High intensity laser-cluster interactions have been studied for over two decades and have demonstrated extremely e fficient coupling of the incident laser energy to the high local density extended cluster medium, launching a strong radiative shock of interest for laboratory astrophysics studies. Laser-cluster interactions have also shown potential as a source of K-alpha
emission. In this work, a long scale length (10 mm), high density (10^19 atoms/cm^3)
cluster source has been commissioned to carry out a range of new experiments investigating
the use of the extended hot plasma lament generated by the laser-cluster gas interaction as
an x-ray source for x-ray back-lighting motivated by the low debris, high repetition rate nature
of laser-cluster gas interactions.
The first high intensity, ultra-short pulse (45 fs) laser interaction experiment with an extended
Kr or Xe cluster medium at densities of 1017 atoms/cm£3 was carried out on the 12 J/45 fs
Astra Gemini laser at a peak laser intensity of 10^19 W/cm^2. Up to 97% of the incident laser
energy was absorbed by the cluster medium, generating free electron temperatures of 2.5-6 keV
measured via a Ross pair continuum x-ray spectroscopy diagnostic. The hot plasma lament
was imaged using an x-ray pinhole camera, showing a hollow x-ray structure with diameter
greater than the initial laser-cluster interaction region, evincing radial energy transport before
the peak in continuum emission was reached.
The Alameda Applied Sciences Corporation (AASC) fast gas valve was deployed for the first
time on a short pulse, high power laser experiment on the 500 mJ/500 fs Cerberus laser at
Imperial College London, demonstrating point projection imaging with an x-ray source size of
150 micrometres above 2 keV in the direction of peak x-ray emission which was found to be along the laser axis on the laser entry side of the cluster gas volume. Up to 94% of the incident laser
energy was absorbed by the Ar, Kr or Xe cluster medium producing free electron temperatures
of 1-3 keV, with a resonance in heating seen at a cluster radius of 2.4 nm, measured by means
of a single photon counting diagnostic. The x-ray conversion e ffciency from incident laser
energy to emitted x-ray energy above 2 keV was estimated at 0.3%, corresponding to 1.5 mJ
of emitted x-ray energy from the interaction. Optical probing of the interaction revealed two
spatially separate regions in which the cluster medium was ionised on the rising edge of the
pulse.