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In this paper, we present a methodology of laser ablation simulation including electronic entropy effects. Ablation by ultrashort laser pulses is suitable for micromachining because of its small thermal damage. To further enhance its effectiveness, it is crucial to explore both theoretically and experimentally the desirable conditions for processing. The density functional theory calculations predict that hot electrons make crystalline lattice thermodynamically unstable at electronic temperature roughly above 20 000 K due to the electronic entropy-driven mechanism. In our simulations, equations combining hydrodynamic equations and the two-temperature model are modeled and are numerically solved, where the electronic entropy effects are included as the electronic temperature-dependent latent heat, boiling point, and melting point. For metal targets, Al and Cu, the calculated ablation rates for 100 fs laser pulses agree with the experimental one at laser fluences up to 10 J/cm 2. The heat-affected zone (HAZ) is numerically evaluated from the thickness of the molten layer. Short pulses produce a high ablation rate and small HAZ because of the suppression of diffusion of the deposited pulse energy. Electronic entropy effects make a clear difference between 100 fs and 10 ps pulses. The calculation method presented in this paper serves as a useful tool for exploring nonequilibrium between electrons and ions in the equation of states for metals such as Al and Cu. [ABSTRACT FROM AUTHOR]

In approaches to analyze material composition or in processing tasks using ultra-short laser ablation, it is of particular interest how ablated materials are distributed across the solid angle in front of the interaction region. We found that with our sub-10-fs laser in the regime from 10 14 W / c m 2 to 10 17 W / c m 2 , the solid angle of the ablation cone decreases significantly along with the laser intensity in a vacuum environment. For this observation, we used ion-beam analysis to investigate the distribution of tungsten collected on silicon catcher plates arranged across the solid angle of the laser-ablation cone. Moreover, we used other post-mortem tools, such as scanning electron microscopy and confocal laser scanning microscopy, to determine the ablation threshold of F t h = 468 mJ / c m 2 of our tungsten samples. Here, clearly, two laser intensity-dependent ablation regimes can be observed in the detection of a crater depth and a ablation cone angle. [ABSTRACT FROM AUTHOR]

We investigate the impact of non-collinear dual optical excitation on magnetization precession in a permalloy thin film using two ultrashort laser pulses. By analyzing the magnetization dynamics using time-resolved magneto-optical methods, we find that excitation with two ultrashort optical pulses introduces a long-lasting modification of the electron system, as indicated by a sizable decrease in the precession frequency and a significant increase (approximately 25%) in the decay time. Our results reveal that the observed effect strongly depends on the respective polarizations of the two excitation pulses and the time delay between the two optical pulses. Our findings indicate the occurrence of a nonlinear opto-spin effect during photoexcitation with two interfering optical pulses, which can potentially be observed in various materials and at different photon wavelengths. [ABSTRACT FROM AUTHOR]

Transient reflectivity measurements are used to probe the strain waves induced by ultrashort laser pulses in bulk [100] germanium. The measurement signals are compared to purely analytical model functions based on the known material parameters for germanium. The modeling includes (i) a derivation of analytical solutions to the wave equation for strain waves coupled to the diffusion equation for heat and charge carriers and (ii) an expression for the impact on reflection coefficients that are caused by perturbations to the dielectric function but extended to cover a non-isotropic, uniaxial dielectric tensorial form. The model is held up against transient reflectivity measurements with an s- and a p-polarized probe and with a probe wavelength in the range of 502–710 nm. Excellent agreement is found when comparing the oscillatory shape of the measurement signals to the models. As for the magnitude of the oscillations, the models reproduce the overall trends of the experiment when using the previously published values for the elasto-optical tensor measured under static strain. [ABSTRACT FROM AUTHOR]

Interaction of intense ultrashort laser pulse with gases generates a transient spatiotemporal electron density distribution via field ionization, which may lead to the spatiotemporal reshaping of the pulse, viz., its beam profile, pulse width, etc. Here, we present an experimental study on ultrashort laser pulse interaction with argon gas sheath in an ionization saturation intensity regime (∼1015–1017 W/cm2). The present investigation has been performed using a 6 mJ, 1 kHz, and 55−60 fs Ti:Sapphire laser pulse interaction with a ∼2.5 mm long argon sheath. After the laser gas interaction, the laser spatial profile exhibits a multi-ring structure around a central maximum spot. Laser gas interaction parameters, such as laser intensity, gas pressure, etc., affect the ring pattern significantly. Under optimum parameter conditions, the laser pulse has two rings in spatial profile, and the pulse width of the central spot is self-compressed to ∼35 fs. A theoretical calculation reveals that the laser beam's spatiotemporal profile evolves as it propagates inside the gas sheath. The calculation also demonstrates that the gas ionization profile plays a crucial role in the spatiotemporal reshaping and self-compression of the laser beam. The calculation also shows that the generation of concentric ring patterns in the spatial profile is mainly due to the ionization of argon atoms into Ar+, Ar2+, and Ar3+ species in the interaction region. Such self-compressed laser pulses with concentric ring beam profiles may be useful for high-harmonic generation and shorter attosecond pulse trains. [ABSTRACT FROM AUTHOR]

Advances in coherent light sources and development of pump–probe techniques in recent decades have opened the way to study electronic motion in its natural time scale. When an ultrashort laser pulse interacts with a molecular target, a coherent superposition of electronic states is created and the triggered electron dynamics is coupled to the nuclear motion. A natural and computationally efficient choice to simulate this correlated dynamics is a trajectory-based method where the quantum-mechanical electronic evolution is coupled to a classical-like nuclear dynamics. These methods must approximate the initial correlated electron–nuclear state by associating an initial electronic wavefunction to each classical trajectory in the ensemble. Different possibilities exist that reproduce the initial populations of the exact molecular wavefunction when represented in a basis. We show that different choices yield different dynamics and explore the effect of this choice in Ehrenfest, surface hopping, and exact-factorization-based coupled-trajectory schemes in a one-dimensional two-electronic-state model system that can be solved numerically exactly. This work aims to clarify the problems that standard trajectory-based techniques might have when a coherent superposition of electronic states is created to initialize the dynamics, to discuss what properties and observables are affected by different choices of electronic initial conditions and to point out the importance of quantum-momentum-induced electronic transitions in coupled-trajectory schemes. [ABSTRACT FROM AUTHOR]

Laser lift-off (LLO) is an important step in the processing chain of nitride-based light-emitting diodes (LEDs), as it enables the transfer of LEDs from the growth substrate to a more suitable carrier. A distinctive feature of LLO with ultrashort pulses is the ability to use either above- or below-bandgap radiation, since nonlinear absorption becomes relevant for ultrashort pulses. This study addresses the differences in the absorption scheme for below- and above-bandgap radiation and investigates the electrical and optical properties of InGaN/GaN LEDs before and after LLO with 347 and 520 nm laser light via current–voltage and power- as well as temperature-dependent photoluminescence measurements. LLO could be successfully realized with both wavelengths. The threshold fluence required for LLO is about a factor of two larger for 520 nm compared to that for 347 nm. Furthermore, an increase in leakage current by several orders of magnitude and a significant decrease in efficiency with laser fluence are observed for below-bandgap radiation. In contrast, leakage current hardly increases and efficiency is less dependent on the laser fluence for samples lifted with 347 nm. This degradation is ascribed to the absorption of laser light in the active region, which facilitates a modification of the local defect landscape. The effect is more severe for below-bandgap radiation, as more laser light penetrates deep into the structure and reaches the active region. Ultimately, we show that LEDs lifted with ultrashort laser pulses can exhibit good quality, making ultrashort pulse LLO a viable alternative to conventional LLO with nanosecond pulses. [ABSTRACT FROM AUTHOR]

In this research, tantalum nanoparticles were prepared by the laser ablation method and the effect of an electric field on their structural properties was investigated. The optical absorption spectra were studied to comprehend the optical properties of nanoparticles. Size and morphology of nanoparticles are illustrated by TEM images. The average size of tantalum nanoparticles is 19 and 45 nm for synthesized samples without and with electric fields, respectively. By applying an electric field, the morphology of nanoparticles changed from spherical to tangled shapes. XRD analysis showed the crystalline structure of nanoparticles. The investigation of bending and stretching of molecular functional groups and the measurement of the hydrodynamic radius were done by FTIR, RAMAN and DLS analyses, respectively. FTIR, RAMAN, XRD and DLS analyses confirm the structure. EDX spectra confirmed the existence of ingredients. The stability of colloidal is indicated by zeta potential analysis. Photoluminescence spectra reveal nanoparticle properties. As the electric field increases, the size of nanoparticles increased, morphology changes from spherical, and oxidation increases. [ABSTRACT FROM AUTHOR]

We report the development of a seeded diode-pumped 1338-nm Nd:YAG amplifier which delivers 400-ps, 6-mJ, single-frequency pulses every half second with a fluctuation of ∼ 0.7%. A highly stable pulsed current controller is constructed to drive an 808-nm diode laser array that ensures the high stability of the laser. Numerical calculations show that 9.2 μm or 10.2-μm picosecond (<10 ps) pulses with 100-μJ energy can be generated by mixing the 1338-nm 6-mJ pulses with 1540-nm chirped pulses in a BGGSe nonlinear crystal and compressing the pulse with a grating compressor. [ABSTRACT FROM AUTHOR]

Coherent mode locking is based on the formation of 2 π pulses of self-induced transparency in the absorbing medium and π pulses in the amplifying medium. In this regime it becomes possible to generate ultrashort laser pulses down to one oscillation cycle with a pulse duration being much shorter than the polarization relaxation time T 2 of the amplifying and absorbing medium. In this article a two-section laser model with a ring resonator based on absorbing and amplifying medium with short relaxation times has been applied. We have demonstrated a self-starting regime of coherent mode locking with picosecond and femtosecond laser pulses using numerical simulations for the given model. In addition, we have shown that there is a significant influence of generation frequency detuning on laser pulse duration and intensity. Moreover, we have compared our numerical results with an analytical model of a coherent mode-locked laser based on the area theorem. We believe that the findings of this work can open a pathway towards the practical application of mode locking in mid-IR and THz quantum cascade lasers. [ABSTRACT FROM AUTHOR]

The formation of dense plasmas inside dielectric materials by ultrashort laser pulses has many applications ranging from refractive‐index modifications to the formation of channels and voids. Furthermore, such plasmas enable the fundamental investigation of ultrafast non‐equilibrium dynamics in highly excited materials. The present paper provides an overview of current experimental approaches to investigating such plasmas. Much information about the plasma relaxation is obtained by measuring the spatial and temporal evolution of the dielectric properties of the excited material through time‐resolved absorption and phase‐shift measurements. In order to investigate and resolve the individual stages of plasma formation, experimental approaches with a temporal resolution beyond the capabilities of traditional optical pump‐probe studies are required. Recent examples for schemes that may enable the investigation of the plasma formation with sub‐cycle time resolution are thus reviewed. These include recent results from time‐resolved high‐harmonic generation as well as the two‐color pump‐probe analysis of non‐perturbative low‐order wave mixing for the tracking of strong‐field excitation dynamics. Alternative approaches employ attosecond transient absorption spectroscopy, attosecond polarization spectroscopy and nonlinear photoconductive sampling for resolving the temporal evolution of the carrier dynamics down to sub‐optical‐cycle timescales. [ABSTRACT FROM AUTHOR]

The different types of optical soliton solutions are investigated for the 2-dimensional nonlinear Schrödinger equation with an instantaneous Kerr nonlinearity. This equation contains the beam propagation in a multimode optical fiber with a parabolic index profile. Different soliton solutions are examined, such as Breather waves, Lump waves, Mixed types, Periodic cross kink, Multiwave, M-shape, M-shape rational one, two kinks, and rogue waves. To obtain these optical solitons, we apply the Hirota bilinear transformation approach. These results are spectral, temporal, and spatial features of ultrashort light pulses that can be controlled in novel ways by this kind of nonlinear multimode optical fiber, which is gaining popularity. Moreover, the 3-dimensional, 2-dimensional, and contour plots are drawn for some solutions that show their physical interactions by selecting different parameters. These results are very helpful for further study of dynamical systems. [ABSTRACT FROM AUTHOR]

The fabrication of stable, tailored domain patterns in ferroelectric crystals has wide applications in optical and electronic industries. All-optical ferroelectric poling by pulse laser irradiation has been developed recently. In this work, we studied the creation of the domain structures in MgO-doped lithium tantalate by focused irradiation with a femtosecond near-infrared laser. Cherenkov-type second harmonic generation microscopy was used for domain imaging of the bulk. We have revealed the creation of enveloped domains around the induced microtracks under the action of the depolarization field. The domain growth is due to a pyroelectric field caused by a nonuniform temperature change. The domains in the bulk were revealed to have a three-ray star-shaped cross-section. It was shown that an increase in the field excess above the threshold leads to consequential changes in domain shape from a three-ray star to a triangular and a circular shape. The appearance of comb-like domains as a result of linear scanning was demonstrated. All effects were considered in terms of a kinetic approach, taking into account the domain wall motion by step generation and kink motion driven by excess of the local field over the threshold. The obtained knowledge is useful for the all-optical methods of domain engineering in ferroelectrics. [ABSTRACT FROM AUTHOR]

The high‐temperature layered superconductor (HTS) BSCCO is one of the key quantum material platforms in THz science and technology. Compact, stable, and reliable BSCCO THz photonic integrated circuit components can be developed to effectively and efficiently control and manipulate THz wave radiation, especially for future communication systems and network applications. Herein, the design, simulation, and modeling of ultrafast THz metamaterial photonic integrated circuits are reported on a few nanometer‐thick HTS BSCCO van der Waals (vdWs), capable of the active modulation of phase with constant transmission coefficient over a narrow‐frequency range. Meanwhile, the metamaterial circuit works as an amplitude modulator without significantly changing the phase in a different frequency band. Under the application of ultrashort optical pulses, the transient modulation dynamics of the THz metamaterial offer a fast‐switching timescale of 50 ps. The dynamics of picosecond light–matter interaction, Cooper pairs breaking, photoinduced quasiparticles generation and recombination, phonon bottleneck effect, and emission and relaxation of bosons in BSCCO vdW metamaterial arrays are discussed for the potential application of multifunctional superconducting photonic integrated circuits in communication and quantum technologies. [ABSTRACT FROM AUTHOR]

Rare-earth-doped barium calcium aluminate (BCA) glasses, having extended infrared (IR) transmission (6 μ m), are attractive materials for near IR (NIR) photonic applications. Nd2O3-doped BCA glasses display broadband emission at 1.07 µ m, but they are limited, with poor glass-forming ability (GFA) and low emission cross sections. In the present study, four different barium zinc calcium aluminate (BZCA) glasses are synthesized with varied ZnO concentrations (from 9.5 to 24.5 mol%) and doped with 0.5 mol% Nd2O3 to decipher the effect on GFA and spectroscopic properties. The addition of ZnO enhances the GFA, and the NdBZCA20 glass shows the maximum GFA. Ultraviolet (UV)–visible (Vis)–NIR absorption spectra reveal a decreasing trend in the nephelauxetic effect, while J – O parameters, emission, and gain properties lead to no significant alteration with increasing ZnO, and the structure–properties correlation is established accordingly. However, the emission cross sections for all ZnO concentrations are found ∼4.5 × 10−20 cm2 accompanied by broadband emission (Δ λ eff ∼ 40 nm), which ensures the potentiality of these glasses for low-threshold high-gain laser applications as well as ultrashort pulse laser applications. Furthermore, a thorough analysis of 1.06 µ m emission as a function of Nd concentration in the BZCA20 glass is reported here. The emission spectra and decay time indicate that 0.5 mol% is the optimized doping concentration. Inokuti–Hirayama and Burshtein equations are adopted to study the decay kinetics and energy-transfer mechanisms, which confirm that the energy-transfer process due to cross-relaxation is dominant up to 0.5 mol% concentration, whereas, beyond that concentration, excitation energy migration via the hopping mechanism supersedes. [ABSTRACT FROM AUTHOR]

AbstractMicro/nano-scale transient thermo-mechanical responses are significantly important with rapid development and applications of ultra-short pulse in micro-machining of viscoelastic structure. This work aims to establish non-Fourier thermo-viscoelastic model based on nonlocal single-phase-lag heat conduction and Eringen’s differential elasticity. The developed model is applied to study thermo-viscoelastic responses for 1D temperature-dependent polymer-based rods subjected to non-Gaussian laser pulse excitation by Kirchhoff and Laplace transformation techniques. The results reveal that the parameters of the deformation, pulse laser, and nonlocal single-phase-lag heat conduction remarkably affect the wave propagations and thermo-viscoelastic response at micro/nano-scale nanoscale. [ABSTRACT FROM AUTHOR]

The sensitivity of molecular spectroscopy based on surface‐enhanced coherent anti‐Stokes Raman scattering (SECARS) is limited by the spectrally overlapping background from nonresonant four‐wave mixing (FWM). While the SECARS signal is mediated by the molecular vibrational eigenstates and exhibits long lifetime (a few picoseconds), the FWM background stems from the instantaneous electronic polarization and decays rapidly with the vanishment of excitation. Therefore, CARS and FWM can be separated by time‐resolved CARS (trCARS) using ultrashort pulsed lasers. The broad spectral bandwidth also enables broadband CARS (BCARS) for simultaneous identification of multiple vibrational signatures. This work combines trCARS and BCARS with an optimized plasmonic system to demonstrate time‐resolved surface‐enhanced BCARS) and show its capability in obtaining background‐suppressed broadband vibrational spectra from a monolayer of 4‐Aminothiophenol (4‐ATP) molecules self‐assembled on a gold grating. The vibrational dephasing time of the ring‐breathing mode for the 4‐ATP monolayer on the gold grating (≈1.00 ± 0.17 ps) is significantly shortened compared to that for 4‐ATP powder on a glass substrate (2.10 ± 0.05 ps). This work presents an effective method to suppress FWM background and investigate the vibrational dynamics of molecules in the vicinity of plasmonic nanostructures. [ABSTRACT FROM AUTHOR]

Improving the energy efficiency in generating high-energy proton or boron ions is crucial for advancing the feasibility of neutronless laser-based proton-boron (p-B11) fusion reactions. The primary objective of this work is to optimize the fusion energy efficiency of a proposed advanced p-B11 fusion scheme. In the proposed scheme, an ultrashort laser pulse is guided by a plasma channel filled with carbon-hydrogen (CH2) clusters. The MeV protons are generated by the Coulomb explosion (CE) of the cluster, which, therefore, interact with surrounding boron to produce alpha particles. To evaluate the fusion energy efficiency under various conditions, 2D particle-in-cell (PIC) simulations are used, supplemented with analytical calculations and estimations. The Bayesian optimization (BO) algorithm is utilized to optimize the key interaction parameters. The BO approach allows us to identify optimal cluster and laser parameters that would have higher fusion energy efficiency. [ABSTRACT FROM AUTHOR]

Laser nanostructuring of thin films with ultrashort laser pulses is widely used for nanofabrication across various fields. A crucial parameter for optimizing and understanding the processes underlying laser processing is the absorbed laser fluence, which is essential for all damage phenomena such as melting, ablation, spallation, and delamination. While threshold fluences have been extensively studied for single compound thin films, advancements in ultrafast acoustics, magneto-acoustics, and acousto-magneto-plasmonics necessitate understanding the laser nanofabrication processes for functional multilayer films. In this work, we investigated the thickness dependence of ablation and delamination thresholds in Ni/Au bilayers by varying the thickness of the Ni layer. The results were compared with experimental data on Ni thin films. Additionally, we performed femtosecond time-resolved pump-probe measurements of transient reflectivity in Ni to determine the heat penetration depth and evaluate the melting threshold. Delamination thresholds for Ni films were found to exceed the surface melting threshold suggesting the thermal mechanism in a liquid phase. Damage thresholds for Ni/Au bilayers were found to be significantly lower than those for Ni and fingerprint the non-thermal mechanism without Ni melting, which we attribute to the much weaker mechanical adhesion at the Au/glass interface. This finding suggests the potential of femtosecond laser delamination for nondestructive, energy-efficient nanostructuring, enabling the creation of high-quality acoustic resonators and other functional nanostructures for applications in nanosciences. [ABSTRACT FROM AUTHOR]

Zirconia ceramics have become an important material for the manufacture of key components in aerospace, military, energy, and other fields due to their excellent mechanical properties. However, their inherent high hardness and brittleness make them difficult to machine with high efficiency and low damage, resulting in poor surface integrity. Inspired by the ribbed groove structure of shark skin and the fractal structure of insect wing veins, two zirconia ceramics with different bionic textures are designed in this paper, and zirconia ceramic surfaces are bionically textured by using an ultrafast picosecond pulse laser. The effects of the special bionic textures on the grinding behavior of zirconia ceramics, specifically surface morphology, surface roughness, edge morphology, and subsurface damage, were investigated. The experimental results show that the surface integrity of the bionic textured zirconia ceramics is better compared to the untextured surface. In particular, the bionic insect wing veins texture exhibits the best surface quality with the least sub-surface damage, and the surface roughness S a is reduced by a maximum of 21.46 %, and S z is reduced by a maximum of 18.87 %. However, the best edge morphology is exhibited by the bionic shark skin texture. Additionally, bionic texturing improves grinding lubrication and cooling conditions. The results confirm that applying bionic texturing to zirconia ceramics effectively enhances grinding performance and improves grinding surface integrity. [ABSTRACT FROM AUTHOR]

2 μm pulsed lasers not only have critical applications in military, medical, and processing fields but are also an important frontier in laser physics. The development of these pulsed lasers has been hindered by the lack of laser crystals with both high thermal conductivity and broad spectral properties. In this work, Tm, Ho:CaGdAlO4 disordered crystal with ultra-broad emission spectra around 2 μm was achieved successfully by modulating the emission intensities of Tm3+ and Ho3+ ions to the same level. The FWHM of the absorption spectra at 793 nm for the <001> and <100> directions are 18.69 and 19.44 nm, respectively, which is beneficial for commercial laser diode pumping. More importantly, the FWHM of the emission spectrum is 264 nm, which is the widest one reported in the previous literature. The results indicate that the Tm, Ho:CaGdAlO4 crystal with its broader spectra has the potential to generate an ultrashort pulse laser. [ABSTRACT FROM AUTHOR]

MgAl 2 O 4 and Ti6Al4V, the greatly suitable materials for industrial application, are rarely explored to realize reliable bonding in current research. In this study, the transparent MgAl 2 O 4 and Ti6Al4V were successfully bonded by innovative use of ultrashort pulse laser with ultra-high peak power. The high energy near the laser focus makes MgAl 2 O 4 and Ti6Al4V mix and react with each other after absorbing the laser energy, thus realizing the bridge between them. The homogeneous mixing of all phases was observed in the joint and the newly generated Ti 6 O phase was identified at the interface. In addition, the effects of laser power and scanning speed on the microstructure and mechanical properties of the joint have been thoroughly clarified. This study creatively used femtosecond laser welding as a new mean to realize ceramic-metal joining, which shows great advantages in superior efficiency and precision compared with other welding methods. [ABSTRACT FROM AUTHOR]

Acceleration of electrons in vacuum directly by intense laser fields holds great promise for the generation of high-charge, ultrashort, relativistic electron bunches. While the energy gain is expected to be higher with tighter focusing, this does not account for the reduced acceleration range, which is limited by diffraction. Here, we present the results of an experimental investigation that exposed nanotips to relativistic few-cycle laser pulses. We demonstrate the vacuum laser acceleration of electron beams with 100s pC charge and 15 MeV energy. Two different focusing geometries, with normalized vector potential a0 of 9.8 and 3.8, produced comparable overall charge and electron spectra, despite a factor of almost ten difference in peak intensity. Our results are in good agreement with 3D particle-in-cell simulations, which indicate the importance of dephasing. Accelerating electrons in vacuum by intense laser fields is a promising yet experimentally challenging field. Here, the authors demonstrate acceleration of 100's of pC of 15 MeV electrons by shining few-cycle laser pulses on nanotips and further investigate the process by using different focusing geometries that leads to unexpected results. [ABSTRACT FROM AUTHOR]

Coherent light has revolutionized scientific research, spanning biology, chemistry and physics. To delve into ultrafast phenomena, the development of high-energy, highly tunable light sources is instrumental. Here, the photoelectric effect is a pivotal tool for dissecting electron correlations and system structures. Particularly, above-threshold ionization (ATI), characterized by the simultaneous absorption of several photons leading to a final electron energy well above the ionization threshold, has been widely explored, both theoretically and experimentally. ATI decouples laser field effects from the structural information carried by photoelectrons, particularly when utilizing ultrashort pulses. In this contribution, we study ATI driven by polarization-crafted (PC) pulses, which offer precise scanning over the electron momentum, through an accurate change of the polarization state. PC pulses enable the manipulation of photoelectron momentum distributions, opening up new avenues for understanding and harnessing coherent light. Our work explores how structured light could allow for a proper understanding of emitted photoelectrons momentum distributions in order to distinguish between light structure effects and target structure effects. [ABSTRACT FROM AUTHOR]

Ultrashort-pulse-laser ablation of dielectric thin films is strongly affected by the interference of the exciting laser pulse with itself, which causes the deposited energy to be confined to narrow regions equidistantly spaced along the propagation direction of the laser. We investigate how this affects the ablation mechanism of freestanding Al 2 O 3 thin films by analyzing the laser-generated structures with several post-mortem imaging and spectroscopic techniques. Close to the ablation threshold, the laser-irradiated region exhibits surface blistering. Higher intensities cause layers of material to be removed corresponding to ejection of material initiated from the regions of high excitation. Significantly above the ablation threshold, the laser-generated structure is remarkably stable and consists of a membrane of thickness corresponding to the distance between neighboring interference maxima, which is uniquely determined by the central wavelength of the laser pulse and the refractive index of the film. The electronic excitation as a function of depth is simulated using a multiple-rate-equation model in combination with finite-difference-time-domain propagation of the laser field. The simulations confirm the strongly localized excitation and thus correlate well with the observed laser-generated structures. [ABSTRACT FROM AUTHOR]

To achieve laser direct welding of glass and metal without optical contact is hard, owing to the large difference in thermal expansion and thermal conductivity between glass and metal and an insignificant melting area. In this study, the high-power picosecond pulsed laser was selected to successfully weld the aluminosilicate glass/6061 aluminum alloy with a gap of 35 ± 5 μm between glass and metal. The results show that the molten glass and metal diffuse and mix at the interface. No defects such as microcracks or holes are observed in the diffusion mixing zone. Due to the relatively large gap, the glass collapsed after melting and caulking, resulting in an approximately arc-shaped microcrack between modified glass and unmodified glass or weakly modified glass. The shape of the glass modification zone and thermal accumulation are influenced by the single-pulse energy and linear energy density of the picosecond laser during welding, resulting in variations in the number and size of defects and the shape of the glass modification zone. By reasonably tuning the two factors, the shear strength of the joint reaches 15.98 MPa. The diffusion and mixing at the interface and the mechanical interlocking effect of the glass modification zone are the main reasons for achieving a high shear strength of the joint. This study will provide reference and new ideas for the laser transmission welding of glass and metal in the non-optical contact conditions. [ABSTRACT FROM AUTHOR]

The Pohang Accelerator Laboratory X‐ray Free‐Electron Laser (PAL‐XFEL) operates hard X‐ray and soft X‐ray beamlines for conducting scientific experiments providing intense ultrashort X‐ray pulses based on the self‐amplified spontaneous emission (SASE) process. The X‐ray free‐electron laser is characterized by strong pulse‐to‐pulse fluctuations resulting from the SASE process. Therefore, online photon diagnostics are very important for rigorous measurements. The concept of photo‐absorption and emission using solid materials is seldom considered in soft X‐ray beamline diagnostics. Instead, gas monitoring detectors, which utilize the photo‐ionization of noble gas, are employed for monitoring the beam intensity. To track the beam position at the soft X‐ray beamline in addition to those intensity monitors, an X‐ray ionization beam position monitor (XIBPM) has been developed and characterized at the soft X‐ray beamline of PAL‐XFEL. The XIBPM utilizes ionization of either the residual gas in an ultra‐high‐vacuum environment or injected krypton gas, along with a microchannel plate with phosphor. The XIBPM was tested separately for monitoring horizontal and vertical beam positions, confirming the feasibility of tracking relative changes in beam position both on average and down to single‐shot measurements. This paper presents the basic structure and test results of the newly developed non‐invasive XIBPM. [ABSTRACT FROM AUTHOR]

The main objective of this work is to provide a basic understanding of the mechanisms and locations of defect formation during percussion laser drilling of microholes using ultrashort pulses. Through the application of high-speed synchrotron X-ray imaging, we have been able to observe the dynamic formation and evolution of these defects in real-time. Our findings indicate that the initial deviations in the borehole geometry are highly dependent on the applied laser fluence. Specifically, while higher peak fluences facilitate deeper drilling, there exists a critical threshold beyond which the position of these deviations begins to decrease as the fluence increases. This behavior can be partially predicted within a certain fluence range using an existing theoretical model, which our experimental observations have tested and validated. Consequently, this research not only advances our understanding of defect formation in laser drilling but also provides a predictive framework for optimizing drilling parameters to minimize defects and enhance borehole quality. [ABSTRACT FROM AUTHOR]

Highly intense bunches of protons and ions with energies of several MeV/u can be generated with ultra-short laser pulses focused on solid targets. In the most common interaction regime, target normal sheath acceleration, the spectra of these particles are spread over a wide range following a Maxwellian distribution. We report on the design and testing of a magnetic chicane for the selection of protons within a limited energy window. This consisted of two successive, anti-parallel dipole fields generated by cost-effective permanent C-magnets with customized configuration and longitudinal positions. The chicane was implemented into the target vessel of a petawatt laser facility with constraints on the direction of the incoming laser beam and guidance of the outgoing particles through a vacuum port. The separation of protons and carbon ions within distinct energy intervals was demonstrated and compared to a ray tracing code. Measurements with radiochromic film stacks indicated the selection of protons within [2.4, 6.9] MeV, [5.0, 8.4] MeV, or ≥6.9 MeV depending on the lateral dispersion. A narrow peak at 4.8 MeV was observed with a time-of-flight detector. [ABSTRACT FROM AUTHOR]

The need for alternative energy storage options beyond lithium-ion batteries is critical due to their high costs, resource scarcity, and environmental concerns. Zinc-ion batteries offer a promising solution, given zinc's abundance, cost effectiveness, and safety, particularly its compatibility with non-flammable aqueous electrolytes. In this study, the potential of laser-ablation-based titanium oxide as a novel cathode material for zinc-ion batteries was investigated. The ultra-short laser pulses for in situ nanostructure generation (ULPING) technique was employed to generate nanostructured titanium oxide. This laser ablation process produced highly porous nanostructures, enhancing the electrochemical performance of the electrodes. Zinc and titanium oxide samples were evaluated using two-electrode and three-electrode setups, with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge (GCD) techniques. Optimal cathode materials were identified in the Ti-5W (laser ablated twice) and Ti-10W (laser ablated ten times) samples, which demonstrated excellent charge capacity and energy density. The Ti-10W sample exhibited superior long-term performance due to its highly porous nanostructures, improving ion diffusion and electron transport. The potential of laser-ablated titanium oxide as a high-performance cathode material for zinc-ion batteries was highlighted, emphasizing the importance of further research to optimize laser parameters and enhance the stability and scalability of these electrodes. [ABSTRACT FROM AUTHOR]

The concept of building logically functional networks employing spintronics or magnetic heterostructures is becoming more and more popular today. Incorporating logical segments into a circuit needs physical bonds between the magnetic molecules or clusters involved. In this framework, we systematically study ultrafast laser-induced spin-manipulation scenarios on a closed system of three carbon chains to which three Ni atoms are attached. After the inclusion of spin–orbit coupling and an external magnetic field, different ultrafast spin dynamics scenarios involving spin-flip and long-distance spin-transfer processes are achieved by various appropriately well-tailored time-resolved laser pulses within subpicosecond timescales. We additionally study the various effects of an external magnetic field on spin-flip and spin-transfer processes. Moreover, we obtain spin-dynamics processes induced by a double laser pulse, rather than a single one. We suggest enhancing the spatial addressability of spin-flip and spin-transfer processes. The findings presented in this article will improve our knowledge of the magnetic properties of carbon-based magnetic molecular structures. They also support the relevant experimental realization of spin dynamics and their potential applications in future molecular spintronics devices. [ABSTRACT FROM AUTHOR]

We demonstrated a stable passively Q-switched fiber laser operation at 1531.57 nm using a double-transition metal MAX phase TiNbAlC saturable absorber. The prepared saturable absorber's modulation depth, saturation intensity, and non-saturation loss are 1.75%, 0.089 MW/cm 2 , and 32.81%, respectively. Using the TiNbAlC saturable absorber within an erbium-doped fiber laser ring cavity, stable Q-switched pulses with a central wavelength of 1531.57 nm, and a 3-dB bandwidth of 1.43 nm are acquired. The minimum pulse duration and the maximum single pulse energy are 3.18 μ s and 51.56 nJ, respectively. Furthermore, the maximum repetition rate is 37.9 kHz with a signal-to-noise ratio of 50 dB. Our results indicate that double-transition metal MAX phase TiNbAlC can be an excellent saturable absorber candidate for an ultrashort pulse fiber laser. [ABSTRACT FROM AUTHOR]

Water-assisted ultrashort laser pulse processing of semiconductor materials is a promising technique to diminish heat accumulation and improve process quality. In this study, we investigate femtosecond laser ablation of deep trenches in GaAs, an important optoelectronic material, using water and ambient air environments at different laser processing regimes. We perform a comprehensive analysis of ablated trenches, including surface morphological analysis, atomic-resolution transmission electron microscopy imaging, elemental mapping, photoluminescence, and Raman spectroscopy. The findings demonstrate that GaAs ablation efficiency is enhanced in a water environment while heat-accumulation-related damage is reduced. Raman spectroscopy reveals a decrease in the broad feature associated with amorphous GaAs surface layers during water-assisted laser processing, suggesting that a higher material quality in deep trenches can be achieved using a water environment. [ABSTRACT FROM AUTHOR]

In nonlinear Schrödinger equations (NLSEs), the third-order generalized NLSE is a significant sculpture which is utilized for modeling ultrashort pulses in fiber optics. In this study, we obtained wave and soliton solutions by using new extended and modified Rational expansion method to get several types of soliton such as bright solitons, dark solitons, perodic solitons and traveling waves. In three-dimensional and two-dimensional plots, we present graphical representations in dissimilar structures of some solutions to understand the phenomena physically. The development and achievements of computing show the power and effectiveness of current technology. In addition, we are able to resolve various other high-order NLSEs with the assistance of effortless and effectual technique. [ABSTRACT FROM AUTHOR]

Comprehending the laser ablation mechanism is fundamental in determining how diverse laser parameters affect the quality of the ablation process. A finite difference model was developed in this study to investigate the ablation depth and temperature distribution in picosecond ablation process. The investigation involved conducting single-point laser experiments on bronze material using an ultrashort pulse laser with a pulse duration of 12 ps. The experiments were carried out with varying numbers of pulses, ranging from 1 to 80 pulses. The calculated depths of ablations were compared with experimental results. The variation of the ablation mechanism on the workpiece's surface during laser radiation was also investigated. The model established the laser-material interaction mechanisms under different incident pulses. The ionization temperature and ablated material temperature during laser processing are also determined. The results show that for the number of pulses higher than 10, the laser-material interaction changes from Multi-Photon Ionization to ablation, while in lower numbers, there are no effects of thermal damages adjacent to the laser points. The relationship between variations in the ablation depth and changes in the incidence angle was also investigated. As the incidence angle increases, the removal mechanism changes from MPI to the thermal. [ABSTRACT FROM AUTHOR]

Ultrashort light pulses have strong research and application values, while nonlinear inverse Thomson scattering has been considered as a unique source of zepto-yoctosecond pulses. Here, the mechanism of nonlinear inverse Thomson scattering of a high-energy electron colliding with a tightly focused intense laser pulse is investigated through numerical simulation. The time-compression effect was proposed to explain the origin of ultrashort pulses and the nonlinear phenomenon of electron radiation in the time–space joint distribution. It is found that the time scale of electron radiation is orders of magnitude shorter than that of electron motion, and the increases in laser intensity and electron initial energy will result in stronger and shorter pulses. Yoctosecond pulses can be generated by a laser pulse with an intensity of 1.384 × 10 20   W / c m 2 and an electron with an initial energy of 51.1   M e V . These results provide theoretical and numerical basis for generating shorter light pulses. [ABSTRACT FROM AUTHOR]

Introduction: Topographic surface patterning in the micro- and nanometer scale has evolved into a well applied approach in surface functionalization following biomimetic blueprints from nature. Depending on the production process an additional impact of process-related substrate modification has to be considered in functional surface optimization. This is especially true in case of antimicrobial applications of Cu surfaces where a modification of the substrate properties might impact bactericidal efficiency. Methods: In this regard, the effect of ultrashort pulsed direct laser interference patterning on the microstructure of pure Cu and resulting antimicrobial properties was investigated alongside line-like patterning in the scale of single bacterial cells. Results and Discussion: The process-induced microstructure modification was shown to play an important role in corrosion processes on Cu surfaces in saline environment, whereas the superficial microstructure impacts both corrosive interaction and ion emission. Surprisingly, antimicrobial efficiency is not predominantly following deviating trends in Cu ion release rates but rather depends on surface topography and wettability, which was shown to be impacted by the substrate microstructure state, as well. This highlights the need of an in-depth understanding on how different surface properties are simultaneously modulated during laser processing and how their interaction has to be designed to acquire an effective surface optimization e.g., to agitate active antimicrobial surface functionalization. [ABSTRACT FROM AUTHOR]

It has been shown that the frequency of an ultrashort microwave pulse of a lowest axisymmetric electric mode at the interaction with a counterpropagating relativistic tubular electron beam under the cyclotron resonance conditions can be doubled due to re-emission into a mode having resonance at the second harmonic of the gyrofrequency. The conversion of the 3-cm 1-ns gigawatt microwave pulse in a circular waveguide from the TM01 mode to the TM02 mode with the doubling of the frequency, reduction of the duration to 0.22 ns, and the achievement of the peak power above the initial value has been demonstrated in a numerical experiment. The possibility of forming an intense ultrashort frontal splash of oscillations with the doubled frequency has been shown for longer initial pulses with a subnanosecond front. [ABSTRACT FROM AUTHOR]

Objectives: In this work we demonstrate the first laboratory study results of lens fragmentation with low-energy picosecond ultrashort laser pulses after artificial induction of cataract with microwave radiation on an ex vivo animal model. Background: This method will be evaluated with regard to the further development of lens fragmentation with novel ultrashort picosecond laser systems instead of ultrasonic phacoemulsification or the significantly more complex femtosecond laser fragmentation. Methods: As samples we used postmortem porcine eyes. The lenses were dissected and then irradiated in a microwave oven for artificial cataract induction. Subsequent computer-driven lens fragmentation was performed with a 12 ps, 1064 nm pulsed laser source with 100 μJ pulse energy, and 10 kHz pulse repetition rate. Results: Both the artificial cataract induction and the lens fragmentation were demonstrated. When inducing cataract, different degrees/stages of opaqueness and hardness could be achieved with different irradiation times and methods. The fragmentation with 12 ps pulses led to good results with regard to ablation depth and rate, especially for the softer lenses. Conclusions: As could be shown, low-energy picosecond ultrashort laser pulses are feasible for cataractous lens fragmentation on an ex vivo animal model with artificial cataract induction. Thus, this technique may influence future cataract surgeries by possibly being an alternative or extension to state-of-the-art methods. This will be evaluated with further tests and studies. [ABSTRACT FROM AUTHOR]

Ultrafast laser technology has moved from ultrafast to ultra-strong due to the development of chirped pulse amplification technology. Ultrafast laser technology, such as femtosecond lasers and picosecond lasers, has quickly become a flexible tool for processing brittle and hard materials and complex micro-components, which are widely used in and developed for medical, aerospace, semiconductor applications and so on. However, the mechanisms of the interaction between an ultrafast laser and brittle and hard materials are still unclear. Meanwhile, the ultrafast laser processing of these materials is still a challenge. Additionally, highly efficient and high-precision manufacturing using ultrafast lasers needs to be developed. This review is focused on the common challenges and current status of the ultrafast laser processing of brittle and hard materials, such as nickel-based superalloys, thermal barrier ceramics, diamond, silicon dioxide, and silicon carbide composites. Firstly, different materials are distinguished according to their bandgap width, thermal conductivity and other characteristics in order to reveal the absorption mechanism of the laser energy during the ultrafast laser processing of brittle and hard materials. Secondly, the mechanism of laser energy transfer and transformation is investigated by analyzing the interaction between the photons and the electrons and ions in laser-induced plasma, as well as the interaction with the continuum of the materials. Thirdly, the relationship between key parameters and ultrafast laser processing quality is discussed. Finally, the methods for achieving highly efficient and high-precision manufacturing of complex three-dimensional micro-components are explored in detail. [ABSTRACT FROM AUTHOR]

In this study, silver nanoparticles (Ag NPs) dispersed in deionized water (DW) are prepared using the Nd:YAG laser ablation method. Transmission electron microscopy (TEM) results were used to investigate the shape and particle size of Ag NPs. The spherical shape and size of about 30 nm are characterized. X-ray diffraction (XRD) analysis shows a good crystallinity of Ag NPs and distinguished peaks at 38° without any impurities. The optical properties of Ag NPs were studied by a UV–visible spectrophotometer, and the surface plasmon resonance was observed at an excitation wavelength of about 402 nm and a direct band gap of about 2.25 eV. The results of the inhibitory activity against Lactobacillus and Streptococcus mutans bacteria indicated areas of high inhibition. The highest inhibition zone was 19 mm at the stock concentration. The anticancer properties of Ag NPs were studied with multi-concentration; the small particle size of Ag NPs led to the killing of about 70% of the MCF-7 line; and the inhibitory concentration (IC50) of Ag NPs was about 93.55 µg/mL−1. [ABSTRACT FROM AUTHOR]

This paper explores the characteristics of processing carbon fiber-reinforced plastic (CFRP) materials with ultra-short pulsed lasers. By combining experimental and numerical simulation methods, the processing characteristics when ultra-short pulsed lasers interact with CFRP are analyzed, including processing depth, processing width, the formation of heat-affected zone (HAZ), and the microstructure of the processed surface. The experimental part involves using picosecond and femtosecond lasers to machine holes or slots in CFRP under different process parameters and comparing their morphologies. Numerical simulation constructs a three-dimensional model to predict the temperature field distribution and material removal dynamics during the laser processing process. The results of experiments and simulations indicate that picosecond laser processing produced a visible HAZ and thermal damage; as the power of the picosecond laser increases, the ablation holes and HAZ gradually expand. In contrast, no HAZ is observed in femtosecond laser processing. Femtosecond pulsed lasers can effectively reduce the thermal damage during the CFRP processing. The anisotropic properties of CFRP materials have a significant impact on the laser processing effects. The research findings provide a theoretical basis and technical support for the precise processing of CFRP materials, which is of great significance for the application of CFRP materials in fields such as aerospace and automotive manufacturing. [ABSTRACT FROM AUTHOR]

The preparation of surfaces for coating processes is indispensable for maximal adhesion and good coating results. These technical surfaces can be treated by chemical, mechanical, or physical procedures. In thermal spray coating, grit blasting is a standard process for surface preparation. This mechanical roughening and activation of the surfaces is fast and easy to handle. On the negative side, the grit gets wasted and the generated pattern is inflexible. Therefore, attempts to substitute grit blasting with a laser application is discussed in this article. Herein, a theoretical evaluation of high‐speed laser surface texturing (LST) is performed to find limits and points for the optimization of these processes. To estimate the surface processing rates, continuous wave, nanosecond, and ultrashort pulse laser machined dimples and grooves are investigated, and results of the spray coatings are presented afterward. The steel substrates are coated with Stellite 6 and tungsten. Adhesion tests and coating structures are analyzed. In terms of the optimization of the laser texturing, in situ temperature measurements show the influence of the laser process speed on the thermal load of the substrate. The influence of the number of scanning repetitions on heat accumulation during LST is also analyzed. [ABSTRACT FROM AUTHOR]

Lasers have established themselves as a versatile tool that generates innovations in a wide range of fields, from automotive to surface engineering, medical applications, etc. A current research field for lasers is surface texturing in biomimetic, which aims to mimic nature‐inspired functionalities and mechanisms, for example, to tailor and control wetting, adhesion/friction, or optical properties of technical surfaces. Therefore, ultrashort pulse lasers are often the right choice to alter surface structures at microscopic scale. Moreover, the ongoing trend toward high‐average power lasers reaching "kilowatt class" levels even for ultrashort pulse lasers seems to be beneficial to increase throughput of this powerful laser technology for industrial production. However, several recent studies are reported on harmful X‐ray emissions arising from high‐intense ultrashort laser pulses which must be considered as a secondary laser beam hazard in risk assessment. Shining light on this topic, this article reports on a set of experiments investigating X‐rays emission induced by ultrashort pulse laser processing of different laser‐pretreated stainless steel sheets. The X‐ray measurements show the effect of roughness and scan number on the laser‐induced X‐ray emission dose. In addition, the dependency of X‐ray emission on the scan direction relatively to the laser beam polarization state is discussed. [ABSTRACT FROM AUTHOR]

Stainless steel (SST) is an important material for a variety of applications including construction, food, and medical. Highly hydrophobic wetting properties enhance the surface properties of SST to support processes such as self‐cleaning. However, applications also require long‐term stability of such properties against chemical and mechanical influences from the environment or technical processes. Therefore, the reduction of highly hydrophobicity of chemically modified, laser‐textured SST surfaces is investigated in relation to abrasive wear using hierarchical structures, micro‐/nanotextured surface, and support structures that shield the highly hydrophobic pattern. Surface textures comprising ridges, grooves (size: 50–500 μm; depth: up to 100 μm), and a nanostructured grooves bottom are machined by infrared ultrashort pulse laser ablation into SST and are subsequently chemically modified by a self‐assembled monolayer of a fluorinated, phosphonic acid‐modified alkane. Abrasive wear tests of these surfaces show decreasing water contact angles with increasing wear of the modified surface of the support structures. However, there is good stability of the highly hydrophobic properties due to the protection of modified areas at the groove bottom. The proposed wetting model for such designed functionalized laser textures shows possibilities for further optimization of such robust highly hydrophobic surfaces and adaptation to specific applications. [ABSTRACT FROM AUTHOR]

Herein, results are presented on the air pressure influence on the resistance of surface structures formed by picosecond processing of aluminum nitride ceramic. It is found that scanning the ceramic surface by laser radiation at the wavelengths of 1064 and 355 nm emitted by a neodymium‐doped yttrium aluminum garnet laser system can produce conductive lines. The resistance value is measured of structures fabricated under different processing conditions related to varying the laser fluence, pulse overlapping, and wavelength at different ambient air pressures from 10−4 Torr to atmospheric pressure. Based on the obtained dependences, the processing parameter windows are defined, allowing formation of a conductive material. It is demonstrated that changing the experimental conditions may change the resistance value by several orders of magnitude. The ambient pressure also affects the morphology of the ablated zones, with different structures being observed, including formation of ripples. The analyses performed of the processed surface indicate that conductivity arises from the presence of aluminum following a thermally induced ceramic decomposition. The influence of the gas flow during the laser processing on the resistance and the possibility of laser scribing of the ceramic are also experimentally estimated. [ABSTRACT FROM AUTHOR]

In this paper, the Kundu–Eckhaus equation which describes the propagation of ultrashort pulses or femtosecond light pulses in nonlinear optics is investigated using the new mapping method. As a result, different structures of chirped solitary and periodic waves were yielded. The dynamic of the soliton and kink soliton chirp waves were illustrated from which we can conclude that the sign of the Raman parameter identifies the chirp wave function direction. [ABSTRACT FROM AUTHOR]

Fuel retention in plasma-facing components (PFCs) is a critical issue in future nuclear fusion reactors operating with Deuterium-Tritium (DT) regarding nuclear safety and fulfillment of the T cycle. However, during DT plasma operation, highly energetic neutrons will induce damage in the lattice of W PFCs causing enhanced fuel retention in defects or traps. Laser-Induced Breakdown Spectroscopy (LIBS) is a potential tool to monitor the T-content in situ in PFCs of future nuclear fusion devices. This article presents an ex situ study on pre-damaged W material after D plasma exposure to qualify the method and mimic conditions expected in a reactor. ITER grade W samples were displacement-damaged by 10.8 MeV W ions to a damage dose of 0.23 dpa and exposed to low temperature deuterium plasma at low energy in PlaQ. The resulting deuterium concentration was analyzed by using 3He Nuclear Reaction Analysis (depth resolution of ≈ 150 nm) as a well-established method, and LIBS (picosecond laser pulses, depth resolution of 15 nm). The sample with the highest deuterium concentration showed a deuterium-rich zone up to a depth of 1.13 μm using both techniques. This is close to the expected W ion-induced damage depth of ≈ 1 μm. The results imply that LIBS as an in situ technique for tritium monitoring could be a viable option for a reactor. [ABSTRACT FROM AUTHOR]

A 2D numerical model based on the finite-difference time-domain (FDTD) method had been developed to investigate the correspondence between the spatio-temporal aspects and intensity evolution of a focused laser beam after the propagation through micro-structured dispersive materials under the pulse duration variation in the few-cycle regime. In parallel with the laser field intensification investigations, a spatio-temporal analysis of the electromagnetic field in the focal point is elaborated as a function of the relative spatial extension of the pulse in order to provide a complex description of this approach. The numerical computations indicate that shorter and more intense pulses may be obtained in well-defined conditions. Also, the major contribution played by the input laser beam profile, numerical aperture, and the dispersive material features in the intensity enhancement process in the focal point is pointed out. The present approach can be used as a versatile method for field intensification in various ultra-short and ultra-intense few-cycle laser pulse experiments. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate an ultrafast diamond Raman laser at 1240 nm with a pulse repetition rate of 956.62 MHz, a pulse duration of 39.5 ps, and an average power of up to 3.3 W based on synchronous pumping. The pump source is an electrical-pulse-modulated picosecond pulsed laser at 1064 nm with a repetition rate of 239.16 MHz and a pulse duration of 65.4 ps. A quadrupling repetition rate of the Raman pulse is achieved by synchronously amplifying both the forward and backward Raman pulses and the amplified Raman pulse undergoing two round trips in the resonator within one pump pulse period. The compression ratio of the pulse duration from the pump to the Raman is 1.66. This work offers a convenient and efficient method to significantly enhance the repetition rate of ultrafast crystalline Raman lasers and proves that a non-coherent ultrafast pump pulsed laser can be converted to a coherent mode-locked ultrafast Raman pulsed laser based on Raman conversion. [ABSTRACT FROM AUTHOR]