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arXiv:2003.06149 · Journal of the Optical Society of America B

Spiking dynamics of frequency upconverted field generated in continuous-wave excited rubidium vapors

A. M. Akulshin, Nafia Rahaman, Sergey A. Suslov, Dmitry Budker, Russell McLean

Published Jul 1, 2020• 11 citations
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Abstract

We report on spiking dynamics of frequency upconverted emission at 420 nm generated on the 6 P 3 / 2 − 5 S 1 / 2 transition in Rb vapor two-photon excited to the 5 D 5 / 2 level with laser light at 780 and 776 nm. The spike duration is shorter than the natural lifetime of any excited level involved in the interaction with both continuous and pulsed pump radiation. The spikes at 420 nm are attributed to temporal properties of the directional emission at 5.23 µm generated on the population-inverted 5 D 5 / 2 − 6 P 3 / 2 transition. A link between the spiking regime and cooperative effects is discussed. We suggest that the observed stochastic behavior is due to the quantum-mechanical nature of the cooperative effects rather than random fluctuation of the applied laser fields.

DOI
10.1364/josab.395087

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Observation of picosecond superfluorescent pulses in rubidium atomic vapor pumped by 100-fs laser pulses

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We study the superfluorescence (SF) from a gas of rubidium atoms. The atoms of a dense vapor are excited to the $5D$ state from the $5S$ state by a two-photon process driven by 100-fs laser pulses. The atoms decay to the $6P$ state and then to the $5S$ state. The SF emission at 420 nm on the $6P$--$5S$ transition is recorded by a streak camera with picosecond time resolution. The time duration of the generated SF is tens of picoseconds, which is much shorter than the time scale of the usual relaxation processes, including spontaneous emission and atomic coherence dephasing. The dependence of the time delay between the reference input pulse and SF is measured as a function of laser power. The experimental data are described quantitatively by a simulation based on the semiclassical atom-field interaction theory. The observed change in scaling laws for the peak intensity and delay time can be elucidated by an SF theory in which the sample length is larger than the cooperation length.

Physical Review A•Oct 20, 2010•52 citations
We report on spiking dynamics of frequency upconverted emission at 420 nm generated on the 6 P 3 / 2 − 5 S 1 / 2 transition in Rb vapor two-photon excited to the 5 D 5 / 2 level with laser light at 780 and 776 nm. The spike duration is shorter than the natural lifetime of any excited level involved in the interaction with both continuous and pulsed pump radiation. The spikes at 420 nm are attributed to temporal properties of the directional emission at 5.23 µm generated on the population-inverted 5 D 5 / 2 − 6 P 3 / 2 transition. A link between the spiking regime and cooperative effects is discussed. We suggest that the observed stochastic behavior is due to the quantum-mechanical nature of the cooperative effects rather than random fluctuation of the applied laser fields.
Temporal spiking of directional infrared and ultraviolet cooperative emission from sodium vapors excited to the 4D5/24D_{5/2}4D5/2​ level with a continuous-wave resonant laser pump is analyzed. Mirrorless lasing at 2207 and 2338 nm on cascade population-inverted transitions and radiation at 330 nm generated due to four-wave mixing demonstrate a high degree of intensity correlation.
Population inversion on the 5D5/2−6P3/2 transition in rubidium atoms produced by cw laser excitation at different wavelengths has been analyzed by comparing the generated mid-infrared radiation at 5.23 μm originating from amplified spontaneous emission (ASE) and isotropic blue fluorescence at 420 nm. Using a novel method for detection of two-photon excitation via ASE, we have observed directional co- and counter-propagating emission at 5.23 μm. Evidence of a threshold-like characteristic is found in the ASE dependences on laser detuning and Rb number density. The power dependences of the backward- and forward-directed emission can be very similar; however, their spectral dependences are not identical. A new type of temporally and spatially coherent radiation is suggested.
We demonstrate how the orientation of the Rb cell can significantly affect the intensity and spectral characteristics of both the frequency up- and downconverted fields generated by nonlinear processes in Rb vapor. The efficiency of parametric wave mixing in Rb vapor excited to the 5D5/2 level by two-color resonant laser light can be significantly increased by seeding the excitation region with coherent and directional radiation at 5.23 μm, which is resonant with the population inverted 6P3/2–5D5/2 transition. It is shown that the process of velocity-insensitive two-photon excitation is central to understanding the observed coherent blue and mid-IR light enhancements, and that velocity-insensitive and velocity-selective two-photon excitations could produce two co-existing but spectrally and spatially distinguishable mid-IR fields at 5.23 μm.
We study the superfluorescence (SF) from a gas of rubidium atoms. The atoms of a dense vapor are excited to the 5D5D5D state from the 5S5S5S state by a two-photon process driven by 100-fs laser pulses. The atoms decay to the 6P6P6P state and then to the 5S5S5S state. The SF emission at 420 nm on the 6P6P6P--5S5S5S transition is recorded by a streak camera with picosecond time resolution. The time duration of the generated SF is tens of picoseconds, which is much shorter than the time scale of the usual relaxation processes, including spontaneous emission and atomic coherence dephasing. The dependence of the time delay between the reference input pulse and SF is measured as a function of laser power. The experimental data are described quantitatively by a simulation based on the semiclassical atom-field interaction theory. The observed change in scaling laws for the peak intensity and delay time can be elucidated by an SF theory in which the sample length is larger than the cooperation length.