Laser–solid interactions are highly suited as a potential source of high energy X-rays for nondestructive imaging. A bright, energetic X-ray pulse can be driven from a small source, making it ideal for high resolution X-ray radiography. By limiting the lateral dimensions of the target we are able to confine the region over which X-rays are produced, enabling imaging with enhanced resolution and contrast. Using constrained targets we demonstrate experimentally a $(20\pm 3)~\unicode[STIX]{x03BC}\text{m}$ X-ray source, improving the image quality compared to unconstrained foil targets. Modelling demonstrates that a larger sheath field envelope around the perimeter of the constrained targets increases the proportion of electron current that recirculates through the target, driving a brighter source of X-rays.

a b s t r a c tUltrafast pulsed laser ablation has been investigated as a technique to machine CdWO 4 single crystal scintillator and segment it into small blocks with the aim of fabricating a 2D high energy X-ray imaging array. Cadmium tungstate (CdWO 4 ) is a brittle transparent scintillator used for the detection of high energy X-rays and γ-rays. A 6 W Yb:KGW Pharos-SP pulsed laser of wavelength 1028 nm was used with a tuneable pulse duration of 10 ps to 190 fs, repetition rate of up to 600 kHz and pulse energies of up to 1 mJ was employed. The effect of varying the pulse duration, pulse energy, pulse overlap and scan pattern on the laser induced damage to the crystals was investigated. A pulse duration of Z 500 fs was found to induce substantial cracking in the material. The laser induced damage was minimised using the following operating parameters: a pulse duration of 190 fs, fluence of 15.3 J cm À 2 and employing a serpentine scan pattern with a normalised pulse overlap of 0.8. The surface of the ablated surfaces was studied using scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy. Ablation products were found to contain cadmium tungstate together with different cadmium and tungsten oxides. These laser ablation products could be removed using an ammonium hydroxide treatment.

The radiation hardness of the 6 Li loaded scintillator CLYC(Ce) to X-rays was investigated. Two crystals were studied; one crystal was irradiated with X-rays and one was kept as a control and only exposed to a moderated 241 Am-Be source. The control crystal was used as a reference sample for photoluminescence excitation and emission measurements. The exposed crystal was given two doses of X-rays, the first was 2.3 Gy and the second was 118.2 Gy after a 22 week annealing period. The total dose was 120.5 Gy and was found to significantly reduce the light yield of the crystal. Pulse height spectra from the moderated 241 Am-Be taken with the irradiated crystal showed a 54% decrease in pulse height and a broadening of the FHWM of the peak from 14.6 % to 44.2%. Analysis of the pulse shapes showed no change to the median decay time to 37% of the scintillator, with values of ~350 ns for the irradiated and control crystal. Photoluminescence excitation and emission measurements revealed a reduction in the relative intensity of the main Ce 3+ emission with respect to the self-trapped exciton luminescence. This indicated a modification to the Ce 3+ luminescence center. There was little recovery at room temperature over the course of 22 weeks after the first irradiation. The irradiated crystal was also found to display significant room temperature luminescence after X-ray irradiation with it being measurable up to 120 minutes after the X-ray irradiation.