Harmonic Generation from Multiple Orbitals in N2
harmonic generation was first discovered in the early 1990s. A
high electric field is associated with a high intensity laser pulse.
The field can get so high, that some of the electrons get pulled out of
an atom or
a molecule when the laser pulse hits them. The electrons are then
accelerated in the electric field of the laser and they
recombine with the atom or molecule they were ionized from. Thereby the
loose their kinetic energy and transform it into light (see detailed explanation).
|Animation of our experiment:
A strong infrared laser pulse is focused in a
nitrogen gas jet (white cone in the middle). In the jet, the strong
laser electric field interacts with
the N2 molecules.
This results in the emission of light in the form of laser harmonics in
extreme ultraviolet spectral range.
can be used to learn about the structure of the electrons in
the atom or molecule. The electrons are governed by the laws of quantum
mechanics and form so called orbitals.
spectral analysis of the harmonics reveal contain information about
the molecular orbital involved in HHG. Up to now,
we only had indications that the orbital
that is highest in energy (the so called HOMO) can contribute to
our article we present evidence, that the HOMO and a lower bound
orbital (HOMO-1) produce high harmonics.
||High harmonics are generated by
electron with an orbital in a strong laser field.
A) Sketch of the nuclear
positions in the nitrogen molecule (green) and the internuclear axis
line in A, B and C). B) Highest occupied molecular orbital (HOMO) with
indicating the sign of the orbital. The recolliding electron is
presented as a
de Broglie wave.
C) Next lower bound
orbital (HOMO-1) with the recolliding electron wave. The HOMO-1
harmonic generation. Its contribution is strongest for an electron
under 90 degrees to the internuclear axis.
see High Harmonic Generation
from Multiple Orbitals in N2
McFarland, J. P. Farrell, P. H. Bucksbaum and M.
online October 30 2008, 10.1126/science.1162780
article in Science
Link to Perspectives: Interrogating molecules by Gilles Doumy and Louis F. DiMauro