Laser Heating Method Research Articles

Optimizing auxiliary laser heating for Kerr soliton microcomb generation.

Auxiliary laser heating has become a widely adopted method for Kerr soliton frequency comb generation in optical microcavities, thanks to its reliable and easy-to-achieve merits for solving the thermal instability during the formation of dissipative Kerr solitons. Here, we conduct optimization of auxiliary laser heating by leveraging the distinct loss and absorption characteristics of different longitudinal and polarization cavity modes. We show that even if the auxiliary and pump lasers enter orthogonal polarization modes, their mutual photothermal balance can be efficient enough to maintain a cavity thermal equilibrium as the pump laser enters the red-detuning soliton regime, and by choosing the most suitable resonance for the auxiliary and pump lasers, the auxiliary laser power can be reduced to 20% of the pump laser and still be capable of warranting soliton generation. Moreover, we demonstrate soliton comb generation using integrated laser modules with a few milliwatt on-chip pump and auxiliary powers, showcasing the potential for further chip integration of the auxiliary laser heating method.

Fatigue life prediction of AA2524 thin plate strengthened using compound laser heating and laser shot peening method

AA2524 is a aluminum alloy based on damage tolerance design, and it is mainly used for the manufacturing of aircraft skins. Aircraft skins often occur fatigue failure due to harsh working conditions. To improve the fatigue resistance of aircraft skins and to accurately predict the fatigue life of AA2524 compact tension (CT) samples. The compound strengthening method of lsear heating (LH) and lsear shot peening (LSP) is proposed to improve the fatigue life of AA2524 in this paper. Considering the effect of stress ratio (R), residual stress (RS), stress intensity factor range (ΔK), and maximum stress intensity factor (Kmax) on the fatigue crack growth rate (FCGR), the fatigue life of CT samples was predicted applying artificial neural networks, support vector regression models. The results show that laser heating and laser shot peening can obviously improve the fatigue life by 30.703% at R = 0.1 and 4.701% at R = 0.5, compared with base materials. The neural networks have better fatigue life prediction ability, and the fit coefficients for the neural networks predicting fatigue life reach 0.97, which is better than that of Walker model (0.91). The prediction value for ANN model is 75,462 cycles, the magnitude for SVR model is 78,234 cycles, and the experimental value is 74,204 cycles. The deviation are 1.7% and 5.43%, respectively. Meanwhile, the effect of R on the FCGR of AA2524 is closely associated with the crack closure effect.

The morphology and composition of nanosized amorphous-phase separation in the Y2O3–Al2O3–SiO2 glass system

A systematic experimental study of the Y2O3–Al2O3–SiO2 (YAS) compositional system has been carried out with a focus on nanoparticle formation in the high SiO2 region, where nanoscale phase separation occurs. The unique capabilities of the aerodynamic levitation coupled to the laser-heating method have been exploited and compared to conventional melt-quenching. This systematic study has mainly focused on the region where melting temperatures exceed 1700 °C, which is the maximum temperature commonly available for the preparation of glass by conventional melt-quenching. The feasibility and the effect of the two synthesis routes on the preparation of glass samples have been compared. The prepared samples were characterised by X-ray diffraction, differential scanning calorimetry, Raman spectroscopy, and scanning and transmission electron microscopy. It is evident from the results that in the part of the phase diagram with SiO2 content above 65 mol% and simultaneously Y2O3 content below 17.5 mol%, the phase separation has led to the formation of amorphous SiO2 nanoparticles. It has been shown that the size and distribution of the nanoparticles can be controlled not only by the chosen technology but also by changing the starting composition.

Laser Heating Method for an Alkali Metal Atomic Cell with Heat Transfer Enhancement

Alkali metal atomic cells are crucial components of atomic instruments, such as atomic magnetometers, atomic gyroscopes, and atomic clocks. A highly uniform and stable heating structure can ensure the stability of the alkali metal atom density. The vapor cell of an atomic magnetometer that uses laser heating has no magnetic field interference and ease of miniaturization, making it superior to hot air heating and AC electric heating. However, the current laser heating structure suffers from low heating efficiency and uneven temperature distribution inside the vapor cell. In this paper, we designed a non-magnetic heating structure based on the laser heating principle. We studied the temperature distribution of the heating structure using the finite element method (FEM) and analyzed the conversion and transfer of laser energy. We found that the heat conduction between the vapor cell and the heating chips (colored filters) is poor, resulting in uneven temperature distribution and low heating efficiency in the vapor cell. Therefore, the addition of graphite film to the four surfaces of the vapor cell was an important improvement. This addition helped to balance the temperature distribution and improve the conduction efficiency of the heating structure. It was measured that the power of the heating laser remained unchanged. After the addition of the graphite film, the temperature difference coefficient (CVT) used to evaluate the internal temperature uniformity of the vapor cell was reduced from 0.1308 to 0.0426. This research paper is crucial for improving the heating efficiency of the non-magnetic heating structure and the temperature uniformity of the vapor cell.

Explosive crystallisation of metal glasses based on Fe-B during pulsed laser heating. Experiment and modelling

The structure evolution of amorphous metallic alloys during different kinds of thermal effects is an important problem of disordered systems physics. A precise evolutional model would allow predicting the formation of such a structural state, providing the necessary physical and mechanical alloy properties.The paper is devoted to the problem of modelling the explosive crystallisation process in metal glasses induced by laser, supplemented by experimental results.A theoretical model of laser-induced explosive crystallisation in metal glasses is proposed. A pulse laser heating method for the surface processing was developed, making it possible to obtain two-layer structures with an adjustable thickness of the amorphous crystalline layer.The proposed model is assumed to test and optimes for metal glasses of other chemical compositions.A theoretical model of laser-induced explosive crystallisation in metal glasses allows for predicting and controlling structure changes to obtain the desired properties.The investigation of structure changes at rapid heating of amorphous alloys by experimental methods is very limited in obtaining data and their interpretation. For that reason, combining the modelling with experimental measurements is proposed. The results of this work have value for a scientist in material science, physics and engineering, which use nonequilibrium physical processes to obtain new materials, including nanoscale systems.

Laser Heating Nanoelectrospray Emitters for Fast Protein Melting Measurements with Mass Spectrometry.

Temperature-controlled nanoelectrospray ionization has been used to measure heat-induced conformational changes of biomolecules by mass spectrometry, but long thermal equilibration times associated with heating or cooling an entire emitter limit how fast these data can be acquired. Here, the tip of a borosilicate electrospray emitter is heated using 10.6 μm light from an unfocused CO2 laser. At 1.2 W, the solution inside the emitter tip can be heated from room temperature to a steady-state temperature of 78.2 ± 2.5 °C in less than 0.5 s and cools from 82.6 ± 0.6 °C back to room temperature within 4 s. The time required to establish a steady-state temperature is more than 100-fold faster than that required for a resistively heated emitter due to the low thermal mass. Protein unfolding curves measured as a function of laser power can be acquired in ∼40 s compared to a resistively heated apparatus that required ∼21 min to acquire similar data. Laser power is calibrated to temperature by comparisons of the average charge state of the protein cytochrome c measured with laser heating and with resistive heating. This laser heating method is applied to a three-component protein mixture to demonstrate the ability to rapidly acquire melting temperatures of proteins in mixtures. The ability to rapidly assess the thermal stabilities of multiple proteins simultaneously shows significant promise for coupling temperature-controlled electrospray ionization (ESI) to separation techniques, providing a high-throughput method for determining the effects of solution composition, drug binding, or sequence mutations on protein thermal stability.

Interface Healing Between Adjacent Tracks in Fused Filament Fabrication Using In-Process Laser Heating.

Fused filament fabrication is one of the most desired thermal plastic additive manufacturing processes because of its ability to fabricate complex objects with high accessibility. However, due to the extrusion track-based direct write process mechanism, parts built using this method exhibit anisotropic mechanical properties. In this work, an in-process laser heating method is introduced to heal interface adhesion between adjacent deposited tracks by increasing the interface temperature to promote polymer reptation and enhance bonding strength of the interface of adjacent tracks. With the use of laser heating induced interface healing, the measured flexural strength between adjacent tracks in the same layer increased and exceeded that of the control sample tested along the track direction. The effect of laser on interface healing was also verified by investigating the load-displacement curve and morphology analysis of the fractured surface.

Study of high-temperature behavior of a heat-protective coating of zirconium dioxide by laser heating

When studying the high-temperature behavior of the heat-protective coating of zirconium dioxide, the method of laser heating has been tested. The coating was applied by the method of high-energy plasma spraying on the intermetallic sublayer of the Ni–Co–Cr–Al–Y system made of a powder material of the composition (ZrO2 + 7% Y2O3) of spherical morphology.The aim of this work was to study the processes of structural-phase transformations, melting and crystallization occurring in a ceramic coating material under the action of a single laser pulse with a duration of 14 ms with different energies (5, 10, 15, and 20 J). It was found that after spraying, the coating in the initial state has a two-phase composition (T-ZrO2 + K-ZrO2), and a layered microstructure with a columnar structure of zirconium dioxide grains. Laser heating with a pulse energy of 5 J stimulates the phase transformation T-ZrO2 → K-ZrO2, the appearance of porosity and microcracks. With an increase in the pulse energy to 10 and 15 J, the processes of melting and ultrafast crystallization, accompanied by grain refinement, intensively occur on the coating surface. According to the theoretical estimates, the reflow processes affect surface layers with a thickness of 2.2 to 6.6 μm, and phase transformations take place at a depth of ~11 μm. With an increase in the laser pulse energy to E = 20 J, the process of destruction of the coating was initiated by the mechanism of cracking with delamination of fragments of the surface layer 5–10 μm thick.The laser heating method is recommended as an express diagnostics for comparative tests of the heat resistance of ceramic coatings obtained by different methods and from different starting materials.

A Scalable Solution Route to Porous Networks of Nanostructured Black Tungsten

This paper studied the feasibility of a new solution-processed method to manufacture black tungsten nanostructures by laser conversion of tungsten hexacarbonyl precursor on the Inconel 625 substrate under argon atmosphere at ambient pressure. The results show that sublimation of the precursor can be prevented if the decomposition temperature (>170 °C) is achieved using the laser heating method. Three different laser powers from 60–400 W were used to investigate the role of laser parameters on the conversion. It was found that lower laser power of 60 W resulted in a mixture of unconverted precursor and converted tungsten. Higher laser powers >200 W resulted in α-W (BCC) in one step without further heat treatment. Different oxygen concentrations from 0.5 ppm to 21 vol% were used in the laser canister to investigate the effect of oxygen concentration on the conversion. It was found that the hard vacuum (>10−4 torr) or hydrogen is not necessary to obtain α-W (BCC). The solar absorptance varied from 63–97%, depending on the amount of precursor deposited on the substrate and oxygen content in the laser canister. This solution-based laser conversion of tungsten precursor is a scalable method to manufacture tungsten coatings for high-temperature applications.

Switching between laser-induced thermophoresis and thermal convection of liquid suspension in a microgap with variable dimension.

Phoretic motion of particles along a temperature gradient formed in a fluid, known as thermophoresis, often takes place under the influence of bulk motion caused by thermal convection. In this paper, using a laser heating method, the significance of two competing effects, that is, thermophoresis and thermal convection, for the particle transport in a liquid phase confined in a microgap is investigated experimentally by changing the gap size as a control parameter. It is found that there is a threshold of the gap size, above which the particles tend to accumulate around the heated spot, forming a ring-like particle distribution. On the contrary, if the gap size is below the threshold, the particles are depleted from the heated spot. Switching between these accumulation and depletion modes is expected to develop novel manipulation techniques.

Relaxation of residual stress in fused filament fabrication part with in-process laser heating

Fused filament fabrication (FFF) has become a preferred method for additive manufacturing due to its cost-effectiveness and flexibility. However, the parts built using FFF process suffer from lower mechanical strength compared to that fabricated using traditional method. In this work, an in-process laser heating method was presented to heal residual stress, therefore improve mechanical behavior along in-plane direction. The enhancement in tensile strength and elongation of fabricated samples with the utilization of laser heating have been demonstrated. In addition, models and hypothesis on the transformation of microstructure were proposed and verified by experimental data. With the utilization of laser pre-deposition heating, tensile strength of printed polyether ether keton (PEEK) part along in-plane direction increased by 11.4%, thus reached 93.5% that of the bulk material property. The fracture behavior was also altered from brittle to stretchable with visible necking effect, backed up with both tensile curve and scanning electron microscope images independently.

The study of high-temperature stability of the thermoprotective coating made of zirconium dioxide

Laser heating method is proposed for the evaluation of high-temperature stability of thermal protective coatings of zirconium dioxide. Structural-phase state of plasma thermal protective coating of zirconium dioxide has been investigated after laser pulse altering with a different energy. Processes of phase transformation, melting and recrystallization are registered. It has been found that the degradation of the coating affects the surface layers with a thickness of several layers. By changing the parameters of laser radiation it is possible to carry out rapid diagnostics and comparative tests of heat resistance of ceramic protective coatings obtained by different methods from different initial materials.

Enhancing the long-term stability of dissipative Kerr soliton microcomb.

A temporal dissipative Kerr soliton (DKS) frequency comb can be generated in an optical micro-cavity relying on the rigid balance between cavity decay (dispersion) and parametric gain (nonlinear phase modulation) induced by an intense pump laser. In practice, to maintain such delicate double balances experienced by the intracavity soliton pulses, it requires precise control of the pump laser frequency and power, as well as the micro-cavity parameters. However, to date there still lacks experimental demonstration that simultaneously stabilizes all these key parameters to enhance the long-term DKS stability. Here, we demonstrate continuous working of a on-chip DKS microcomb for a record-breaking 14 days without showing any sign of breakdown. Such improved microcomb stability is enabled mainly by robust pump power coupling to the micro-cavity utilizing packaged planar-lightwave-circuit mode converters, and faithful locking of the pump frequency detuning via an auxiliary laser heating method. In addition to superior stability, the demonstrated DKS microcomb system also achieves favorable compactness, with all the accessory modules being assembled into a standard 4U case. We hope that our demonstration could prompt the practical utilization of Kerr microcombs in real-world applications.

An Externally-Heated Diamond Anvil Cell for Synthesis and Single-Crystal Elasticity Determination of Ice-VII at High Pressure-Temperature Conditions.

The externally-heated diamond anvil cell (EHDAC) can be used to generate simultaneously high-pressure and high-temperature conditions found in Earth's and planetary interiors. Here we describe the design and fabrication of the EHDAC assemblies and accessories, including ring resistive heaters, thermal and electrical insulating layers, thermocouple placement, as well as the experimental protocol for preparing the EHDAC using these parts. The EHDAC can be routinely used to generate megabar pressures and up to 900 K temperatures in open air, and potentially higher temperatures up to ~1200 K with a protective atmosphere (i.e., Ar mixed with 1% H2). Compared with a laser-heating method for reaching temperatures typically >1100 K, external heating can be easily implemented and provide a more stable temperature at ≤900 K and less temperature gradients to the sample. We showcased the application of the EHDAC for synthesis of single crystal ice-VII and studied its single-crystal elastic properties using synchrotron-based X-ray diffraction and Brillouin scattering at simultaneously high-pressure high-temperature conditions.

New laser-based method for the synthesis of stable and active Ti/SnO2–Sb anodes

The main drawback impairing the application of highly electrocatalytic SnO2–Sb anodes in the removal of recalcitrant pollutants from wastewater is their short service life. Here, we report the synthesis of Ti/SnO2–Sb anodes with improved stability through a CO2 laser as the primary heating source. The influence of different calcination temperatures (400, 500, 600 °C), and varied composition of the solvent in the precursor solution, on the stability and activity of the anodes, were investigated. Notably, the use of the CO2 laser heating method at 600 °C improves the service life up to 5-fold as compared to the conventionally prepared anodes. The laser-made Ti/SnO2–Sb anode calcined at 600 °C exhibits the best electrocatalytic performance with the fastest color removal rates in the oxidation of methylene blue dye. Therefore, for the first time, Ti/SnO2–Sb anodes with superior properties were produced by a fast method employing CO2 laser, envisaging its future applications in wastewater treatment.

Triple-wavelength lasing at 1.50 μm, 1.84 μm and 2.08 μm in a Ho3+/Tm3+ co-doped fluorozirconate glass microsphere

Simultaneous 1.50 μm, 1.84 μm and 2.08 μm laser emission is observed in a Ho3+/Tm3+ co-doped ZrF4–BaF2–YF3–AlF3 (ZBYA) fluoride glass microsphere when pumped using a 793 nm laser diode. The ZBYA fluoride glass microsphere was prepared using a CO2 laser heating method and whispering-gallery modes (WGM) were excited when the pump light was coupled using a tapered fiber. The introduction of Ho3+ ions reduced the population of the long-lived Tm3+:3F4 level and removed the 3H4→ 3F4 self-termination effect, resulting in the population of the Ho3+:5I7 level through a resonant energy transfer process. As the 793 nm laser pump power grows, lasing occurs initially at 2.08 μm, followed by the cascade outputs at 1.50 μm and 1.84 μm.

Near-Infrared Luminescence and Single-Mode Laser Emission From Nd3+ Doped Compound Glass and Glass Microsphere

In this letter, an Nd3+-doped compound fluorosilicate glass was successfully fabricated with the method of melt-quenching. Under the excitation of a 808 nm laser, enhanced near-infrared photoluminescence emission at the range from 1065 to 1140 nm was observed in the glass sample. To characterize its stability and resistance to environmental effects, transmission spectra at the range of NIR-MIR were measured under different environments, including humidity and temperature. In addition, the obtained fluorosilicate glass was also developed as a microsphere resonator by using CO2 laser heating method. When the diameter of the microsphere was controlled at 61.5 μm, coupling with a tapered fiber, single-multimode lasing in the wavelength range λ1056-1071 nm was achieved with a low lasing threshold of 1.5 mW. Compared to the traditional compound tellurate and fluoride glasses, this fluorosilicate glass has higher transition temperature; means that this resonator can be pumped by higher power. Therefore, using it as the raw material, the developed microsphere resonator offers a high transition temperature and with a low lasing threshold, which are promising it for high performance sensing and detection applications.

On modelling of laser assisted machining: Forward and inverse problems for heat placement control

Abstract Laser assisted machining (LAM) is one of the most efficient ways to improve the machinability of difficult-to-cut materials (e.g. Nickel-based superalloys). In the conventional LAM process, the laser beam is focused ahead of the cutting area at a fixed location, which leads to a series of restrictions, e.g. small heating area and non-uniform heat distribution due to the limitation of beam size and energy distribution. In this paper, a novel spatially and temporally (S&T) controlled laser heating method was proposed, in which a large area can be heated up with a small laser spot by controlling the beam scanning, i.e., laser power, path and speed of scanning. The laser configuration for the prescribed HAZ (heat affected zone) was achieved by solving the inverse heat conduction problem where the laser power together with either laser path or laser speed were optimised to achieve a particular temperature distribution in the chip to be removed by the following milling cutter. The proposed S&T laser heating method was thoroughly validated both for the direct and, the more important, inverse heating models by performing extensive temperature experiments by both infrared thermal camera and thermocouple array and further verified by laser assisted milling (LAMill) tests of Inconel 718 for large widths of cuts. The results showed that by applying path-optimised LAMill based on the inverse solution of the thermal problem, the peak and mean principal cutting forces were reduced by 55% and 47.8% respectively compared with the conventional dry milling process while the surface roughness improved by at least 14%. Moreover, after controlling the HAZ using the inverse thermal problem, a microstructure analysis of the machined surface showed that the proposed laser heating method avoids overheating of the workpiece below the planned depth of cut for the milling operation.

Spin Seebeck effect and spin Hall magnetoresistance in the Pt/Y3Fe5O12 heterostructure under laser-heating**Project supported by the National Natural Science Foundation of China (Grant Nos. 11604265, 51471134, 51572222, and 11704386) and the Fundamental Research Funds for the Central Universities, China (Grant Nos. 3102018zy044 and 3102017jc01001).

In the previous study of longitudinal spin Seebeck effect (LSSE), the thermal gradient was often generated by inserting the sample between the cool bath and the hot bath. For practical use, this method is too cumbersome to be easily integrated into modern electrical circuits. Since the laser can be easily focused into a small region, it will be more convenient and friendly to the integrated circuit. In this paper, we systematically investigate the LSSE and spin Hall magnetoresistance (SMR) of the Pt/Y3Fe5O12 heterostructure under focused laser-heating. We find that the extremely large voltage of inverse spin Hall effect (VISHE) can be obtained by reducing the diameter of laser or increasing the number of light spots. Meanwhile, even under the illumination of the ultraviolet light which will excite the electron from the valence band to the conduction band in yttrium iron garnet (YIG), the magnitude of SMR is nearly constant. It indicates that the spin transport behavior of the adjacent Pt is independent of the electron configuration of YIG. The laser-heating method to generate LSSE will be very promising for modern integrated electronic circuits and will promote the application of spin caloritronics in practice.

Static characteristics calibration of Pt/Au thin-film thermocouple by means of laser heating and temperature extrapolation method

Thin-film thermocouples (TFTCs), owing to their fast response, show promise for use in temperature measurements with high spatial and temporal resolution. Because of the huge difference in the temperature profiles in the calibration and application, in the strictest sense, the standardised thermocouple calibration method is no longer suitable for TFTCs. However, this issue is always ignored in some TFTC research literature. To realise accurate calibration of a TFTC, a novel method is proposed in this article. The highlight of this method is the use of a laser to heat the hot junction of the TFTC. Then, according to the surrounding calibrated platinum resistance thermometers and the temperature distribution model, the temperature of the hot junction is calculated with an extrapolation method. Finally, the static characteristics of the TFTC are calibrated through establishing the function between the calculated temperatures and the electromotive forces (EMFs). In order to verify the applicability of this method, a Pt/Au TFTC sensor is designed on a thin cylindrical substrate. Through numerical simulation, a logarithmic model is obtained to describe the temperature distribution regularity of the sensor under laser heating. With screen-printed sensor fabrication and experimental setup realisation, the EMFs and resistances of the platinum resistors are recorded simultaneously. The results leads to the following three conclusions. First, this method can calibrate the Seebeck coefficient of the legs of the TFTC, where the temperature gradient is concentrated in applications. Second, the method shows good repeatability and stability in three repeated experiments. Third, the value of the calibrated temperature and the EMF curve of the TFTC are similar to those of bulk Pt/Au thermocouple. This signifies that the proposed calibration method is reliable and effective.