Fabrication of 3-μm diameter pin hole array (PHA) on thick W substrates

Pin-hole arrays are used for a variety of applications including, for example, X-ray imaging of laser-plasmas for fusion relevant studies [1]. More recently, a novel X-ray imaging technique has been proposed (this conference L.A. Gizzi et al.) within the High Power Laser Energy Research Facility (HiPER) to obtain spectrally resolved X-ray imaging [2] using single photon detection [3]. This technique requires a large number of images or, alternatively, large arrays of pin-holes, possibly with very small diameter («10 μm) [4]. In view of this, a technique was implemented for the fabrication of large arrays of pin-holes in thick metal substrates. Here we report on the optimizations of the laser-matter interaction process to obtain high aspect ratio cylinder-like pin-hole on heavy metal substrate by using a frequency-doubled Ti:Sa femtosecond laser pulses operating at 10Hz. The influence of an air breakdown and a (ns)prepulse, on the drilled pin-hole, is showed by means of SEM images both for surface effects and internal quality of the channels, with evidence of micro and nano-sized structures. The holes drilled at an intensity just below the laser breakdown threshold for plasma creation in air, have an internal diameter of about 3 μm on a W substrate of 70 μm thickness, a micro-cylinder-like shape and no detectable deviations of the axis from a straight line. Arrays of up to 800 pin-holes were produced with the pin-hole properties being highly stable across the array. The final X-ray transmission is showed by using a μ-focus X-ray source.