Leora Dresselhaus-Cooper, Dmitro Martynowych, Alex Maznev, David Veysset.
The lab is located in NE47-580.
We are exploring alternate approaches to laser shock, in which the shock wave propagates laterally within a thin layer confined between solid walls. The confined layer is amply accessible for optical diagnostics enabling the direct visualization of shock waves. This approach is especially beneficial for studying cylindrically focused shock waves. We are developing a range of spectroscopic probes for studying not only shock wave propagation but also the material evolution under shock, including phase transitions, chemical reactions, and other shock-assisted effects.
Shock wave focusing in water
Direct real-time visualization of converging shock waves in a few micron-thick liquid layer was demonstrated in an all-optical experiment. The set-up includes an axicon that focuses an intense picosecond excitation pulse into a ring-shaped pattern in a water layer (see Fig. 1). Optical excitation induces a shock wave that propagates in the plane of the sample and converges toward the center resulting in cylindrical focusing of the shock front. Streak-camera images with a quasi-cw probe beam yield real-time records of the entire shock. Using a Mach-Zehnder interferometer and time-delayed femtosecond laser pulses, we obtain a series of images tracing the shock wave as it converges at the center of the ring before reemerging as a diverging shock, resulting in the formation of a cavitation bubble. Through quantitative analysis of the interferograms, density profiles of shocked samples are extracted (see Fig. 2, left). The experimental geometry used in our study opens prospects for spatially resolved spectroscopic studies of cavitation and (see Fig. 2, right) materials under shock compression.
Fig. 1. (a) Excitation pulse is focused into a ring in the plane of the water layer using an axicon-lens configuration. Interferometric imaging is performed in the Mach-Zehnder configuration using a variably delayed probe pulse. The probe pulse is split into two arms and recombined using two beamsplitters (BS). The sample plane is imaged onto a CCD camera using a two-lens telescope. Since a single probe pulse is used for imaging and the sample is permanently altered (with long lasting bubbles at the excitation ring) after each excitation laser shot, the sample has to be moved to an undisturbed area after every shot using a motorized stage. (b) Cutaway-view representation of the sample. After laser absorption by the carbon nano-particles, two counter-propagating shock waves are launched and remain confined in the plane of the sample.
Fig. 2. (left) Water density profiles extracted along a ring diameter for five delays between the excitation pulse and the probe pulse: 34.6 ns, 43.3 ns, 69.9 ns, 86.5 ns, and 94.7 ns. Rapid density jumps indicate shock fronts, with the arrows showing the propagation direction. The horizontal dashed line marks the undisturbed density of water at room temperature. The density drop at x = ± 95 µm is caused by bubble formation at the excitation ring location (a-e). A density dip at the center in (d-e) and (i-j) indicates the formation of a cavitation bubble. (right) Non-interferometric images recorded (a) at 150 ns, (b) 300 ns, (c) 500 ns and (d) at 5 s delay showing bubble cavitation following shock focusing.
More details regarding shock focusing can be found in:
Pezeril T, Saini G, Veysset D, Kooi S, Fidkowski P, et al. 2011. Direct visualization of laser-driven focusing shock waves. Phys. Rev. Lett. 106(21):2145031.
Veysset D, Pezeril T, Kooi S, Bulou A, Nelson KA. 2015. Laser-induced versus shock wave induced transformation of highly ordered pyrolytic graphite. Appl. Phys. Lett. 106(16):161902
Veysset D, Мaznev AA, Pezeril T, Kooi S, Nelson KA. 2016. Interferometric analysis of laser-driven cylindrically focusing shock waves in a thin liquid layer. Sci. Rep. 6(1):24
Laser-induced particle impact experiments
High velocity ballistic impact phenomena range in scale from catastrophic events such as impact of asteroids on planets to impact of micron– and sub–micron–sized particles, which, while attracting less public attention, plays a large role in many areas of science and technology. In space exploration, micrometeoroids present both an object for investigation and a hazard to spacecraft. In many earthly technologies microparticle impact often poses a problem by causing erosion, but can also be put to a good use, for example in powder blasting and cold spraying. In medicine and biology ballistic microparticles are used for needle–free gene and drug delivery. Despite the wide range of applications, the dynamics of microparticle impact remain unexplored. While macroscale projectile impact has been studied in real time using high–speed imaging techniques, investigations of microscale impact have been limited to post–mortem analysis of impacted samples.
We have devised a novel, bench-top technique, called laser-induced particle impact test (LIPIT), to investigate material responses to high strain rate deformation, as well as material behavior under high speed impact at the micron scale (see Fig. 3).
- Mono-disperse micro-particles are deposited on a laser-absorbing polymer-coated glass substrate (launch pad) to form a monolayer on top of it.
- Upon intense laser excitation, vaporization and the rapid expansion of gas causes acceleration of the particles to speeds up to 4 km/s.
- Sample response to impact is observed using a high-speed camera (>30 million fps) revealing dynamics of microparticle impact in real-time.
Fig. 3. Schematic representation of LIPIT. A picosecond laser pulse is focused on a launching pad on top of which micro-particles are deposited. Particles are accelerated upon laser ablation to supersonic speed (3 km/s).
Fig. 4. (a) Multi–frame sequences with 5 ns exposure time showing single–projectile impacts on (a) a protein-base hydrogel, (b) a poly(urethane urea) (PUU) elastomer, and (c) an aluminum substrate. (a) Impact of a silica sphere (7.4 um diameter) at 500 m/s followed by projectile penetration. (b) Impact of a silica sphere (7.4 um diameter) on PUU at 670 m/s followed by projectile rebound. (c) Impact of a aluminum particle (40 um diameter) at 800 m/s followed by particle adhesion.
The described method is applicable to a wide range of materials (see Fig. 4). The particle motion, deformation of the specimen and stress waves in the material can be imaged with a temporal resolution of 3 ns – or better if a femtosecond pulse sequence synchronized with the camera frame rate is used to illuminate the sample. The experimental tool will be capable of guiding the modeling effort and supporting the design of novel high-performance materials through direct experimental validation.
For more details regarding LIPIT experiments see:
Lee J-H, Veysset D, Singer JP, Retsch M, Saini G, et al. 2012. High strain rate deformation of layered nanocomposites. Nat. Commun. 3(May):1164
Veysset D, Hsieh AJ, Kooi S, Maznev AA, Masser KA, Nelson KA. 2016. Dynamics of supersonic microparticle impact on elastomers revealed by real–time multi–frame imaging. Sci. Rep. 6(April):25577
Hassani-Gangaraj M, Veysset D, Nelson KA, Schuh CA. 2016. Supersonic impact of metallic micro-particles. arXiv:1612.08081