Laser Induced Research Articles

Crosstalk-Free, High-Resolution Pressure Sensor Arrays Enabled by High-Throughput Laser Manufacturing.

Simultaneously achieving high spatial resolution and low crosstalk interference has been a fundamental challenge for flexible pressure sensor arrays. Here the authors present a high-resolution flexible pressure sensor array fabricated through a two-step laser manufacturing process, where individual sensing pixels and their interconnects are sequentially defined by laser-induced graphenization and ablation to minimize crosstalk interferences. The geometry of the interconnects is optimized through theoretical modeling and experimental validation. Characterization results show that the new device design induces a remarkable reduction of the crosstalk coefficient, from -8.21 to -43.63 dB, of the 0.7 mm-resolution sensor arrays, and the crosstalk suppression is particularly beneficial for application scenarios involving pressure sensing on soft surfaces (e.g., human skin and organs). Applications of the sensor array in tactile pattern recognition and minimally-invasive cancer surgery are demonstrated.

Laser-induced microjet-assisted ablation for high-quality microfabrication

Liquid-assisted laser ablation has the advantage of relieving thermal effects of common laser ablation processes, whereas the light scattering and shielding effects by laser-induced cavitation bubbles, suspended debris, and turbulent liquid flow generally deteriorate laser beam transmission stability, leading to low energy efficiency and poor surface quality. Here, we report that a continuous and directional high-speed microjet will form in the laser ablation zone if laser-induced primary cavitation bubbles asymmetrically collapse sequentially near the air-liquid interface under a critical thin liquid layer. The laser-induced microjet can instantaneously and directionally remove secondary bubbles and ablation debris around the laser ablation region, and thus a very stable material removal process can be obtained. The shadowgraphs of high-speed camera reveal that the average speed of laser-induced continuous microjet can be as high as 1.1 m s−1 in its initial 500 μm displacement. The coupling effect of laser ablation, mechanical impact along with the collapse of cavitation bubbles and flushing of high-speed microjet helps achieve a high material removal rate and significantly improved surface quality. We name this uncovered liquid-assisted laser ablation process as laser-induced microjet-assisted ablation (LIMJAA) based on its unique characteristics. High-quality microgrooves with a large depth-to-width ratio of 5.2 are obtained by LIMJAA with a single-pass laser scanning process in our experiments. LIMJAA is capable of machining various types of difficult-to-process materials with high-quality arrays of micro-channels, square and circle microscale through-holes. The results and disclosed mechanisms in our work provide a deep understanding of the role of laser-induced microjet in improving the processing quality of liquid-assisted laser micromachining.

Effects of various pulse width laser with 1064 nm wavelength on thermal ablation and phase transition of monocrystalline silicon

ABSTRACT Taking into consideration of the phase transition of silicon, the threshold prediction model of the melting starting and completion and vaporization starting and completion irradiated by laser with pulse width from 400 fs to 1 ms and 1064 nm wavelength is established based on the results of temperature field. The laser-induced ablation threshold of silicon is measured experimentally. The variation tendency of the associated threshold of silicon with the laser pulse width is analyzed quantitatively by the heating depth model, which can predict the generation of periodic linear and circular ripples on silicon surface.

Ratio of water/fuel concentration in a group of composite droplets on high-temperature heating

The paper presents the experimental research findings on the water/Diesel fuel concentration ratio in a group of composite droplets after passing through a heated gaseous medium. The research was carried out using the optical methods of Planar Laser Induced Fluorescence and Shadow Photography. The experimental method involved measurements carried out while a group of composite droplets (water/Diesel fuel) was free-falling through a tubular muffle furnace. The findings have shown combined effects of droplets on the water and Diesel fuel concentration ratio at the furnace outlet. We have also shown how droplet collisions with each other and with a heated chamber wall affected the number and size of droplets of water and combustible liquid as they left the high-temperature zone. The limiting temperatures of the gaseous medium have been determined that are sufficient for the breakup of a group of composite droplets free-falling through a fixed-length operating section with heated gases. We have also calculated the required heating time and the length of the channel with a heated gas, so that parent composite drops break up into individual droplets of water and a combustible liquid. The numbers and sizes of fragments with different component compositions after passing through a heated gaseous medium have been determined as well. The relative proportion of composite droplets containing vapor bubbles at the furnace exit.

Comparison of ultrashort pulse ablation of gold in air and water by time-resolved experiments

Laser ablation in liquids is a highly interdisciplinary method at the intersection of physics and chemistry that offers the unique opportunity to generate surfactant-free and stable nanoparticles from virtually any material. Over the last decades, numerous experimental and computational studies aimed to reveal the transient processes governing laser ablation in liquids. Most experimental studies investigated the involved processes on timescales ranging from nanoseconds to microseconds. However, the ablation dynamics occurring on a sub-nanosecond timescale are of fundamental importance, as the conditions under which nanoparticles are generated are established within this timeframe. Furthermore, experimental investigations of the early timescales are required to test computational predictions. We visualize the complete spatiotemporal picosecond laser-induced ablation dynamics of gold immersed in air and water using ultrafast pump-probe microscopy. Transient reflectivity measurements reveal that the water confinement layer significantly influences the ablation dynamics on the entire investigated timescale from picoseconds to microseconds. The influence of the water confinement layer includes the electron injection and subsequent formation of a dense plasma on a picosecond timescale, the confinement of ablation products within hundreds of picoseconds, and the generation of a cavitation bubble on a nanosecond timescale. Moreover, we are able to locate the temporal appearance of secondary nanoparticles at about 600 ps after pulse impact. The results support computational predictions and provide valuable insight into the early-stage ablation dynamics governing laser ablation in liquids.

Effect of hydrogen addition on flame stability and structure for low heating value coaxial nonpremixed flames

ABSTRACT An investigation of effect of hydrogen addition on flame stability and structure i.e. combustion characteristics of low heating value gases (LHVGs) that consist of methane, propane, nitrogen is carried out experimentally and numerically. For the experiment, a coaxial non-premixed jet-type combustor and Planar Laser Induced Fluorescence (PLIF) system are used to evaluate the flame stability limit and flame shapes and visualize OH radical distribution, respectively. For the numerical analysis of hydrogen added LHVGs, the calculation using the FLUENT software with decreased GRI 3.0 mechanism is performed to study the 2D flame temperature distribution and radial flame structure. As a result, the flame length of LHVGs reduces as hydrogen is added. CH* and OH* radicals visualized by chemiluminescence system are distributed closer to the nozzle as hydrogen is added to LHVGs. OH-PLIF images show that OH intensity of LHVG 6000 is higher with hydrogen addition. The flame stability of LHVGs is improved with hydrogen addition. As for the numerical result, the reduction of flame length and width of LHVG 6000 are predicted with adding the hydrogen.

Multiplexed Active Optical Fiber Bragg Grating Sensor Array Enabled by Femtosecond Laser Induced Nanoscattering Centers

Optical fiber sensors (OFS) such as fiber Bragg gratings (FBGs) are passive and versatile sensor devices that have been used to perform a wide range of physical and chemical measurements. However, the performance and functionality of the OFS are limited by its passivity. This letter demonstrates an active fiber sensor scheme for multiparameter measurements. FBG-based optic fiber sensors are fabricated in an optical fiber core by femtosecond laser direct writing scheme. Guided light scattered out from laser-induced nanograting in fiber core is harnessed by on-fiber coating. Energy conversion films coated on the optical fiber convert scattered optical energy into thermal energy to heat the FBG sensor above ambient temperatures for active measurements. Functionalities of optically heated fiber sensor array are demonstrated for both temperature and liquid level measurements at the room temperatures.

Measurement and analysis of species distribution in laser-induced ablation plasma of an aluminum–magnesium alloy

We proposed a theoretical spatio-temporal imaging method, which was based on the thermal model of laser ablation and the two-dimensional axisymmetric multi-species hydrodynamics model. By using the intensity formula, the integral intensity of spectral lines could be calculated and the corresponding images of intensity distribution could be drawn. Through further image processing such as normalization, determination of minimum intensity, combination and color filtering, a relatively clear species distribution image in the plasma could be obtained. Using the above method, we simulated the plasma ablated from Al–Mg alloy by different laser energies under 1 atm argon, and obtained the theoretical spatio-temporal distributions of Mg I, Mg II, Al I, Al II and Ar I species, which are almost consistent with the experimental results by differential imaging. Compared with the experimental decay time constants, the consistency is higher at low laser energy, indicating that our theoretical model is more suitable for the plasma dominated by laser-supported combustion wave.

Ultrafast Shaped Laser Induced Synthesis of MXene Quantum Dots/Graphene for Transparent Supercapacitors.

Ultratransparent electrodes have attracted considerable attention in optoelectronics and energy technology. However, balancing energy storage capability and transparency remains challenging. Herein, an in situ strategy employing a temporally and spatially shaped femtosecond laser is reported for photochemically synthesizing of MXene quantum dots (MQDs) uniformly attached to laser reduced graphene oxide (LRGO) with exceptional electrochemical capacitance and ultrahigh transparency. The mechanism and plasma dynamics of the synthesis process are analyzed and observed at the same time. The unique MQDs loaded on LRGO greatly improve the specific surface area of the electrode due to the nanoscale size and additional edge states. The MQD/LRGO supercapacitor has high flexibility and durability, ultrahigh energy density (2.04 × 10-3 mWhcm-2 ), long cycle life (97.6% after 12000 cycles), and excellent capacitance (10.42mF cm-2 ) with both high transparency (transmittance over 90%) and high performance. Furthermore, this method provides a means of preparing nanostructured composite electrode materials and exploiting quantum capacitance effects for energy storage.

Self‐Adaptive Surface with Tunable Superamphiphobicity Fabricated by Femtosecond Laser Induced Backward Transfer

AbstractIn recent years, a rapid advance in fabricating smart surfaces with tunable wettability have been witnessed. However, switchable superamphiphobic surface remains a great challenge today. Here, glass surfaces with tunable wetting performance between amphipathicity and amphiphobicity, “lotus effect” and “petal effect,” isotropic and anisotropic amphiphobicity are obtained by femtosecond‐laser‐induced backward transfer (LIBT) method. By printing simple patterns, polytetrafluoroethylene (PTFE) is spatial‐selectively transferred with composite micro/nano‐structures formed on the glass surfaces, ensuring a strong repellence for water and oil. Besides, the surface topography and chemistry can be finely regulated in a single‐step process without damage to the glass, which provides the feasibility of controlling the surface wettability. Herein, applications such as high precision mixing reactor, droplet volume screening micro‐device, auto‐filtering droplet channel are designed and demonstrated. Compared to other methods, the LIBT method featuring rapid, large‐area, maskless prototyping is proved to be a promising method for programmable manipulations of functional surfaces with diverse wettability.

Underfocus Laser Induced Ni Nanoparticles Embedded Metallic MoN Microrods as Patterned Electrode for Efficient Overall Water Splitting.

Transition metal nitrides have shown large potential in industrial application for realization of the high active and large current density toward overall water splitting, a strategy to synthesize an inexpensive electrocatalyst consisting of Ni nanoparticles embedded metallic MoN microrods cultured on roughened nickel sheet (Ni/MoN/rNS) through underfocus laser heating on NiMoO4·xH2O under NH3 atmosphere is posited. The proposed laser preparation mechanism of infocus and underfocus modes confirms that the laser induced stress and local high temperature controllably and rapidly prepared the patterned Ni/MoN/rNS electrodes in large size. The designed Ni/MoN/rNS presents outstanding catalytic performance for hydrogen evolution reaction (HER) with a low overpotential of 67 mV to deliver a current density of 10 mA cm−2 and for the oxygen evolution reaction (OER) with a small overpotential of 533 mV to deliver 200 mA cm−2. Density functional theory (DFT) calculations and Kelvin probe force microscopy (KPFM) further verify that the constructed interface of Ni/MoN with small hydrogen absorption Gibbs free energy (ΔG H*) (−0.19 eV) and similar electrical conductivity between Ni and metallic MoN, which can explain the high intrinsic catalytic activity of Ni/MoN. Further, the constructed two‐electrode system (−) Ni/MoN/rNS||Ni/MoN/rNS (+) is employed in an industrial water‐splitting electrolyzer (460 mA cm−2 for 120 h), being superior to the performance of commercial nickel electrode.

Experimental study on the direct planar metallization on glass by the particle sputtering in laser-induced plasma-assisted ablation

Laser-induced plasma-assisted ablation (LIPAA) is an efficient and low-cost method for processing the metallic pattern on glass. In this study, the metallic sacrificed target was used in the LIPAA process, the feasibility of direct planar metallization on the glass substrate was explored. For this purpose, the morphology and chemical composition of the planar metallization layer on glass substrate, which was fabricated by line-by-line LIPAA, was characterized in detail, and the corresponding metallization regime was clarified. The experimental results indicate that gap distance between the glass specimen and metallic sacrificed substrate has a significant influence on the homogeneity, thickness, compactness, and chemical composition of the metallization layer. In addition, with a small gap distance, the periodic behaviors of generation, accumulation, blockage and spray of the metallic oxide powders between the gap bring about stripes embedded in the metallization layer. Moreover, based on the prepared metallization layer by line-by-line LIPAA, the patterned circuit was fabricated on the glass by laser patterning method and its conductivity was enhanced by successive chemical reduction. The comprehensive performance test for the patterned circuit in terms of morphology, adhesion strength, conductivity demonstrate that the line-by-line LIPAA method presents a great potential for preparing the patterned circuit on glass.

Laser-induced thermal source for cold atoms

We demonstrate a simple and compact approach to laser cool and trap atoms based on laser-induced thermal ablation (LITA) of a pure solid granule. A rapid thermalisation of the granule leads to a fast recovery of the ultra-high vacuum condition required for a long trapping lifetime of the cold gas. We give a proof-of-concept of the technique, performing a magneto-optical trap on the 461 nm ^1S_0rightarrow ,^1P_1 transition of strontium. We get up to 3.5 million of cold strontium-88 atoms with a trapping lifetime of more than 4 s. The lifetime is limited by the pressure of the strontium-free residual background vapour. We also implement an original configuration of permanent magnets to create the quadruple magnetic field of the magneto-optical trap. The LITA technique can be generalized to other atomic elements such as transition metals and lanthanide atoms, and shows a strong potential for applications in quantum technologies ranging from quantum computing to precision measurements such as outdoor inertial sensing.

Micro-reactors fabricated by Subaquatic indirect Laser-Induced Plasma-Assisted Ablation on soda-lime glass substrates

Synchronization control of complex systems is a field that emerged with huge interest and aims to study new possible routes to synchronization in networks of non-locally coupled chemical oscillators. Light can be used to stimulate these systems and to be able to synchronize the different micro-reactors involved in the complex system. To this end, transparent reactors with good optical qualities are needed. Glass is the most appropriated material to be used for fabricating the micro-reactors. Subaquatic indirect Laser-Induced Plasma-Assisted Ablation is presented as a laser technique that combines underwater ablation with shock waves as a potential technique for fabricating these micro-reactors by using a Nd:YVO4 laser.

Determination of Oil Pollutants by Microchannel Laser Induced Fluorescence Technology

Laser-induced fluorescence technology is an effective method for detecting oil pollutants. The laser induced fluorescence detection system was developed, and four parallel microchannel sample pools were designed to improve the detection accuracy of fluorescence signals. The grating scanning system is improved by introducing grating feedback link to improve the wavelength scanning accuracy of the system.The experimental results show that the wavelength scanning resolution of the microchannel laser-induced fluorescence detection system is improved by 0.4 nm. Aiming at the defects of the traditional parallel factor algorithm which is sensitive to the sample components, slow operation speed and easy to fall into local convergence, the generalized inverse singular value decomposition is used to improve the parallel factor algorithm. Configure different concentrations of diesel, gasoline and kerosene solution samples. The experimental verification shows that the excitation-emission spectra of each component obtained by the improved parallel factor algorithm are highly consistent with the measured spectral characteristics, indicating that the microchannel laser-induced fluorescence detection system combined with the improved parallel factor analysis method can accurately identify oil pollutants.

In Situ Simultaneous Quantitative Analysis Multi-Elements of Archaeological Ceramics Via Laser Induced Breakdown Spectroscopy Combined with Machine Learning Strategy

In Situ Simultaneous Quantitative Analysis Multi-Elements of Archaeological Ceramics Via Laser Induced Breakdown Spectroscopy Combined with Machine Learning Strategy

Experimental investigation of deep-hole micro-drilling of glass using LIPAA process

ABSTRACT This paper aims to study the mechanism of glass deep-hole micro-drilling by the Laser-Induced Plasma-Assisted Ablation (LIPAA) process. The Micro-drilling of glass was studied under various laser intensities. Nd:YAG nanosecond pulsed laser with 12 ns pulse duration was used as the laser light source. Copper was used as the metal target for the experiments. It is shown that laser glass micro-drilling is divided into two ablation stages. In the first stage, ablation is done by the brittle failure of glass caused by the collision of plasma plume with the glass surface. Exertion of mechanical pressure is also an important factor in the first few laser shots. Due to mechanical failure, glass microstructure changes in the focal spot. Second stage ablation is directly conducted by the thermal mechanism through absorption of laser by the glass. The hole produced on the glass by thermal mechanism is free of cracks. Cylindricity and roundness of the hole are very desirable. Laser intensity plays a vital role in material removal rate, hole depth and diameter. The process can be used for high-speed deep-hole micro-drilling of transparent materials to laser with good surface integrity and high-aspect ratio.

Effect of Laser Pulse Repetition Rate on the Detection Limits of the Elemental Composition of Pollutants in Aqueous Solutions by Femtosecond Laser Induced Breakdown Spectroscopy

Effect of Laser Pulse Repetition Rate on the Detection Limits of the Elemental Composition of Pollutants in Aqueous Solutions by Femtosecond Laser Induced Breakdown Spectroscopy

Temperature recording of the ice–water system using planar laser induced fluorescence

The study explores the temperature recording of the ice particle – liquid layer system by means of Planar Laser Induced Fluorescence. Before the experiment, water droplets with fluorophore were frozen until they became ice particles. The most promising dyes for water were used: Rhodamine B and Rhodamine 6G. As ice particles were heated, the fluorescence of fluorophore was recorded. Three types of ice melting conditions with various concentration of dyes were investigated: without external influence (at room temperature); exposing to local heating by a laboratory burner; using convective heating by a blowing air flow. The curves were obtained for the fluorescence of fluorophores versus temperature in each of the three types of experiments. The specific behavior of the dye was analyzed when exposing it to low temperatures, i.e., crystallization. Typical water temperature differences during ice melting were determined. The ranges of validity and accuracy, as well as specific aspects of using Planar Laser Induced Fluorescence during two phase transformations – melting and evaporation – were established.

High-Conversion Efficiency Pulse Compression by Stimulated Raman Scattering and Laser Induced Breakdown in Water

A novel temporal pulse compression technique, combining stimulated Raman scattering (SRS) and laser induced breakdown (LIB) principles was presented in this work, which employing an energy controllable dual-cell setup. As a novel type of plasma shutter, the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> cell was used to transmit the high-power peak at the leading pulse edge and successfully block its low-power tail. The effect resulted in a 7 ns pulse duration from a Nd: YAG laser compressed into 330 ps, the pulse compression ratio was about 21×. The magnified optical power of the leading edge diminished the threshold of SRS and improved the beam quality of the output pulse. In addition, the output energy of Stokes was approximately 2 times than that of the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> cell process, and the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> cell process increased the energy conversion efficiency from 4.2% to 15.8%. Thus, the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> -order Stokes SRS was greatly improved, and the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order Stokes SRS was more easily generated. The method provided a simple but convenient way to generate a short pulse with a high energy conversion efficiency Raman laser.