Summary of focal plane measurements - to 25th May 1998
It has been intended for some time to measure the laser beam profile in the focal plane
using an infra-red sensing camera.
The MO laser system has already been measured
and showed a Gaussian like beam.
This series of measurements aimed to measure the
MO-LPA
laser system with the 6J pulse. The optical system for this is shown below.
Scheme of the laser beam divergence measurement.
Measuring along the light axis of the parabolic mirror, we find astigmatism in the beam,
i.e. the foci in the horizontal and vertical plane are not coincident. This is seen in
the figure below, where the two beam sizes in the horizontal and vertical planes are plotted
at different positions.
4s widths of the laser beam as a function of position along the focal axis of the 20 m focal length parabolic mirror.
A typical measurement of the MO-LPA beam at the point where the horizontal and vertical plane
beam widths are the same is shown below. The astigmatism results in a power density 3 times
less than that previously predicted.
Beam profile in the focal plane.