A compact all-fiber displacement interferometer for measuring the foil velocity driven by laser

Propellants Explo Pyrotec

Dlott

Williams

et al. 2014

Nanocomposite 8Al ⋅ MoO3 thermite particles were prepared using arrested reactive milling and ignited using two experimental techniques. In spark ignition, a monolayer of powder was placed on a conductive substrate and heated in air by a pulsed electrostatic discharge. In shock ignition, an individual particle was targeted by a miniature, laser‐driven flyer plate accelerated to a speed in the range of 0.5–2 km s−1. In both experiments, time‐dependent optical emission produced by the ignited material was monitored and recorded. The heating rates achieved in the present experiments are on the order of 109−–1011 K s−1. These ignition methods result in a very fast combustion with characteristic burn times reduced by 1–3 orders of magnitude compared to the burn times measured previously for the same material ignited in the CO2 laser beam, where it was heated at a much lower rate of about 106−–107 K s−1. Ignition delays observed in both shock and spark ignition experiments are close to each other and vary in the range of 120–200 ns. The times of characteristic rapid increase in the optical emission of the ignited particles are also close to each other for the two experiments; however, these times are somewhat shorter (less than one μs) for the spark ignition tests compared to few μs observed for the shock initiated particles. Preliminary ideas enabling one to interpret the present results are discussed. This work establishes an approach for systematic studies of high rate ignition and respective combustion of nanocomposite reactive materials.

Section: Apparatusmentioning

confidence: 99%

Ignition of Nanocomposite Thermites by Electric Spark and Shock Wave

Propellants Explo Pyrotec

Dlott

Williams

et al. 2014

“…6 The term "simplified" was applied because the system used a commercial one-box launch laser and a flyer launch assembly with minimal complexity, so that 100 or more shock experiments could be accomplished in one day. In this report, we investigate flyer launch and target impact processes using high-speed optical interferometry (photon Doppler velocimetry, PDV) 5,6,[8][9][10][11][12] to study different flyer launch designs with laser pulses of different energies, pulse durations and beam diameters, that impacted different transparent target materials.…”

Section: Introductionmentioning

confidence: 99%

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

Curtis

Банишев

Review of Scientific Instruments

et al. 2014

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.

“…Here we combined ultrafast stroboscopic microscopy, using a femtosecond white-light supercontinuum strobe, with photon Doppler velocimetry (PDV) [16][17][18] to study the impacts of 0.5 mm diameter km s -1 laserlaunched Al and Cu flyer plates with flat transparent glass targets. PDV uses a high-speed laser interferometer, where the flyer plate forms one arm of the interferometer and the flyer velocity history is derived from the time-dependent interferogram [16][17][18][19]. In previous works [17,18], we investigated the laser launching and target impact processes with PDV, using Al flyers that were about 0.5 mm in diameter and 25-75 lm thick.…”

Section: Introductionmentioning

confidence: 99%

High-Speed Laser-Launched Flyer Impacts Studied with Ultrafast Photography and Velocimetry

Банишев

J. dynamic behavior mater.

Bassett

et al. 2016

Pulsed lasers can launch thin metal foils at km s -1, but for precision measurements in shock compression science and shock wave spectroscopy, where onedimensional shock compression is vital, flyer plate impacts with targets must have a high degree of flatness and minimal tilt, and the flyer speeds and impact times at the target must be highly reproducible. We have developed an apparatus that combines ultrafast stroboscopic optical microscopy with photon Doppler velocimetry to study impacts of laser-launched Al and Cu flyer plates with flat, transparent glass targets. The flyer plates were 0.5 mm in diameter, and ranged from 12 to 100 lm thick, with flyer speeds up to 6.25 km s -1 . The velocity variations over 30-60 launches from the same flyer plate optic can be as low as 0.6 %, and the impact time variations can be as low as 0.8 ns. Stroboscopic image streams (reconstructed movies) show uniform, flat impacts with a glass target. These stroboscopic images can be used to estimate the tilt in the flyer-target impact to be \1mrad.