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Optics Letters

Bichromatic two-photon coherent excitation of sodium to provide a dual-wavelength guidestar

Jens Biegert, Jean‐Claude Diels, Peter W. Milonni

Published May 15, 2000• 11 citations
Publisher

Abstract

A bichromatic sodium guide star based on two-photon coherent excitation followed by cascade emission is considered. Results of density matrix computations, including Doppler averaging, are presented for both a three-level model and the full hyperfine structure of the sodium 3S, 3P, and 4S levels. These results indicate that the proposed scheme for a bichromatic guide star is feasible.

DOI
10.1364/ol.25.000683

Related papers

Feasibility study of a bichromatic guidestar-coherent 2-photon bichromatic excitation of mesospheric sodium

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Theoretical results from a full hyperfine structure density matrix computation indicate that a bichromatic sodium guidestar based on two-photon bichromatic coherent excitation should require laser powers only on the order of 10 W.

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Summary form only given. We exploit coherent interaction properties to efficiently pump sodium from the 3s/sub 1/2/ ground state to the 4s/sub 1/2/ upper state via the 3p/sub 3/2/ state. Even though the excitation is nonlinear, the required intensities are reduced to levels required to resonantly pump single photon transitions in sodium, because of the particular choice of laser frequencies which are near resonance with the intermediate levels. Furthermore, the intermediate state is left unpopulated after the excitation sequence. A computer simulation solves the nonlinear Schrodinger equation for this system, comprised of 32 hyperfine levels connected by 112 possible transitions. The levels are summed over the velocity distribution for mesospheric sodium to account for Doppler broadening which is the dominant dephasing process.

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Summary form only given. Adaptive optics systems, guided by artificial sodium beacons have reached fundamental limits, because of (i) the low densities of atoms in the mesosphere; (ii) the low level of excitation dictated by the requirement to avoid saturation, and (iii) the monochromatic return which makes it impossible to correct for differential tilt (the largest error-about 90%-in image formation). Different attempts are being made to taylor laser pulse profiles to more efficiently access the Doppler groups of the atomic lines, while avoiding saturation (e.g. only 6.4 mW/cm/sup 2/ for the D2 line), and to assist in the correction for differential tilt by adding Rayleigh or natural beacons. Both problems severely limit the further advancement in this field due to the increased complication and cost. We have presented an alternative, which circumvents these problems by using coherent excitation of sodium with short pulses. The saturation limitation is avoided in this approach in which each pulse totally inverts (3s /spl rarr/ 4s) the interaction volume. Subsequent cascade resonance fluorescence at two wavelengths allows for correction of the tilt.

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Comparison of the Efficiency of Sodium Atom Excitation Schemes for Generating Monochromatic and Polychromatic Laser Guide Stars

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Abstract The efficiency of ten sodium atom excitation schemes that can potentially be used to generate a sodium polychromatic laser guide star (PLGS) and a monochromatic laser guide star (LGS) is compared. It is shown that for creating an LGS in sodium vapor using the cascade fluorescence effect with single-photon excitation, the most suitable is the 42P3/2 ← 32S1/2 transition excited at a wavelength of 330.237 nm and demonstrating the highest LGS characteristics, while the efficiency decreases by two orders of magnitude compared to a monochromatic LGS at a wavelength of 588.995 nm.

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Seven possible variants of the sodium atom excitation are considered for creating a polychromatic laser guide star (LGS). It has been shown that the 42P3/2 ← 32S1/2 transition excited at a wavelength of 330.237 nm is most suitable for creating a polychromatic LGS in sodium vapor using the effect of cascade fluorescence at one-photon excitation. In this case, the excitation efficiency will be 2 orders of magnitude lower compared to the efficiency of creating a monochromatic LGS at a wavelength of 589 nm.

International Conference on Pulsed Lasers and Laser Applications (AMPL)•Nov 2, 2023•0 citations
A bichromatic sodium guide star based on two-photon coherent excitation followed by cascade emission is considered. Results of density matrix computations, including Doppler averaging, are presented for both a three-level model and the full hyperfine structure of the sodium 3S, 3P, and 4S levels. These results indicate that the proposed scheme for a bichromatic guide star is feasible.
Summary form only given. We exploit coherent interaction properties to efficiently pump sodium from the 3s/sub 1/2/ ground state to the 4s/sub 1/2/ upper state via the 3p/sub 3/2/ state. Even though the excitation is nonlinear, the required intensities are reduced to levels required to resonantly pump single photon transitions in sodium, because of the particular choice of laser frequencies which are near resonance with the intermediate levels. Furthermore, the intermediate state is left unpopulated after the excitation sequence. A computer simulation solves the nonlinear Schrodinger equation for this system, comprised of 32 hyperfine levels connected by 112 possible transitions. The levels are summed over the velocity distribution for mesospheric sodium to account for Doppler broadening which is the dominant dephasing process.
Summary form only given. Adaptive optics systems, guided by artificial sodium beacons have reached fundamental limits, because of (i) the low densities of atoms in the mesosphere; (ii) the low level of excitation dictated by the requirement to avoid saturation, and (iii) the monochromatic return which makes it impossible to correct for differential tilt (the largest error-about 90%-in image formation). Different attempts are being made to taylor laser pulse profiles to more efficiently access the Doppler groups of the atomic lines, while avoiding saturation (e.g. only 6.4 mW/cm/sup 2/ for the D2 line), and to assist in the correction for differential tilt by adding Rayleigh or natural beacons. Both problems severely limit the further advancement in this field due to the increased complication and cost. We have presented an alternative, which circumvents these problems by using coherent excitation of sodium with short pulses. The saturation limitation is avoided in this approach in which each pulse totally inverts (3s /spl rarr/ 4s) the interaction volume. Subsequent cascade resonance fluorescence at two wavelengths allows for correction of the tilt.
Abstract The efficiency of ten sodium atom excitation schemes that can potentially be used to generate a sodium polychromatic laser guide star (PLGS) and a monochromatic laser guide star (LGS) is compared. It is shown that for creating an LGS in sodium vapor using the cascade fluorescence effect with single-photon excitation, the most suitable is the 42P3/2 ← 32S1/2 transition excited at a wavelength of 330.237 nm and demonstrating the highest LGS characteristics, while the efficiency decreases by two orders of magnitude compared to a monochromatic LGS at a wavelength of 588.995 nm.
Seven possible variants of the sodium atom excitation are considered for creating a polychromatic laser guide star (LGS). It has been shown that the 42P3/2 ← 32S1/2 transition excited at a wavelength of 330.237 nm is most suitable for creating a polychromatic LGS in sodium vapor using the effect of cascade fluorescence at one-photon excitation. In this case, the excitation efficiency will be 2 orders of magnitude lower compared to the efficiency of creating a monochromatic LGS at a wavelength of 589 nm.