On the effect of pitch and yaw angles in oblique impacts of smallcaliber projectiles

A terminal ballistic analysis of the effects of 7.62 mm × 51 AP P80 rounds on inclined high-strength armor steel plates is the focus of the presented study.The findings of an instrumented ballistic testing combined with 3D advanced numerical simulations performed using the IMPETUS Afea? software yielded the conclusions.The experimental verification proved that slight differences in the pitch-andyaw angles of a projectile upon an impact caused different damage types to the projectile’s core.The residual velocities predicted numerically were close to the experimental values and the calculated core deviations were in satisfactory agreement with the experimental results.An extended matrix of the core deviation angles with combinations of pitch-and-yaw upon impact angles was subsequently built on the basis of the numerical study.The presented experimental and numerical investigation examined thoroughly the influence of the initial pitch and yaw angles on the after-perforation projectile’s performance.

Measurements of the ablation-front trajectory and low-mode nonuniformity in direct-drive implosions using x-ray self-emission shadowgraphy

Self-emission x-ray shadowgraphy provides a method to measure the ablation-front trajectory and low-mode nonuniformity of a target imploded by directly illuminating a fusion capsule with laser beams. The technique uses time-resolved images of soft x-rays(>1 ke V) emitted from the coronal plasma of the target imaged onto an x-ray framing camera to determine the position of the ablation front. Methods used to accurately measure the ablation-front radius(δ R= ±1.15 μm), image-to-image timing(δ( t)= ±2.5 ps) and absolute timing(δt= ±10 ps) are presented.Angular averaging of the images provides an average radius measurement of δ( Rav)= ±0.15 μm and an error in velocity of δV / V= ±3%. This technique was applied on the Omega Laser Facility [Boehly et al., Opt. Commun. 133, 495(1997)] and the National Ignition Facility [Campbell and Hogan, Plasma Phys. Control. Fusion 41, B39(1999)].

Plasma and nanoparticle shielding during pulsed laser ablation in liquids cause ablation efficiency decrease

Understanding shielding cross-effects is a prerequisite for maximal power-specific nanosecond laser ablation in liquids(LAL).However,discrimination between cavitation bubble(CB),nanoparticle(NP),and shielding,e.g.,by the plasma or a transient vapor layer,is challenging.Therefore,CB imaging by shadowgraphy is performed to better understand the plasma and laser beam-NP interaction during LAL.By comparing the fluence-dependent CB volume for ablations performed with 1 ns pulses with reports from the literature,we find larger energy-specific CB volumes for 7 ns-ablation.The increased CB for laser ablation with higher ns pulse durations could be a first explanation of the efficiency decrease reported for these laser systems having higher pulse durations.Consequently,1 ns-LAL shows superior ablation efficiency.Moreover,a CB cascade occurs when the focal plane is shifted into the liquid.This effect is enhanced when NPs are present in the fluid.Even minute amounts of NPs trapped in a stationary layer decrease the laser energy significantly,even under liquid flow.However,this local concentration in the sticking film has so far not been considered.It presents an essential obstacle in high-yield LAL,shielding already the second laser pulse that arrives and presenting a source of satellite bubbles.Hence,measures to lower the NP concentration on the target must be investigated in the future.

Ultrafast dynamics observation during femtosecond laser-material interaction

Femtosecond laser technology has attracted significant attention from the viewpoints of fundamental and application;especially femtosecond laser processing materials present the unique mechanism of laser-material interaction.Under the extreme nonequilibrium conditions imposed by femtosecond laser irradiation,many fundamental questions concerning the physical origin of the material removal process remain unanswered.In this review,cutting-edge ultrafast dynamic observation techniques for investigating the fundamental questions,including timeresolved pump-probe shadowgraphy,ultrafast continuous optical imaging,and four-dimensional ultrafast scanning electron microscopy,are comprehensively surveyed.Each technique is described in depth,beginning with its basic principle,followed by a description of its representative applications in laser-material interaction and its strengths and limitations.The consideration of temporal and spatial resolutions and panoramic measurement at different scales are two major challenges.Hence,the prospects for technical advancement in this field are discussed finally.

Shadowgraphic Imaging of Fibre-Delivered Pulsed IR Laser-Induced Heat Transfer across Thin Aluminized Polymer Film

Shadowgraphic imaging was employed to investigate the mid-IR laser induced heat transfer through a double layer thin film. The effect of thin metal coat on the polymer film enhanced the transfer of heat and shock waves due to rapid thermal expansion and the explosive evaporation of the thin fluid layer. Sixty two percent of deposited heat expended for water enthalpy and 38% for other factors. A power of 8.8 kW was launched at the surface of aluminium. The thermal coupling of 45% further reduced the input energy to the film and the non-adiabatic heat diffusion (i.e., ) was transmitted instantaneously within the metal with very small loss. The temperature at the surface of the film was determined ≈301 K, well below the aluminium melting point. The Biot number showed that the metal as single layer and the whole film as double layer satisfies the thermally thin film (i.e., ). Considering the Newtons’s law of cooling, the overall film heat transfer coefficient was found 3 k W·m-2·K-1 equivalent of 3.3 × 10-3 W·m2·K-1 thermal resistance. The analysis of images indicated a reducing percentage of heat transfer as a function of delay time based on the comparison of volume ratios. A calculated power of ≈3 kW was transmitted from the rear side of the film sufficient to thermalize the surrounding water layer and form vapor bubble.

Synchronized off-harmonic probe laser with highly variable pulse duration for laser-plasma interaction experiments

This paper presents the development and experimental utilization of a synchronized off-harmonic laser system designed as a probe for ultra-intense laser±plasma interaction experiments. The system exhibits a novel seed-generation design,allowing for a variable pulse duration spanning over more than three orders of magnitude, from 3.45 picoseconds to 10 nanoseconds. This makes it suitable for various plasma diagnostics and visualization techniques. In a side-view configuration, the laser was employed for interferometry and streaked shadowgraphy of a laser-induced plasma while successfully suppressing the self-emission background of the laser±plasma interaction, resulting in a signal-to-self-emission ratio of 110 for this setup. These properties enable the probe to yield valuable insights into the plasma dynamics and interactions at the PHELIX facility and to be deployed at various laser facilities due to its easy-to-implement design.

A High-speed Nature Laminar Flow Airfoil and Its Experimental Study in Wind Tunnel with Nonintrusive Measurement Technique

This article deals with an experimental study on the aerodynamic characteristics of a low-drag high-speed nature laminar flow (NLF) airfoil for business airplanes in the TST27 wind tunnel at Delft University of Technology, the Netherlands. In this experiment, in an attempt to reduce the errors of measurement and improve its accuracy in high-speed flight, some nonintrusive meas- urement techniques, such as the quantitative infrared thermography (IRT), the digital particle imaging velocimetry (PIV), and the s...

Enhancing precision in fs-laser material processing by simultaneous spatial and temporal focusing

In recent years,femtosecond(fs)-lasers have evolved into a versatile tool for high precision micromachining of transparent materials because nonlinear absorption in the focus can result in refractive index modifications or material disruptions.However,when high pulse energies or low numerical apertures are required,nonlinear side effects such as self-focusing,filamentation or white light generation can decrease the modification quality.In this paper,we apply simultaneous spatial and temporal focusing(SSTF)to overcome these limitations.The main advantage of SSTF is that the ultrashort pulse is only formed at the focal plane,thereby confining the intensity distribution strongly to the focal volume and suppressing detrimental nonlinear side effects.Thus,we investigate the optical breakdown within a water cell by pump-probe shadowgraphy,comparing conventional focusing and SSTF under equivalent focusing conditions.The plasma formation is well confined for low pulse energies,2 mJ,but higher pulse energies lead to the filamentation and break-up of the disruptions for conventional focusing,thereby decreasing the modification quality.In contrast,plasma induced by SSTF stays well confined to the focal plane,even for high pulse energies up to 8 mJ,preventing extended filaments,side branches or break-up of the disruptions.Furthermore,while conventional focusing leads to broadband supercontinuum generation,only marginal spectral broadening is observed using SSTF.These experimental findings are in excellent agreement with numerical simulations of the nonlinear pulse propagation and interaction processes.Therefore,SSTF appears to be a powerful tool to control the processing of transparent materials,e.g.,for precise ophthalmic fs-surgery.

INVESTIGATION ON INHOMOGENEOUS STRUCTURES IN LASER-PRODUCED PLASMA

The optical shadowgraphy has been used to investigate the inhomogeneous structures in laser-produced plasmas, especially the small-scale jet structure on the rearside of the A1 foil target due to hydrodynamic instability.