Laser-driven flyer plates for shock compression science: Launch and target impact probed by photon Doppler velocimetry

Abstract

We investigated the launch and target impact of laser-driven Al flyer plates using photon Doppler velocimetry (PDV). We studied different flyer designs launched by laser pulses of different energies, pulse durations and beam diameters, that produced km s(-1) impacts with transparent target materials. Laser-launching Al flyers 25-100 μm thick cemented to glass substrates is usually thought to involve laser vaporization of a portion of the flyer, which creates many difficulties associated with loss of integrity and heating of the flyer material. However, in the system used here, the launch mechanism was surprising and unexpected: it involved optical damage at the glass/cement/flyer interface, with very little laser light reaching the flyer itself. In fact the flyers launched in this manner behaved almost identically to multilayer flyers that were optically shielded from the laser pulses and insulated from heat generated by the pulses. Launching flyers with nanosecond laser pulses creates undesirable reverberating shocks in the flyer. In some cases, with 10 ns launch pulses, the thickest flyers were observed to lose integrity. But with stretched 20 ns pulses, we showed that the reverberations damped out prior to impact with targets, and that the flyers maintained their integrity during flight. Flyer impacts with salt, glass, fused silica, and acrylic polymer were studied by PDV, and the durations of fully supported shocks in those media were determined, and could be varied from 5 to 23 ns.

Exploration of CdTe quantum dots as mesoscale pressure sensors via time-resolved shock-compression photoluminescent emission spectroscopy

“…An all-reflective beam stretcher was used to stretch the nominal 10 ns laser pulse to 20 ns full-width half-maximum. 20 The PDV and spectroscopic measurements probed smaller regions of 0.07 mm and 0.2 mm in diameter, respectively, at the center of the uniform launch pulse. 18 The QD photoluminescent emission was excited by 250 ns FWHM pulses from a Q-switched 527 nm Nd:YLF laser (Quantronix 527 DP) and recorded with 0.5 ns effective time per CCD pixel using a streak camera.…”

Shock compression dynamics under a microscope

“…Our simplified flyer system, characterized by extensive PDV studies, has been described in detail previously [1,2]. We have overcome most of the problems mentioned above using a commercial one-box Q-switched Nd:YAG laser (Quanta-Ray Pro 350-10), a diffractive beam homogenizer, a pulse stretcher [8], and a different launch mechanism [2].…”

“…We have overcome most of the problems mentioned above using a commercial one-box Q-switched Nd:YAG laser (Quanta-Ray Pro 350-10), a diffractive beam homogenizer, a pulse stretcher [8], and a different launch mechanism [2]. In our apparatus, most of the laser pulse is absorbed at the foil/epoxy/glass interface of a glass substrate, producing a shock in the glass that launches a cold flyer with a thin layer of epoxy.…”

“…We have also launched Cu and other metal foils, but Al is our workhorse. shows sample PDV traces for the launch of a 0.7 mm diameter x 50 m thick Al flyer onto a glass witness plate [1,2]. Figure 4a was computed using short-time Fourier transform [2,9].…”

“…Our laboratory has developed a tabletop laser miniflyer launcher [1,2] that can be used for a variety of studies in physical and chemical sciences. A microgram quantity of sample sits at the focus of a microscope objective that transmits the photon Doppler velocimeter (PDV) online flyer plate diagnostic to the sample and transmits and receives probe light from the shocked sample.…”