High-energy Laser Pulses Research Articles

High-energy 2.8-μm Ultrashort Pulses Generation in an Er:ZBLAN Fiber Amplifier

Compact, high-energy ultrashort pulsed fiber lasers in the 2.8 μm wavelength have attracted extensive interest in many scientific and industrial applications. Here, we demonstrated the generation of μJ-level ultrashort pulses from a quasi-all-fiberized Er:ZBLAN amplifier employing a 2.8-μm frequency-shifted soliton as a seed laser. With backward pumping, the pulse energy was enhanced to 0.282 μJ when the average output power was amplified to 1.023 W. Mechanisms for the generation and amplification of ultrashort pulses were theoretically revealed by numerical simulation, and further cascaded indium fluoride (InF3) fiber to obtain a 4.26-μm redshift soliton numerically. This compact fiber amplification system consisting of frequency-shifted-based seed pulses and fluoride fiber amplifiers will be of practical interest in applications.

Direct generation of 3.17 mJ green pulses in a cavity-dumped Ho3+-doped fiber laser at 543 nm

High-energy pulsed lasers in the green spectral region are of tremendous interest for applications in space laser ranging, underwater detection, precise processing, and scientific research. Semiconductor pulsed lasers currently are difficult to access to the so-called “green gap,” and high-energy green pulsed lasers still heavily rely on the nonlinear frequency conversion of near-IR lasers, precluding compact and low-cost green laser systems. Here, we address this challenge by demonstrating, for the first time to the best of our knowledge, millijoule-level green pulses generated directly from a fiber laser. The green pulsed fiber laser consists of a 450 nm pump laser diode, a Ho3+-doped ZBLAN fiber, and a cavity-dumping module based on a visible wavelength acousto-optic modulator. Stable pulse operation in the cavity-dumping regime at 543 nm is observed with a tunable repetition rate in a large range of 100 Hz–3 MHz and a pulse duration of 72–116 ns. The maximum pulse energy of 3.17 mJ at 100 Hz is successfully achieved, which is three orders of magnitude higher than those of the rare-earth-doped fiber green lasers previously reported. This work provides a model for compact, high-efficiency, and high-energy visible fiber pulsed lasers.

Comparative study on passive Q-switching laser properties of Yb:CaWO4 and Yb:NaY(WO4)2 crystals

Yb:CaWO4 and Yb:NaY(WO4)2 are two tetragonal tungstates, possessing exactly the same crystal symmetry and local site symmetry for the Yb ion. In this work, a detailed comparison of spectroscopic properties was made between the two tungstates, showing a large degree of similarity in their polarized absorption and emission features. Stable passive Q-switching of an Yb:CaWO4 laser was demonstrated, generating 0.40 W of pulsed output power at 1024.7 nm at a repetition rate of 33 kHz; the resulting pulse energy, duration, and peak power were, respectively, 12.1 μJ, 50 ns, and 242 W. Compared to an Yb:NaY(WO4)2 laser operating under the same passive Q-switching conditions, while most of the output characteristics were similar, the pulse energy generated by the Yb:CaWO4 laser proved to be much higher. This may imply the greater potential of Yb:CaWO4 in generating high-energy laser pulses.

Ablation of porcine subcutaneous fat and porcine aorta tissues by a burst-mode nanosecond-pulsed laser at 355 nm.

High-energy laser pulses used in laser angioplasty are challenging the laser cost, delivery system damage, efficiency, and laser catheter operating time. 355 nm nanosecond-pulsed laser in burst mode has shown potentials in reducing the system complexity and selective ablation of tissues. In this paper, burst mode laser ablation of porcine subcutaneous fat and porcine aorta is investigated. A histopathological analysis demonstrates that porcine subcutaneous fat can be ablated at a rate of greater than 0.2 mm/s when the number of pulses per burst is 1500 (corresponding to a fluence of 0.12 mJ/mm2 per pulse and 180 mJ/mm2 per burst), and the temperature of tissue during lasing is lower than 45°C. The porcine aorta remains nearly unaffected at the same laser parameter, and the tissue temperature during lasing is lower than 35°C. It shows the feasibility of using a burst-mode laser for selective ablation of tissue.

Clean production and characterization of nanobubbles using laser energy deposition

We have demonstrated the production of laser bulk nanobubbles (BNB) with ambient radii typically below 500 nm. The gaseous nature of the nanometric objects was confirmed by a focused acoustic pulse that expands the gas cavities to a size that can be visualized with optical microscopy. The BNBs were produced on demand by a collimated high-energy laser pulse in a “clean” way, meaning that no solid particles or drops were introduced in the sample by the generation method. This is a clear advantage relative to the other standard BNB production techniques. Accordingly, the role of nanometric particles in laser bubble production is discussed. The characteristics of the nanobubbles were evaluated with two alternative methods. The first one measures the response of the BNBs to acoustic pulses of increasing amplitude to estimate their rest radius through the calculation of the dynamics Blake threshold. The second one is based on the bubble dissolution dynamics and the correlation of the bubble’s lifetime with its initial size. The high reproducibility of the present system in combination with automated data acquisition and analysis constitutes a sound tool for studying the effects of the liquid and gas properties on the stability of the BNBs solution.

Decomposition of CrN induced by laser-assisted atom probe tomography

It is known that measurement parameters can significantly influence the elemental composition determined by atom probe tomography (APT). Especially results obtained by laser-assisted APT show a strong effect of the laser pulse energy on the apparent elemental composition. Within this study laser-assisted APT experiments were performed on Cr0.51N0.49 and thermally more stable (Cr0.47Al0.53)0.49N0.51, comparing two different base temperatures (i.e. 15 and 60 K), laser wavelengths (i.e. 532 and 355 nm) and systematically modified laser pulse energies. Absolute chemical compositions from laser-assisted APT were compared to data obtained from ion beam analysis. The deduced elemental composition of CrN exhibited a strong increase of the Cr content when the laser pulse energy was increased for both laser wavelengths. For low laser pulse energies Cr, CrN, N and N2 ions were identified, while the amount of detected Cr ions increased and the amount of N ions strongly decreased at higher laser pulse energies. Further, increased detection of more complex Cr-containing ions such as Cr2N at the expense of CrN was observed at higher pulse energies. At the highest pulse energy levels used within this work, the resulting Cr content was > 80 at%, dominated by the amount of detected elemental Cr ions. The change of the mass spectrum of the detected ions with increasing laser pulse energy provides evidence that high laser pulse energies initiate the decomposition of CrN during the APT measurement, consistent with the known thermal decomposition path into Cr2N and subsequently into Cr and gaseous N. In contrast, variation of the laser pulse energy for the thermally more stable CrAlN resulted only in a slight increase of Cr and a decrease of the resulting concentrations of Al and N with increasing laser pulse energy and no change in the type of detected ions. In conclusion, within the present study, the decomposition of a coating material with low thermal stability induced by laser-assisted APT was reported for the first time, emphasizing the importance of the selection of suitable measurement parameters for metastable materials, which are prone to thermal decomposition.

Ultralow confinement loss anti-resonant fibers designed by swarm intelligence

Anti-resonant fibers featured with multiple cladding tubes are promising light guiding media with a broadband low-loss transmission window in the optical spectrum. Herein, we numerically demonstrate anti-resonant fibers with ultra-low confinement loss and good single mode property, which is automatically designed by swarm intelligence. The basic idea of the particle swarm optimization algorithm is to find the optimal solution by the cooperation and information sharing among particles in the group. It is demonstrated that the particle swarm optimization algorithm can be utilized to design such anti-resonant fibers with multiple geometry parameters. By breaking the mirror symmetry of the fiber’s cross section, the coupling between the fundamental mode and cladding mode is further suppressed than the mirror symmetry one. As a result, ultra-low confinement loss as small as 2.2 × 10−8 dB/m can be achieved in simulation. Our results might facilitate the advanced applications of nested anti-resonant fibers in optical communication and high energy pulsed laser, etc.

Design and Analysis of Femtosecond Laser-Generated Metasurface for Optical Filter Application

This work investigates a Fano filter design based on a nano-hole array, patterned in fused silica using high-energy ultrafast femtosecond laser pulses. After carefully observing the experimental results, the structural profile of the nano-holes is numerically modeled in a 3D finite-difference time-domain-based software platform. The metasurface design consists of conical shaped air holes structured in the substrate, and a later deposited waveguide layer which leaves craters on the surface as the material fills inside the nano-holes. The spectral properties of the device are studied against variations in the structural parameters, such as the depth of the nano-holes, its surface diameter, and the depth of the craters on the surface of the waveguide. The proposed Fano filter device is designed to operate in the near-infrared (NIR) wavelength range around a telecommunication window of 1550 nm. Multiple narrowband resonances are observed with a linewidth in the range of 1.4 to 24.2 nm and a quality factor of 66.51 to 1090.12. The device shows good spectral tunability over a wide range from 1380 to 1650 nm comprising multiple narrowband resonances and variations in the structural parameters. Since the device can be implemented using a cost-effective and rapid fabrication method, it can be proposed for use in various optical filtering and sensing applications.

Tunable ultrafast near-infrared nonlinear optical properties of Eu3+ and silver nanoparticles doped alkali borate glasses

Achieving strong optical nonlinearities in vitreous nanocomposites is imperative for the advancement of futuristic telecommunication and photonic technologies. In this regard the borate materials (vitreous) are deemed to be important and currently available commercial hosts. In the current work, we demonstrate the tuning of the third-order nonlinear optical (NLO) attributes of borate-based glass samples doped with metal nanoparticles (NPs) and rare earth ions through annealing process. The NLO attributes, such as nonlinear optical absorption and refraction have been analysed by the sensitive Z-scan approach in the open and closed aperture configurations, respectively. The NLO features were examined in the near-infrared spectral region using ultrafast laser pulses fired at a high repetition rate from a Ti: sapphire laser oscillator. The open aperture data unveiled the existence of two-photon absorption whilst closed aperture indicated the occurrence of self-focusing nonlinear refraction. The NLO coefficients improved with heat treatment duration but the nonlinear absorption coefficient reduced at longer heat treatment schedules. The enhancement in the NLO coefficients is ascribed to the local field enriched by metallic silver NPs in the proximity of the rare earth ions when high-energy laser pulses irradiate the hosts. The results suggest the glasses routed with rare earth ions and metallic silver NPs annealed for 40 hrs at 450 °C are beneficial for optical communication and nonlinear photonic device applications, including optical limiting functionalities.

Synthesis of Titanium Oxide Nanoparticles Using Pulsed Laser Ablation Method in Deionized Water

The synthesis of titanium oxide nanoparticles (TiO2NPs) has been successfully carried out using pulsed laser ablation in deionized water to produce titanium oxide nanoparticles. This synthesis is included in the top-down method which aims to produce high-purity nanoparticles synthesis. Experimentally, an Nd:YAG laser beam (with 1064 nm, 85 mJ and 10 Hz) was focused on the surface of a high-purity (99.9%) titanium plate placed in deionized water. The high energy pulsed laser Nd:YAG laser makes the titanium plate ablate for 30 minutes. This is because the melting of the titanium plate surface causes the formation of small titanium oxide particles. When these particles hit deionized water this synthesis titanium oxide will form a colloid. Furthermore, colloidal titanium oxide nanoparticles have been successfully produced with a bluish-white color. The absorbance of TiO2NPs was shown at 239.75 nm as the appearance of colloidal TiO2NPs and the average diameter at 73.47 nm. Therefore the synthesis of TiO2NPs by pulsed laser ablation method can produce nanoparticles.

High-Strain Rate Spall Strength Measurement for CoCrFeMnNi High-Entropy Alloy

In this study, we experimentally investigate the high stain rate and spall behavior of Cantor high-entropy alloy (HEA), CoCrFeMnNi. First, the Hugoniot equations of state (EOS) for the samples are determined using laser-driven CoCrFeMnNi flyers launched into known Lithium Fluoride (LiF) windows. Photon Doppler Velocimetry (PDV) recordings of the velocity profiles find the EOS coefficients using an impedance mismatch technique. Following this set of measurements, laser-driven aluminum flyer plates are accelerated to velocities of 0.5–1.0 km/s using a high-energy pulse laser. Upon impact with CoCrFeMnNi samples, the shock response is found through PDV measurements of the free surface velocities. From this second set of measurements, the spall strength of the alloy is found for pressures up to 5 GPa and strain rates in excess of 106 s−1. Further analysis of the failure mechanisms behind the spallation is conducted using fractography revealing the occurrence of ductile fracture at voids presumed to be caused by chromium oxide deposits created during the manufacturing process.

Methods for the behaviour analysis of continuous flat water jet structures

This paper deals with visualization and geometrical analysis of flat water jet structures. The shadowgraphy method created by a CCD camera and high-energy pulsed laser, as well as the image analysis method were tested. The jet structures were captured in the centre of axis symmetry. The influence of water pressures on water clusters dimensions and droplets was studied. The designed diagnostic water line consisting of a pressure sensor and a turbine flowmeter was used for flow monitoring during experimental flow visualization. The impact pressures of impinging water clusters and droplets were measured in centre of the jet. The experimental tests were performed in the following range of operating conditions: water pressure up to 20 MPa at maximal flow rate of 39 l/min and hydraulic power of 13.32 kW. A linear relationship between the number of small droplets and the distance from the nozzle was analysed.

RETRACTED: Bridging the shocked monazite gap – Deformation microstructures in natural and laser shock-loaded samples

Impact-related damage in minerals and rocks provides key evidence to identify impact structures, and deformation of U-Th-minerals in target rocks, such as monazite, makes possible precise dating and determination of pressure-temperature conditions for impact events. Here a laser-driven shock experiment using a high-energy laser pulse of ns-order duration was carried out on a natural monazite crystal to compare experimentally produced shock-deformation microstructures with those observed in naturally shocked monazite. Deformation microstructures from regions that may have experienced up to ∼50 GPa and 1000°C were characterized using Raman spectroscopy and transmission electron microscopy. Experimental results were compared with nanoscale observations of deformation microstructures found in naturally shocked monazite from the Vredefort impact structure (South Africa). Raman-band broadening observed between unshocked and shocked monazite, responsible for a variation of ∼3 cm−1 in the FWHM, is interpreted to result from the competition between shock-induced distortion of the lattice, and post-shock annealing. At nanoscale, three main plastic deformation structures were found in both naturally and experimentally shocked monazite: deformation twins, mosaïcism, and deformation bands. The element Ca is enriched along host-twin boundaries, which further confirms that the laser shock loading experiment produced both comparable styles of crystal-plastic deformation, and also localized element mobility, as that found in natural shock-deformed monazite. Deformation twins form in the experiment were only along the (001) plane, an orientation which is not considered diagnostic of shock deformation. However, both mosaïcism and deformation, expressed in SAED patterns as streaking of spots, and the presence of extra spots (more or less pronounced), are interpreted as unambiguous nano-scale signatures of shock metamorphism in monazite. Experimentally calibrated deformation features, such as those documented here at TEM-scale, provide new tools for identifying evidence of shock deformation in natural samples.

Deploying the high-power pulsed lasers in precision force metrology – Towards SI traceable and practical force quantization by photon momentum

Abstract Design and operational performance of table-top measurement apparatus is presented towards direct Planck constant traceable high accuracy and high precision small forces and optical power measurements within the SI unit system. Electromagnetic force compensation weighing balances, highly reflective mirrors and high-energy pulsed laser unit (static average power 20 W) are tailored together with a specially developed opto-electro-mechanical measurement infrastructure for cross-mapping the scale-systems of two different precision small force measurement methods. One of these methods obtains the force measurements by a state-of-the-art classical kinematic system employing the partial use of Kibble balance principle in the range of 10 nN to 4000 nN to be compared with forces generated due to quantum-mechanical effect namely the transfer of the momentum of photons from a macroscopic object. Detailed overview of the adapted measurement methodology, the static and the limits of dynamic measurement, the metrological traceability routes of the measurement parameters, quantities and their measurement uncertainties, parametric estimation of up (down)-scaling perspectives of the measurements are presented with respect to the state-of-the-art measurement principles and standard procedures within the newly redefined International System of Units (SI).

Dissipative-soliton-resonance and evolution in an all-normal dispersion Er-doped fiber laser

The generation of dissipative soliton resonance (DSR) in an all-normal dispersion erbium-doped fiber laser based on a real saturable absorber is amazing in both experiment and theory. However, it’s rarely to realize DSR in an all-normal Er-doped fiber laser in experiments to our knowledge. In this work, we analyze the principle of DSR generated in an all-normal dispersion erbium-doped fiber laser based on a real saturable absorber, and prove that the key reason is the reverse saturable absorption (RSA) effect of the real saturable absorber (SA). Then, we investigate the impacts of pump power, filter, and RSA coefficient in generating DSR pulse. In addition, when the saturable power of SA is above 25 W and the modulation depth of SA above 50%, a novel soliton explosion phenomenon based on RSA in DSR region is obtained for the first time to our knowledge. The work can be used for understanding the dissipative soliton resonance as well as the evolution in an all-normal dispersion Er-doped fiber laser. Furthermore, it also paves a way to realize high stable and high energy pulsed lasers in telecommunication region.

Optical properties of Nd,Th:LaAlO3 demonstrates its potential in high-energy pulsed laser

Report, to the best of our knowledge, the first laser operation of perovskite oxide LaAlO3 doped with 1 at.% Nd ions and 0.2 at.%Th (Nd,Th:LaAlO3). Optical properties of Nd,Th:LaAlO3 were demonstrated. We study the influence of Th dopants on the domain structure and spectroscopic properties of LaAlO3. Under 793 nm diode-pumped excitation, we achieve a continuous-wave laser output at 1080 nm with a slope efficiency of 36 % and an optical-to-optical efficiency of 34 % under a Toc = 5 % output coupler. The emission cross section of Nd,Th:LaAlO3 reaches 3.65 × 10−20 cm2 at 1080 nm, the saturation flux is 5 J/cm2. The fluorescence lifetime reaches 317 μs and the thermal conductivity is 10.3 W/m·K at 25 °C. Considering its excellent mechanical properties and thermal conductivity, Nd,Th:LaAlO3 is a promising high-energy pulsed laser material.

Influence of beam waist radius on radiation characteristics of high energy electron and laser pulse collision

Influence of beam waist radius on radiation characteristics of high energy electron and laser pulse collision

Geochemistry study of soil affected catastrophically by tsunami disaster triggered by 2004 Indian Ocean earthquake using a fourth harmonics (λ = 266 nm) Nd:YAG laser induced breakdown spectroscopy

In this work, laser induced breakdown spectroscopy (LIBS) analysis of the soil samples collected from Aceh, a place in Indonesia worst affected by 2004 Indian Ocean tsunami, was conducted. In the LIBS experimental system, a high energy pulsed laser beam was focused on the tsunami affected soil samples and the atomic emission lines, originating from the laser induced plasma were recorded using locally developed laser induced breakdown spectrometer. Our results show that the concentrations of many elements especially terrestrial markers, namely titanium, iron, and carbonate marker such as magnesium, are higher in the tsunami-affected samples than that in the unaffected samples collected from the same neighborhood. The quantification of Ti, Fe and Mg were carried out using Ti II 334.94, Fe I 438.35, and Mg I 277.98 nm atomic transition lines respectively by drawing the calibration curve by preparing the samples of known concentrations in unaffected soil matrix. In order to ensure accurate quantification, the local thermal equilibrium of the laser-induced plasma was verified using Mc Writher criterion, for which the plasma temperature was estimated using linearized Boltzmann plot for six iron atomic transition lines and the electron number density in the plasma was estimated using Stark broadened Fe I 540.4 nm atomic lines. The estimated temperature and electron number density of the laser induced plasma are 9642 K and 3.5 × 10 16 cm −3 respectively. The concentrations of Ti, Fe and Mg in tsunami unaffected soil are 0.09, 3.2 and 0.02 w/w% and in tsunami affected soil are 0.14, 7.9 and 0.048 w/w% respectively. These values are in good agreement with XRF data. The elemental ratios extracted from LIBS signal intensity revealed that LIBS emission intensity ratios of several elements, such as Si/Ti, Al/Ti and Sr/Ba are potential candidates as the distinctive geochemical signature for identification the soil impacted and unimpacted by the 2004 Indian Ocean giant tsunami. The advantage of using LIBS for the elemental analysis is that the sample can be analyzed in its pristine form without any need cumbersome sample preparation method, which has the risk of bringing in external additives through chemicals used for the sample preparation. Other advantages of LIBS technique are that the analysis can be in situ and can be carried out remotely.

Stable passively Q-switched 1537 nm Er:Yb:Lu2Si2O7 pulse microlaser with peak output power higher than 10 kW at 1–2 kHz

Compact and stable passively Q-switched 1537 nm pulse microlasers operating at 1–2 kHz were developed based on Er:Yb:Lu2Si2O7 crystal. A stable 1537 nm pulse microlaser with single pulse energy of 33.0 μJ, width of 3.0 ns, repetition frequency of 1.0 kHz, and peak output power of 11.0 kW was realized, when the crystal was end-pumped by a 975.6 nm pulsed laser diode with pulse width of 0.3 ms and period of 1.0 ms. When the pump pulse period of the LD was changed to 0.5 ms, the repetition frequency of the output pulse laser increased to 2.0 kHz and the peak output power was still higher than 10.0 kW. The results show that the Er:Yb:Lu2Si2O7 crystal is an excellent gain medium for high-energy eye-safe pulse laser operating at kilohertz level.

Control of the wetting properties of stainless steel by ultrashort laser texturing using multi-parallel beam processing

The laser surface microtexturing is increasingly used for the production of surfaces with desired wetting characteristics (i.e., superhydrophobicity). For this not only precise but also fast laser processing is needed. Microtextures not based entirely on laser induced material self-organization require relatively tight focusing of the laser beam which can not be achieved using fast beam scanning systems. Therefore, in this work, the possibility to use parallel laser processing by multi-beam array for control of the EN 1.4301 (AISI 304) stainless steel surface was investigated. High-energy picosecond laser pulses were used to pattern the polished steel surface using 8 × 8 beam array with two different patterning strategies: mesh and dot. The multi-beam patterning inevitably brings some irregularities due to variation of properties of the beams in the array. However, after the investigation of the influence of laser patterning parameters on the wetting properties of the steel surface, it was determined that multi-beam mesh patterning allows obtaining superhydrophobic surface properties through the right combination of texture depth, surface chemical properties and laser induced surface ripples. The dot patterning was even more promising and was found suitable for obtaining a broad spectrum of wetting states ranging from superhydrophobic to superhydrophilic, when appropriate patterning parameters were used, mostly by controlling self-organized surface structure shape by changing texture period (laser spot overlap).