Studies using a
Magnetic Angle Changing (MAC)
Page constructed by Andrew
This Page has been updated on the 12th January, 2006.
Happy New Year!
describes the super-elastic scattering studies that are being conducted
Other pages which may be of interest in these laboratories are given
at the bottom of this page, with links to the different pages.
Murray A J, Hussey M J &
Needham M, Meas. Sci. Tech. 17
Useful papers in this area from members of the group include:
characterization of an atomic beam source for alkali and alkali-earth
targets with narrow angular divergence.”
The purpose of this page is to detail for the interested reader the Super-elastic electron scattering experiments which
have been conducted in the
Atomic, Molecular & Laser Manipulation Group, School of
Physics & Astronomy, Schuster Laboratory, Manchester University,
Manchester, M13 9PL, United Kingdom.
Although there is an implicit assumption that the reader has a
familiarity with these experiments, it is not completely necessary to
enjoy this page and the associated pages that accompany this home page.
For those who are interested, numerous papers are available on this
subject, including those in which we have been associated. The papers
from members of the group are shown above.
The references found in these papers give a good appreciation of the
work that has been done in this area from different groups around the
Overview of Inelastic
Most detail about inelastic collision process is obtained from
Experiments catch SINGLE
electron which excites SINGLE
atom, then look for time-correlated PHOTON
emitted from this atom.
this many times to build up a picture of the excited atom
Measurements - Inelastically scattered electron measured as function of
experiment showing the scattering geometry and position of detectors.
Information on state of atom obtained
from Fluorescence Polarization
Complete Description of excitation
obtained by measuring polarization of photon in coincidence with
allows us to Fully Characterise Atomic state (ie measure it's 'shape')
Note that Coincidence technique slow as have to wait for photon
correlated to detected electron (ie if photon is emitted in a direction
where the detector is not positioned, there is no correlated photon for
the detected electron).
Alternative Method -
What if we Run experiment backwards in
time? (?emit ni sdrawkcab tnemirepxe nuR)
This is the SUPER-ELASTIC SCATTERING
Superelastic Scattering using Laser Prepared Atoms
The superelastic experiment showing the scattering
geometry and position of lasers and detectors.
Atomic Collision Parameters
= angular momentum orthogonal to scattering plane.
= alignment of P-state in scattering plane.
= degree of polarization.
Note laser photon is ALWAYS in same
Only have to wait for a super-elastically scattered electron
Don’t have to wait for both electrons & photons!
Get same information as with coincidence technique by varying laser
polarization in 3 steps, not 4. Hence the xxperiment produces data 102
times faster than the Coincidence Method!
We can therefore measure very small
signals at high scattering angles.
Obviously this is a very attractive
method for producing data! So what are the disadvantages?
1. Need very well
controlled laser system.
We use a Coherent MBR-110 Ti:Sapphire laser, MBD-200 external Doubler
and a 10W Verdi Pump laser to produce radiation with a bandwidth of 1
part in 1010
1.5W (Ti:Sapphire) ~150mW (MBD-200)
TEM00 mode (Ti:Sapphire) ~ (MBD-200)
Linewidth: 100kHz (Ti:Sapphire)
2. Need an atom
that can be excited by the Laser Beam!
In the present studies we choose Calcium as it can be excited by our
laser system at a wavelength of ~423nm.
So WHY CALCIUM?
Calcium is Good for our teeth & bones!
Calcium also looks a bit like Helium –
It has 2 electrons in outer shell, so models which assume a 'frozen'
core may be applicable.
Simple representation of Helium and Calcium showing the
similarity between the systems ((assuming frozen core approximation).
This means that models that work for the simpler atom (Helium) might
also be applicable for Calcium, which actually has 20 electrons!
Also, the Energy Level structure of
Calcium is simple (which makes it easy to theoretically model the
Excitation of Calcium at
~423nm, showing the electron energy levels and the states excited by
different laser polarizations.
Note that the structure is very simple for this excitation (no
So why do scattering experiments in a
Conventional apparatus limited in angular range by physical size of
electron gun and analyser
Conventional electron spectrometer from above, showing
restricted angular range.
of Magnetic Field allows measurements to be conducted over the
complete scattering plane, since incident
and scattered electron trajectories can be ‘steered’ by the B-Field.
Trajectories of electrons in the MAC field, with a
B-field of 20 Gauss for an Electron Energy of 45eV
By using the Magnetic Angle Changer
(MAC device) in an electron spectrometer, a FULL comparison with theoretical models can
therefore be made for first time over the complete scattering plane!
Excitation of Calcium in
a B-field, showing the Zeeman split energy levels and the states
excited by different laser polarizations.
Application of Magnetic field
complicates Laser Interaction due to Zeeman Splitting of energy levels
However, new model of the interaction
has been developed to allow for this effect.
New Magnetic Angle Changing (MAC) Spectrometer developed at Manchester.
Figure of the new
spectrometer at Manchester.
Photograph of the new
spectrometer which has been developed at Manchester.
Photograph of Excitation of Calcium Atoms between MAC
coils using radiation at 423nm
have now been carried out from 55eV down to 17eV equivalent Incident
Example of results for
equivalent coincidence Incident Energy of 45eV, showing the regions of
inaccessibility (the MAC was not used for these experiments).
Movie of the shape of
the charge cloud as calculated from theory (quicktime movie).
The MAC device is now being used to measure the shape of the atoms
created by electron excitation over the full scattering geometry.
Experimental results will be shown soon!
Links to other pages which might be of interest:
at the (e,2e) Computer Controlled Spectrometer Hardware
at the Symmetric (e,2e) Data collected by this spectrometer
at the Symmetric data parameterisation
at the Data where the Ion is left in an Excited State
at the 64.6eV Data where the detected electrons have unequal energies
the results that were collected in the Perpendicular plane
Link to the Experiments conducted
in the Laser Collisions Laboratory at Manchester
theManchester Electron Scattering group Home Page
Link to the Atomic, Molecular
& Laser Manipulation Group Home Page
the Manchester Physics & Astronomy Department Home Page