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Linewidth of frequency up-converted radiation in alkali vapours

A. M. Akulshin, Christopher Perrella, Gar-Wing Truong, Andre Nicholas Luiten, Russell McLean

Published Jan 30, 2013• 0 citations
OpenAlex

Abstract

We present a study of the spectral linewidth of collimated blue light (CBL) that results from wave mixing of low-power cw laser radiation at 780 nm and 776 nm in Rb vapours. Using a high-finesse Fabry-Perot interferometer the spectral width of the CBL is found to be less than 1.3 MHz for a wide range of our experimental conditions. We also demonstrate that the measured linewidth is mainly limited by the temporal coherence of the applied laser fields rather than laser light intensities and the atomic medium itself.

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Optics Letters•Jun 11, 2024•5 citations
We present a study of the spectral linewidth of collimated blue light (CBL) that results from wave mixing of low-power cw laser radiation at 780 nm and 776 nm in Rb vapours. Using a high-finesse Fabry-Perot interferometer the spectral width of the CBL is found to be less than 1.3 MHz for a wide range of our experimental conditions. We also demonstrate that the measured linewidth is mainly limited by the temporal coherence of the applied laser fields rather than laser light intensities and the atomic medium itself.
An evaluation of the absolute frequency and tunability of collimated blue light (CBL) generated in warm Rb vapour excited by low-power cw laser radiation at 780 nm and 776 nm has been performed using a Fabry–Perot interferometer and a blue diode laser. For the conditions of our experiments, the CBL tuning range is more than 250 MHz around the resonant frequency of the 85 Rb 5S 1/2 ( F = 3)→6P 3/2 ( F ′ = 4) transition. A simple technique for stabilizing the power and frequency of the CBL to within a few per cent and 10 MHz, respectively, is suggested and demonstrated.
We investigate frequency up-conversion of low power cw resonant radiation in Rb vapour as a function of various experimental parameters. We present evidence that the process of four wave mixing is responsible for unidirectional blue light generation and that the phase matching conditions along a light-induced waveguide determine the direction and divergence of the blue light. Velocity-selective excitation to the 5D level via step-wise and two-photon processes results in a Doppler-free dependence on the frequency detuning of the applied laser fields from the respective dipole-allowed transitions. Possible schemes for ultraviolet generation are discussed.
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.
The effect of hyperfine optical pumping on the parametric four-wave mixing process responsible for the generation of collimated blue light (CBL) in alkali atoms is explored. Over a wide range of atomic densities (4.5 × 10 10 cm −3 ⩽ N ⩽ 1.4 × 10 11 cm −3 ), a more than ten-fold enhancement of CBL is obtained from optical pumping produced by an additional laser. Pulsed optical pumping has been applied to investigate the temporal characteristics of CBL generation. It is shown that optical pumping offers efficient control of the mixing process and the collimated light generation that may be useful for probing a small number of atoms.
We report a study on the transfer of intensity correlation properties in frequency upconversion via four-wave mixing (FWM) in rubidium (Rb) vapor. The 5S1/2−5P3/2−5D5/2 two-photon transition in Rb85 leads to collimated blue light (CBL) generation at 420 nm by absorbing two input photons of wavelengths 780 nm and 776 nm. The g(2)(τ) intensity correlation measurement of the CBL field reveals that the intensity correlations of the input fields are transferred to the CBL field due to strong atomic coherence in the FWM loop. We also demonstrate that the measured values of g(2)(τ) of the CBL field are reduced by the effect of Doppler broadening of Rb vapor.
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.