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The short pulse laser is a research focus due to its high precision, non-contact and high controllability advantages. In this paper, nanosecond laser pulse ablation experiments on the titanium alloy surface were conducted to explore the interaction between nanosecond laser and titanium alloy. The formation mechanism of a volcano-like pit under the combined influence of surface tension, the Marangoni effect and recoil pressure was clarified and verified. Thereafter, a multi-pulse laser parameter experiment was carried out. Ablation morphology, quality and feature sizes of the volcano-like pit and micro-groove were studied under different laser parameters. Thus, the correlation between laser parameters and feature sizes was built. This study contributes to micromachining technology with nanosecond laser, which suggests that micro-pit and micro-groove with specific sizes and high processing quality can be obtained. [ABSTRACT FROM AUTHOR]

Electromagnetic plasma waves related to nonuniform electron-ion and electron-positron-ion plasma in interaction with short pulse laser in the quantum state have been investigated. These investigations have been done in low-frequency approximation. In these two plasmas, the initial quantities of number density, streaming velocity, and external magnetic field are inhomogeneous. The investigations have shown that in the perpendicular direction, the amount of these initial quantities affects the wave velocities, their instability rate, and their gradients affect the waves, strongly. The behavior of the perpendicular waves has been analyzed for variation in these initial quantities and the investigations show that these behaviors are different in these two plasmas. In the parallel direction, the factor that most affects the waves is the ponderomotive force related to the laser, so an increase in this force cause to increase in the wave velocities and their instability rate. The dependence of the parallel waves on the initial quantities of the number density and streaming velocity is direct, and their reliance on the external magnetic field is through the ponderomotive force (presence of laser). The waves in this direction are not affected by the transverse gradients of the initial quantities. The plasma waves in both plasmas have also been affected by the quantum correction terms. It has been demonstrated that our resulting equations are in accordance with the references mentioned in the article.

Based on the dual phase lag heat conduction model(DPL model), the asymptotic analysis of the transient heat conduction behavior of a thin metal sheet irradiated by ultra-short pulse laser was conducted. The governing equation with temperature representation of a thin metal plate was proposed in the context of the DPL model. The asymptotic solutions of temperature distribution through the whole thin plate induced by external ultra-short pulse laser were derived by combing the Laplace transform and the inverse transform techniques. The results were compared with those from the numerical methods in the literature to verify the accuracy of the analytical method. The effects of the phase-lag terms τ_q,τ_T and the sheet metal thickness on heat transfer behavior were also investigated. The results show that the peak value of heat wave and the change rate of temperature are increased with the increasing of τ_q. On the contrary, as the τ_T increases, the peak value of heat wave and the temperature change rate are decreased. The metal plate thickness has slight effect on the temperature change. [ABSTRACT FROM AUTHOR]

Short pulse laser heated buried layers experiments have been performed on the Orion laser facility to study the time-resolved emission characteristics of plasmas with mass densities  ≥ 1 g/cc and electron temperatures  > 500 eV. Our streak camera measurements focused on the K-shell emission lines of He-like and H-like aluminum from a buried aluminum layer. The data were analyzed by comparison to synthetic spectra generated with the non-local thermodynamic equilibrium (NLTE) radiation transfer code Cretin, which yielded maximum temperatures of nearly 800 eV at near solid density. The time precise history of the temperature evolution was reproduced with a 1-D radiation hydrodynamic code; however, the known effect of lateral transport of energy out of the focal spot made exacting agree with theory difficult. Thus, we have observed densities of  ≥ 1 g/cc and temperatures of  > 500 eV using the 1-D analysis, which supports the idea that the aluminum plasma is locally hotter than inferred from our spatially integrating measurements and that modeling requires the inclusion of 2-dimensional effects. [ABSTRACT FROM AUTHOR]

Ultrashort pulsed laser is an indispensable tool for the evolution of photonic technology in the present and future. This laser has been progressing tremendously with new pulse regimes and incorporating novel devices inside its cavity. Recently, a nanomaterial based saturable absorber (SA) was used in ultrafast laser that has improved the lasing performance and caused a reduction in the physical dimension when compared to conventional SAs. To date, the nanomaterials that are exploited for the development of SA devices are carbon nanotubes, graphene, topological insulators, transition metal dichalcogenides (TMDs) and black phosphorous. These materials have unique advantages such as high nonlinear optical response, fiber compatibility and ease of fabrication. In these, TMDs are prominent and an emerging two-dimensional nanomaterial for photonics and optoelectronics applications. Therefore, we review the reports of Q-switched and mode-locked pulsed lasers using TMDs (specifically MoS 2 , MoSe 2 , WS 2 and WSe 2 ) based SAs. [ABSTRACT FROM AUTHOR]

This study evaluated the influence of the irradiation with a short-pulse Er:YAG laser on the adhesion of composite resin to sound and eroded dentin (SD and ED). Forty-six samples of occlusal dentine, obtained from human molars, had half of their surface protected, while the other half was submitted to erosive cycles. Afterward, 23 samples were irradiated with Er:YAG laser, resulting in four experimental groups: SD, sound irradiated dentine (SID-Er:YAG, 50 μs, 2 Hz, 80 mJ, and 12.6 J/cm2), ED, and eroded irradiated dentin (EID-erosion + Er:YAG laser). A self-etching adhesive system was used, and then cylinders of composite resin were prepared. A microshear bond strength test was performed after 24 h storage (n = 20). The morphology of SD and ED, with or without Er:YAG laser irradiation, was evaluated under scanning electron microscopy (n = 3). Bond strength values (MPa) were subjected to analysis of variance followed by Tukey's test. Statistically significant differences were found among the experimental groups: SD (9.76 ± 3.39 B), SID (12.77 ± 5.09 A), ED (5.12 ± 1.72 D), and EID (7.62 ± 3.39 C). Even though erosion reduces the adhesion to dentin, the surface irradiation with a short-pulse Er:YAG laser increases adhesion to both ED and SD. [ABSTRACT FROM AUTHOR]

In heat-assisted magnetic recording (HAMR), a higher recording density is pursued. Short-pulse laser heating is a good way to improve the thermal distribution in the media and to reach the full potential of recording density for the HAMR technology. In this paper, the effects of short-pulse laser qualities, such as pulse frequency deviation, pulse power deviation, and pulsewidth deviation, on recording performances for the HAMR with 100 ps pulse laser heating have been analyzed by simulation. The results indicated that the frequency jitter has the most significant effect on the recording performance among these three parameters. The decreases of signal-to-noise ratio (SNR) for 6% deviations of pulse frequency, pulse power, and pulsewidth are 5, 2, and 1.5 dB, respectively. A certain degree phase delay of pulse laser related to magnetic field switching time is beneficial to reducing the effect of pulse frequency deviation on SNR. When the phase delay changes from 0° to 180°, an SNR improvement of $\sim 2$ dB is obtained. The measurement result of a real laser diode output (pulsewidth of 97 ps and pulse frequency of 2 GHz) by gain-switching technology presents a very low frequency deviation (<0.5%). It indicates that the gain-switching technology is a suitable approach for a short-pulse laser generation for the HAMR application. [ABSTRACT FROM AUTHOR]

Due to poor thermal performance of media, it is difficult for heat-assisted magnetic recording (HAMR) to achieve densities greater than 3 Tb/in ^ 2 for continuous-wave laser heating. Short-pulse laser heating is an attractive approach to improve the thermal response of media. In this paper, the recording performances of HAMR using short-pulse laser heating are studied by dynamic micromagnetic simulations solving the Landau–Lifshitz–Bloch equation. The results show that the magnetic damping constant of the media, $\alpha $ , and applied magnetic field, H$ , exhibit significant effects on recording quality at a pulse-width of 100 ps. From analyses of the relationships among readout signal and noise ratio, recorded track width, \alpha $ , and H is achievable for FePt recording media. [ABSTRACT FROM AUTHOR]

The effects of the polarized incident laser pulse on the electrons of the plasma surface and on the reflected pulse in the relativistic laser-plasma interaction is investigated. Based on the relativistic oscillating mirror and totally reflecting oscillating mirror (TROM) regimes, the interaction of the intense polarized laser pulses with over-dense plasma is considered. Based on the effect of ponderomotive force on the characteristic of generated electron nano-bunches, considerable increasing in the localization and charges of nano-bunches are realized. It is found that the circularly polarized laser pulse have Ne/Ncr of 1500 which is almost two and seven times more than the amounts for P-polarized and S-polarized, respectively. [ABSTRACT FROM PUBLISHER]

Background: To compare pain score of single spot short duration time (20 milliseconds) panretinal photocoagulation (PRP) with conventional (100 milliseconds) PRP in diabetic retinopathy. Methods: Sixty-six eyes from 33 patients with symmetrical severe non-proliferative diabetic retinopathy (non-PDR) or proliferative diabetic retinopathy (PDR) were enrolled in this prospective randomized controlled trial. One eye of each patient was randomized to undergo conventional and the other eye to undergo short time PRP. Spot size of 200 μm was used in both laser types, and energy was adjusted to achieve moderate burn on the retina. Patients were asked to mark the level of pain felt during the PRP session for each eye on the visual analog scale (VAS) and were examined at 1 week, and at 1, 2, 4 and 6 months. Results: Sixteen women and 17 men with mean age 58.9 ± 7.8 years were evaluated. The conventional method required a mean power of 273 ± 107 mW, whereas the short duration method needed 721 ± 406 mW ( P = 0.001). An average of 1,218 ± 441 spots were delivered with the conventional method and an average of 2,125 ± 503 spots were required with the short duration method ( P = 0.001). Average pain score was 7.5 ± 1.14 in conventional group and 1.75 ± 0.87 in the short duration group ( P = 0.001). At 1 week, 1 month, and 4 months following PRP, the mean changes of central macular thickness (CMT) from baseline in the conventional group remained 29.2 μm ( P = 0.008), 40.0 μm ( P = 0.001), and 40.2 μm ( P = 0.007) greater than the changes in CMT for short time group. Conclusion: Patient acceptance of short time single spot PRP was high, and well-tolerated in a single session by all patients. Moreover, this method is significantly less painful than but just as effective as conventional laser during 6 months of follow-up. The CMT change was more following conventional laser than short time laser. [ABSTRACT FROM AUTHOR]

The plasma mirror effect is demonstrated by the KrF laser for the first time. It is shown that plasma reflectivity starts to increase at the plasma threshold of 1012 W/cm2 and it saturates at 1014 W/cm2 with ∼ 35% reflectivity. Vacuum ultraviolet spectroscopy of laser plasmas on low-Z material shows that the optimum reflectivity conditions are reached at plasma temperatures of 20-25 eV. [ABSTRACT FROM AUTHOR]

Abstract: Warm Dense Matter (WDM) physics has been a growing field of high energy density physics, driven by the fundamental urge to understand the convergence between plasma and condensed matter physics, and the practical need to understand dynamic behavior of materials under extreme conditions. A platform for creating and probing WDM by isochoric heating of free-standing nano-foils has been developed recently to study the non-equilibrium processes. Results of optical measurements reveal the existence of a quasi-steady state in the time history, during which the interband component of the dielectric function shows both enhancement and a red shift. First-principles calculations of the dielectric function suggest that the enhanced red shift of the interband transition peak might be explained by a positive charge state of the gold foil due to ejection of electrons by the high intensity laser pulse. The impact on optical properties by the formation of an electronic sheath was examined by the Thomas–Fermi theory with local equilibrium approximation. [Copyright &y& Elsevier]

Abstract: Heating of thin foil targets by an high power laser at intensities of 1017–1019 W/cm2 has been studied as a method for producing high temperature, high density samples to investigate X-ray opacity and equation of state. The targets were plastic (parylene-N) foils with a microdot made of a mixture of germanium and titanium buried at depth of 1.5μm. The L-shell spectra from the germanium and the K-shell spectra from the titanium were taken using crystal spectrometers recording onto film and an ultra fast X-ray streak camera coupled to a conical focussing crystal with a time resolution of 1ps. The conditions in the microdot were inferred by comparing the measured spectra to synthetic spectra produced by the time-dependent collisional–radiative (CR) models FLY and FLYCHK. The data were also compared to simulated spectra from a number of opacity codes assuming local thermodynamic equilibrium (LTE). Temperature and density gradients were taken into account in the comparisons. The sample conditions were inferred from the CR modelling using FLYCHK to be 800±100eV and 1.5±0.5g/cc. The best fit to the LTE models was at a temperature 20% lower than with the CR model. Though the sample departs from LTE significantly useful spectral comparisons can still be made. The results and comparisons are discussed along with improvements to the experimental technique to achieve conditions closer to LTE. [Copyright &y& Elsevier]

Abstract: This paper compares results from theoretical predictions to experimental emission data from germanium obtained on the HELEN laser at AWE. The aim of the comparison was to test opacity predictions of highly stripped, medium Z elements, a regime which has received relatively little attention due the difficulty of achieving conditions near LTE at high temperatures. The data show emission from the 2p–3d and 2s–3p transitions from a layer of germanium buried in plastic and heated by the HELEN CPA beam. Predictions of spectra constructed using data generated by the grasp2K atomic structure code coupled to Saha–Boltzman population dynamics were compared to the experimental emission. It was found that the grasp2K calculations match the position of all the features in the experiment well, but non-LTE effects in the experiment make it unreasonable to expect a match to line strengths. Two opacity codes, CASSANDRA and DAVROS, were benchmarked against the grasp2K simulations. It was shown that the major difference in the two opacity codes is due to different approaches to calculating total ion energies. For this reason the DAVROS line positions are significantly more accurate than those of CASSANDRA. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to analyze the temperature distributions and heat affected zone in skin tissue medium when irradiated with either a collimated or a focused laser beam from a short pulse laser source. Experiments are performed on multi-layer tissue phantoms simulating skin tissue with embedded inhomogeneities simulating subsurface tumors and as well as on freshly excised mouse skin tissue samples. Two types of lasers have been used in this study – namely a Q-switched pulsed 1064nm Nd:YAG short pulse laser having a pulse width of 200ns and a 1552nm diode short pulsed laser having a pulse width of 1.3ps. Experimental measurements of axial and radial temperature distribution in the tissue medium are compared with the numerical modeling results. For numerical modeling, the transient radiative transport equation is first solved using a discrete ordinates method for obtaining the intensity distribution and radiative heat flux inside the tissue medium. Then the temperature distribution is obtained by coupling the bio-heat transfer equation with either hyperbolic non-Fourier or parabolic Fourier heat conduction model. The hyperbolic heat conduction equation is solved using MacCormack’s scheme with error terms correction. It is observed that experimentally measured temperature distribution is in good agreement with that predicted by hyperbolic heat conduction model. The experimental measurements demonstrate that converging laser beam focused directly at the subsurface location can produce desired high temperature at that location compared to that produced by collimated laser beam for the same laser parameters. Finally the ablated tissue removal is characterized using histological studies as a function of laser parameters. [Copyright &y& Elsevier]

Abstract: Targets of plastic with a buried layer of aluminium were heated using the HELEN CPA laser to irradiate one surface of the plastic. The emission spectra from the aluminium were used to infer the conditions in the target by comparing the measured spectra against synthetic spectra generated by the FLY code. The input to the FLY code was the temperature and density history calculated by a radiation-hydrodynamics code, which was iterated to achieve the best match to the experimental data. Aluminium layers at different depths in the plastic were used to measure how heat was transported into the target. Measurements were taken with the laser at wavelengths of 1.06μm and wavelength converted to 0.53μm. The laser irradiance was varied between 2×1017–1019 W/cm2 by varying the laser pulse length, energy and wavelength. The data show that the plastic target was heated above 200eV to a depth of about 4μm. The FLY comparisons indicate that the buried layers heated with 0.53μm light remained near solid density for the duration of the X-ray emission pulse and achieved a peak temperature of 450±50eV. In the case where the target was heated with 1.06μm radiation, the density was an order of magnitude lower and the peak temperature achieved was also substantially lower, at 320±50eV. The depth to which the target was heated was similar at the two wavelengths studied and was not a strong function of irradiance. The aluminium data are presented and compared to radiation-hydrodynamic and spectral modelling. [Copyright &y& Elsevier]

Abstract: The ionization and recombination dynamics of transient aluminum plasmas was measured using point projection K-shell absorption spectroscopy. An aluminum plasma was produced with a subpicosecond beam of the 100-TW laser at the LULI facility and probed at different times with a picosecond X-ray backlighter created with a synchronized subpicosecond laser beam. Fourier-Domain-Interferometry (FDI) was used to measure the electron temperature at the peak of the heating laser pulse. Absorption X-ray spectra at early times are characteristic of a dense and rather homogeneous plasma, with limited longitudinal gradients as shown by hydrodynamic simulations. The shift of the Al K-edge was measured in the cold dense plasma located at the edge of the heated plasma. From the 1s–2p absorption spectra, the average ionization was measured as a function of time and was also modeled with a collisional-radiative atomic physics code coupled with hydrodynamic simulations. [Copyright &y& Elsevier]

Abstract: The use of short pulse laser for minimally invasive detection scheme has become an indispensable tool in the technological arsenal of modern medicine and biomedical engineering. In this work, a time-resolved technique has been used to detect tumors/inhomogeneities in tissues by measuring transmitted and reflected scattered temporal optical signals when a short pulse laser source is incident on tissue phantoms. A parametric study involving different scattering and absorption coefficients of tissue phantoms and inhomogeneities, size of inhomogeneity as well as the detector position is performed. The experimental measurements are validated with a numerical solution of the transient radiative transport equation obtained by using discrete ordinates method. Thus, both simultaneous experimental and numerical studies are critical for predicting the optical properties of tissues and inhomogeneities from temporal scattered optical signal measurements. [Copyright &y& Elsevier]

We measure the He-like, time-resolved emission from two types of thin foils (1) consisting of 250 A˚ of carbon together with 250 A˚ of aluminum and (2) 500 A˚ aluminum, illuminated with a 150 fs laser pulse at an intensity of 1019 W/cm2. Dielectronic satellite contributions to the resonance transitions 1s2–1s2p(1P), 1s2–1s3p(1P), and 1s2–1s4p(1P) are modeled using the configuration-averaged code AVERROE&grave;S and is found to be significant for all three resonance lines. The effects of opacity are inferred from the data and found to be significant only in the 1s2–1s2p(1P). [Copyright &y& Elsevier]

Ultrashort laser pulses allow for the generation of hot plasmas near solid state densities. For this purpose a Ti:Sapphire laser was used, which delivers after frequency doubling, pulses of high contrast with an energy of about 60 mJ and a duration of 150 fs at 395 nm. The typical intensity on the target was a few 1017 W/cm2. To achieve a high degree of uniformity we used targets consisting of a 25 nm thin Al tracer layer buried at different depths up to 400 nm in solid carbon. Time-integrated Al K-shell spectra are presented. Characteristic features of the spectra are significant high-order satellite line emission, strong line broadening and a center-of-mass line shift to the red, which was observed in transitions from principal quantum number n=2 or 3 to 1. Accurate measurement of the shift was made possible by using the cold Si Kα line as an absolute wavelength calibration. In addition to time-integrated measurements, we used an ultrafast X-ray streak camera to obtain time and spectrally resolved spectra. Typical durations of the Lyα and Heα lines are in the range 2–4 ps. The experimental results are compared with a time-dependent model, which combines hydrodynamic simulations, time-dependent atomic kinetics, detailed spectral line shapes including line shifts, and radiation transport. [Copyright &y& Elsevier]

High density and temperature plasmas have been generated by irradiating thin foils of various elements with a high-energy subpicosecond laser pulse. The X-ray emission duration was studied by time-resolved X-ray spectroscopy. Frequency domain interferometry provided a measurement of the hydrodynamic expansion of the back of the foil as a function of time. The effect of longitudinal temperature gradients, i.e., gradients perpendicular to the surface, were decreased using very thin foil targets. Additionally, radial gradients effects, i.e., gradients parallel to the surface, were limited by using a 50 μm pinhole on target. The Al, Se and Sm spectra, recorded in the range 7.7–8 A˚ using a conical crystal spectrometer coupled to an 800 fs resolution streak camera, lasted a few picoseconds. Sm spectra showed no spectral features in this wavelength range, providing a spectrally homogeneous backlighter for future experiments. The main features of the experimental time-resolved spectra have been well reproduced with one-dimensional hydrodynamic simulations of the free expansion of a plasma heated at a given initial temperature obtained from the expansion velocity of the rear critical surface of the plasma. [Copyright &y& Elsevier]