|
CU-Boulder
Develops Laser for ARPES |
BOULDER, Colo., Jan. 11, 2006 --
Researchers have developed a new application for
lasers in the field of condensed matter physics
that they say leads the way for their use in
angle-resolved photoemission, or ARPES. The team,
led by University of Colorado at
Boulder (CU-Boulder) physics professor Dan Dessau,
has developed a system to perform ARPES using 6 eV
photons from the fourth harmonic of a mode-locked
Ti:sapphire laser.
Fig. 1: Schematic of the
laser ARPES system. SHG = second harmonic
generation, FHG = fourth harmonic generation, and
UHV = ultrahigh vacuum. (Image courtesy University
of Colorado, Boulder)
ARPES is the most direct
way to observe the quantum mechanical structure of
electrons in solids and is one of the key tools
used in the quest to understand the complex
electronic interactions responsible for
high-temperature superconductivity. The technique
is based on Einstein’s photoelectric effect, where
photons of sufficient energy eject electrons from
a solid. Because the electron momentum is
conserved in this process, the angular
distribution of photoelectrons is representative
of the initial electronic states in the solid.
Typically, ARPES experiments
are performed at large multi-user synchrotron
light sources costing on the order of a hundred
million dollars. Instead, the CU-Boulder system
uses 6 eV photons from the fourth harmonic of a
Ti:Sapphire laser produced through two stages of
nonlinear second harmonic generation in BBO. The
resulting flux of 2 x 1014 photons/s in
a bandwidth of less than 5 meV represents about
two orders of magnitude of improvement over even
the best synchrotron beamlines, said Jake Koralek,
a graduate student working under phsycis professor
Dan Dessau to develop this system. The relatively
low photon energy also greatly increases the
momentum resolution and decreases the background
signal of ARPES relative to higher energy
synchrotrons, he said.
Fig. 2: Comparison of ARPES
data taken using laser and synchrotron light
sources (Image courtesy University of Colorado,
Boulder)
"The pulsed nature of the
Ti:sapphire laser also opens up the possibility to
directly observe electron dynamics using ARPES,"
according to Koralek. "These advantages have
enabled us to produce the clearest images yet of
electrons in a high-temperature superconductor."
Koralek said the team
expects the laser will be used more and more for
ARPES experiments in the future, although they
won't eliminate the usefulneess of synchrotrons.
He said their laser sits on an 8-by-4-foot table
and costs approximately $200,000; it also has the
benefit of allowing researchers complete control
over their experiments, in their own labs.
Their results are being
published this week in Physical Review
Letters and recently appeared in Science
Magazine.
For more
information, visit: http://www.photonics.com/clickthru/webclickthru.asp?url=http://www.colorado.edu/physics&codivid=university%20of%20colorado%20at%20boulder&placement=News
View
Next Article (News Briefs (Jan. 11, 2006))
Discuss
this article in the new Photonics.com Community
Forum
| |
Sponsors:  
| |
top of page
