Laser-induced Thermal Effect Research Articles

Investigation of thermally induced nonlinear optical response of polyurethane-graphene composite by SSPM method

We conducted a study on composites made of polyurethane and graphene (PU-G). We synthesized these composites and then examined their far-field diffraction patterns at various concentrations of dimethylformamide (DMF) using the spatial self-phase modulation (SSPM) method. By analyzing the intensity-dependent far-field ring patterns, we were able to estimate the samples' thermally induced nonlinear refractive index and thermo-optical coefficient. We found that these variables, as well as other observable phenomena such as the “diffraction ring collapse effect” and “variation in nonlinear refractive index,” depended on the sample's concentration rate. Our results indicate that the laser-induced thermal effect is a significant factor in the SSPM phenomena observed in our experiments. Furthermore, our findings suggest that the PU/G combination in DMF has promising nonlinear optical properties that could be beneficial in a variety of nonlinear optics applications.

Laser-induced electro-response of oil shale: Principles and applications

This study introduces a laser-induced electro-response (LIER) method to address the challenges arising from the harsh detection environment and energy consumption in the conversion engineering of oil shale. LIER system with pulsed laser and continuous-wave laser was used to investigate the feasibility of oil yield detection and real-time pyrolysis characterization, respectively. The equivalent circuit model for oil shale measurement under the pulse laser irradiation was established, considering the laser-induced plasma and photoelectric effect. While the laser-induced thermal effect is the main cause of the LIER response of oil shale under continuous-wave laser irradiation. Due to the complex interactions between laser and oil shale, the LIER of oil shale is affected by many factors, such as external electric field, laser source type, laser wavelength, and laser energy or power. The external electric field can improve the responsivity of LIER. The LIER signal of oil shale strongly positively correlates with oil yield. Hence, the LIER evaluated oil yield more quickly without pyrolysis than traditional methods, which is helpful for the exploration for oil shale. In addition, the multi-stage LIER responses were monitored in real time during the combustion and pyrolysis processes of oil shale samples in air and N2 atmosphere, respectively, realizing an evaluation of the organic and mineral decomposition, which provides a supplementary approach to conventional chemical techniques. These results show that LIER has great significance for the precise evaluation and effective development of oil shale reservoirs, which will drive the advances in the exploration for oil shale.

Experimental and MD simulation study of surface residual stress and surface quality of SiCp/Al in pulsed laser-ultrasonic assisted grinding

The utilisation of aluminium-based silicon carbide composites (SiCp/Al) is on the rise. However, during the grinding process, where abrasive particles compel SiC particles into the aluminium matrix, stress concentration occurs near the interface between the two phases. This phenomenon results in adverse surface deformation accompanied by residual compressive stress (RCS). Consequently, a pulsed laser-ultrasonic-assisted grinding method (PL-UAG) has been proposed. The effectiveness of the method is verified through grinding experiments. Moreover, the influence process of the thermal effect of pulsed laser and the evolution mechanism of microscopic RS near the SiCp/Al two-phase interface are revealed through molecular dynamics simulation. The experimental results show that the surface RCS of SiCp/Al gradually decreases and transforms into residual tensile stress (RTS) with the increase of laser power. The RCS increases with the grinding depth. The RCS is reduced to 17 Mpa and the surface roughness Sa value is reduced to 0.110 μm with the laser power is 40 W and the grinding depth is 1 μm. The simulation results show that the energy dissipation process of pulsed laser helps to reduce thermal deformation and damage. The laser-induced thermal effect reduces the deformation of the aluminium matrix caused by particle extrusion and inhibits the formation and slip of dislocations in the aluminium matrix. In addition, the ultrasonic shock effect effectively weakens the RTS generated by the laser.

Laser-induced thermal effect on the electrical characteristics of photosensitive PbSe films

Laser-induced thermal effect on the electrical characteristics of photosensitive PbSe films

All-optical manipulation of charge density waves in kagome metal CsV3Sb5

A major challenge in condensed matter physics is to manipulate collective quantum phases by all-optical methods, which can open enormous new possibilities for materials and device engineering. Here we report an anomalous optical modulation of charge density waves (CDWs) in recently discovered kagome metal $\mathrm{Cs}{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ using femtosecond-resolved coherent phonon spectroscopy. This optically suppressed CDW phase surprisingly persists for nanoseconds, exhibits a monotonically lowering of transition temperature with increasing fluence, and does not require a critical absorbed photon density, which is intriguingly distinct from those found in the ``optically suppressed potential energy'' scenario. Pump-pump-probe experiments conclusively rule out the laser-induced thermal effect and time-dependent density functional theory simulations confirm that this nonthermal modulation stems from an optical tuning of the energy resonance between the band fermiology and the Van Hove singularity in kagome lattices. These findings open exciting prospects for all-optical engineering of the Van Hove scenario to tune correlated quantum phases in topology networks.

Uncovering the roles of laser action modes in surface mechanical properties of 2024 aluminum alloy

The surface state/performance after laser action is as essential as the interplay mechanism between laser and material. Through the designed experiments, the effect of distinct laser action modes on the evolution mechanism of aluminum alloy surface's microstructure and mechanical property was discussed. Under laser-induced thermal effect, the procedure of “vaporization - plasma plume - recoil effect - solidification” occurred. The grains grew longitudinally with an average size of 13.49 μm, which is smaller than that of substrate. Under the thermal oxidation, new oxides were formed. However, laser-induced force effect did not purpose a change in the composition. Importantly, force effect refined the grains to an average grain size as low as 6.21 μm. Notably, an anomaly was discovered. The thermal effect produced stress concentration that increases the residual stress by 64.7%, which caused the hardness to rebound. Additionally, surface composition and microstructure evolution led to the first decrease and then increase of friction coefficient. Due to grain refinement and residual stress induced by force effect, the hardness improved continuously and the friction coefficient decreased continuously. Understanding the influence mechanism of laser action modes on surface structure/property can furnish theoretical guidance for development of laser processing technology in the industrial field.

Laser-Induced Heating in GdVO4: Yb3+/Er3+ Nanocrystals for Thermometry

Photoluminescent temperature sensors based on gadolinium orthovanadate (GdVO4) doped with 10% ytterbium and 2% erbium are developed and dispersed in different media (lubricant fluid, sol–gel glass, and PDMS) to evaluate the best conditions for temperature measurement. Two excitation modes are considered: (i) visible excitation by a downshifting (DS) process or (ii) NIR excitation by energy transfer upconversion (UC) between Yb and Er. The luminescence intensity ratio (LIR) of the thermally coupled Er3+ emission peaks varies linearly with temperature in the range of 25–300 °C, and this variation is reversible. The impact of the laser power density on thermometry via the UC process that has been verified with GdVO4: Yb3+/Er3+ powders and with its different dilutions (low and high concentration) shows that the LIR is highly dependent on the laser source intensity, the environmental temperature, and the dispersed medium. When GdVO4: Yb3+/Er3+ powders are dispersed at high concentration, high laser power density leads to significant laser-induced thermal heating. However, at low concentration, this laser thermal effect is no longer influenced by the laser intensity. In this paper, we propose a method to directly measure the laser-induced heating temperature and to correct the error caused by this effect on temperature measurement. According to these results, GdVO4: Yb3+/Er3+ upconversion nanoparticles can be applied for temperature sensing even if the laser-induced thermal effect occurs in the system.

Optical and Thermal Behavior of Germanium Thin Films under Femtosecond Laser Irradiation.

In this study, we theoretically investigate the response of a germanium thin film under femtosecond pulsed laser irradiation. Electron and lattice temperatures, as well as material-specific optical properties such as dielectric function and reflectivity, were calculated during the irradiation using an extended two-temperature model coupled with the carrier density rate equation and the Drude model. Melting and ablation fluence thresholds were also predicted, resulting in 0.14 J cm-2 and 0.35 J cm-2, respectively. An ultrafast change in both optical and thermal properties was detected upon laser irradiation. Results also indicate that thermal melting occurs after germanium takes on a metallic character during irradiation, and that the impact ionization process may have a critical role in the laser-induced thermal effect. Therefore, we suggest that the origin of the thermal modification of germanium surface under femtosecond laser irradiation is mostly due the impact ionization process and that its effect becomes more important when increasing the laser fluence.

Theoretical and experimental studies on high-power laser-induced thermal blooming effect in chamber with different gases

High-power laser induced thermal blooming effects in a closed chamber with three different gases are investigated theoretically and experimentally in this work. In the theoretical treatment, an incompressible gas turbulent model is adopted. In the numerical simulation the gas refractive index as a function of both the temperature and pressure is taken into consideration. In the experimental study the pump-probe technology is adopted. A high-power 1064-nm fiber laser with maximum output power of 12 kW is used to drive the gas thermal blooming, and a 50-mW high-beam-quality 637-nm laser diode (LD) is used as a probe beam. The influences of the gas thermal blooming in the chamber on the probe beam wavefront and beam quality are analyzed for three different gases of air, nitrogen, and helium, respectively. The results indicate that nitrogen is well suitable for restraining thermal blooming effect for high-power laser. The measured data are in good agreement with the simulated results.

Laser Induced Thermal Effect on the Polymerization Behavior in Upconversion Particle Assisted Near-Infrared Photopolymerization.

Laser induced thermal effect is inevitable in upconversion particle assisted near-infrared polymerization (UCAP). Herein, the influence of thermal effects on the polymerization behavior are investigated. The effects of up-conversion particles content and NIR laser intensity on the polymerization rate and surface oxygen inhibition were systematically investigated, and the temperature evolution and complex viscosity changes in the polymerization system during the polymerization process were also monitored. In addition, polymerization experiments conducted on a controlled temperature platform were used to study the effect of NIR heating on the polymerization behavior. The results show that the near-infrared thermal effect promotes the polymerization reaction, but also causes severe oxygen inhibition which has an adverse effect on polymerization. Finally, NIR curing materials with enhanced mechanical properties than those of conventional UV curing materials were obtained.

Compensation Method for Laser-Induced Thermal Effect Using Passive Optics

Compensation Method for Laser-Induced Thermal Effect Using Passive Optics

Laser pressure welding of copper

Industrial application of copper often requires a joining. Unfortunately, a commercial laser welding of this material is challenging due to extremely high reflectivity of copper at the near-infrared wavelength. In this work, the sound copper joints were produced at relatively high welding speed of 15 m/min by using a pressure-assisted fiber-laser welding. It was theoretically shown that the material melting arisen from a convergence of multiple reflections of the laser beam. By using electron backscatter diffraction (EBSD), it was found that microstructural changes were induced by a laser-induced thermal effect as well as a roller-induced pressure. It was deduced that the molten material solidified before feeding to the pressure rolls and thus it experienced a notable plastic strain during the welding process. The present work provides an effective method for commercial joining of high-reflective metals by using the near-infrared fiber laser.

Spin pumping and laser modulated inverse spin Hall effect in yttrium iron garnet/germanium heterojunctions

In this work, undoped semiconductors, germanium (Ge) and germanium tin (GeSn), were grown on ferrimagnetic insulator yttrium iron garnet (YIG) thin films using ultra-high vacuum molecular beam epitaxy. The crystallinity of the structure was determined from x-ray diffraction and high-resolution transmission electron microscopy combined with energy dispersive x-ray spectroscopy. Both spin pumping and inverse spin Hall effects (ISHEs) of YIG/Ge and YIG/GeSn heterojunctions have been investigated with the help of broadband ferromagnetic resonance (FMR). We observe that the spin mixing conductances of YIG/Ge (60 nm) and YIG/GeSn (60 nm) are 5.4 × 1018 m−2 and 7.2 × 1018 m−2, respectively, responsible for giant spin current injection. Furthermore, it is found that spin pumping injects giant spin current from ferrimagnetic YIG into the Ge semiconductor. The infrared laser modulated ISHE was examined using heavy metal platinum as a spin current collector. Also, it has been noted that the variation in the power of laser irradiation significantly changed the ISHE voltage of YIG/Ge/Pt spin junctions, saturated magnetization, FMR linewidth, and Gilbert damping parameter of YIG, which could be attributed to the laser-induced thermal effect. The outcomes from this study are promising for the development of Ge-based spintronic and magnonic devices.

Laser-induced thermal effect and the role of Nd3+ in Tm3+/Yb3+/Nd3+ triply doped LaNbO4 up-conversion phosphors under 808 nm excitation

In this work, intense blue up-conversion (UC) luminescence in LaNbO4: Tm3+/Yb3+/Nd3+ phosphors were obtained under the excitation of 808 nm. The laser-induced thermal effect and the role of Nd3+ in this type of phosphors were discussed. Compared with Tm3+ singly doped and Tm3+/Yb3+ doubly doped samples, thousands-fold and 30-fold overall enhancement in the blue emission intensity of Tm3+ in Tm3+/Yb3+/Nd3+ triply doped LaNbO4 were achieved with the help of Nd3+ sensitizing and the energy transfer bridging Yb3+ ion. The luminescence-enhancement effect exhibited a strong dependence on Nd3+ doping concentration, and the optimal concentration of Nd3+ was found to be 1.0 mol%. Once the doping concentration of Nd3+ exceeded this value, concentration dependent luminescence quenching occurred. Moreover, the laser-induced thermal effect on Tm3+-doped samples was investigated by using Er3+-doped sample as the thermal probe. It was found that the elevation of sample temperature induced by laser irradiation depended on both the doping concentrations of Nd3+ and the excitation power density of 808 nm laser.

Numerical study of the effect of diode laser-induced optical, thermal, and residual stresses on CZTS thin-films

This paper presents a numerical study of the continuous wave (CW) diode laser processing of Cu2ZnSnS4 (CZTS) thin-film. The CZTS film’s structural, optical, surface morphological, and electrical properties improvement due to the localized and instantaneous heating provided by the diode laser mandates a detailed understanding of how laser processing affects the CZTS thin-film during thermal treatment to ensure a high-quality processing result as well as optimization and characterization. However, understanding of such process suffers from the restricted accessibility as most of the important phenomena occur inside the film during a very short duration time, where numerical simulations can serve as a valuable alternative to gain accessibility. This contribution, therefore, presents a numerical approach to examine the CW diode laser-induced thermal effect on the CZTS thin-film. A numerical model in OpenFOAM has been developed to elucidate the influence of laser processing parameters on the optical, heat transfer, and residual stress, as well as design architecture, of the CZTS thin-films. The model results predicted that the inappropriate settings of the laser parameters, as well as the thickness of the CZTS films, generate thermal gradient within the film and hence induce delamination and propagation of crack at the interfaces. The developed model helped in understanding the laser-induced thermal behavior of the CTZS thin-film and can be utilized as a guide to using lasers as an effective tool for fabricating the high-efficiency CZTS thin-film based solar cells.

Optical temperature sensing properties of KLu2F7: Yb3+/Er3+/Nd3+ nanoparticles under NIR excitation

Yb3+/Er3+/Nd3+ tri-doped KLu2F7 nanoparticles were fabricated via a typical co-precipitation method, and their phase structure, up-conversion (UC) emission and temperature sensing properties have been investigated in this work. An intense UC green emission originated from Er3+ ions is observed under the near infra-red (NIR) excitation. The maximum sensitivity of temperature is approximately 0.0044 K−1 at 533 K and 0.0041 K−1 at 413 K under the excitation of 980 and 808 nm, respectively. Meanwhile, KLu2F7: Yb3+/Er3+/Nd3+ nanoparticles exhibit excellent thermal stability under the NIR excitation. However, the thermal effect induced by 808 nm laser excitation is negligible compared with that of induced by 980 nm excitation, especially under a high pump power density excitation. It indicates that the employment of 808 nm excitation on KLu2F7: Yb3+/Er3+/Nd3+ system circumvents the laser-induced thermal effect as well as improves the accuracy of temperature sensing. Thus, it was proved that these nanoparticles provide a potential multifunctional application as thermometers and biosensors.

Coherent terahertz radiation via ultrafast manipulation of spin currents in ferromagnetic heterostructures

The development of efficient terahertz (THz) radiation sources is driven by the scientific and technological applications. To date, as far as the radiation of THz pulses is concerned, the widely used methods are biased semiconductor, electro-optical crystal and air plasma, which are excited separately by femtosecond laser pulses. The mechanisms involved in these THz sources are photo-carrier acceleration, second order nonlinear effect, and plasma oscillations, respectively. Here, we report the generation of coherent THz radiation in the designed ferromagnetic/non-magnetic metallic W/CoFeB/Pt and Ta/CoFeB/Pt trilayers on SiO2 substrates, excited separately by ultrafast laser pulses. The transient THz electric field is fully inverted when the magnetization is reversed, which indicates a strong connection between THz radiation and spin order of the sample. We present the THz radiation results of the bilayers, CoFeB/W, CoFeB/Pt and CoFeB/Ta, which are comprised of the trilayer heterostructures used in our experiments. We find that all experimental results are in good agreement with the results from the inversed spin-Hall effect (ISHE) mechanism. Owing to the ISHE, the transient spin current converts into a transient transverse charge current, which launches the THz electromagnetic wave. In our experiments, W or Ta has an opposite spin Hall angle to Pt. Therefore, the amplitude of the THz emission can be increased by a constructive superposition of two charge currents in metallic layers. Our results indicate that the peak-values of the THz radiation covering the 0-2.5 THz range from W/CoFeB/Pt and Ta/CoFeB/Pt are stronger than that from 0.5 mm thick ZnTe (110) crystal, under very similar excitation conditions. Finally, we investigate the dependence of peak-to-peak values for two different heterostructures on the pump fluence. The saturations of THz pulse at pump fluences of~0.47 mJ/cm2 and~0.61 mJ/cm2 are found for W/CoFeB/Pt and Ta/CoFeB/Pt heterostructures, respectively. The saturation can be generally attributed to the spin accumulation effect and laser-induced thermal effect. Our results indicate that the spin accumulation effect, by which the density of spin-polarized electrons is restricted in a non-magnetic metallic layer, is slightly less pronounced for Ta/CoFeB/Pt system at high fluences. Our findings provide a new pathway for fabricating the spintronic THz emitter, which is comparable to the conventional nonlinear optical crystals.

Optical temperature sensing properties of Yb3+/Tm3+ co-doped NaLuF4 crystals

Yb3+/Tm3+ and Yb3+/Er3+ co-doped NaLuF4 crystals were synthesized by a facile hydrothermal method. The optical temperature sensing properties of Tm3+ based upon its two thermally coupled energy levels 3F2, 3 and 3H4 were systematically investigated by means of fluorescence intensity ratio (FIR) technique. The 980 nm laser-induced thermal effect on Tm3+ doped NaLuF4 crystals was studied by using Er3+ doped sample as thermal probe. The temperature sensitivity of Tm3+ in NaLuF4: Yb3+/Tm3+ crystals shows a nonlinear dependence on temperature, and the maximum value is about 0.00045 K−1 at 600 K. The accuracy and reliability of the optical thermometry based on Tm3+ in NaLuF4: Yb3+/Tm3+ crystals has been checked by using Yb3+/Er3+ co-doped sample as temperature sensing unit. The results demonstrate that NaLuF4: Yb3+/Tm3+ crystals have good sensing stability and may have potential application for the optical thermometry.

Nd3+-Sensitized Upconversion Nanostructure as a Dual-Channel Emitting Optical Probe for Near Infrared-to-Near Infrared Fingerprint Imaging.

Lanthanide upconversion nanophosphors (Ln-UCNPs) have attracted great attention in a variety of fields, benefiting from low background fluorescence interference and a high signal-to-noise ratio of upconversion luminescence. However, the establishment of Ln-UCNPs with dual near-infrared (NIR) emission channels still remains challenging. Herein, we report the design and synthesis of Nd3+-sensitized NaYbF4:Tm@NaYF4:Yb@NaNdF4:Yb hierarchical-structured nanoparticles that emit NIR luminescence at 696 and 980 nm under excitation at 808 nm. The sensitizer-rich NaYbF4 core promotes efficient energy transfer to Tm3+. The interlayer of NaYF4:Yb effectively prevents the cross-relaxation process from Tm3+ to Nd3+ and thus enhances the luminescence emission. The introduction of Nd3+ ion as the sensitizer transforms the excitation wavelength from 980 to 808 nm, which subtly averts the laser-induced thermal effect and offers a new pathway for the NIR emission channel at 980 nm. The as-prepared nanoparticles were further applied in developing latent and blood fingerprint images, which exhibited high signal-to-noise ratio and distinguishable details under 808 nm excitation with negligible thermal damage to the sample. Our work provides a promising strategy to realize NIR-to-NIR dual-channel emissions in Ln-UCNPs. With further functionalization, such nanoparticles are expected to have great potential in forensic and biological sciences.

Femtosecond laser filament induced condensation and precipitation in a cloud chamber.

A unified picture of femtosecond laser induced precipitation in a cloud chamber is proposed. Among the three principal consequences of filamentation from the point of view of thermodynamics, namely, generation of chemicals, shock waves and thermal air flow motion (due to convection), the last one turns out to be the principal cause. Much of the filament induced chemicals would stick onto the existing background CCN’s (Cloud Condensation Nuclei) through collision making the latter more active. Strong mixing of air having a large temperature gradient would result in supersaturation in which the background CCN’s would grow efficiently into water/ice/snow. This conclusion was supported by two independent experiments using pure heating or a fan to imitate the laser-induced thermal effect or the strong air flow motion, respectively. Without the assistance of any shock wave and chemical CCN’s arising from laser filament, condensation and precipitation occurred. Meanwhile we believe that latent heat release during condensation /precipitation would enhance the air flow for mixing.