Focused Laser Beam Research Articles

Spatially selective actuation of liquid-crystalline polymer films through two-photon absorption processes

Soft materials that respond to external stimuli are promising candidates for next-generation actuators with human-friendly nature1,2. Among various stimuli to induce strain, light offers spatial selectivity, which allows versatile motion of a continuous body. However, spatial selectivity of photoactuation has been limited in two dimension due to the predominant absorption of photons by chromophores near a light source in accordance with Beer-Lambert law. Here, we report the deformation of crosslinked liquid-crystalline polymer films triggered by two-photon absorption. The films containing azotolane moieties show photoinduced deformation upon irradiation with fs laser pulses through two-photon absorption. The direction of photoinduced bending is controlled by depth-selective excitation with a focused laser beam. Furthermore, the mode of deformation is transformed from bending to twisting by irradiating spots near an edge of the film. Inhomogeneous photoirradiation with high spatial selectivity allows an infinite variation of three-dimensional motions even apart from preprogrammed behavior, which would be advantageous especially in application to microactuators.

Evaluation of a Novel Femtosecond Laser Ablation System for In Situ Analysis Based on Two-Dimensional Galvanometer Scanners.

Uneven energy distribution of femtosecond lasers presents a significant challenge for single-spot analysis, which often leads to concave ablation craters. This study assesses the performance of a femtosecond laser ablation system for in situ analysis using novel galvanometer scanners. A galvanometer rapidly moved the laser beam focus to create craters with a small beam spot. We first examined the inductively coupled plasma mass spectrometry (ICP-MS) signal sensitivity to laser parameters, establishing a strong linear correlation with the laser energy, repetition rate, scanning ablation area, and galvanometer scanning frequency. Elemental fractionation analysis of NIST SRM 610 suggests minimal bias, with fractionation indices of different elements approaching unity. Subsequently, the elemental concentration of six reference material glasses was measured by fsLA-ICP-MS to evaluate the elemental quantification capabilities of the Galvo-femtosecond laser (Galvo-fsLA). The laser's capability for in situ U-Pb dating was demonstrated by concordant U-Pb ages of five zircon reference materials that are highly consistent with the ID-TIMS ages reported previously. Finally, the reliability of the new Galvo-fsLA for isotope analysis was verified by the accurate determination of radiogenic Hf, Pb isotopes, and stable Cu isotopes, all agreeing well with their reference values within uncertainties. These assessments underscore the significant potential of Galvo-fsLA for enhanced accuracy and precision of single-spot in situ analysis.

Laser-induced thermo-compression bonding for Cu–Au heterogeneous nanojoining

Abstract Surface tension-induced shrinkage of heterogeneously bonded interfaces is a key factor in limiting the performance of nanostructures. Herein, we demonstrate a laser-induced thermo-compression bonding technology to suppress surface tension-induced shrinkage of Cu–Au bonded interface. A focused laser beam is used to apply localized heating and scattering force to the exposed Cu nanowire. The laser-induced scattering force and the heating can be adjusted by regulating the exposure intensity. When the ratio of scattering forces to the gravity of the exposed nanowire reaches 3.6 × 103, the molten Cu nanowire is compressed into flattened shape rather than shrinking into nanosphere by the surface tension. As a result, the Cu–Au bonding interface is broadened fourfold by the scattering force, leading to a reduction in contact resistance of approximately 56%. This noncontact thermo-compression bonding technology provides significant possibilities for the interconnect packaging and integration of nanodevices.

Spatial photoinduced doping of graphene/hBN heterostructures characterized by quantum Hall transport

Abstract Doped semiconductors are a central and crucial component of all integrated circuits. By using a combination of white light and a focused laser beam, and exploiting hexagonal boron nitride (hBN) defect states, heterostructures of hBN/Graphene/hBN are photodoped in-operando, reproducibly and reversibly. We demonstrate device geometries with spatially-defined doping type and magnitude. After each optical doping procedure, magnetotransport measurements including quantum Hall measurements are performed to characterize the device performance. In the unipolar (p+–p–p+ and n–n+–n) configurations, we observe quantization of the longitudinal resistance, proving well-defined doped regions and interfaces that are further analyzed by Landauer–Buttiker modeling. Our unique measurements and modeling of these optically doped devices reveal a complete separation of the p- and n-Landau level edge states. The non-interaction of the edge states results in an observed ‘insulating’ state in devices with a bi-polar p–n–p configuration that is uncommon and has not been measured previously in graphene devices. This insulating state could be utilized in high-performance graphene electrical switches. These quantitative magnetotransport measurements confirm that these doping techniques can be applied to any two-dimensional materials encapsulated within hBN layers, enabling versatile, rewritable circuit elements for future computing and memory applications.

Physical coherent cancellation of optical addressing crosstalk in a trapped-ion experiment

Abstract We present an experimental investigation of coherent crosstalk cancellation methods for light delivered to a linear ion chain cryogenic quantum register. The ions are individually addressed using focused laser beams oriented perpendicular to the crystal axis, which are created by imaging each output of a multi-core photonic-crystal fibre waveguide array onto a single ion. The measured nearest-neighbor native crosstalk intensity of this device for ions spaced by 5 µm is found to be ∼ 10 − 2 . We show that we can suppress this intensity crosstalk from waveguide channel coupling and optical diffraction effects by a factor > 10 3 using cancellation light supplied to neighboring channels which destructively interferes with the crosstalk. We measure a rotation error per gate on the order of ϵ x ∼ 10 − 5 on spectator qubits, demonstrating a suppression of crosstalk error by a factor of > 10 2 . We compare the performance to composite pulse methods for crosstalk cancellation, and describe the appropriate calibration methods and procedures to mitigate phase drifts between these different optical paths, including accounting for problems arising due to pulsing of optical modulators.

Temperature Induced, Reversible Switching of Ferro-Rotational Order Coupled to Superlattice Commensuralibity.

High-quality 1T-TaS2 crystals are investigated by angle-resolved photoelectron spectroscopy, Raman spectroscopy, and low-energy electron diffraction. The Ferro-Rotational Order (FRO) of the charge density wave switches configuration at the transition between the commensurate and the nearly commensurate phase. This process requires samples without built-in or externally induced strain. Moreover, temperature gradients generated by a focused laser beam can be employed in order to freeze the in-plane chirality. Based on such observations, we propose a protocol to obtain durable and nonvolatile state switching of the FRO configuration in bulk 1T-TaS2 crystals.

Fourier Ptychographic Coherent Anti-Stokes Raman Scattering Microscopy with Point-Scanning for Super-Resolution Imaging.

Fourier ptychography (FP) is a high resolution wide-field imaging method based on the extended aperture in the Fourier space, which is synthesized from raw images with varying illumination angles. If FP is extended to coherent nonlinear optical imaging, the resolution could be further improved due to the increase of the cutoff frequency of the synthesized coherent optical transfer function (C-OTF) with respect to the order of nonlinear optical processes. However, there is a fundamental conflict between wide-field FP and nonlinear optical imaging, whereby the nonlinear optical imaging typically requires a focused excitation laser beam with high power density. To tackle the problem, in this work, a unique point-scanning FP (PS-FP) method is presented for super-resolution nonlinear optical imaging, in which the nonlinear optical signal is obtained by using focused laser beam, while the conventional FP algorithm can still be used to retrieve the super-resolution image. PS-FP coherent anti-Stokes Raman scattering (PS-FP-CARS) imaging on a variety of samples, where a 1.8-fold expansion of the OTF is achieved experimentally for enhancing vibrational imaging. Further theoretical calculation shows that the C-OTF of PS-FP higher-order CARS (PS-FP-HO-CARS) can be expanded up to ≈4.9-fold, thereby improving the spatial resolution by ≈3-fold in comparison with conventional point-scanning CARS with under tightly focused beams. The generality of PS-FP method developed in this work can be adapted to other coherent nonlinear optical imaging modalities for super-resolution imaging in tissue and cells.

Interferometric Rayleigh Scattering for Flow Temperature and Velocity Analysis

A new processing method is developed to analyze images from a Fabry–Pérot interferometer in order to extract point measurements of temperature and velocity within a gas flow, using Rayleigh scattering. Two types of interferograms are generated from a Fabry–Pérot model combined with a simulated light source. The first type is obtained from a diffuse coherent light source, namely, a laser beam on a diffuser. The interferometer characteristics, defined by only two independent parameters, are retrieved within 0.1% accuracy. The knowledge of these parameters is mandatory to analyze interferograms from Rayleigh scattered light. The second type corresponds to Rayleigh scattered light from a small volume under flow conditions, lighted with a focused laser beam and captured with long exposure time. Several flow parameters are chosen to generate these interferograms. The relative errors on the temperature and velocity estimates are found to be weak. Noise is also added to assess the robustness of the processing method. The error induced by the estimates of the instrument function is found to be of second order compared to the error induced by the image analysis.

Functional light diffusers based on hybrid CsPbBr3/SiO2 aero-framework structures for laser light illumination and conversion

The new generation of laser-based solid-state lighting (SSL) white light sources requires new material systems capable of withstanding, diffusing, and converting high intensity laser light. State-of-the-art systems use a blue light emitting diode or laser diode in combination with color conversion materials, such as yellow emitting Ce-doped phosphors or red and green emitting quantum dots (QD), to produce white light. However, for laser-based high-brightness illumination thermal management and uniform light diffusion are still major challenges in the quest to convert a highly focused laser beam into an efficient lighting solution. Here, we present a material system consisting of a highly open porous (> 99%) framework structure of hollow SiO2 microtubes. This framework structure enables efficient and uniform light distribution as well as ensuring good thermal management even at high laser powers of up to 5 W, while drastically reducing the speckle contrast. By further functionalizing the microtubes with halide perovskite QDs (SiO2@CsPbBr3 as model system) color conversion from UV to visible light is achieved. By depositing an ultrathin (~ 5.5 nm) film of poly(ethylene glycol dimethyl acrylate) (pEGDMA) via initiated chemical vapor deposition (iCVD), the luminescent stability of the QDs against moisture is enhanced. The demonstrated hybrid material system paves the way for the design of advanced and functional laser light diffusers and converters that can meet the challenges associated with laser-based SSL applications.Graphical

Tuning the Resistance of a VO2 Junction by Focused Laser Beam and Atomic Force Microscopy

Tuning the Resistance of a VO₂ Junction by Focused Laser Beam and Atomic Force Microscopy

Optical trapping-induced crystallization promoted by gold and silicon nanoparticles.

This study investigates the promotion of sodium chlorate (NaClO3) crystallization through optical trapping, enhanced by the addition of gold nanoparticles (AuNPs) and silicon nanoparticles (SiNPs). Using a focused laser beam at the air-solution interface of a saturated NaClO3 solution with AuNPs or SiNPs, the aggregates of these particles were formed at the laser focus, the nucleation and growth of metastable NaClO3 (m-NaClO3) crystals were induced. Continued laser irradiation caused these m-NaClO3 crystals to undergo repeated cycles of growth and dissolution, eventually transitioning to a stable crystal form. Our comparative analysis showed that AuNPs, due to their significant heating due to higher photon absorption efficiency, caused more pronounced size fluctuations in m-NaClO3 crystals compared to the stable behavior observed with SiNPs. Interestingly, the maximum diameter of the m-NaClO3 crystals that appeared during the size fluctuation step was consistent, regardless of nanoparticle type, concentration, or size. The crystallization process was also promoted by using polystyrene nanoparticles, which have minimal heating and electric field enhancement, suggesting that the reduction in activation energy for nucleation at the particle surface is a key factor. These findings provide critical insights into the mechanisms of laser-induced crystallization, emphasizing the roles of plasmonic heating, particle surfaces, and optical forces.

Temperature and stress distributions during laser cutting with different materials

Laser cutting is an extremely precise and versatile industrial technique that utilizes a focused laser beam to accomplish precise and accurate material cutting or engraving. Because of its efficiency and adaptability, laser cutting has become an essential component of modern production and design. The transient thermal and stress distribution of laser cutting of a sheet is introduced numerically in this study. Temperature, equivalent elastic strain, and equivalent stresses at different workpiece materials (structural steel, titanium alloy, and aluminum alloy) are investigated. Three different laser beams (500 W, 1000 W, and 1500 W) were used in this study. The modeling applies a heat source based on a Gaussian distribution to predict heat flow with an accurate temperature distribution field. The numerical model is validated with experimental data, and the error percentage is consistent and reasonable. The results showed that titanium could attain higher temperatures for the material of the workpiece under the same working conditions as both stainless steel and aluminum alloy. In comparison to stainless steel, the temperature increase ratios for titanium and aluminum are 121 % and 113.5 %, respectively. Aluminum expands rapidly, structural steel endures stresses, and titanium withstands high temperatures effectively. In comparison to 500 W, the temperature rise ratios for laser beams of 1000 W and 1500 W are 174 % and 237 %, respectively. These results highlight how critical it is to select the ideal laser power dependent on the properties of the material, adding to a more sophisticated knowledge for increased accuracy and effectiveness in laser cutting procedures.

Laser dressing process monitoring of superabrasive grinding wheel based on spectroscopy

In order to solve the problems of poor efficiency and low automation in laser dressing of superabrasive grinding wheels, the spectral monitoring research based on the automatic dressing of superabrasive grinding wheels was systematically carried out in this paper. For the first time, the characteristic element spectral lines that could respectively characterize the identity information of grain and bond were established, and by monitoring the characteristic element spectral line waveforms, the profiling/sharpening processing status identification was realized. It was the first to propose using the presence or absence of line spectrum during the laser dressing process as a monitoring indicator, which could achieve qualitative identification of the high-efficiency processing status of the laser beam focus. When the laser beam was in the positive defocus state, the material could be removed more accurately. A greater quantity of material would be eliminated when the laser beam was in the negative defocus state. The mapping relationship between the spectral characteristic waveform and the defocus amount of the laser beam during the laser dressing process was revealed, and a spectral monitoring theory of the defocus amount fluctuation of superabrasive grinding wheels was constructed. A high-efficiency automated laser profiling method for grinding wheels based on spectrum-assisted monitoring and self-adaptive feed was innovatively explored, and experiments had proven that this method could achieve self-adaptive feed for laser beam fast slow compensation, ultimately achieving high efficiency and automatic dressing of superabrasive grinding wheels.

Adaptive circumferential distance location of the laser energy beam in the laser-assisted turning of Al/SiC metal matrix composites

Laser-assisted turning (LAT) involves locally heating a rotating workpiece using a focused laser beam before the removal of material. A key aspect in optimising productivity with laser-assisted turning is understanding the thermal relationship between laser heating, the improved material removal rate, and machinability. Consequently, in this paper, a thermal heating and laser-assisted turning finite element model and experiments were conducted to assess the machinability of an Al/SiCp MMC workpiece, considering the circumferential location of the laser beam from the cutting point. The results confirm that laser power and cutting velocity influence the temperature profile from the laser spot to the tool point and the heat-affected depth. Positioning the cutting tool closer to the laser spot effectively reduces the Von Mises stress during cutting at higher cutting temperatures. At the same time, the experiment indicates an increased risk of directly heating the tool, which can affect the integrity of the cutting tool. The work further reveals that at specified cutting velocities, lower specific cutting energy improves the tool condition and surface quality of the machined parts. Based on a range of material removal rates and laser-specific energy density, a new criterion for optimal laser-tool circumferential distance was determined. Establishing this distance can act as a guide for the laser-assisted turning of Al/SiCp metal matrix composites and potentially other materials.

MALDI-2-Enabled Oversampling for the Mass Spectrometry Imaging of Metabolites at Single-Cell Resolution.

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) can provide valuable insights into the metabolome of complex biological systems such as organ tissues and cells. However, obtaining metabolite data at single-cell spatial resolutions presents a few technological challenges. Generally, spatial resolution is defined by the increment the sample stage moves between laser ablation spots. Stage movements less than the diameter of the focused laser beam (i.e., oversampling) can improve spatial resolution; however, such oversampling conditions result in a reduction in sensitivity. To overcome this, we combine an oversampling approach with laser postionization (MALDI-2), which allows for both higher spatial resolution and improved analyte ionization efficiencies. This approach provides significant enhancements to sensitivity for various metabolite classes (e.g., amino acids, purines, carbohydrates etc.), with mass spectral intensities from 6 to 8 μm pixel sizes (from a laser spot size of ∼13 μm) being commensurate with or higher than those obtained by conventional MALDI at 20 μm pixel sizes for many different metabolites. This technique has been used to map the distribution of metabolites throughout mouse spinal cord tissue to observe how metabolite localizations change throughout specific anatomical regions, such as those distributed to the somatosensory area of the dorsal horn, white matter, gray matter, and ventral horn. Furthermore, this method is utilized for single-cell metabolomics of human iPSC-derived astrocytes at 10 μm pixel sizes whereby many different metabolites, including nucleotides, were detected from individual cells while providing insight into cellular localizations.

Individual Addressing and State Readout of Trapped Ions Utilizing Radio-Frequency Micromotion.

Excess "micromotion" of trapped ions due to the residual radio-frequency (rf) trapping field at their location is often undesirable and is usually carefully minimized. Here, we induce precise amounts of excess micromotion on individual ions by adjusting the local static electric field they experience. Micromotion modulates the coupling of an ion to laser fields, ideally tuning it from its maximum value to zero as the ion is moved away from the trap's rf null. We use tunable micromotion to vary the Rabi frequency of stimulated Raman transitions over two orders of magnitude, and to individually control the rates of resonant fluorescence from three ions under global laser illumination without any changes to the driving light fields. The technique is amenable to situations where addressing individual ions with focused laser beams is challenging, such as tightly packed linear ion strings or two-dimensional ion arrays illuminated from the side.

Effect of laser power on the structure and specific surface area of laser-induced graphene

Laser-induced graphene (LIG) is a highly porous carbon material with prospects for application in various fields of modern electronics, energy and medicine. In this work, LIG film samples with the size of 5 × 10 mm were synthesized on the surface of polyimide film using line-by-line scanning of focused radiation from a cw carbon dioxide laser. Studies using scanning electron microscopy and Raman spectroscopy revealed that the structure of the resulting material depends significantly on the laser power. Measurements of the specific surface area Ssa of the synthesized carbon material, carried out by the well-known BET method during adsorption and desorption of gaseous nitrogen, showed that Ssa significantly depends on the laser power. At a line scanning speed of 220 mm/s, 25 μm spacing between lines and a focused laser beam diameter of 120 μm, an increase in power from ~1.7 to 8.2 W leads to a decrease in Ssa from ~370 to ~100 m2/g. At the same time, the ratio of the total area of all LIG pores to the area of the obtained film varies in the range ~ 365–660 and reaches its maximum value of 660 at a power ~ 4.3 W.

Finite Element Modeling of Ring and Gaussian Dual Laser Heat Sources for Aluminum Butt Welding

Aluminum alloys have been used extensively for automotive industries for the structural applications with their high specific strength and corrosion resistance. In order to use aluminum alloys for automotive components, laser welding has been used due to the advantage of being capable to weld thick products due to its deep penetration depth. In this regard, a dual laser heat source combining an outer ring laser beam with a centrally focused Gaussian laser beam was proposed to compensate for insufficient melting caused by laser reflection of aluminum alloy. The purpose of this study is to develop a simulation model that can consider heat input from the dual laser beams individually, for analyzing melting and heat distribution behavior during the laser welding. Two different heat source models were proposed. One model used 3D Gaussian distribution of heat input for the centrally focused laser while the other model utilized Gaussian cylinder heat input. The proposed heat input models were implemented by finite element analyses, and the results were compared with aluminum butt welding experiments. It was shown that Gaussian cylinder heat input for the centrally focused laser beam reproduced much better the experimentally observed melting behavior in comparison to the 3D Gaussian distribution.

Dynamics of RBCs and Their Charge Development Due to Laser Beam During The Pre- Ionization Period

In this paper it is attempted to have a closer understanding of a cell when it is subjected to a highly focused laser beam giving a special attention to a single ionized cell during its pre-ionization phase. Cells of varying size are subjected to a 1064nm near infrared (NIR) radiation one by one and their trajectory (radial and tangential) towards the center of the trap has been recorded and analyzed. The result showed that the cells gain charge even before being trapped by the trapping center i.e. while they are on their way to the center. As a result, the charged cells have been observed interacting with the electromagnetic field creating a Coulomb force in the direction of polarization. Consequently, the developed charge significantly affected the trajectory of each cell towards the trap center by retarding those cells whose gradient force vector and direction of polarization are in opposite direction while accelerating those cells whose gradient force vectors align to the direction of polarization.

Raman spectroscopic study of concentration dynamics in glycine crystallization achieved by optical trapping

This study investigates concentration dynamics during optical trapping-induced crystallization (OTIC) of glycine using Raman spectroscopy. In-situ Raman spectroscopy demonstrated that tightly focused laser beams induced faster concentration increase and crystal nucleation at higher supersaturation compared to loosely focused beams. Also, by varying numerical aperture (NA) values of the objective lens used, it was revealed that higher NA led to achieving a shorter induction time and higher crystallization probability. Remarkably, optical trapping using objective lenses with higher NA generated stable liquid droplets, inhibiting crystallization until considerably higher supersaturation was realized. These findings elucidate the complex interplay between optical forces, supersaturation, and crystallization dynamics on the mechanism of OTIC and offer a new method for precise control of laser-induced crystallization. We believe that the insights gained by this study pave the way for innovative developments in crystal chemistry and promising advancements in photochemistry.