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Violent explosion of N2 molecule
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Violent explosion of N2 molecule

March 20, 2014
A violent explosion of an N2 molecule after interaction with an X-ray beam results in the sudden loss of two electrons. The Henry Kapteyn/Margaret Murnane group at JILA is working to develop both strong field ionization and high-harmonic generation (HHG) as powerful tools to capture the behavior of electrons and the evolution of molecular structure when molecules are exposed to strong laser fields. The group has observed that atoms and molecules have a universal response to strong laser fields. Part of the electron wave function undergoes tunnel ionization, a quantum mechanical phenomenon in which an electron passes through an energy barrier it otherwise could not surmount. The electron can later recombine with the parent ion. By monitoring this process, the group hopes to probe the evolution of electron orbitals and changes in the structure of the atomic nuclei inside a molecule. The group is developing HHG for this and other projects. In HHG, the researchers harness attosecond laser pulses to manipulate electrons and generate bright beams of coherent X-rays. The process begins with the focusing of an intense femtosecond laser into a gas where an electron can literally be ripped from an atom or molecule as the laser suppresses the Coulomb barrier that binds the electron to the ion. Once released, the electrons oscillate in the light field, and some of them can coherently recombine with the same atom or molecule. The excess energy of the recombining electron is then emitted as an X-ray photon. This extreme nonlinear process results in the generation of coherent, laser-like beams of X-rays that emerge in bursts lasting from a few femtoseconds (10-15 s) to <100 attoseconds (10-18 s). HHG can be thought of as a coherent version of the original Roentgen X-ray tube. JILA is a joint institute of the University of Colorado Boulder and the National Institute of Standards and Technology. (Date of Image: August 2007) Credit: Greg Kuebler, JILA


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