Small Laser Power Research Articles

Preparation and Decomposition of Spherical CL-20 Composites with Enhanced Laser Absorbance and Decreased Mechanical Sensitivity.

Direct initiation of secondary explosives by a semiconductor laser is highly demanded, but it is challenging to exclude the use of sensitive primers. Most laser-sensitive energetic materials are usually mechanically sensitive. In order to reduce the mechanical sensitivity (MS) of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) while improving laser absorbance in the near-infrared band, spherical CL-20 composites (SCCs) embedded with nano aluminum (Al) powder and graphene-based catalyst (GO-CHZ-Co) were prepared by a spray drying method. These SCCs have been characterized comprehensively in terms of their morphologies, particle size distribution, laser absorbance, thermal decomposition behaviors, MS, and laser ignition properties. Results show that the maximum critical impact energy of SCCs was 3.8 J, which is 2.8 J higher than that of pristine ε-CL-20. The critical friction load was increased by at most 108 N compared to pristine CL-20. The absorbance has also been significantly increased up to almost 70% in the wavelength between 400 and 1400 nm, where the peak absorption is located in the region of 800-900 nm. In addition, the initial decomposition temperature (Ti) of SCCs is lower than that of pure CL-20, especially in the presence of GO-CHZ-Co. The apparent activation energy (Ea) for the decomposition of SCCs was largely dependent on the particle size of Al. Preliminary ignition tests indicate that the SCCs can be ignited successfully by a small-power laser.

Effect of process optimization on laser additive manufacturing of Inconel 718 alloy based on finite element analysis: Thermal and structural evaluation

In this study, a three-dimensional transient thermo-elastic-plastic model with sequential thermal-force coupled is established based on an improved temperature field model, which can realize dynamic simulations of the temperature and stress fields in laser additive manufacturing of Inconel 718 alloy under different process parameters and scanning strategies. The results show that the Von-Mises stress inside cladding layers is high and reaches the peak at the end of the clad or the connection with the substrate, and well explain the end ablation and core cracking in cladding layers. On the premise of ensuring the quality of cladding parts, a relatively small laser power and a large scanning speed should be selected as possible, and a reasonable scanning strategy can effectively avoid excessive stress concentration in cladding layers with the maximum stress reduced by about 50 MPa. The tensile limit of cladding parts can reach 902.41 MPa under the a-scanning strategy as found by tensile experiments, and the surface residual stress measured by X-ray diffraction technology varies from 186 MPa to 272 MPa. By comparing with experiment, the simulation error is controlled within 21 %, indicating that this research can provide reasonable theoretical guidance for the process optimization of the actual processing.

Molecular Dynamics Simulation of NiTi Shape Memory Alloys Produced by Laser Powder Bed Fusion: Laser Parameters on Phase Transformation Behavior.

In this study, the deposition, powder spreading, and laser fusion processes during the laser powder bed fusion (L-PBF) process were studied using molecular dynamics (MD) simulation. The effect of Ni content on the characteristic phase transformation temperatures was also investigated. Shape memory effect and superelasticity of NiTi alloys with Ni content ranged from 48.0% to 51.0% were analyzed. By employing MEAM potentials, the effects of the laser power, spot diameter, and scanning speed on the molten pool size and element evaporation were studied. Simulation results showed that a larger spot diameter renders a higher Ni content in the molten pool, also a larger molten pool. A faster scanning speed leads to a higher Ni content in the molten pool, and a smaller molten pool. The element is difficult to evaporate using small laser power and a large spot diameter. The element in the molten pool expresses a great evaporation effect when the Es is larger than 0.4 eV/ų. According to Ni content within the molten pool during laser fusion, characteristic phase transition temperatures in single crystalline NiTi alloys with variant Ni content were investigated by employing a 2NN-MEAM potential. Characteristic phase transition temperature changes as the Ni content increases from 48.0% to 51.0%. Austenite boundaries and Ni content in the boundary were found to be the keys for controlling the characteristic phase transformation temperature.

Investigation on shape deviation of horizontal interior circular channels fabricated by laser powder bed fusion

Abstract The fabrication of horizontal interior circular channels poses some unique challenges to the laser powder bed fusion (L-PBF) process. The engineering challenge is to be able to print horizontal interior channels using L-PBF without using support structures, while the scientific challenge is to predict the shape deviation in the horizontal channel. This paper studies the geometric fidelity (roundness and shape deviation) of L-PBF printed horizontal interior circular channels (diameters 1−3 mm) by developing experiment-based regression models and a preliminary computational fluid dynamics (CFD) simulation model. The roundness error is found to be affected by the shape/size of the melt pool, thermal stresses, beam offset, and the slicing algorithm. It is recommended that to decrease the roundness error, in addition to choosing a proper beam offset, the width/depth of the melt pool should be minimized by minimizing the volumetric energy density (smaller laser power or higher scanning speed). Shape deviation in overhanging structures is determined by the thermo-mechanical driven molten flow in the melt pool. Hanging structures with irregular profiles (dross) are formed due to the sinking of the melt pool on an unconsolidated powder bed under the effect of gravity, surface tension, and poor thermal conductivity. (Partially) unmelted powder randomly adheres to the edges of the melt pool enlarging the hanging structure and roughening the profile. Small laser power or large scanning speed benefits reducing the roundness error and hang-diameter ratio. 0° or 45° rotational linear scanning strategy can be selected for minimizing the roundness error or the hang-diameter ratio, respectively.

Motion of Optically Heated Spheres at the Water-Air Interface.

A micrometer-sized spherical particle classically equilibrates at the water-air interface in partial wetting configuration, causing about no deformation to the interface. In condition of thermal equilibrium, the particle just undergoes faint Brownian motion, well visible under a microscope. We report experimental observations when the particle is made of a light-absorbing material and is heated up by a vertical laser beam. We show that, at small laser power, the particle is trapped in on-axis configuration, similarly to 2-dimensional trapping of a transparent sphere by optical forces. Conversely, on-axis trapping becomes unstable at higher power. The particle escapes off the laser axis and starts orbiting around the axis. We show that the laser-heated particle behaves as a microswimmer with velocities on the order of several 100 μm/s with just a few milliwatts of laser power.

Novel homodyne frequency-shifting interference pattern locking system

We present a novel homodyne frequency-shifting interference pattern locking system to enhance the exposure contrast of interference lithography and scanning beam interference lithography (SBIL). The novel interference pattern locking system employs a special homodyne redundant phase measurement interferometer (HRPMI) as the sensor and an acousto-opto modulator (AOM) as the actuator. The HRPMI offers the highly accurate value as well as the direction recognition of the interference pattern drift from four quadrature interference signals. The AOM provides a very fine resolution with a high speed for phase modulation. A compact and concise system with a short optical path can be achieved with this new scheme and a small power laser head in tens of microwatts is sufficient for exposure and phase locking, which results in a relatively low-cost system compared with the heterodyne system. More importantly, the accuracy of the system is at a high level as well as having robustness to environmental fluctuation. The experiment results show that the short-time (4 s) accuracy of the system is ±0.0481 rad(3σ) at present. Moreover, the phase of the interference pattern can also be set arbitrarily to any value with a high accuracy in a relatively large range, which indicates that the system can also be extended to the SBIL application.

A study of narrow gap laser welding for thick plates using the multi-layer and multi-pass method

This paper details a new method that combines laser autogenous welding, laser wire filling welding and hybrid laser-GMAW welding to weld 30 mm thick plate using a multi-layer, multi-pass process. A “Y” shaped groove was used to create the joint. Research was also performed to optimize the groove size and the processing parameters. Laser autogenous welding is first used to create the backing weld. The lower, narrowest part of the groove is then welded using laser wire filling welding. Finally, the upper part of the groove is welded using laser-GMAW hybrid welding. Additionally, the wire feeding and droplet transfer behaviors are observed by high speed photography. The two main conclusions from this work are: the wire is often biased towards the side walls, resulting in a lack of fusion at the joint and the creation of other defects for larger groove sizes. Additionally, this results in the droplet transfer behavior becoming unstable, leading to a poor weld appearance for smaller groove sizes. • It is a new method to weld 30mm thick plate by small power laser. • It presents the mechanism of wire melting and droplet transfer mode. • A good joint without obvious defects can be achieved by a proper groove size.

Study on Laser Brazing for Copper

The power at 400 Watts Nd: YAG laser is used for laser brazing on copper. By improving the process parameter,a good joint will be achieved. Because of the stainless steel material, more lasers will be absorbed, which can actualize the small power laser weld the thicker red copper. The test of the joint pull shows that the tensile strength of the copper brazing joint can reach more than 80% of its base mental.

The PL Characteristics of ZnO Thin Film on Flexible Polymer by Pulse Laser Deposition

In this study, ZnO films have been grown on PES (polyethersulfone) of flexible polymer substrate by PLD (pulsed laser deposition) and characterized for crystalline and optical properties. Growing conditions were changed with substrate temperatures ranging from 50 to <TEX>$200^{\circ}C$</TEX> and laser power density ranging from 0.2 to <TEX>$0.4J/cm^2$</TEX>. When ZnO thin films are deposited at low temperature with a small laser power density, the (002) peaks of XRD to signify the crystal quality of ZnO thin films appear to be very weak and the (101) peaks to signify the chemical composition of oxygen and zinc are strong. The (002) peaks increase with the substrate temperature and laser power density because the energy needed for the supply of the combination regarding zinc and oxygen has increased. In this study, the best condition for growing ZnO thin film on PES is at a substrate temperature of <TEX>$200^{\circ}C$</TEX> and with a laser density of <TEX>$0.3J/cm^2$</TEX>. The characteristics of PL were measured by UV and green luminescence.

Influence of Process Parameters on Temperature Field in Laser Remelting Coating Prepared by Plasma Spraying on Titanium Alloy Surface

In order to research the effect of process parameters on temperature field evolution in laser remelting coating prepared by plasma spraying on titanium alloy surface，the finite element model of laser multi-tracks remelting temperature field was established based on ANSYS, and remelting temperature field was analyzed. The analysis results show that: under certain scanning velocity and laser spot diameter, too small laser power can't achieve metallurgical combination between coating and substrate; the effect on temperature field of scanning velocity was smaller than laser power; the influence on molten pool center temperature and remelting width of spot diameter is bigger; preheating coating and substrate can be effectively balance remelting process temperature field, thereby reducing the thermal stress and coating cracks appear chance.Through the calculation model can master the evolution of the temperature of lasre remelting process and can provide the theory basis for process parameter selection and optimization.

Stimulation of mucoperiostal slice epithelization by small power laser after the primary plastic of oroantral communication

The oroantral communication is a pathologic communication between the oral cavity and maxillary sinus. It originates with extraction of the upper lateral teeth. Primary plastics communication, which is more extensive than 5 mm has been unsuccessful in 16%. Small power lasers have positive reaction on wounds healing. The aim of this work was to determine the lasers effects on slice epithelization after the plastics more extensive than 5 mm. The experimental research was done on dogs with extraction of the upper second premolars on both sides, and formed oroantral communication having diameter of 10 mm. After the plastics of sinus, the left side slices were exposed to radiation for 7 days, and the opposite slices healed spontaneously. Eight points (8x1J) were treated for 100s by GaAlAs laser, power 10 mW and wavelength 670 nm. Biopses of the slices connections were taken on the 14th day to be laboratory treated and examined microscopially. The study included 36 examinees with communication diameter of 10 mm and performed plastics of sinuses. In half of the examinees wounds were exposed to radiation for 7 days, and in other examinees they healed spontaneously. The results were analyzed on the fourteenth day according to the scale: (1) complete healing, without dehiscention; (2) incomplete healing, with minimal dehiscention; (3) communication did not heal, with partial dehiscention; (4) open communication, with significant dehiscention. The microscopic analysis shows that no wounds exposed to radiation were overcast with mucous membrane which had smooth sub epithelia chronic inflammation and inflammable infiltrate, and strong fibroplasias and granulations. Wounds exposed to radiation had mucous membrane without any signals of inflammation. Laser radiation causes anti-inflammatory reaction, i.e., it provokes reduction of exudation, alteration and proliferation, it blocks cyclo- and lipo-oxygenation by delaying the synthesis of prostaglandin, stimulates neutrophyll, macrophage and lissome activity and it activates the function of immune complex T and B lymphocytes, so this difference could be primary referred to the action of laser. Our clinical study shows that complete healing of oroantral communication was recorded in 88.8% of the examinees who were exposed to radiation in relation to 50%, of those who did not receive radiation therapy which is statistically much higher percentage (chi2 test < 0.05). The surgery was repeated in 5.6% of those who had received radiation therapy and in 16.7% of those who had not been exposed to radiation. Laser radiation stimulates changing of ADP in ATP and it accelerates cells metabolism, it increases microcirculation and accelerates substance exchange of cells, it increases DNK and RNK synthesis and stimulates cells division, which cause quicker regeneration of epithelia, i.e., it accelerates the process of wound healing. It can be concluded that small power laser can be used successfully as additional method of treatment, after closing of oroantral communication surgically.

Blind Via Hole in Multi-layer AFRP Printed Wiring Boards by Build-Up Process

In the printed wiring board manufacturing sector, methods have been developed to improve the circuit packaging density. The multi-layer printed wiring board manufacturing process is receiving particular attention. In the current manufacture of these boards, the method frequently used is to laminate the core with insulating resin, namely a build-up process. Etching is generally used to form the holes connecting the circuits of these boards. However, a problem has emerged in that the strength of the substrate decreases due to the insulating resin part as the multi-layers are progressively formed. Thus, it becomes necessary to use FRP for the insulation layer part. Since it is very difficult to etch composites, lasers have been proposed for a new way to drill holes in such materials. By appropriate adjustment of the laser penetration energy, the holes are drilled only in the insulation part, and a technique is proposed to stop the holes using the copper foil forming the circuit. AFRP has been considered a suitable FRP for such laser processing. In the present study, attempts were made to experimentally produce multi-layer boards using AFRP and GFRP for the build-up insulation layer, and the characteristics of blind via holes drilling with a small power laser were investigated.

Determination of Aerosol Extinction-to-Backscattering Ratio from Multiwavelength Lidar Observation

We propose a method to determine the extinction-to-backscattering ratio (S1 parameter) in the troposphere from multiwavelength (355, 532, 756, and 1064 nm) lidar data. In our approach, reference profiles are prepared by using the wavelength dependence of the extinction coefficient as derived either from the sun photometer data or from the Mie calculation. By comparing these reference profiles with the profiles calculated using the conventional Fernald inversion method, the S1 parameter is determined for each wavelength. When a reasonable range is covered at 532 nm, this method makes it possible to determine the S1 parameters for shorter or longer wavelengths for which full range observation cannot be attained, due presumably to small laser power or limited detector efficiency. In addition, information about the vertical uniformity of aerosol properties can be derived from the S1 dependence of the difference between the reference and retrieved profiles.

Blind Via Hole in Multi-layer AFRP Printed Wiring Boards by Build Up Process. Quality of Drilled Hole by Small Power Laser.

In the printed wiring board manufacturing sector, methods are developed to improve the circuit packaging density. The multi-layer printed wiring board manufacturing process is receiving particular attension. In the current manufacture of these boards, the method frequently used is to laminate the core with insulating resin. Photo-etching is generally used to form the holes connecting the circuits of these boards. However, a problem has emerged in that the strength of the substrate decreases due to the insulating resin part as the multi-layers are progressively formed. Thus, it becomes necessary to use FRP for the insulation layer part. Since it is very difficult to etch composites, lasers have been proposed for a new way to drill holes in such materials. By appropriate adjustment of the laser panetration energy, the holes are drilled only in the insulation part, and a technique is proposed to stop the holes using the copper foil forming the circuit. AFRP has been considered a suitable FRP for such laser processing. In the present study, attempts were made to experimentally produce multi-layer boards using AFRP and GFRP for the insulation layer, and the characteristics of blind via holes drilling with a small power laser were investigated.

Forced oscillations of the keyhole in penetration laser beam welding

The dynamic behaviour of the keyhole in penetration laser beam welding is essential for the entire welding process, and is closely connected to welding seam defects and splash generation. To improve understanding of the process and to help interpret measured process signals, forced oscillations of the keyhole due to fluctuations of the CW laser power are theoretically studied. It is shown that even very small laser power fluctuations can lead to strong keyhole oscillations dominated by eigenfrequency response. Because the governing differential equation is nonlinear, bifurcation effects can occur which tend to broaden eigenfrequency peaks in the keyhole vibration spectrum. Calculated Fourier spectra are in good agreement with corresponding measurements of the ultraviolet and near infrared light emission during welding with an industrial CW laser.

Cu CVD from Copper(II) Hexafluoroacetylacetonate: II . Laser‐Assisted Selective Area Deposition

The laser‐assisted chemical vapor deposition of copper onto thermal Si wafers in a cold wall atmospheric pressure reactor, using , or argon as carrier/diluent is discussed. The substrate was biased thermally at or 200°C in Ar. A multiline continuous wave 4 μm focused spot diameter, 150 mW argon ion laser was used to heat the spot to a temperature at, or above, the required decomposition temperature, and ≥250°C in Ar. The steady‐state temperature on the prior to the beginning of deposition was estimated using a modified Lax model, since there is no convenient way of measuring it experimentally. Under the conditions employed, a maximum copper spot growth rate of 0.12 μm/min was obtained at 0.095 W laser power. The laser‐assisted growth rates in the present system can be predicted within a factor of two from the kinetic model of Ehrlich and Tsao. An incubation time which varies inversely with power, and with the composition of the carrier gas was observed on , due to the low absorption of the incident energy in the at the small laser power used. Auger electron spectroscopy, of the copper deposits has shown small levels of carbon and oxygen. It is possible that the temperature at the center of the beam spot is greater than 400°C after copper begins to nucleate, and that the organic ligands undergo some fragmentation, or that some degree of oxidation and carbonaceous contamination occurs upon exposure to air when specimens are removed from the reactor. Using the described deposition methods, it should be possible to effect repair of broken copper lines on a microelectronic package in a minute or two.

Comparison of several methods of fluorescence quenching in protein molecules

Abstract Several methods to detect Raman signals by quenching the fluorescence from protein molecules which show high fluorescence have been studied. The several methods include changing the wavelength of the excitation source, exposing the sample to small power laser radiation for a long time, exposing the sample to high radiation, surface enhanced Raman scattering and aqueous solution extraction by nitrobenzene. The best means of quenching the fluroscence from the bovine serum albumin sample in aqueous solution is the nitrobenzene extraction technique. The laser Raman spectrum of bovine serum albumin is reported.

The effect of laser radiation on the permeation of gases through polymer membranes

The effect of a multiline cw CO 2 laser radiation on the permeation of He, H 2, Ne, Ar and Kr through a polytetrafluoroethylene, PTFE, membrane was investigated. It was found that the laser radiation determines modifications of the permeation, diffusion and solubility of gases in PTFE. It was assumed that the results obtained were caused mainly by the thermal heating of the polymer and the resonant enhancement of the motions of the polymer chains following the absorption of energy from the laser radiation. As a result the permeation selectivity of PTFE and the dynamics of a transition between two regimes of steady-state permeation through PTFE can be easier altered with a laser radiation than with traditional pressure or/and pressure changes. Thus, from a practical point of view a small power laser radiation acts on the PTFE as a stopcock which switches rapidly the flux of gas through the membrane and/or controls, in a certain range, the amount and composition of a gas mixture which permeates through the PTFE membrane.