Ultrafast observation of multiple shock waves evolution and interaction processes in femtosecond laser processing

Dynamics of regular polygonal shock waves (SWs), generated at thin wire explosion, with a closed surface front and numbers of sides n = 3, 4, 5, 6, 8, 10, 12, and 16 in the plane of polygons is experimentally studied. Depending on the initial Mach number MPSW0 of such waves and the number n, two convergence modes are implemented: convergence with and without changes in the number of sides n. It is shown that the shape of the reflected wave front differs from the shape of the converging SW front for polygonal SWs with n ≥ 8, i.e., it becomes smooth. The number MPSW0 is determined depending on initial characteristics of an SW generator and gas. A significant amplification of such SWs with n ≥ 12 is observed near to the center of polygons; their maximum amplification is estimated.

The behavior of sinusoidally-rippled shock fronts is a fundamental research topic in the dynamics of shock waves [1]. The Whitham’s ray-shock theory, which is sometimes called the geometrical-shock-dynamics (GSD) theory, is known as a simple method for analyzing the behavior of a non-planar shock front. In this theory, narrow ray tubes corresponding to the light rays in the geometrical optics are placed perpendicularly to the every portions of a non-planar shock front, and the evolution of the shock front is calculated by tracking the shock front in each ray tube sequentially. When the behavior of an inert sinusoidally-rippled shock front is analyzed by the GSD theory and the Chester-Chisnell-Whitham’s (CCW’s) A-M relationship [2], where A is the cross-sectional area of a ray tube and M is the propagation Mach number of the shock wave in the ray tube, the amplitude of the shock-front ripple oscillates as the shock wave propagates [3]. Actually, the behavior of an inert sinusoidally-rippled shock front is influenced by the fluid motion in the shock-compressed region, and the amplitude of the shock-front ripple shows damped oscillation as the shock wave propagates [1,3,4,5].

The results of computer blast-hole experiments with copper wire electro-explosion in the polyethylene-concrete media has been analyzed with shock and pressure wave dynamics depending on the spatiotemporal distribution of electrical power deposition in plasma channel. Pressure and stress-wave dynamics of tensely-deformed material state has been analysed by means of physical and mathematical model, which consistently describes the operation of the discharge circuit, plasma channel expansion, generation and propagation of the shock and pressure waves in the condensed media1. It has been shown the significant dependence of the stress-wave profile on the pressure pulse wave shape on the borehole wall which is determined by the rate of electrical energy release in the plasma channel and is weakly depended on the time of energy release (at given rate of its release). Analysis of stress-wave dynamics have been shown that the rapid power deposition results to the higher amplitude of compressive stresses in the wave. The lower energy deposition rate in plasma channel leads to the higher amplitude of tensile stresses both in radial and tangential direction.

The synchronization of laser and X-ray sources is essential for time-resolved measurements in the study of ultrafast processes, including photo-induced piezo-effects, shock wave generation, and phase transitions. On the one hand, optical diagnostics (by synchronization of two laser sources) provides information about changes in vibration frequencies, shock wave dynamics, and linear and nonlinear refractive index behavior. On the other hand, optical pump–X-ray probe diagnostics provide an opportunity to directly reveal lattice dynamics. To integrate two approaches into a unified whole, one needs to create a robust method for the synchronization of two systems with different repetition rates up to the MHz range. In this paper, we propose a universal approach utilizing a field-programmable gate array (FPGA) to achieve precise synchronization between different MHz sources such as various lasers and synchrotron X-ray sources. This synchronization method offers numerous advantages, such as high flexibility, fast response, and low jitter. Experimental results demonstrate the successful synchronization of two different MHz systems with a temporal resolution of 250 ps. This enables ultrafast measurements with a sub-nanosecond resolution, facilitating the uncovering of complex dynamics in ultrafast processes.

In this four-year project (including one-year extension), the project director and his research team built a shock-wave-plasma apparatus to study shock wave dynamics in glow discharge plasmas in nitrogen and argon at medium pressure (1–20 Torr), carried out various plasma and shock diagnostics and measurements that lead to increased understanding of the shock wave acceleration phenomena in plasmas. The measurements clearly show that in the steady-state dc glow discharge plasma, at fixed gas pressure the shock wave velocity increases, its amplitude decreases, and the shock wave disperses non-linearly as a function of the plasma current. In the pulsed discharge plasma, at fixed gas pressure the shock wave dispersion width and velocity increase as a function of the delay between the switch-on of the plasma and shock-launch. In the afterglow plasma, at fixed gas pressure the shock wave dispersion width and velocity decrease as a function of the delay between the plasma switch-off and shock-launch. These changes are found to be opposite and reversing towards the room temperature value which is the initial condition for plasma ignition case. The observed shock wave properties in both igniting and afterglow plasmas correlate well with the inferred temperature changes in the two plasmas.

Experimental study on the ice suppression characteristics of TC4 microstructure surface induced by femtosecond pulsed laser

MP29-06 A NEW SURGICAL TECHNOLOGY WITH FEMTOSECOND LASERS TOWARDS NO THERMAL INJURY IN ENDOSCOPIC SURGERY

Pulse volume discharge behind shock wave in channel flow with obstacle

Dispersive shock waves dominate wave-breaking phenomena in Hamiltonian systems. In the absence of loss, these highly irregular and disordered waves are potentially reversible. However, no experimental evidence has been given about the possibility of inverting the dynamics of a dispersive shock wave and turn it into a regular wave-front. Nevertheless, the opposite scenario, i.e., a smooth wave generating turbulent dynamics is well studied and observed in experiments. Here we introduce a new theoretical formulation for the dynamics in a highly nonlocal and defocusing medium described by the nonlinear Schroedinger equation. Our theory unveils a mechanism that enhances the degree of irreversibility. This mechanism explains why a dispersive shock cannot be reversed in evolution even for an arbitrarirly small amount of loss. Our theory is based on the concept of nonlinear Gamow vectors, i.e., power dependent generalizations of the counter-intuitive and hereto elusive exponentially decaying states in Hamiltonian systems. We theoretically show that nonlinear Gamow vectors play a fundamental role in nonlinear Schroedinger models: they may be used as a generalized basis for describing the dynamics of the shock waves, and affect the degree of irreversibility of wave-breaking phenomena. Gamow vectors allow to analytically calculate the amount of breaking of time-reversal with a quantitative agreement with numerical solutions. We also show that a nonlocal nonlinear optical medium may act as a simulator for the experimental investigation of quantum irreversible models, as the reversed harmonic oscillator.

Numerical and experimental investigations on the jet and shock wave dynamics during the cavitation bubble collapsing near spherical particles based on OpenFOAM

In this study, we employ femtosecond pump–probe transmission microscopy and complex Nomarski interferometry to investigate the ultrafast dynamics of laser-induced plasma and shock waves in bulk fused silica subjected to high laser intensities. It was found that the plasma channel, in its development, takes on a columnar shape with minimal variations during the early expansion stage between 130 and 200 ps. However, after 200 ps, the cylindrical shock wave commenced its departure from the plasma channel and gradually expanded outward along the radial direction. An electron density in the evolving plasma channel approached a level of ∼ 1.9 ∗ 10 20 cm − 3 , at a delay time of 50 ps. The resulting change in refractive index caused by electronic plasma was 0.05, while the reflectivity of the probe beam was ≈0.03 % . The blast wave model described the plasma and cylindrical shock wave expansion. A pressure of 65 GPa and a plasma temperature of a few eV were registered at a delay time of 150 ps. The resulting extreme conditions mapped to the cross-section analysis of the void and shock wave-affected area reveal polycrystalline structures near the periphery of the cavity at the geometrical focus. The areas more distant from the focus tend to show an amorphous character. These findings enrich the interpretation of femtosecond laser–dielectric interactions, with significant implications for micromachining, optical data storage, and the advancement of photonic device technologies.

Results are presented of a numerical solution of the Korteweg-de Vries-Burgers equation that describes the propagation and establishment process for a stationary structure to a shock wave in a gas-liquid medium. Data are obtained on the time for the establishment of a stationary structure of a shock wave, propagation velocity, and amplitude oscillations in the front of the shock wave. Experiments are discussed on the basis of the results obtained for the study of shock waves in a liquid containing gas bubbles.

Experimental studies on shock wave and particle dynamics in a needle-free drug delivery device

Physics of meteor generated shock waves in the Earth’s atmosphere – A review

Femtosecond laser processing has been widely applied in glass processing owing to its ability to fabricate microscale components. To improve processing efficiency, a transient and selective laser (TSL) processing technique was previously developed, in which electron excitation was induced inside a transparent medium by a single pulse of femtosecond (fs) laser, and a single pulse of microsecond (µs) laser can be selectively absorbed in this excited region to heat and remove the material. However, because of its high speed removal process, the unclear mechanism and inefficient evaluation of its processing performance limit its further application. This study analyzes the transient spatiotemporal evolution of the induced plasma and the related material removal mechanism of the TSL processing using a side high-speed monitoring method. To achieve a rapid performance evaluation, a quantitative analysis of the optical plasma signals (on a microsecond timescale) generated in TSL processing was performed by employing a developed coaxial high-speed monitoring method using a photodetector. The variations in the shapes, intensity distribution, and dimensions of the plasma were quantitatively investigated. In addition, the relation between the plasma signal and drilling performance under different laser parameters, including hole depth, hole types, and cracks, was explored and quantitatively analyzed. The revealed mechanism is expected to contribute to the broadening of the application of TSL processing in microfabrication. Furthermore, the developed high-speed and precision monitoring technology can be utilized for high-speed evaluation and precision control of machining quality in real time during ultrahigh-speed laser machining, without time-consuming camera observations.