To cite this version:J. P. Pique, Ioana Cristina Moldovan, Vincent Fesquet. Concept for polychromatic laser guide stars: one-photon excitation of the 4P3/2 level of a sodium atom. Journal of the Optical Society of America, Optical Society of America, 2006, 23 (11) photons/s/m 2 . This paper describes a model which is validated on experimental results on the sky at the observatory of Keck, the LLNL and Pierrelatte. We give the results of this model for the solution already suggested which consists in exciting the 4D 5/2 level of mesospheric sodium atoms with two photons, using two lasers operating at 589nm and 569nm (case 2). We present a new method which consists in exciting the level 4P 3/2 with a single photon, using a laser operating at 330nm (case 1). Thanks to a modeless laser weshow that 1W in case 1 produces the same flux as 30W in case 2. Moreover, to reach necessary flux at 330nm one needs 10W in case 1 whereas one would need more than 1 400W in case 2. This new method is very promising in terms of flux but also in terms of simplicity.
The polychromatic laser guide star (PLGS) is one of the solutions proposed to extend the sky coverage by large telescopes to 100% by enabling a complete knowledge of all perturbation orders of the wavefront. The knowledge of the tip-tilt is deduced from the monitoring of the chromatic components of the PLGS, from 330 nm to the visible or near infrared. Here we study the original scheme to create the PLGS by resonant excitation of the mesospheric sodium by two pulsed lasers (tens of kilohertz repetition rate, tens of watts average power, tens of nanoseconds pulse duration), at 589 and 569 nm, respectively. The efficiency of this process is investigated numerically by means of both Bloch equation and rate equation models. The influence of numerous laser parameters is studied. In the best case, having optimized all laser parameters, the return flux at 330 nm should not exceed 7x10(4) photons/s/m2 for 2x18 W laser average power at the mesosphere. This maximum is obtained for a modeless laser whose spot diameter corresponds to 4 times the diffraction limit. For a diffraction-limited spot, the return flux falls down to 4x10(4)photons/s/m2.
International audienceIn the framework of Laser Guide Star projects and more particularly of VASAO project of the Canada France Hawaii Telescope, we have developed a modeless laser at 330 nm and we have carried out photometry experiments in laboratory, in order to evaluate the feasibility of the sodium atom excitation at 330 nm. Our modeless laser is a DCM dye laser frequency doubled by a BBO crystal. A high efficiency acousto-optical crystal assures the modeless property. We present the experimental results of sodium atom excitation of 3S{1/2} to 4P{3/2} transition at 330.24 nm and 3S{1/2} to 3P{3/2} transition at 589 nm. The rate equation model gives a good interpretation of the experimental results
We propose what we believe is a novel method for enabling the complete suppression of noise due to Rayleigh scattering in sodium laser guide star systems by means of selective discrimination between Rayleigh and fluorescence signals based on polarization properties. We show that, contrary to the nearly 100% polarized Rayleigh scattering, fluorescence from the D(2) sodium line is strongly depolarized under excitation by a modeless laser. This offers the possibility of completely cancelling the effects of the Rayleigh scattering background while preserving the fluorescence signal to about 40% of its maximal value, leading to an improvement of the signal-to-noise ratio by several orders of magnitude. Both theoretical and experimental data confirm this new proposal.
International audienceIn this paper, we present the simple and high efficient intra-cavity preamplifier of the laser channel we are developing. In usual laser channel the preamplifier medium is placed inside an additional extra-cavity. Here we have experimented a new configuration. The preamplifier is simply an intra-cavity high quality dye cell at Brewster angle. Our new preamplifier configuration is extremely simple and reliable. We will discuss the dynamics of such laser arrangement, temporal delay and pulse width reduction
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.