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The response of a DPbS3200 infrared detector irradiated by a nanosecond pulsed laser and CW laser has been investigated to study laser-induced interference. A laser interference experiment system was constructed to measure the time-varying response signal. A nanosecond pulsed laser and a CW laser of 10 Hz were used, with a 1064 nm wavelength and a millimeter-scale irradiation spot diameter. Firstly, the characteristics of transient interference signals induced by pulsed lasers were analyzed. Then, the characteristics of response signal interference by both CW laser and pulsed laser irradiation were further investigated. The results showed that the pulsed laser only produced transient interference. However, the CW laser led to a significant amplitude reduction of the response signal, which could continuously interfere in the operating time. For transient interferences, the amplitude of the interference signal increased linearly with the laser fluence. The relation between the pulse repetition rate of the incident laser and the operating frequency of the detector determined the numbers of transient interference signals in one response period; for the interference induced by both the CW laser and pulsed laser, CW laser interference played a leading role when CW laser power density increased to 4.1 W/cm2 or more. As the CW laser fluence reached 6.1 W/cm2, the PbS infrared detector was no longer able to detect any signal, which caused temporary blindness. In the end, a probit model was used to determine the interference threshold. [ABSTRACT FROM AUTHOR]

The spectral and laser output characteristics of Cr:ZnSe single crystals optically polished at four different lengths of 2, 3, 5, and 10 mm combined with or without antireflection (AR) coatings were investigated under pulse and continuous wave (CW) laser diode excitation at the wavelength of ~1.7 μm. The absorption and fluorescence spectra of Cr2+ ions were measured at room temperature. Optimization of laser system efficiency was performed step-by-step in dependence on the active length of the crystal sample, output coupler reflectivity, the duration of the pump pulse, and the repetition rate. For a given 1 : 1 transferring optics, a 3-mm thick AR-coated Cr:ZnSe crystal was chosen as optimal in pulse mode of operation: The ~10% higher maximum slope efficiency of ~39% with respect to optical-to-optical power conversion was obtained with the 3-mm thick AR-coated sample compared to the uncoated one. The laser system was characterized by an optimal repetition rate of 10 Hz and a pump pulse duration of 20 ms selected for its best efficiency performance. In CW mode, better results were observed with a thicker sample (5 mm, AR-coated). Specifically, the output power of ~2.7 W at the wavelength of ~2.4 μm with a slope efficiency of ~24% was obtained. In this case, the M2 beam parameter was measured as low as ~1.1 ± 0.1. Using a 0.8 mm thick MgF2 birefringent filter plate, the laser oscillations were continuously tunable in the range of ~2.1–2.7 μm within narrow spectral linewidths (5–10 nm FWHM) and a Gaussian beam profile in both the pulse and CW regimes. [ABSTRACT FROM AUTHOR]

This work conducts ablation experiments and multi-scale numerical simulations of C/SiC composite materials under CW laser action. The highest surface temperature, macroscopic and microscopic ablation morphology, and approximate ablation threshold for C/SiC composites at different power densities were obtained. A multi-scale ablation calculation method for C/SiC composite materials under CW laser action was established using the level-set method. At the meso-scale, a macro-mesoscopic cross-scale surface ablation model was established, taking into account factors such as solid heat transfer, heat exchange of chemical reactions, differential temperature rise process between internal fibers and matrix, and differences in ablation behavior of two-dimensional plain weave fabrics. The experimental and microscale simulation results indicate that different ablation behaviors (oxidation and sublimation) occur in different regions, resulting in "shoot tip" fibers and residual matrix pore morphology. This work can provide theoretical and experimental basis for the design and precision machining of C/SiC materials. [ABSTRACT FROM AUTHOR]

This study involves a simulation-based optimization of a wavelength division multiplexing (WDM) in a passive optical network system, and an RZ modulator, with incorporating a vertical cavity surface emitting laser (VCSEL) and an edge-emitting (CW) laser alternately. Two scenarios have been proposed. First, 8 VCSEL/CW lasers, having distinctive frequency, are assigned for each user in the WDM PON. In the second scenario, only one optical source (193.1 THz) is employed to share among the eight users of the PON. The first scenario supports 5 Gbps up to 150 km fiber length, and comparably, the VCSEL-based system provides a better Q-factor performance comparable with the CW laser-based system. The second scenario confirmed the transmission of 20 Gbps up to 150 km by the VCSEL-based system, while the CW laser system allowed 20 Gbps up to only 100 km, while demonstrating a lower Q-factor. [ABSTRACT FROM AUTHOR]

The development of high-energy continuous wave (CW) laser has enabled the generation of output powers ranging from 300 to 500 kW. Understanding the ablation mechanism of CW lasers at high laser fluence is crucial for the design of effective high-energy laser protection materials. We note that the particle-like impurities present in the protective coating material can induce defects on the ceramic-like target surface during high-energy CW laser ablation, which can alter the laser absorptivity and manifest a completely different ablation mechanism. Here, we systematically investigate the mechanism of high-energy CW laser ablation of alumina ceramic, with a specific focus on the roles of defect induction, energy transfer, and impact sputtering in the dynamic ablation of target. Specifically, the transient processes between high-energy CW laser and ceramic target will be investigated in terms of the evolution results of the ablation region, the microscopic characteristics of the ablated material, the high time-resolved on-line monitoring, and the multiphase hydrodynamics simulation. Finally, the transparent property of molten alumina ceramic to laser is proved to allow for penetrating damage to ceramic-metal composites.

The response of a DPbS3200 infrared detector irradiated by a nanosecond pulsed laser and CW laser has been investigated to study laser-induced interference. A laser interference experiment system was constructed to measure the time-varying response signal. A nanosecond pulsed laser and a CW laser of 10 Hz were used, with a 1064 nm wavelength and a millimeter-scale irradiation spot diameter. Firstly, the characteristics of transient interference signals induced by pulsed lasers were analyzed. Then, the characteristics of response signal interference by both CW laser and pulsed laser irradiation were further investigated. The results showed that the pulsed laser only produced transient interference. However, the CW laser led to a significant amplitude reduction of the response signal, which could continuously interfere in the operating time. For transient interferences, the amplitude of the interference signal increased linearly with the laser fluence. The relation between the pulse repetition rate of the incident laser and the operating frequency of the detector determined the numbers of transient interference signals in one response period; for the interference induced by both the CW laser and pulsed laser, CW laser interference played a leading role when CW laser power density increased to 4.1 W/cm2 or more. As the CW laser fluence reached 6.1 W/cm2, the PbS infrared detector was no longer able to detect any signal, which caused temporary blindness. In the end, a probit model was used to determine the interference threshold.

This study has presented spatial continuous wave laser and spatiotemporal vertical cavity surface emitting laser (VCSEL) for high speed long haul optical wireless communication channels. Possible data rates range from 40 Gb/s to 250 Gb/s over propagation distance ranges from 500 km to 2500 km. The optical wireless communication (OWC) system performance is tested through the measurement of maximum Q-factor, minimum bit error rate (BER) and signal to noise ratio (SNR). It is observed that spatiotemporal VCSEL has presented better performance than CW laser in the OWC system, especially for long haul transmission applications. It is observed that SNR improvement ratio ranges from 8.15 % to 19 % by using spatiotemporal VCSEL than CW laser for bit rate of 40 Gb/s over propagation distance ranges from 500 km to 2500 km. Max. Q-factor improvement ratio ranges from 4.62 % to 13.71 % by using spatiotemporal VCSEL than CW laser for data rate of 40 Gb/s over propagation distance ranges from 500 km to 2500 km. So it is clear that spatiotemporal VCSEL is more suitable for long haul OWC applications than other optical sources. [ABSTRACT FROM AUTHOR]

Continuous wave (CW) laser irradiation induces temperature changes in various phases within porous media, accompanied by phase change and gas transport. Water saturation is a crucial factor influencing this context's moisture and heat transfer process. This paper addresses this issue by establishing a theoretical model for CW laser irradiation on unsaturated porous media. Through experiments and simulations, it studies the effects of different water saturations on heat and mass transfer under laser irradiation. The results indicate that the critical depth reflects the influence of water saturation under laser irradiation on the distribution of solid-phase temperature in both time and space dimensions. Specifically, an increase in water saturation enhances the uniformity of solid-phase temperature distribution, while the gas temperature exhibits a similar distribution pattern. For mass transfer processes, it increases the evaporation rate and Darcy velocity of porous media within the effective range of laser irradiation. Lower water saturation facilitates phase change processes and accelerates gas transport rates. Importantly, this trend remains consistent even with the emergence of dry-saturation zones. Additionally, the decrease in water saturation has a coupled promoting effect on gas temperature and mass transfer processes. Lowering water saturation can increase gas temperature and consequently enhance mass transfer processes. Simultaneously, enhancing mass transfer processes benefits heat exchange between the two phases. In the four sets of experiments, the conformity of the surface temperature rise curves obtained from experiments and simulations is good, indicating that the model can accurately reflect the temperature rise patterns of sand particles. In summary, this work provides valuable research results on the effects of different water saturations on laser irradiation-induced temperature rise, phase change, and gas and moisture transport within porous media. It lays a specific theoretical foundation for laser soil remediation technology. [ABSTRACT FROM AUTHOR]

The study shows the basic interaction between different optical sources and optical detectors for high-speed optical communication networks. Optical sources that are namely continuous wave (CW) laser, laser rate equations as well as the vertical cavity surface emitting laser (VCSEL). The utilized optical modulators are indicated as Mach Zehnder modulator (MZM) as well as the Electro-absorption modulator (EAM). The data rate available 40 Gb/s for propagation length ranges from 10 km to 50 km. It is observed that the interaction between CW laser/MZM or CW laser/EAM has presented better performance than other combinations. In order to measure the system performances, many interesting parameters have been investigated. These can be including the electrical received power, highest signal quality factor, Optical signal per noise ratio as well as the lowest data error rates. [ABSTRACT FROM AUTHOR]

• A method of CW laser-assisted splitting of SiC wafer based on modified layer by picosecond laser. • A model of modified layer under CW laser was established, the mechanism of CW laser induced SiC wafer splitting was analyzed. • The splitting of 1cm×1cm×500μm SiC wafers was achieved without applying external force with optimized laser parameters. Silicon carbide (SiC), the third-generation semiconductor material, is important in developing electronic power devices. Compared to wire sawing technology, Laser splitting SiC is an efficient way to produce SiC wafers with reduced material loss. In this work, we propose a new method of continuous wave (CW) laser-assisted splitting of SiC wafer based on modified layer by picosecond laser. For the process of CW laser irradiation on the modified layer, thermal–mechanical numerical simulations were performed to calculate the temperature and stress fields during laser loading. The mechanism of CW laser-assisted SiC wafer splitting was analyzed to guide the selection of CW laser parameters. The microstructure, element distribution, and stress state of the split SiC wafer surface were investigated and analyzed. The results showed that laser processing did not affect the crystal structure and carrier concentration of SiC. Compressive stress was generated on the splitting surface. Polycrystalline carbon and single crystalline silicon appeared on the splitting surface with a 50-250 nm thickness. The layer with compressive stress and polycrystalline microstructures can be removed after grinding and polishing. [ABSTRACT FROM AUTHOR]

This paper presents the development and characterization of high-speed ON-OFF Keying (OOK) Optical Transmitter up to 12 Gbps using External Modulation Technique that comprises Continuous Wave (CW) laser, Mach-Zehnder Modulator (MZM), and ultra-high bandwidth driver amplifier for MZM. The CW laser driver and high bandwidth modulator driver amplifier has been designed and integrated with the modulator which is biased for OOK modulation scheme. This work includes Direct Current (DC), Optical and Radio Frequency (RF) characterization of MZM modulator; selection of suitable bias point for modulator to achieve OOK modulation format, design and development of wideband driver amplifier in microstrip configuration on 25-mil alumina using Hittite device. The biasing circuit for distributed feedback laser is designed as an unmodulated CW optical signal to feed optical modulator. In this work, the assembly and characterization of optical transmitter is also carried out and performance is analyzed in terms of different parameters such as Extinction ratio and Signal-to-Noise Ratio (SNR) etc. [ABSTRACT FROM AUTHOR]

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In general, pulsed lasers with high peak power have been used for the micro-groove formation. However, the processing speed is limited by the pulse repetition rate. On the other hand, CW laser can be expected to perform the high-speed processing by continuous energy input. The mechanism of micro-groove formation by CW laser was investigated by high-speed observation and the thermal fluid analysis. In the perpendicular irradiation of CW laser, the molten metal flows symmetrically around the keyhole to the backward direction, and micro-grooves remain at both edges of molten region. In contrast, in the angled irradiation, the molten metal at the reflection-side scatters as spatters. The remained molten metal flows from the reflection-side to the incident-side through the bottom of keyhole, since the recoil pressure is generated from the reflection-side to the incident-side. In addition, high-speed scanning contributes to keeping the sufficient time and force to move the molten metal in the backward direction. Then, the micro-groove remains at the reflection-side, while the upheaval is formed at the incident-side by gathering the molten metal from the reflection-side and the front of keyhole. Asymmetrical behavior of molten metal flow in angled irradiation of CW laser can create micro-groove in the reflection-side. [ABSTRACT FROM AUTHOR]

Coherent communication aims to support high-speed dynamic networks by making their installation easier along with their monitoring and maintenance. In addition, Orthogonal Frequency Division Multiplexing (OFDM) which has shown gradual emergence in radio frequency (RF) domain during the past years, has now encroached into the optical domain. Combination of these two provides vigorous dispersion transmission as well as enhanced spectral efficiency. Free Space Optical (FSO) communication link performance deteriorates with scintillations, atmospheric turbulences and weather induced attenuations. The optical amplifiers, their arrangement used in the FSO link design has a drastic influence on the performance of the link. This work involves evaluating the proposed Coherent Optical OFDM FSO communication link at 30 Gbps data rate using Cascaded Erbium Doped Fiber Amplifier. The system has been evaluated in clear weather, rainfall and fog (Moderate to Dense) in terms of Q-Factor, BER, SNR and constellation diagram. The system has been designed considering moderate turbulent environment and geometric losses. The FSO communication link shows optimal performance up to 26 km for clear weather, 3.73 km under rainfall, 1.44 km under moderate foggy and 0.66 km under dense foggy environment. [ABSTRACT FROM AUTHOR]

Aluminum alloy is the main material of pole ear plate and bus bar of power cells for new energy electric vehicles. In this paper, quasi-continuous wave (QCW) pulsed laser and single-mode continuous wave (CW) laser were used to conduct laser lap welding experiments on a 0.5 mm thick 1060 aluminum alloy and 2 mm thick 6061 aluminum alloy. The effects of these two laser sources on weld zone morphology and tensile force were compared. The experimental results show that the QCW pulsed laser welding is more likely to have porosity cracks and other defects, while the overall weld performance of the single-mode CW laser welding is obviously better than the former. In addition, the maximum tensile strength of the weld joint in QCW welding is about 861.02 N, while it can reach 1521.36 N in CW welding. The tensile force with CW laser welding is much higher than that required by the power battery industry standard, i.e., the tensile force of 800 N. [ABSTRACT FROM AUTHOR]

In this study, the CW laser is used as a local heat source to simulate the extreme thermal environment generated by shock wave interference at discontinuities in spacecraft. The ablation behavior of the thermal protection material (C/SiC) is investigated under the combined impact of high-temperature airflow and the local extreme heat source. A novel multi-field coupling numerical computation software was presented to examine this strong coupling process of fluid-solid-thermal-ablation. The program was modified using the ALE + umeshmotion ablation calculation method in the ABAQUS software to mimic the process of the material's ablative boundary retreating under the action of the CW laser until the target was perforated. ANSYS Fluent software was used to do the numerical analysis of the high-speed airflow. The results of wind tunnel experiments and numerical simulations indicate that, compared to the effect of local heat sources in static air, irregular ablation pits are formed on the material surface under the action of local heat sources in high-temperature flow fields, resulting in higher ablation rates due to mechanical denudation effects. Analysis of the localization characteristics of the flow field near the ablation pit reveals that the shock wave generated downstream of the ablation pit leads to an increase in gas temperature, pressure, and density. When the ablation amount reaches a certain threshold, the gas in the ablation pit forms vortices, leading to an increase in local heat flow and pressure. [ABSTRACT FROM AUTHOR]

This paper is the first report of advancement in the drastic reduction of the laser power density from 105 to 7.5 W/cm² for the synthesis of silver nanoparticles (SNPs) using a low power (60mW) continuous-wave (cw) laser and a specially designed ultralow duty cycle (3%) optical chopper wheel for modulating the laser beam at low frequencies (2 Hz). The target is irradiated by keeping it in a liquid medium at 40-60 °C to produce quantum dots to SNPs of size less than 40 nm. The UV-visible spectroscopic and electron microscopic analyses confirm the formation of quantum dots and SNPs of size-dependent bandgap energy varying from 1.92 to 2.37 eV. The photoluminescence studies not only support the above observations but also reveal the blue emission upon UV excitation through the chromaticity diagram. The proposed greener approach using the low power cw laser is cost-effective when compared with the high-power laser-assisted synthesis of SNPs reported until now. [ABSTRACT FROM AUTHOR]

The oxidation ablation of carbon fiber-reinforced polymer (CFRP) induced by a continuous wave (CW) laser under tangential airflow was modeled in this study. The fluid of the airflow and the diffusion of the oxygen in the boundary layer were simulated. The numerical predictions indicated that the center of the ablation pit deviated from the center of laser spot, which moved to the downstream area from the upstream area as the ablation time increased. These results were proven by the laser ablation experiments. The vortex appeared in the airflow when the ablation pit was deep enough. It significantly modified the mass transport of oxygen due to the recirculation in the ablation pit. Based on this model, the impacts of the airflow velocity, the laser power density, and the laser spot radius on the shift were investigated. The results of this work can be referenced for the applications of laser processing and laser damage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fabrication notch and pre-crack sharpening for the fracture toughness test by the laser ablation method. • Repeatable and controllable results for the fracture toughness of 5052-epoxy resin and 5052-epoxy resin/MWCNTs composites. • Accurate control of the CW CO 2 laser parameters for sample preparation. In this work, a repeatable, controllable, non-contact, cost-effective, and fast method of producing notches and pre-cracks for the accurate measurement of the fracture toughness test of epoxy resin composites is suggested. The fabrication of the notches and pre-cracks for the fracture toughness test of a 5052-epoxy resin and 5052-epoxy resin/0.1, 0.5, and 1.0 wt% MWCNTs nanocomposites were done using a steel razor blade method and a laser ablation method. A continuous-wave CO 2 laser with a power of 150 W, a wavelength of 1064 nm, a spot size of 100 µm for the Gaussian beam, and a focusing distance of 50 mm in atmospheric conditions was applied. The fracture toughness results of the laser ablation and the steel razor blade methods were compared. The created notches and sharp pre-cracks had the highest accuracy and reproducibility with no plastic deformation ahead of the pre-cracking tip compared to other similar investigations. The radius of the pre-cracking tips in the as-prepared samples with the laser method was less than approximately 5 µm. The average values of the fracture toughness of an epoxy resin and epoxy resin/0.1, 0.5, and 1.0 wt% MWCNTs nanocomposites with sharpened pre-cracks produced by the laser method were 0.826 ± 0.005, 1.10 ± 0.025, 1.23 ± 0.025, and 1.09 ± 0.015 MPa m1/2, respectively. The obtained fracture toughness values of the laser method were repeatable with an error accuracy of less than ± 0.005 and corresponded to the ISO and ASTM standards. [ABSTRACT FROM AUTHOR]

In order to improve the anti-laser performance of optical thin film sinthesophisticated laser application systems, the thermal effect of MWIR filter, inducedby1.06 μm and2.0 μm CW laser from either the lower cut-off side or the upper cut-off side, have been carefully studied with the approaches of both simulation and experiment．In this paper, the electric field distribution, thermal loss and temperature change of MWIR filter are investigated to show their dependence on the input laser wavelength, the difference between the lower cut-off side and the upperc ut-off side of the films, respectively．The results demonstrate that the main factors affecting the thermal effect of MWIR filter include laser power density, irradiated side,size and absorption rate of the MWIR filter．In addition, the thermal effect of MWIR filter induced by 1.06 μmCW laser shows more significance than that inducedby 2.0 μm CW laser． [ABSTRACT FROM AUTHOR]

• A 3D model considering ablation rates related to laminated structure is developed. • Non-monotonic temperature rising is observed during laser irradiation. • An elliptic ablation morphology is predicted by our model and proved by experiment. The influences of structure on the ablation characteristics of carbon fiber composites under CW laser irradiation are investigated experimentally and numerically. The different ablation performance, that presented parallel and perpendicular to the carbon fiber orientation within the same layer, and the laminated structure of the carbon fiber composites are included in the proposed 3D numerical model to study the ablation characteristics of composites. The model is verified by laser ablation experiments. The numerical results indicate that the variation of the orientation of the elliptic ablation profile is decided by the difference of ablation performance and the laminated structure. The non-monotonic temperature rising and the shape of heat affect zone at the material surface exposed to the laser radiation are associated with the heat flux in the laminated structure and has little to do with the difference of ablation performance. [ABSTRACT FROM AUTHOR]

Single-crystal fibers (SCFs) have a great application potential in high-power lasers due to their excellent performance. In this work, high-quality and crack-free Yb3+:Lu3Al5O12 (Yb:LuAG) SCFs were successfully fabricated by the micro-pulling-down (μ-PD) technology. Based on the laser micrometer and the X-ray Laue diffraction results, these Yb:LuAG SCFs have a less than 5% diameter fluctuation and good crystallinity along the axial direction. More importantly, the distribution of Yb ions is proved to be uniform by electron probe microanalysis (EPMA) and the scanning electron microscope (SEM). In the laser experiment, the continuous-wave (CW) output power using a 1 mm diameter Yb:LuAG single-crystal fiber is determined to be 1.96 W, at the central wavelength of 1047 nm, corresponding to a slope efficiency of 13.55%. Meanwhile, by applying a 3 mm diameter Yb:LuAG SCF, we obtain a 4.7 W CW laser output at 1049 nm with the slope efficiency of 22.17%. The beam quality factor M2 is less than 1.1 in both conditions, indicating a good optical quality of the grown fiber. Our results show that the Yb:LuAG SCF is a potential solid-state laser gain medium for 1 μm high-power lasers.

This paper presented a three dimensional deformation and full-field temperature measurement method for continuous wave laser irradiated structures over a range extending from the room temperature to the melting point. The deformation was measured by the three dimensional digital image correlation technique. The speckle pattern was made on the specimen surface by the high temperature glue with a maximum service temperature of 1700 °C. A bandpass filter and a blue light source were used to eliminate the effect of thermal radiation from the laser irradiated region. The accuracy of present method was validated by the coordinate measurement machine and the laser Doppler vibrometer. According to the relationship between the gray value of images and the temperature, the full-field temperature distribution were measured by the colorimetry temperature measurement method. Finally, parameters that affect the response of laser irradiated thin plates, including laser power, high-speed airflow, plate thickness and material properties are investigated. [ABSTRACT FROM AUTHOR]

Abstract Remote processes with brilliant continuous wave lasers enable highly efficient laser processes. When cutting and abrading metal or composite materials, a large amount of particles and emissions arise. In general the emissions will be exhausted. But a high amount of substances contaminates the treated part as well as the laser machine equipment and is a high health risk for the machine operator. Based on this challenge, scientific investigations were done during laser structuring with high power fiber lasers. The generated particles and emissions were evaluated and classified. To minimize the part decontaminations new air knife – cross jet solutions were tested and optimized using gas and particle flow simulations. The results of this work support the user of remote processes in guaranteeing the health and environmental regulations. [ABSTRACT FROM AUTHOR]

The aim of this work is to investigate the influence of surface structures on the adhesion strength of metal-plastic hybrids. Aluminum substrates were structured with continuous wave and picosecond pulsed laser systems and overmolded with a thermoplastic polyamide material. The materials were examined in terms of structure topography, molding accuracy, and a tensile shear test. It was found that the surface pretreatment by laser structuring with continuous wave laser enhances the effective joining surface, creates a mechanical interlocking, and increases the adhesion strength of the hybrid compared to the untreated condition significantly. A shear strength of 11.9 MPa was achieved, which exploits 90% of the pure polyamide properties. [ABSTRACT FROM AUTHOR]

The unsteady measurement of spatiotemporally varying flow structures in a low-speed wind tunnel using a continuous wave (CW) laser-based time-resolved particle image velocimetry (TR-PIV) setup was extensively evaluated in the near wake behind a circular cylinder. A CW laser with a maximum power of 25 W in combination with a high-speed camera operating at 7 kHz was used to determine the wake flows at two different free-stream flow speeds: U = 5 and 10 m/s. Three different camera exposure times were selected for comparison: τ = 20, 50, and 80 μs. In the experiments, the low-repetition conventional PIV setup using the high-power pulsed laser ( τ = 8 ns, 135 mJ/pulse) was used to determine the time-mean and statistical flow quantities, which served as the reference for determining the deviation in the TR-PIV measurements. At the lower flow speed of U = 5 m/s, the time-mean-separated flow patterns and the streamwise velocity profiles in all of the TR-PIV systems showed satisfactory agreement with the conventional PIV measurements, along with accurate capture of the large-scale Karman vortex and its harmonic behaviors. At the higher flow speed of U = 10 m/s, the measurement at τ = 50 μs gave a relatively accurate representation of the statistical flow quantities. At the longest exposure time of τ = 80 μs, considerable deviations in the time-mean streamwise fluctuation intensity and the TKE (turbulence kinetic energy) were observed due to the streaky particle image. The strong swirling motion of the large-scale vortical structures increased the deviation in the TR-PIV measurements, which increased with the increasing camera exposure time. Further POD analysis demonstrated that the leading energetic modes in the system with τ = 50 μs accurately determined the spatial features of the Karman-like vortex and its harmonic events. However, inaccurate vector representation of the second harmonic events was observed in the system with τ = 80 μs. Finally, for both flow speeds, the lower-order reconstructed phase-dependent representations of the Karman-like vortex and its harmonic behaviors were composed of the time-series velocity vector fields determined using the system with τ = 50 μs, thus providing a straightforward quantitative view of the coupled unsteady events. Graphical Abstract: [ABSTRACT FROM AUTHOR]

[Display omitted] • Laser direct writing into (GeS 2) x (As 2 S 3) (1-x) bulk glasses with 0 < x < 1. • Microlenses formation by CW 532 nm laser with threshold power density < 3 W/cm2. • Chemical composition and illumination conditions study for microlens formation. • Local temperature increase and in-situ microlens formation and relaxation studied. • Potential applicability of created microlenses in miniaturization optics. Laser direct writing using continuous-wave laser emitting at 532 nm was successfully performed into stoichiometric (GeS 2) x (As 2 S 3) (1-x) bulk glasses, where 0 ≤ x ≤ 1. The illumination of the samples led to the microlenses and microcraters formation. The influence of chemical composition and illumination conditions was studied especially on the microlens formation in order to create the highest one. The created microlenses and non-illuminated area were characterized with the help of digital holographic and atomic force microscopies, energy-dispersive X-ray analysis, Raman and Force spectroscopies in order to find the potential differences in properties between them. The created microlenses have the potential applicability in miniaturization optics due to their radius of curvature and focal length. The increase in local temperature caused by the laser illumination was estimated by COMSOL software. For the comparison, in–situ microlens formation was studied by the modified thermo-mechanical analyzer. [ABSTRACT FROM AUTHOR]

Bubbles generated with lasers in liquids under confinement have been investigated for their potential use as the driving mechanism for liquid micro-jets in various microfluidic devices, such as needle-free jet injectors. Here, we report on the study of bubble formation by a continuous-wave (CW) and a pulsed laser inside an open-ended microfluidic capillary. This results in a direct comparison between bubbles generated by laser sources emitting light in different time scales (ms and ns). The bubble kinetics represents an important parameter because it determines the available kinetic energy for a subsequent liquid jet. We show that the bubble growth rate increases linearly with the delivered energy for both the CW and the pulsed laser. Experiments show that at equal absorption coefficient, the bubble growth for both lasers is similar, which indicates that they can be used interchangeably for jet generation purposes. However, bubbles generated by a CW laser require more optical energy, which is due to heat dissipation. Furthermore, the bubbles generated by the CW laser show a slightly larger variation in size and growth rate for identical initial conditions, which we attribute to the stochastic nature of thermocavitation. [Display omitted] • Pulsed and CW lasers can create similar bubbles for needle-free jet injectors. • The bubble growth rate increases linearly with delivered laser energy. • The energy threshold is proportional to irradiated volume for pulsed lasers. • Bubbles generated by CW lasers are slightly less reproducible. [ABSTRACT FROM AUTHOR]

We report on diode-pumped disordered Nd:LuYSiO 5 (Nd:LYSO) crystal lasers operating on the 4 F 3/2 → 4 I 11/2 and 4 F 3/2 → 4 I 13/2 transitions. Simultaneous laser operation at 1074 and 1078 nm is achieved with maximum output power of 4.46 W and slope efficiency of 39.6%. Single wavelength laser at 1358 nm with maximum output power of 1.15 W and slope efficiency of 11.8% is also obtained. Moreover, four single-wavelength lasers at 1058, 1107, 1330 and 1386 nm with relatively low gains are achieved with maximum output powers of 2.72, 1.22, 0.52 and 0.42 W, respectively, for the first time to our knowledge. Lasing at non-traditional emission lines was obtained by using output couplers with dielectric coatings for specific wavelength ranges. [ABSTRACT FROM AUTHOR]

A novel architecture of bidirectional gigabit signal transport system over long-haul single-mode fiber (SMF) using wavelength division multiplexed passive optical network technique is proposed and demonstrated. In order to offer multimedia services of high bandwidth, four signals of 5 Gbps data rates are externally modulated and transmitted through four channels over 100-km SMF in uplink and downlink. In our proposed scheme, an excellent bit error rate, good Q-factor and clear eye diagrams are observed for both 100-km uplink and downlink transmission. This architecture has potential to transmit 4 × 5 Gbps over long-haul fiber backbone and it will be useful in future broadband communications. [ABSTRACT FROM AUTHOR]

Laser irradiation effects on the combination of levodopa and carbidopa in the presence and absence of magnetic field were studied. The structural and surface morphology of irradiated targets were measured by X-ray diffractometer (XRD) and scanning electron microscopy (SEM), respectively. Energy dispersive X-ray spectrometry (EDS) was used for chemical analysis. XRD analysis indicates increase in grain size for 2 min laser irradiation in the absence of magnetic field, but for 4 and 6 min it revealed decrease in grain size. While grain size decreased at 2 and 4 min exposures in the presence of magnetic field but grain size slightly increased with the increase of exposure time up to 6 min. Micro-nano-sized structures (including hydrodynamic sputtering, splashing and crater) were observed by SEM analysis. EDS displayed peaks for carbon (C) and oxygen (O), but peaks for hydrogen (H) and nitrogen (N) are missing. The present study will provide basis for the use of low-cost and environment-friendly diode laser to enhance the characteristics of this combination (levodopa + carbidopa). [ABSTRACT FROM AUTHOR]

The failure response of aluminum alloys (Al-6061 and Al-7075) under the condition of simultaneously pre-stressing and laser heating was investigated. Specimens were subjected to predetermined preloading states and then irradiated by continuous wave fiber (Yb) laser. For all specimens, it was found that the yield stress decreased with increasing laser power density. This implies that the load-bearing capacity of the specimens reduced under increased thermal or tensile loading. Consequently, the specimen's failure time was shortened by increasing either laser power density or preloaded speed. For Al-6061, a remarkable reduction in failure time by the increase of laser power density is found. However, for Al-7075, under higher preloaded speeds, comparatively smaller impact of laser power density on the failure time is reported. Moreover, for Al-6061, relatively a more non-uniform variation in the average failure time with the increase of laser power density or preloaded speed is observed. The failure mode of Al-6061 turned from brittle to ductile at higher laser power densities; whereas for Al-7075, it changed from quasi-brittle to ductile. At higher preloaded speeds, a greater degree of melting and ablation phenomenon can be seen due to relatively higher temperatures and higher heating rates. [ABSTRACT FROM AUTHOR]

This current project is dedicated to a fast, easy and one step method for the synthesis of gold nano-particles. Gold (Au) nano-particles have been fabricated by laser ablation method in de-ionized water. The purpose was to explore the dependence of the various properties of the gold nano particles on the nature of laser. In order to prepare colloidal solutions, a low power continuous wave (CW) diode laser and a nanosecond pulsed Nd:YAG laser have been used to ablate the gold target. The structural, physical, optical and thermal characteristics of prepared nano-particles have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), UV–vis spectroscopy and thermal conductivity of liquids and gases unit (TCLGU), respectively. The XRD analyses revealed the formation of polycrystalline gold nano-particles with (111), (200) and (220) plans in case of both the lasers. AFM micrographs showed that prepared nano-particles are spherical in dimensions. The size of nanoparticles synthesized by CW laser ranges from 5 to 20 nm whereas the size ranges from 12 to 49 nm in case of pulsed laser. UV–vis spectroscopy showed surface plasmon resonance (SPR) peak at 512 nm for CW laser prepared nanoparticles as compared to pulsed laser at 525 nm which is also indicative of the smaller size in case of CW laser. The thermal conductivity of colloidal solution prepared by CW laser is 33% whereas in case of pulsed laser is 48% more as compared to the deionized water (base liquid). [ABSTRACT FROM AUTHOR]

This paper presents a theoretical model to evaluate the thrust generated by a continuous wave (CW) laser, operating at moderate intensity (<100 GW/m 2 ), ablating an S-type asteroid made of Forsterite. The key metric to assess the performance of the laser system is the thrust coupling coefficient which is given by the ratio between thrust and associated optical power. Three different models are developed in the paper: a one dimensional steady state model, a full 3D steady state model and a one dimensional model accounting for transient effects resulting from the tumbling motion of the asteroid. The results obtained with these models are used to derive key requirements and constraints on the laser system that allow approaching the ideal performance in a realistic case. [ABSTRACT FROM AUTHOR]

Recently, ultrafast lasers exhibiting high peak powers and extremely short pulse durations have created a new paradigm in materials processing. The precision and minimal thermal damage provided by ultrafast lasers in the machining of metals and dielectrics also suggests a novel application in obtaining precise cross-sections of fragile, combustible paint layers in artwork and cultural heritage property. Cross-sections of paint and other decorative layers on artwork provide critical information into its history and authenticity. However, the current methodology which uses a scalpel to obtain a cross-section can cause further damage, including crumbling, delamination, and paint compression. Here, we demonstrate the ability to make controlled cross-sections of paint layers with a femtosecond pulsed laser, with minimal damage to the surrounding artwork. The femtosecond laser cutting overcomes challenges such as fragile paint disintegrating under scalpel pressure, or oxidation by the continuous-wave (CW) laser. Variations in laser power and translational speed of the laser while cutting exhibit different benefits for cross-section sampling. The use of femtosecond lasers in studying artwork also presents new possibilities in analyzing, sampling, and cleaning of artwork with minimal destructive effects. [ABSTRACT FROM AUTHOR]

Laser marking has the characteristics of a dry process and has been widely used in many industries. Making more colors on the material would be more applicable; however, it is challenging to fabricate green colors through laser heating on titanium (Ti). In this study, a CW (continuous wave) laser with a wavelength of 1064 nm was used to make various colors on the Ti surface. CIE (Commission Internationale de l'Eclairage) color measurement shows that almost green color was achieved. Furthermore, the relationship between laser process parameters and surface temperature is established with an infrared (IR) camera. • The CIE spectrometer analysis validating colors close to green is available. • Green color has been achieved on Ti by CW laser. • The surface temperature was close to the heating threshold. [ABSTRACT FROM AUTHOR]

A practical study has been carried out on axial flow CW CO2 laser bychanging the output coupler with a wide range of reflectivities. ZnSe mirrorswere used in various reflectivities (20, 30, 40, 45, 50, 55, 60, 65, 70,75,80,85,90).It has been found that the output power varies considerably with varies thereflectivity of the output coupler. Thus the optimum reflectivity for 1moptical length and 1cm discharge tube of CW CO2 laser is found to be 65±5%. Our results have been compared with other published data.

The nonlinear optical properties of Giemsa dye in chloroform solution for different concentrations and dye mixed with poly(methylmethacrylate) (PMMA) as a dye-doped polymer film were investigated using continuous wave (CW) low power solid-state laser (SSL) operating at wavelength of 532 nm as an excitation source. Using the single beam z-scan technique, the nonlinear refractive index (n 2 ), the nonlinear absorption coefficient (β), and the third-order nonlinear optical susceptibility (χ (3) ) of Giemsa dye were measured. The measurements reveal that both n 2 and β are dependent on the dye concentration. The obtained results indicate that the Giemsa dye exhibits positive nonlinear saturable absorption (SA) and negative refraction nonlinearity, manifestation of self-defocusing effect. Optical power limiting characteristics of the Giemsa dye at different concentrations in solution and polymer film were studied. The observed large third-order optical nonlinearity of Giemsa dye confirms that Giemsa dye is a promising nonlinear material for the optical power limiting and photonic devices applications. [ABSTRACT FROM AUTHOR]