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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 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.

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]

• 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]

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]

[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]