed by cascaded decay of 6 D 5/2 → 7 P 3/2 → 6 S 1/2 , producing 456-nm CBL under phase matching conditions. The fluorescence in multiple bands from blue to near- and far-infrared in the FWM process is demonstrated under different experimental conditions. To optimize the experimental parameters, we investigate the dependence of 456-nm CBL on the vapor temperature, frequency, and intensity of the two pump lasers. A maximum power of 2.94 mW is achieved with pump powers of 430 mW (for 852 nm) and 470 mW (for 917 nm). The corresponding conversion efficiency is 1.5%/W, three-fold higher than those in previous studies. Our results can contribute to fundamental research on atom—photon interactions and quantum metrology.
We demonstrate the generation of coherent and collimated blue light (CBL) based on cesium (Cs) 6S1/2(F = 4)→6P3/2(F' = 5)→6D5/2(F'' = 6)→7P3/2(F' = 5)→6S1/2(F = 4) diamond-type atomic system in a heated vapor cell. Two infrared pumping lasers with wavelengths at 852 nm (6S1/2→6P3/2) and 917 nm (6P3/2→6D5/2), provide step-wise excitation to the 6D5/2 excited state, and induce strong two-photon coherence between the 6S1/2 state and 6D5/2 state. The atoms undergo a double cascade accompanied with the amplified spontaneous emission at 15.1 μm via the 7P3/2 intermediate excited state, and produce a beam of 455 nm (7P3/2→6S1/2) CBL with highly spatiotemporal coherence through a parametric four-wave mixing process. We investigate the influence of experimental parameters such as polarization combination of the two pumping lasers, and their power, and the temperature of Cs vapor cell on the CBL. Especially, we add a beam of 894 nm laser operating at the 6S1/2(F = 3) →6P1/2 transition as repumping laser, which can pump atoms back to the 6S1/2(F = 4) state from the 6S1/2(F = 3) state, thus significantly improving the power of CBL. This technique of the CBL enhancement via optical pumping is also useful for the other alkali metal atoms.
The frequency evaluation of collimated blue light (CBL) generated by parametric four-wave mixing (FWM) in hot atomic vapor is presented. The cesium ( 133 Cs) 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.
We have generated a stable and continuously tunable single frequency (420 nm) coherent blue light (CBL) by the cavity-enhanced four-wave mixing process in Rb vapor. With the bow-tie-type ring cavity, the output power was 3.3 mW, two orders of magnitude higher than that of the CBL generated by the single-pass four-wave mixing process. The measured power stabilities of the 420 nm CBL operated at 2.5 mW and 1.5 mW for 1000 s were 2.89% and 1.88%, respectively. Under the scanning pump laser frequency, the continuously tunable range of the generated CBL reached 1.68 GHz without mode hopping. The measured beam qualities of the generated laser were M x 2 = 1.117 and M y 2 = 1.179 . The excellent performance of the 420 nm CBL was characterized by velocity transfer spectroscopy with 780 nm probe laser. This high quality short wavelength coherent light is potentially applicable to photon-atom interactions in quantum optics and fundamental research fields.
We demonstrate highly efficient generation of coherent 420 nm light via up-conversion of near-infrared lasers in a hot rubidium vapor cell. By optimizing pump polarizations and frequencies we achieve a single-pass conversion efficiency of 260% per Watt, significantly higher than in previous experiments. A full exploration of the coherent light generation and fluorescence as a function of both pump frequencies reveals that coherent blue light is generated close to (85)Rb two-photon resonances, as predicted by theory, but at high vapor pressure is suppressed in spectral regions that do not support phase matching or exhibit single-photon Kerr refraction. Favorable scaling of our current 1 mW blue beam power with additional pump power is predicted.
We demonstrate the generation of polychromatic and collimated lights at 456 nm, 459 nm, and 761 nm based on cesium ( 133 Cs) 6S 1/2 - 6P 3/2 - 8S 1/2 - 7P 3/2 , 7P 1/2 , 6P 1/2 - 6S 1/2 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 (7P 3/2 , 7P 1/2 → 6S 1/2 ) collimated blue lights result from the self-seeded four-wave mixing process (FWM), and the 761 nm coherent light (8S 1/2 → 6P 1/2 ) 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 133 Cs 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.
Nondegenerate four-wave mixing (FWM) in diamond-type atomic systems has important applications in a wide range of fields, including quantum entanglement generation, frequency conversion, and optical information processing. Although the efficient self-seeded nondegenerate FWM with amplified spontaneous emission (ASE) has been realized extensively, the seeded nondegenerate FWM without ASE is inefficient in reported experiments so far. Here we present the experimental realization of the seeded nondegenerate FWM in cesium atoms with a significantly improved efficiency. Specifically, with two pump lasers at 852 and 921 nm and a seed laser at 895 nm, a continuous-wave laser at 876 nm is efficiently generated via FWM in a cesium vapor cell with a power up to 1.2 mW, three orders of magnitude larger than what has been achieved in previous experiments. The improvement of the efficiency benefits from the exact satisfaction of the phase-matching condition realized by an elaborately designed setup. Our results may find applications in the generation of squeezing and entanglement of light via nondegenerate FWM.