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arXiv:1311.4626 · Optics Letters

Collimated blue and infrared beams generated by two-photon excitation in Rb vapor

J. F. Sell, M. A. Gearba, B. D. DePaola, R. J. Knize

Published Jan 21, 2014• 59 citations
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Abstract

Utilizing two-photon excitation in hot Rb vapor we demonstrate the generation of collimated optical fields at 420 and 1324 nm. Input laser beams at 780 and 776 nm enter a heated Rb vapor cell collinear and circularly polarized, driving Rb atoms to the 5D(5/2) state. Under phase-matching conditions coherence among the 5S(1/2)→5P(3/2)→5D(5/2)→6P(3/2) transitions produces a blue (420 nm) beam by four-wave mixing. We also observe a forward and backward propagating IR (1324 nm) beam, due to cascading decays through the 6S(1/2)→5(1/2) states. Power saturation of the generated beams is investigated by scaling the input powers to greater than 200 mW, resulting in a coherent blue beam of 9.1 mW power, almost an order of magnitude larger than previously achieved. We measure the dependences of both beams in relation to the Rb density, the frequency detuning between Rb ground-state hyperfine levels, and the input laser intensities.

DOI
10.1364/ol.39.000528

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Utilizing two-photon excitation in hot Rb vapor we demonstrate the generation of collimated optical fields at 420 and 1324 nm. Input laser beams at 780 and 776 nm enter a heated Rb vapor cell collinear and circularly polarized, driving Rb atoms to the 5D(5/2) state. Under phase-matching conditions coherence among the 5S(1/2)→5P(3/2)→5D(5/2)→6P(3/2) transitions produces a blue (420 nm) beam by four-wave mixing. We also observe a forward and backward propagating IR (1324 nm) beam, due to cascading decays through the 6S(1/2)→5(1/2) states. Power saturation of the generated beams is investigated by scaling the input powers to greater than 200 mW, resulting in a coherent blue beam of 9.1 mW power, almost an order of magnitude larger than previously achieved. We measure the dependences of both beams in relation to the Rb density, the frequency detuning between Rb ground-state hyperfine levels, and the input laser intensities.
Utilizing two-photon excitation in hot Rb vapor we demonstrate the generation of collimated optical fields at 420 and 1324 nm. Input laser beams at 780 and 776 nm enter a heated Rb vapor cell collinear and circularly polarized, driving Rb atoms to the 5D5/2 state. Under phase-matching conditions coherence among the 5S1/2 → 5P3/2 → 5D5/2 → 6P3/2 transitions produces a blue (420 nm) beam by four-wave mixing. We also observe a forward and backward propagating IR (1324 nm) beam, due to cascading decays through the 6S1/2 → 5P1/2 states. Power saturation of the generated beams is investigated by scaling the input powers to greater than 200 mW, resulting in a coherent blue beam of 9.1 mWpower, almost an order of magnitude larger than previously achieved. We measure the dependences of both beams in relation to the Rb density, the frequency detuning between Rb ground-state hyperfine levels, and the input laser intensities. (C) 2014 Optical Society of America
We demonstrate production of continuous coherent blue laser light by using a five-level system in rubidium vapor. Two low-power lasers, at 780 and 776 nm, induce strong atomic coherence in the 5S-5P-5D states. The atoms decay to the 6P excited state, from which stimulated emission produces a coherent blue (420 nm) beam. We have coupled both ground-state hyperfine levels, effecting coherence between four levels. The coherent blue output is enhanced by several mechanisms, including stronger coupling to a larger fraction of the atomic population, operation at a detuning such that the vapor is nominally transparent to the 780 nm pump field, reduced losses owing to optical pumping, and optimal phase matching. We report experimental findings and compare them with results from a semiclassical Maxwell-Bloch model.
We use two continuous-wave laser beams of 780 nm and 515 nm to optically drive Rb85 atoms in a heated vapor cell to a low-lying Rydberg state 10D5/2. We observe a collimated ultraviolet (UV) beam at 311 nm, corresponding to the transition frequency from the 11P3/2 state to the 5S1/2 state. This indicates the presence of a coherent four-wave mixing process, built up by two input laser fields as well as terahertz (THz) radiation of 3.28 THz, which is generated by amplified spontaneous emission between the 10D5/2 and 11P3/2 states. We characterize the 311 nm UV light generation and its dependence on various physical parameters. This scheme could open up a new possibility for generating narrow-band THz waves as well as deep UV radiation.
Abstract We demonstrate 1.37 µ m coherent near-infrared light generation via self-seeded parametric four-wave mixing (FWM) process in Rb atomic vapor. Two lasers (780 nm and 776 nm) in the co-propagating configuration, drive the Rb atoms from the 5S 1/2 ground state to the 5D 5/2 excited state. The parametric FWM around the 5P 3/2 –5D 5/2 –6P 3/2 –6S 1/2 –5P 3/2 transition loop is effectively established under phase matching conditions. The generated coherent light wavelength is confirmed using an optical spectrum analyzer, and the output power is investigated with the input laser frequency, power and atomic density. Consequently, a 1.37 µ m coherent light with the power of 27 µ W and the beam quality of M x 2 = 1.22 and M y 2 = 1.25 is obtained. An additional 795 nm laser is introduced to enhance the output power by 1.5 times through velocity-selective optical hyperfine repumping.
Abstract The coherent blue light generated in rubidium vapor due to the combined action of an ultrashort pulse train and a continuous wave diode laser is investigated. Each step of the two-photon transition 5S–5P 3 / 2 –5D is excited by one of the lasers, and the induced coherence between the 5S and 6P 3 / 2 states is responsible for generating the blue beam. Measurements of the excitation spectrum reveal the frequency comb structure and allow us to identify the resonant modes responsible for inducing the nonlinear process. Further, each resonant mode excites a different group of atoms, making the process selective in atomic velocity. The signal dependency on the atomic density is characterized by a sharp growth and a rapid saturation. We also show that for high intensity of the diode laser, the Stark shift at resonance causes the signal suppression observed at low atomic density.
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.