Interaction Of Nanosecond Laser Pulses Research Articles

A computational study on the optical shaping of gas targets via blast wave collisions for magnetic vortex acceleration

Abstract This research work emphasizes the capability of delivering optically shaped targets through the interaction of nanosecond laser pulses with high-density gas-jet profiles, and explores proton acceleration in the near-critical density regime via magnetic vortex acceleration (MVA). Multiple blast waves (BWs) are generated by laser pulses that compress the gas-jet into near-critical steep gradient slabs of a few micrometres thickness. Geometrical alternatives for delivering the laser pulses into the gas target are explored to efficiently control the characteristics of the density profile. The shock front collisions of the generated BWs are computationally studied by 3D magnetohydrodynamic simulations. The efficiency of the proposed target shaping method for MVA is demonstrated for TW-class lasers by a particle-in-cell simulation.

Metal microspheres propelled by shock wave based on the fiber structure laser propulsion

An intriguing method of propelling stainless steel (SS, metallic) microsphere by employing the nanosecond laser pulses output from the end face of the fiber was demonstrated, in order to investigate the interaction of nanosecond laser pulses with metal microsphere. Using a two-dimensional model of the shock wave acting on the metal microsphere, the propagation characteristics of shock wave such as propagation distance and pressure have been calculated. Experimentally, we observed that the propulsion efficiency is dependent on the laser pulse energy and the gap distance. The momentum coupling coefficient and the energy coupling efficiency of SS microsphere were analyzed, which showed that metal microsphere has the high propulsion efficiency. In addition, an experiment was performed to remove the SS contamination particles on the surface of the microstructure. Compared with conventional technology, this new method has advantages of high controllability, directional and non-contact, and can be used for the removal of metal pollution particles and the manipulation of metal micromachines.

Shielding effects in interaction of nanosecond laser pulses with solid target

We present experimental study of radiation absorption in copper plasma created by Nd:YAG laser fundamental (1064nm) harmonic. Absorption is recorded by monitoring attenuation of HeNe laser (633nm) illuminating plasma side on. Assuming that inverse bremsstrahlung is dominant process, absorbtion of the Nd:YAG 1064nm wavelength is evaluated relying on measurements conducted at 633nm specific for He–Ne laser and using common analytical expressions. Radial profile of the absorption, the absorption coefficient, is deduced applying inverse Abel transform. The absorption is measured for several distances from the copper target and for various delays at each position. This procedure is repeated for three different energies of 1064nm wavelength. It is shown that for high laser energies in IR domain absorption of radiation in the plasma is, within accuracy of the experiment, close to 92% while for lower energies considerable amount of the laser energy reaches the target surface. The absorption of the plasma attains its maximal value after the maximum of the laser power and remains at this value for couple of nanoseconds after the laser pulse ceases. It is also found that total energy absorbed by the plasma depends linearly on total incident energy in the investigated range of energy.

Optical coherence tomography (OCT) with 2\u2009nm axial resolution using a compact laser plasma soft X-ray source

We present optical coherence tomography (OCT) with 2 nm axial resolution using broadband soft X-ray radiation (SXR) from a compact laser plasma light source. The laser plasma was formed by the interaction of nanosecond laser pulses with a gaseous target in a double stream gas puff target approach. The source was optimized for efficient SXR emission from the krypton/helium gas puff target in the 2 to 5 nm spectral range, encompassing the entire “water-window” spectral range from 2.3 nm to 4.4 nm wavelength. The coherence parameters of the SXR radiation allowed for the OCT measurements of a bulk multilayer structure with 10 nm period and 40% bottom layer thickness to period ratio, with an axial resolution of about 2 nm and detect multilayer interfaces up to a depth of about 100 nm. The experimental data are in agreement with OCT simulations performed on ideal multilayer structure. In the paper, detailed information about the source, its optimization, the optical system, OCT measurements and the results are presented and discussed.

2-D elemental mapping of an extreme ultraviolet-irradiated PET with a compact near edge X-ray fine structure spectromicroscopy

We present a near edge X-ray fine structure (NEXAFS) spectromicroscopy, that was developed based on a compact laboratory laser-plasma soft X-ray light source. The presented approach to spectromicroscopy is different from the usual synchrotron-based one when the series of full-field microscopy images are obtained at different energies. Herein, spatially localized NEXAFS spectra are obtained using a broad-band SXR emission, and the microscopic image is obtained by a raster scanning. The plasma is formed by the interaction of nanosecond laser pulses with a double stream gas puff target. The laser plasma source was optimized for efficient soft X-ray emission from a krypton plasma in the range ~2 nm to 5 nm wavelength radiation (energy of ~250 eV – 620 eV). This emission is used to acquire simultaneously emission and absorption spectra of soft X-ray light from the source and from the investigated sample. The spectra were acquired from a small area of PET polymer ~30 × 30 μm2 in size. A raster scanning was implemented to obtain 2-D elemental composition maps. A chemical (elemental) composition of EUV-irradiated PET was investigated. The data are in agreement with the reference measurements and the theoretical values. EUV irradiated PET spectra are showing hydrogen decrease in the PET structure due to the EUV irradiation. In the paper, a detailed information about the source, the system, the spectral measurements and the results are presented and discussed.

Mechanisms governing the interaction of metallic particles with nanosecond laser pulses.

The interaction of nanosecond laser pulses at 1064- and 355-nm with micro-scale, nominally spherical metallic particles is investigated in order to elucidate the governing interaction mechanisms as a function of material and laser parameters. The experimental model used involves the irradiation of metal particles located on the surface of transparent plates combined with time-resolved imaging capable of capturing the dynamics of particle ejection, plume formation and expansion along with the kinetics of the dispersed material from the liquefied layer of the particle. The mechanisms investigated in this work are informative and relevant across a multitude of materials and irradiation geometries suitable for the description of a wide range of specific applications. The experimental results were interpreted using physical models incorporating specific processes to assess their contribution to the overall observed behaviors. Analysis of the experimental results suggests that the induced kinetic properties of the particle can be adequately described using the concept of momentum coupling introduced to explain the interaction of plane metal targets to large-aperture laser beams. The results also suggest that laser energy deposition on the formed plasma affects the energy partitioning and the material modifications to the substrate.

The thermo-mechanical behavior of thin metal films under nanosecond laser pulse excitation above the thermoelastic regime

This article presents experimental results supported by advanced three-dimensional modeling for the dynamics emerging from the interaction of nanosecond laser pulses with thin metal films on dielectric substrates, especially at the melting and ablation regimes. Matter dynamics, such as the generation and propagation of surface acoustic waves and permanent deformations, are imaged with the use of a very high spatial and temporal resolution interferometric method accompanied by white-light interferometry. A three-dimensional finite element model is developed aiming to fully describe the spatiotemporal dynamics and predict with high accuracy the thermo-mechanical phenomena around melting and ablation regimes where phase changes take place. The ability of very high spatial and temporal resolution, the whole-field three-dimensional imaging as well as the simultaneous study of the laser pulse–thin film interaction regimes, makes this study valuable for applications where detailed knowledge of the thermo-mechanical behavior of matter under pulsed laser excitation is critical.

Towards acousto-optic tissue imaging with nanosecond laser pulses

We present a way to generate acousto-optical signals in timovssue-like media with nanosecond laser pulses. Our method is based on recording and analyzing speckle patterns formed by interaction of nanosecond laser pulses with tissue, without and with simultaneous application of ultrasound. Stroboscopic application allows visualizing the temporal behavior of speckles while the ultrasound is propagating through the medium. We investigate two ways of quantifying the acousto-optic effect, viz. adding and subtracting speckle patterns obtained at various ultrasound phases. Both methods are compared with the existing speckle contrast method using a 2D scan and are found to perform similarly. Our method gives outlook on overcoming the speckle decorrelation problem in acousto-optics, and therefore brings in-vivo acousto-optic measurements one step closer. Furthermore it enables combining acousto-optics and photoacoustics in one setup with a single laser.

Sampling considerations when analyzing micrometric-sized particles in a liquid jet using laser induced breakdown spectroscopy

Pollution of water is a matter of concern all over the earth. Particles are known to play an important role in the transportation of pollutants in this medium. In addition, the emergence of new materials such as NOAA (Nano-Objects, their Aggregates and their Agglomerates) emphasizes the need to develop adapted instruments for their detection. Surveillance of pollutants in particulate form in waste waters in industries involved in nanoparticle manufacturing and processing is a telling example of possible applications of such instrumental development. The LIBS (laser-induced breakdown spectroscopy) technique coupled with the liquid jet as sampling mode for suspensions was deemed as a potential candidate for on-line and real time monitoring.With the final aim in view to obtain the best detection limits, the interaction of nanosecond laser pulses with the liquid jet was examined. The evolution of the volume sampled by laser pulses was estimated as a function of the laser energy applying conditional analysis when analyzing a suspension of micrometric-sized particles of borosilicate glass. An estimation of the sampled depth was made. Along with the estimation of the sampled volume, the evolution of the SNR (signal to noise ratio) as a function of the laser energy was investigated as well. Eventually, the laser energy and the corresponding fluence optimizing both the sampling volume and the SNR were determined. The obtained results highlight intrinsic limitations of the liquid jet sampling mode when using 532nm nanosecond laser pulses with suspensions.

Interaction of nanosecond laser pulse with tetramethyl silane (Si(CH3)4) clusters: Generation of multiply charged silicon and carbon ions

Present work reports significantly high levels of ionization, eventually leading to Coulomb explosion of Tetramethyl silane (TMS) clusters, on interaction with laser pulses of intensity ∼109 W/cm2. Tetramethyl silane clusters, prepared by supersonic expansion were photoionized at 266, 355 or 532 nm and the resultant ions were detected using time-of-flight mass spectrometer. It is observed that wavelength of irradiation and the size of the cluster are crucial parameters which drastically affect the nature of charge species generated upon photoionization of cluster. The results show that clusters absorb significantly higher energy from the laser field at longer wavelengths (532 nm) and generate multiply charged silicon and carbon ions which have large kinetic energies. Further, laser-cluster interaction at different wavelengths has been quantified and charge densities at 266, 355 and 532 nm are found to be 4x 1010, 5x 1010 and 5x 1011 charges/cm3 respectively. These unusual results have been rationalized based on dominance of secondary ionization processes at 532 nm ultimately leading to Coulomb explosion of clusters. In another set of experiments, multiply charged ions of Ar (up to +5 state) and Kr (up to +6 state) were observed when TMS doped inert gas clusters were photoionized at 532 and 355 nm. The extent of energy absorption at these two wavelengths is clearly manifested from the charge state of the atomic ions generated upon Coulomb disintegration of the doped cluster. These experiments thus demonstrate a novel method for generation of multiply charged atomic ions of inert gases at laser intensity of ∼ 109 W/cm2. The average size of the cluster exhibiting Coulomb explosion phenomena under giga watt intensity conditions has been estimated to be ∼ 6 nm. Experimental results obtained in the present work agree qualitatively with the model proposed earlier [D. Niu, H. Li, F. Liang, L. Wen, X. Luo, B. Wang, and H. Qu, J. Chem. Phys. 122, 151103(2005)] and point towards interaction of quasi-free electrons, generated during primary multiphoton ionization step, with a given wavelength in the presence of Coulombic field.

Time-resolved study of the mechanical response of tissue phantoms to nanosecond laser pulses

We present a time-resolved study of the interaction of nanosecond laser pulses with tissue phantoms. When a laser pulse interacts with a material, optical energy is absorbed by a combination of linear (heat generation and thermoelastic expansion) and nonlinear absorption (expanding plasma), according to both the laser light irradiance and material properties. The objective is to elucidate the contribution of linear and nonlinear optical absorption to bubble formation. Depending on the local temperatures and pressures reached, both interactions may lead to the formation of bubbles. We discuss three experimental approaches: piezoelectric sensors, time-resolved shadowgraphy, and time-resolved interferometry, to follow the formation of bubbles and measure the pressure originated by 6 ns laser pulses interacting with tissue phantoms. We studied the bubble formation and pressure transients for varying linear optical absorption and for radiant exposures above and below threshold for bubble formation. We report a rapid decay (of 2 orders of magnitude) of the laser-induced mechanical pressure measured (by time-resolved shadowgraphy) very close to the irradiation spot and beyond 1 mm from the irradiation site (by the piezoelectric sensor). Through time-resolved interferometry measurements, we determined that bubble formation can occur at marginal temperature increments as low as 3°C.

Experimental study on the momentum coupling efficiency of laser plasma

During the interaction of laser with solid targets, the counteracting force is generated by the plasma, which can be used as a new type source of propulsion. Compared with the chemical propulsion, laser plasma has unique advantages such as high specific impulse and large load ratio. In this paper, the momentum generated by the laser plasma is measured during the interaction of nanosecond laser pulses with aluminum, graphite, lead and CH targets. The relation of target momentum with laser focal area in atmosphere and vacuum ambient pressure is obtained,and the comparison is performed between the experimental and analytical results. It is shown that the target momentum in vacuum is different from that in atmosphere. In vacuum, the target momentum shows a dependence on the target property. These results are different from those generated by long width pulses.

Physical chemistry of the femtosecond and nanosecond laser–material interaction with SiC and a SiC–TiC–TiB 2 composite ceramic compound

The interaction of nanosecond laser pulses in the ultraviolet wavelength range and femtosecond laser pulses in the near-infrared region with the semiconductor SiC and the composite compound SiC–TiC–TiB 2 was investigated. Surface analytical techniques, such as XPS, depth profile (DP), and micro-Raman spectroscopy (μ-RS) were used to identify the chemical changes between untreated and laser-treated areas. Single-pulse irradiation led to material modifications in the condensed state in most instances. Multi-pulse results differed depending on the pulse duration. Crystal structure changes were observed as a consequence of laser-induced melting and resolidification. In air contact all components underwent oxidation reactions according to thermodynamic expectations. Exceptions were observed under exclusion of oxygen, SiC was reduced to elemental Si.

Diagnostics of parchment laser cleaning in the near-ultraviolet and near-infrared wavelength range: a systematic scanning electron microscopy study

A detailed diagnostic study of the interaction of nanosecond laser pulses from the near-ultraviolet to the near-infrared wavelength range with various types of contemporary and ancient parchments is presented. The advantages of laser cleaning due to the absence of chemical agents, spectroscopic selectivity, micro-precision and computer-aided handling can only be verified when physico-chemical diagnostics guarantee destructionless processing. Scanning electron microscopy data are correlated with chemical degradation and morphological changes dependent on the laser fluence and wavelength. It is also shown how transmission electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy, and pyrolysis capillary gas chromatography can be employed in the chemical diagnostics of laser cleaning of parchment. This study suggests that the ageing status of parchment artefacts plays a major role in assessing the laser cleaning limits.

Interaction of nanosecond laser pulses with plastic foams

Some results of an experimental and theoretical study of the interaction of laser pulses with plastic foams are reported. The propagation velocity of a hydrodynamic peturbation which was initiated in foam target under the action of a laser pulse with intensityq≈2·1013 W/cm2 and the velocity distribution function of plasma ions were measured; the preliminary results of time-integrated spectroscopic measurements of an intense red-shifted signal are also reported. A self-consistent model of the foam target’s laser plasma formed in a hydrodynamic mode was derived. The predictions of this model are consistent with experimental results. A model of microprocesses of laser plasma formation in a structured material was also developed. The results of numerical simulations by 1D and 2D computer codes are also reported.

Two-wave interaction of nanosecond laser pulses in CdTe crystals and the origin of their nonlinearity

An investigation was made of the formation of photorefractive gratings in CdTe crystals with an enhanced carrier (electron) mobility μ = 500 cm2 V-1 s-1 when they were excited by nanosecond light pulses. The photorefractive effect was separated in its pure form from the background of various nonlinear optical phenomena such as two-photon absorption, generation of nonequilibrium free carriers, and self-interaction of laser beams. The nature of the competing nonlinearity mechanisms was analysed.