A program to compute the two-step excitation of mesospheric sodium atoms for the Polychromatic Laser Guide Star Project

Abstract A program to compute the two-step excitation of sodium atoms ( 3 S 1 / 2 → 3 P 3 / 2 → 4 D 5 / 2 ) using the density-matrix formalism is presented. The BEACON program calculates population evolution and the number of photons emitted by fluorescence from the 3 P 3 / 2 , 4 D 5 / 2 , 4 P 3 / 2 , 4 S 1 / 2 levels. Program summary Title of program: BEACON Catalogue identifier: ADSX Program Summary URL: http://cpc.cs.qub.ac.uk/cpc/summaries/ADSX Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: none Operating systems under which the program has been tested: Win; Unix Programming language used: FORTRAN 77 Memory required to execute with typical data: 1 Mw Number of bits in a word: 32 Number of processors used: 1 (a parallel version of this code is also available and can be obtained on request) Number of lines in distributed program, including test data, etc.: 29 287 Number of bytes in distributed program, including test data, etc.: 830 331 Distribution format: tar.gz CPC Program Library subprograms used: none Nature of physical problem: Resolution of the Bloch equations in the case of the two-step laser excitation of sodium atoms. Method of solution: The program BEACON calculates the evolution of level population versus time using the density-matrix formalism. The number of photons emitted from the 3 P 3 / 2 , 4 D 5 / 2 and 4 P 3 / 2 levels is calculated using the branching ratios and the level lifetimes. Restriction on the complexity of the problem: Since the backscatter emission is calculated after the excitation process, excitation with laser pulse duration longer than the 4 D 5 / 2 level lifetime cannot be rigorously treated. Particularly, cw laser excitation cannot be calculated with this code. Typical running time: 12 h