Speaker
Description
In this paper we describe the development of an stable, microfocus X-ray source driven
by an ultrashort high intensity laser. This source follows a new route to high brightness
and small source size somewhere in the middle of low cost microfocus X-rays and large
scale synchroton facilities. We explore one application of this new type of sources with
emphasis on the stability of the source at high repetition rate and the advantage over
similar conventional sources.
The availability of ultrashort laser pulses with high power [1,2] has lead to the
development of the Laser Driven Plasma Accelerator (LDPA) [3] where a short and
ultraintense pulse can produce plasma structures which can accelerate particles to
relativistic velocities.
In this paper, we report the development and application of a microfocus X-ray source
for phase contrast tomography in the lambda cube regime. In this regime the laser pulse
is compressed in space and time to the physical limit. This allow the use of laser with
moderate energy (~ 1 mJ) and high repetition rate (~ KHz) to produce high intensities
relevant to the physics of the LDPAs.
The X-ray source produced at the Laser Laboratory for Acceleration and Applications
(L2A2) of the University of Santiago de Compostela (USC), is made by focusing a 1mJ,
35 fs, 1kHz pulses at 800 nm wavelength on metallic foils close to the diffraction limit.
In this experiment, we use a microscope objective to focus the light to intensities larger
than 1017 W/cm2
.
As the laser pulse destroy the target at every shot and due to the tight focusing (~ 4 um
Rayleigh length), the stable operation of the source must combine a fast refreshing of the
target combined with a high precision positioning to maintain the target on focus as the
intensity drops dramatically out of focus.
We first characterize the source and then optimize the stability to perform the
applications. The X-ray spectra of this source are measured with a CdTe spectrometer
and consist of a broad Bremsstrahlung continuum up to 150 of keV and K-alpha peaks of
the target material (8.12 and 8.8 keV for Cu). Typical temperatures of the distributions
are around 20 to 150 keV. The source size is measured by the knife edge technique and
is 10 µm diameter.
We describe how the characteristics of this X-ray source can be used to produce high
resolution images and how the online methods can be used to make phase contrast images.
The stability of the source allows to do phase contrast tomography which can determine
the real part of the index of refraction of materials. Finally, we compare different
synchrotrons, conventional microfocus and laser driven X-rays with respect to this
application to understand the opportunities of challenges of these new sources.
