FELLA (Free Electron Laser Atomic, Molecular, and Optical Physics Program Package)

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The Software:  Exploring the Ultrafast and the Ultrasmall!

The authors have written the software package FELLA for highly specialized basic research in atomic, molecular, and optical physics. The atomic physics programs treat the atomic electronic structure in Hartree-Fock-Slater approximation and the interaction of electrons with light of up to two colors. The molecular physics programs treat the x-ray absorption by laser-aligned molecules. An optical physics code describes the propagation of a laser and x-rays through a gaseous medium. There are additional miscellaneous small helper programs.  Especially, FELLA has been inspired by the upcoming x-ray free electron lasers (FEL) to study atoms and molecules in their light in combination with intense optical lasers. However FELLA is more general and has been used so far to study atoms and molecules in the light of third-generation synchrotrons such as Argonne’s Advanced Photon Source.  (See Argonne Scientists Use Lasers to Align Molecules.)

The software, written in FORTRAN95, currently is in Version 1.3.0. The software can be run on a PC with the Linux operating system and the free g95 FORTRAN95 compiler. There is no manual at this time. The source code is well documented with comments. An example input is provided with a description of the input parameters. The meaning  of the values selected is published. The authors feel the code is relatively user-friendly and running times can vary from 15 minutes to several weeks depending upon the input parameters, with most cases being run in a few days.

It is expected that this software will be of value to universities studying laser-matter interactions as well as to national laboratories that can generate x-rays for experimental use. Especially, the upcoming x-ray FEL facilities such as those at Stanford, CA (LINAC Coherent Light Source (LCLS)), Hamburg, Germany (European X-Ray Laser Project (XFEL), and Harima Science Garden City, Hyogo, Japan (SPring-8 Compact SASE Source (SCSS) may benefit from FELLA.

Publications (FELLA Applications)

C. Buth, R. Santra, and L. Young, "Refraction and absorption of x rays by laser-dressed atoms," Revista Mexicana de Fisica (accepted for publication)

L. Young, C. Buth, R. W. Dunford, P. J. Ho, E. P. Kanter, B. Krässig, E. R. Peterson, N. Rohringer, R. Santra, and S. H. Southworth, "Using strong electromagnetic fields to control x-ray processes," Revista Mexicana de Fisica (accepted for publication)

C. Buth and R. Santra, "X-ray refractive index of laser-dressed atoms," Physical Review A 78, 043409 (2008). 

C. Buth and R. Santra, "Rotational molecular dynamics of laser-manipulated bromotrifluoromethane studies by x-ray absorption," The Journal of Chemical Physics 129, 134312 (2008).

E. R. Peterson, C. Buth, D. A. Arms, R. W. Dunford, E. P. Kanter, B. Krässig, E. C. Landahl, S. T. Pratt, R. Santra, S. H. Southworth, and L. Young, “An x-ray probe of laser-aligned molecules,” Applied Physics Letters 92, 094106 (2008).

C. Buth and R. Santra, “Theory of x-ray absorption by laser-aligned symmetric-top molecules,” Physical Review A 77, 013413 (2008). 

C. Buth, R. Santra, and L. Young, “Electromagnetically induced transparency for x-rays,” Physical Review Letters 98, 253001 (2007). 

R. Santra, C. Buth, E. R. Peterson, R. W. Dunford, E. P. Kanter, B. Krässig, S. H. Southworth, and L. Young, "Strong-field control of x-ray absorption," J. Phys. Conf. Ser. 88, 012052 (2007).

Z-H. Loh, M. Khalil, R. E. Correa, R. Santra, C. Buth, and S. R. Leone, "Quantum state-resolved probing of strong-field-ionized xenon atoms using femtosecond high-order harmonic transient absorption spectroscopy," Phys. Rev. Lett. 98, 143601 (2007).

C. Buth and R. Santra, "Theory of x-ray absorption by laser-dressed atoms," Phys. Rev. A 75, 033412 (2007).

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Funding

Funding was provided by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences, and by the Alexander von Humboldt Foundation, Bonn, Germany.