Using a short pulse width x-ray source and measuring the time-of-flight of photons that scatter from an object under inspection allows for the point of interaction to be determined, and a profile of the object to be sampled along the path of the beam. A three dimensional image can be formed by interrogating the entire object. Using high energy x rays enables the inspection of cargo containers with steel walls, in the search for concealed items. A longer pulse width x-ray source can also be used with deconvolution techniques to determine the points of interaction. We present time-of-flight results from both short (picosecond) width and long (hundreds of nanoseconds) width x-ray sources, and show that the position of scatter can be localised with a resolution of 2 ns, equivalent to 30 cm, for a 3 cm thick plastic test object.
The beam of Free-Electron Laser in Hamburg (FLASH) tuned at either 32.5 nm or 13.7 nm was focused by a grazing
incidence elliptical mirror and an off-axis parabolic mirror coated by Si/Mo multilayer on 20-micron and 1-micron spot,
respectively. The grazing incidence and normal incidence focusing of ~10-fs pulses carrying an energy of 10 μJ lead at
the surface of various solids (Si, Al, Ti, Ta, Si3N4, BN, a-C/Si, Ni/Si, Cr/Si, Rh/Si, Ce:YAG, poly(methyl methacrylate)
- PMMA, stainless steel, etc.) to an irradiance of 1013 W/cm2 and 1016 W/cm2, respectively. The optical emission of the
plasmas produced under these conditions was registered by grating (1200 lines/mm and/or 150 lines/mm) spectrometer
MS257 (Oriel) equipped with iCCD head (iStar 720, Andor). Surprisingly, only lines belonging to the neutral atoms
were observed at intensities around 1013 W/cm2. No lines of atomic ions have been identified in UV-vis spectra emitted
from the plasmas formed by the FLASH beam focused in a 20-micron spot. At intensities around 1016 W/cm2, the OE
spectra are again dominated by the atomic lines. However, a weak emission of Al+ and Al2+ was registered as well. The
abundance ratio of Al/Al+ should be at least 100. The plasma is really cold, an excitation temperature equivalent to 0.8 eV was found by a computer simulation of the aluminum plasma OE spectrum. A broadband emission was also
registered, both from the plasmas (typical is for carbon; there were no spectral lines) and the scintillators (on Ce:YAG
crystal, both the luminescence bands and the line plasma emission were recorded by the spectrometer).
Measurements taken in 2006 using Daresbury Laboratory's long trace profiler on the BESSY P1 'round robin' mirror
highlighted a high level of background noise, believed to be principally from a combination of thermal and vibration
sources. In addition, long-term thermal drifts within the instrument enclosure negated the benefit of multiple passes for
averaging purposes. Further static stability tests on the LPT−V demonstrated noise levels on the slope measurement to
be of the order of 0.5 μrad rms over an hour long period. We will demonstrate how the addition of a secondary
instrument enclosure has reduced the background noise level in comparison tests to less than 0.1 μrad rms. We will detail
the design of new granite supports for the translation beam and reference mirror, which are intended to minimise sources
of vibration. Information will be provided regarding the replacement of the CCD detector/filter assembly and we will
outline some proposed future developments.
The proposed 4GLS is a suite of temporally synchronised accelerator based light sources, including a low-Q cavity free
electron laser operating in the energy range 3 - 10 eV (the VUV-FEL), a seeded XUV-FEL designed to operate in the
range 8 - 100 eV, an infra-red cavity FEL (the IR-FEL), as well as spontaneous radiation sources. The output from these
sources is summarized. With respect to radiation damage, the two main areas of concern are the high average power
from the VUV-FEL and the high peak power from the XUV-FEL. The suitability of different materials for the cavity
mirror for the VUV-FEL and beamline optics is investigated. Beamline design strategies to militate against radiation
damage are described and an example of a high throughput beamline in the XUV-FEL is given. The need for accurate
optical constants in the VUV region, as well as damage threshold measurements, is highlighted and we outline a program
of experimental measurements to be undertaken in the near future.