Fast pulsed cluster jet

Abstract

Summary form only given. Short burst, ultrafast laser pulses interact intensely with matter to generate beams of secondary radiation such as coherent x-rays via high harmonic generation, electron bunches via laser wakefield acceleration, and protons via laser-driven ion acceleration. These secondary radiation sources have applications in biological imaging, medical diagnostics and treatment, and nondestructive evaluation. The emerging field of laser-plasma acceleration (LPA) has demonstrated electron accelerators with unprecedented electric field gradients. Supersonic, highly collimated gas jets and gas-filled capillary discharge waveguides are two primary targets of choice for LPA. A new LPA accelerated beam energy record of >2 GeV has been recorded using the Texas Petawatt laser (150 J) focused into a 7 cm He gas cell. The electron beams were highly-collimated (<;1 mrad divergence), containing high charge (>1 nC), and had a broad energy spectrum (peaked at ~2 GeV, with electrons up to 2.4 GeV). A fast opening and closing gas valve is essential to a LPA. This paper describes a fast valve (developed under a DOE SBIR grant) that opens in <;100μs, closes in <;400μs and can run (in cooled mode) at ~10Hz rep-rates at pressures as high as 1000psia. Recently we have designed advanced versions of the nozzle to create ~10-15mm long supersonic gas jets with tailored density gradients to test the concept of phase locking in an LPA. Dense gas jets with high concentrations of clusters are also of interest for such ultra-fast laser interactions. Development of a dense cluster jet using our ultra-fast opening/closing valve is also described.