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A nanocomposite (NC) of polyaniline (Pani), polyvinyl pyrrolidone (PVP) and zinc sulfide (ZnS) nanoparticles (NP) was prepared using chemical coprecipitation and ex-situ casting procedures. ZnS NP were synthesized using the chemical coprecipitation technique in atmospheric air. The x-ray diffraction (XRD) scans indicated that the synthesized ZnS had a nanonature and fit the cubic zinc blended structure. We used an infrared pulsed laser to irradiate the Pani/PVP/ZnS NC samples with fluences ranging from 3 to18 J/cm2. The induced changes in the NC were investigated using the UV spectroscopy and International Commission on Illumination (CIE) color difference methodology. When the laser fluence increased up to 18 J/cm2 both the direct and indirect optical bandgaps (Eg) decreased. Additionally, we used the optical dielectric loss (ε") to detect the type of microelectronic transition for the NC samples. The Eg of the exposed NC samples and the pristine samples exhibited indirect allowed transitions. The laser effects on the absorbance, extinction coefficient, transmission, refractive index, dielectric parameters and optical conductivity of the NC were studied. Lastly, the color differences between the pristine and exposed samples were determined. The pristine Pani/PVP/ZnS showed a significant color difference with the laser irradiated samples. The changes of the studied optical parameters with the laser fluence indicated that the laser radiation represents a convenient tool that would allow the application of Pani/PVP/ZnS NC in optoelectronic devices. [ABSTRACT FROM AUTHOR]

During kiwifruit storage, quality monitoring is required for inventory planning and consistent quality maintenance. Commercial near-infrared (NIR) spectrophotometers showed reduced performance in the estimation of kiwifruit flesh firmness (FF) as the FF estimation is indirect and can be affected when both, textural structures and absorbing compounds, change during postharvest ripening. Laser backscattering imaging (LBI) records the backscattered signal after a single laser beam interacts with kiwifruit tissue, including merged information on light absorption and scattering. Measurements were carried out at 830 nm, where scattering is most dominant. In this work, time series of kiwifruit 'Zesy002' (n = 30) and 'Hayward' (n = 30) LBI were collected through the postharvest ripening during a 15-day shelf life at 20°C. Four LBI parameters capturing DIP, FWHM, SLP and HWQM were selected in this study. "Zesy002' DIP, FWHM, SLP, and HWQM increased approx. 0.6 cm, 0.2 cm, 0.3 and 0.14 cm, respectively. 'Hayward' LBI increased approx. 0.2 cm, 0.1 cm, 0.2 and 0.04 cm, respectively. Different initial LBI values between cultivars and LBI changes may reflect the actual stage of softening, affected by kiwifruit ripeness. In conclusion, time series analysis could be useful in describing kiwifruit LBI change during ripening and making forecasts. [ABSTRACT FROM AUTHOR]

In this paper, the technique of surface absorption of a uniform laser radiation is used to illuminate the upper surface of a thermoelastic layer whose properties are temperature-dependent utilizing the new modification of Green's and Lindsay's thermoelasticity theory. The upper surface of the layer is exposed to heat losses and the lower surface is considered insulated, while both are traction free. The general solution of the problem obtained by applying Laplace transform in which whose inverse obtained computationally. In addition to the usual temperature-dependent consideration, we also investigate the case of temperature-dependent absorption coefficient of the surface. [ABSTRACT FROM AUTHOR]

Second-harmonic generation of hollow Gaussian laser beams (HGLBs) in inhomogeneous plasmas is investigated in the presence of an external wiggler magnetic field. The wiggler magnetic field and electric field of the laser pulse exert a ponderomotive force on electrons deriving electron velocity. Electron velocity, wiggler magnetic field and magnetic field of the laser pulse beat to exert a nonlinear ponderomotive force on electrons at the second-harmonic frequency. The nonlinear ponderomotive force can derive a nonlinear current density. Using linear and nonlinear current densities and wave equation in cylindrical coordinates, two equations obtaining different components of the electric field of second-harmonic wave (SHW) are derived. Results indicate that by increasing the external wiggler magnetic field, order of HGLB, rippled electron density, rippled wave number and initial intensity of the laser pulse, the amplitude of the excited SHW increases. Finally, it is found that by decreasing the initial width of the laser beam, the amplitude of SHW increases, attains a maximum and then decreases. [ABSTRACT FROM AUTHOR]

AbstractPulsed laser cladding provides a periodical thermal accumulation, enabling a greater temperature gradient and cooling rate inside the substrate, which can efficiently ameliorate the microstructure of the cladding layer. It is crucial to quantitatively investigate the mechanism of the interaction for the cladding process parameters on the transient evolution of the multi-field coupling to improve the cladding quality. In this paper, a 3-D model during the single-channel multilayer pulsed laser cladding process was constructed which is grounded on the temperature-variable physical properties parameters of the material. The integrated consideration in the masking impact of the molten powder waist beam on the pulsed laser beam, the molten pool liquid metal surface tension, the influence of buoyancy on the flow, and the transient evolution of the molten pool edge morphology. The temperature, flow, and stress fields of the single-channel multilayer cladding process were computed and resolved. The mechanism in multi-field coupling impact of laser pulse frequency, laser power, and pulse duty cycle on the single-channel multilayer cladding process was emphasized. The response surface equations between each influencing factor and the cladding temperature, temperature change gradient, and thermal stress were determined according to the response surface method, and the sensitivity of each parameter was attained from the Monte Carlo method. Using SEM to observe the profile and microstructure of the cladding layer, the material hardness distribution was measured experimentally, and the effectiveness of the model was confirmed. This research supplies an essential rationale for upgrading the quality of pulsed laser cladding layers. [ABSTRACT FROM AUTHOR]

A nano-structured surface containing an Au nano-island film is used to fabricate hybrid liquid crystal (HLC) cells. HLCs are characterized by faster response times. The dynamic holographic technique is applied to make the conversion of the laser pulse shape by using HLCs. From a comparative analysis of experimental results with theoretical modeling of a dynamic process, the time constants of the dynamic grating recording and relaxation have been determined. [ABSTRACT FROM AUTHOR]

This paper describes a new active method of controlling the position of the burning surface of a solid fuel strand in an opposed-flow burner experiment. This method is designed to avoid biases to the combustion process introduced by retaining wires and to avoid experimental delays caused by wire failures. Regression rates are presented for hydroxyl-terminated polybutadiene fuel strands burning in various oxidizer streams. The active control method uses a control loop composed of a diode laser, a photodiode, and a stepper motor. For comparison, tests were also performed using the commonly used passive control method of spring-loading the fuel against a retaining wire. This active control method can only be used at high values of oxidizer mass flux; at low mass flux, soot accumulation obstructs the laser beam. In passive control tests, the retaining wire conducts heat from the flame into the fuel and increases regression rate. The presence of the wire also modifies the extinction limits of the flame. A model was developed for regression rate as a function of oxidizer mass flux, oxidizer composition, and retaining wire diameter. This model can be used to correct future regression rate data for the bias introduced by retaining wires. [ABSTRACT FROM AUTHOR]

Enhancing the terahertz emission at hybrid resonant frequencies is observed from a warm collisional inhomogeneous plasma irradiated by intense laser beams in the presence of an external transverse magnetic field. To reach this result, we utilize the dielectric permittivity tensor of the plasma affected by the strength and the direction of the magnetic field and analyze the nonlinear current density induced by the ponderomotive force due to the beating of two Gaussian laser beams. The calculations reveal resonance emission at several frequencies, which depend on the thermal speed of the electrons, the wavenumber, the electron plasma frequency, the collision frequency, and the cyclotron frequency. However, the amplitude of THz waves at these frequencies mainly depends on the electron temperature as well as the external magnetic field strength. [ABSTRACT FROM AUTHOR]

The primary focus of the present contribution is to develop a new system of differential equations describing the nonlocal thermoelasticity theory. The problem deals with the thermoelastic interaction in a nonhomogeneous thermoelastic layer induced by absorbing penetrating laser radiation throughout its volume. The heat conduction equation has been formulated in the context of memory dependent three-phase lag model. The surfaces of the layer are thermally insulated and free of traction. Employing the integral Laplace transform technique, the solutions of the field quantities have been achieved in the transformed domain. The corresponding solutions in the space–time domain have been derived using the numerical inversion of the Laplace transform by Riemann-sum approximation technique. The numerical estimates of the field quantities have been depicted graphically to address the effects of nonlocality and memory effects on the temperature profile, displacement and stress components. The effect of the delay time, nonhomogeneity and various choices of linear and nonlinear kernel functions in the heat transport law have also been reported. [ABSTRACT FROM AUTHOR]

The accurate three-dimensional wind field obtained from a Doppler lidar not only helps to comprehend the refined structure of complex airflow but also provides important and valuable solutions for many fields. However, the underlying homogeneity assumption of the typical wind retrieval methods, such as Doppler Beam Swinging (DBS) and Velocity Azimuth Display (VAD) based on a single-lidar, will introduce the measurement uncertainty in complex terrain. In this paper, a new design of a wind measurement campaign involving seven lidars was carried out, which contained the three-lidar-based Virtual Tower (VT) using a time-space synchronization technique and four single-lidars with different elevation angles. This study investigates the performance of VT and VAD measurements under various conditions and evaluates the sensitivity of wind measurement uncertainty of VAD to the horizontal spatial- and probe volume-average effects associated with elevation angles of the laser beam. The inter-comparison results between VT and four VADs show consistent trends with small relative errors under neutral atmospheric conditions with weak wind velocity. Under convective or high Turbulence Intensity (TI) conditions, the relative errors between VT and VAD become larger and more fluctuant. Moreover, it is found that the measurement uncertainty of VAD increases at a given elevation angle with the increasing measurement heights, which is caused by the horizontal homogeneity associated with the conical scanning area. Additionally, the simulated and measured results of four VADs indicate that a larger elevation angle corresponds to a lower measurement uncertainty for a given height. [ABSTRACT FROM AUTHOR]

A method was developed to verify the viable counts of BioTrakTM (TSI Model 9510-BD) without using test bacteria. In this method, an inkjet aerosol generator (IAG) was used to deliver a known number of test aerosol particles to BioTrak in the given sampling time. An IAG generates two types of monodisperse test particles, inert particles and fluorescent particles. Inert particles consist of a chemical substance that does not emit fluorescence when particles are irradiated by the laser beam of BioTrak. Inert particles were used to test whether a BioTrak generates false positive in viable counts or not. Depending on the version of the discrimination algorithm, BioTrak generated false positive in viable counts over 2 − 6-µm particle-diameter range. Fluorescent particles are monodisperse particles with a trace mass of fluorophores, which simulate the autofluorescence emission of surrogate bacteria. In this study, two types of fluorophore pairs, β-NADH and riboflavin sodium phosphate (riboflavin in short) and Coumarin 30 and riboflavin, were used. The counting efficiency of viable particle (CEviable) were evaluated by generating fluorescent particles at a 3.0–8.3-µm particle diameter. The average of CEviable, and its uncertainty among three BioTrak used in this study, were 0.701 ± 0.090 (k = 2), which is close to the physical sampling efficiency of BioTrak reported by the manufacturer. The relative standard uncertainty of CEviable due to day-to-day variation was 0.8% and 3.5%, when the first and second fluorophore pairs were used, respectively. These results proved that the proposed method can be regularly used to verify the viable counts of BioTrak. [ABSTRACT FROM AUTHOR]

Porous materials have been extensively used in electronic communications, aerospace, bio-medicine and petrochemical, etc. due to their attractive attributes such as low relative density, thermal and acoustical insulation and good permeability. Ultrashort laser pulses have a series of unique advantages including high energy density, ultrashort interaction time and high accuracy, which are widely used in the fields of precision machining and microelectronic manufacture. For porous materials heated by an ultrashort laser pulse, revealing the interplay between deformation field and temperature field is crucial to guide their engineering application and optimization design. The present work devotes to investigating the transient response of a porous half-space heated by a non-Gaussian laser beam on its boundary surface based on the newly established linear thermoelastic theory with strain and thermal relaxations. The coupled governing equations are formulated and solved through the Laplace transform and its numerical inversion. The distributions of the non-dimensional temperature, displacement, stress as well as volume fraction field are obtained and illustrated graphically. In calculation, the effects of the thermal relaxation factor, the strain relaxation factor on the temperature field, volume fraction field, displacement field as well as stress field are examined and discussed in detail. [ABSTRACT FROM AUTHOR]

Adjustable Ring Mode (ARM) laser technology combined with Beam Oscillation optics module was introduced to effectively enhance weld quality in joining aluminium alloys. This study developed a three-dimensional (3-D) thermo-mechanical finite element (FE) model to analyze the distribution of thermally induced residual stresses in laser-welded 3003 aluminium alloy. The accuracy of model was validated through comparisons with experimental weld cross-sections and further reinforced by X-ray diffraction residual stress measurements. The transient temperature field and stress distribution during the welding process were investigated using the verified model. Additionally, the hardness and microstructure of the welded samples were examined through micro-hardness tests and scanning electron microscopy. Results showed that welding with beam oscillation resulted in less penetration but higher hardness and finer columnar grain size in the fusion zone. Additionally, the influence of varying standoff distances between two sequential weld beads on residual stress distribution was investigated. Numerical findings revealed that higher residual stress concentrations were located at the weld seam and dominated by tensile longitudinal residual stress and compressive transverse residual stress. As the distance between weld beads increased, transverse and equivalent residual stresses decreased, while longitudinal residual stress away from the bead increased. [ABSTRACT FROM AUTHOR]

Integrated parameter design and tolerance design (IPTD) is an effective way to improve product quality and reduce manufacturing cost in micro-manufacturing processes. However, the current modeling techniques rarely analyze the influence of model uncertainty on the optimal machining parameters. It may not obtain the robust optimal machining parameters due to model uncertainty. This paper proposes a novel economically integrated design method which considers the correlations among quality characteristics, the variability of manufacturing process, and uncertainty in the model predictions. First, a new rework and scrap cost functions are established via Monte Carlo simulation. Meanwhile, an integrative expected quality loss function is constructed based on interval analysis theory for quantifying model uncertainty. Second, to make the proposed method closer to the practical micro-manufacturing problem, we consider the trade-offs among cost, time, and success rate in the modeling process. Finally, a total cost model is proposed to take into account the quality loss, tolerance cost, unit manufacturing cost, and scrap cost. The effectiveness of the proposed modeling method is verified by a laser beam micro-drilling manufacturing. The results illustrate that the proposed method can achieve better robustness property and economically than the traditional method that does not consider model uncertainty. [ABSTRACT FROM AUTHOR]

A nanocomposite (NC) of polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and nickel oxide (NiO) nanoparticles (NP) was prepared using sol–gel and ex-situ casting techniques. The results indicated that the NiO had a single phase with the space group (R-3m). Its average grain size was 18 nm. We used an infrared pulsed laser to irradiate the PVA/CMC/NiO NC samples with energy fluences ranging from 4 to 16 Joule/cm2. The induced changes in the linear and nonlinear optical properties of the NC samples due to the laser irradiation were investigated by means of UV spectroscopy. When the laser fluence increased up to 16 Joule/cm2, the maximum fluence used, both the direct and indirect bandgaps decreased. Additionally, we used the optical dielectric loss (ε″) to detect the type of microelectronic transition for the PVA/CMC/NiO NC samples, which was found to be a direct allowed transition. The laser effects on the absorbance, extinction coefficient, refractive index, dielectric parameters, optical conductivity, and the nonlinear parameters of the NC were studied. The enhancement in the optical properties indicated that the laser radiation is a useful tool that allows the application of the resulting PVA/CMC/NiO NC in optoelectronic devices. [ABSTRACT FROM AUTHOR]

The overview describes the synergy between biological sciences and cellular structures processed by additive manufacturing to elucidate the significance of cellular structured implants in eliminating stress shielding and in meeting the bio-mechanical property requirements of elastic modulus, impact resistance, and fatigue strength in conjunction with the biological functionality. The convergence of additive manufacturing, computer-aided design, and structure-property relationships is envisaged to provide the solution to the current day challenges in the biomedical arena. The traditional methods of fabrication of biomedical devices including casting and mechanical forming have limitations because of the mismatch in micro/microstructure, mechanical, and physical properties with the host site. Additive manufacturing of cellular structured alloys via electron beam melting and laser powder bed fusion has benefits of fabricating patient-specific design that is obtained from the computed tomography scan of the defect site. The discussion in the overview consists of two aspects - the first one describes the underlying reason that motivated 3D printing of implants from the perspective of minimising stress shielding together with the mechanical property requirements, where the mechanical properties of cellular structured implants depend on the cellular architecture and percentage cellular porosity. The second aspect focuses on the biological response of cellular structured devices. [ABSTRACT FROM AUTHOR]

In this study, the role of a scan strategy in the fabrication of a single crystal (SX) structure of face-centered cubic (fcc) pure Ni using a flat-top laser profile by a laser powder bed fusion (LPBF) process was investigated. A flat-top laser with a uniform heat intensity across the beam profile was employed to fabricate the SX structure with a <001> texture parallel to the build direction (║BD). A meander scan strategy with an XY–90° scan rotation was required to achieve the flat-top-derived SX structure. The meander scanning strategy promoted the epitaxial <001> fcc growth along the direction ║BD, leading to the <001>║BD texture formation. Meanwhile, the XY–90° scan rotation induced the epitaxial growth of <001> fcc phase on the hatch direction (HD)–scan direction (SD) plane in the direction deviated by approximately 45° relative to the SD. This 45° deviation relative to the SD occurred to accommodate the beam movement and the circular beam geometry on the HD – SD plane, resulting in the preferred configurations of <011>║SD and HD. Thus, this paper reports the importance of meander scanning with a 90° scan-rotation strategy to yield a flat-top-LPBF-derived SX structure with <001>║BD and <011>║SD and HD textures. [ABSTRACT FROM AUTHOR]

We present a procedure, based on established principles, to accurately determine the ionisation energies of medium-sized to large polyatomic molecules in supersonic beams. The method combines single-photon excitation from the electronic ground state using tunable vacuumultraviolet laser radiation, the delayed pulsed-field ionisation of high Rydberg states with sequences of pulsed electric fields, and the modelling of the lineshapes from calculations of the fieldionisation dynamics of high Rydberg states and of the rotational contours of the photoelectron bands. The method is illustrated by a measurement of the adiabatic ionisation energy of p-diaminobenzene (p-DB), for which we obtain the value of 54,617.47(15) cm-1, which represents a more than 20-fold accuracy improvement over previous determinations. [ABSTRACT FROM AUTHOR]

Potassium dihydrogen phosphate (KDP) is an effective NLO substance. Much research has been concentrated on KDP crystals to increase the effectiveness of KDP's nonlinear optical property. The effectiveness of laser radiation conversion can be increased by altering its expansion. The excellent molecular chirality of organic acids is employed to improve the properties of KDP. Our main objective in this study was to describe the studies on the mechanical, thermal, surface, antibacterial, self-defocusing, and electro-optic properties of doped potassium dihydrogen phosphate solitary crystals for optical, electronic, and biological applications. The effect of itaconic acid (ITA) at concentrations ranging from 1, 3, and 5 mol% on the thermal, SEM, microhardness behaviors, NLO, antibacterial properties, and half-wave voltage of KDP (potassium dihydrogen phosphate) single crystals grown by the slow cooling technique. The existence of dopants was proved with energydispersive spectrometry. The mechanical properties of various temperatures for undoped and doped-KDP crystals with rising dopant combinations have been prepared, and the hardness was expanded due to doping. In contrast to several potentially dangerous microorganisms like Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, the produced crystals were exposed to antibiotic activity. The superiority of the fully-fledged crystal is determined by the etching studies. Using the Z-scan method, the good third-order nonlinear response for different planes (2 0 0), (2 1 1), and (1 1 2) of the ITAdoped KDP crystal sample was determined. Half-wave voltage may be discovered in the crystal produced via electro-optic examination. The Z-scan analysis of pure and ITA-doped KDP crystals for different planes reveals good self-defocussing and NLO responses. The electro-optic experiment generated a significant and consistent half-wave voltage. The photoelastic behavior of KDP crystals with ITA as a variable birefringent compensator has been investigated. [ABSTRACT FROM AUTHOR]

The purpose of this study is to see how inclined loads and the gravitational field affect a two-dimensional thermoelastic medium influenced by thermal loading from a laser pulse in the context of dual-phase lag model. A linear combination of a normal load and a tangential load is assumed for the inclined load. The surface of the bounding plane is heated by a non-Gaussian laser beam. Analytical formulas for several physical quantities have been produced on the transformed domain using the Laplace and Fourier transform techniques as tools. The numerical inversion of the Fourier transforms have been performed analytically whereas numerical inversion of the Laplace transform is carried out using the Zakian method. All physical quantities have been graphically depicted in the dual-phase-lag model (DPL) and Lord-Shulman (L-S) theory to indicate the effect of pulsed laser, gravity and the angle of inclination of the medium. [ABSTRACT FROM AUTHOR]

In this work, we develop a fluidic laser beam shaper based on the thermal lens effect in MoS2 suspensions. It is demonstrated that another weak unfocused Gaussian beam (probe beam) is transformed into an annular beam due to the thermal lens effect resulting from a strong focused Gaussian beam (pump beam). The time evolution of the generated annular beam is studied, and the result shows that the annular beam exhibits asymmetric caused by heat convection with the high pump beam power. In addition, the tunability of the generated annular beam is investigated. Furthermore, the optical trapping of micro-sized particles in air using the annular beam is researched. It is found that this method exhibits stable performance capture for 3 h. The advantages of adjustable size, flexible setup and low cost of annular beam generated method are significant for lots of laser applications, such as optical trapping, optical imaging and laser machining. [ABSTRACT FROM AUTHOR]

This article presents an analytical study of the shift/splitting of the rovibrational energy levels of diatomic polar molecules under the elliptically-polarized laser field. First, there are derived general formulas for the matrix elements of the energy shift operator between arbitrary rovibrational states. Then there are provided, as an example, explicit analytical results for the energy shifts/splitting of the rotational level J-2 and illustrate them. Based on the derived analytical results, there is proposed a new method for the spectroscopic diagnostic of the parameters of the elliptically-polarized laser field inside low-temperature plasmas. [ABSTRACT FROM AUTHOR]

In this paper, we show the impact of the outer scale on beam wander for laser beam propagation in non-Kolmogorov turbulence. The analysis is based on a new relation between non-Kolmogorov and Kolmogorov structure constants anchored on the outer scale. This approach is based on a measurable physical entity, the outer scale, and it insures the total power of the fluctuations of the refractive index is conserved when the power law changes. [ABSTRACT FROM AUTHOR]

We describe an approach to detecting off-axis radiation of laser beams propagating in scattering media, especially in the atmosphere, in the presence of background (solar) radiation. The method relies on a generalization of the conventional intensity interferometry (II) theory to scenarios involving coexisting sources of relatively long (laser radiation) and much shorter (background) coherence times. In such circumstances, the high coherence of the laser light allows its discrimination against even much stronger, but low-coherence, background. We propose a simple detection system consisting of a small array of photodetectors (e.g. photodiodes) and estimate the ratio of the background-to-laser irradiances at which the laser radiation is expected to be detectable. [ABSTRACT FROM AUTHOR]

Hybrid-order Poincaré Sphere (HyOPS) is always used to describe arbitrary vector vortex beams and it makes the physical process of polarisation and phase evolution more intuitive. In this paper, we present a method to generate high-order vector vortex beams on multiple HyOPSs electronically using liquid crystal (LC) q-plates and LC phase viable retarder (LCVR), offering us an electrically controlled method to achieve orbital angular momentum (OAM) modes switching. Arbitrary generation and switching on three HyOPSs are achieved by loading certain voltages on the LC devices in this system. Experiments' separate verification of several peculiar points on these HyOPSs is conducted and the results fit well with theoretical predictions. This method of generating high-order vector vortex beams avoids the deviation caused by mechanical operation, and also provides an efficient, handy, fast tunable, easy-to-integration way to electronically generate and manipulate arbitrary high-order vector vortex beams on three HyOPSs with different topological charges instead of manual replacement of q-plates. This affords another passage for picophotonics as well as the science of interactions of picometre-scale events with light. Applications are vector vortex beam lasers, photo-communication, laser processing and super-resolution imaging. [ABSTRACT FROM AUTHOR]

A methodical study of the thermal properties of a hydrogen molecular ion strongly confined in a flat semiconductor quantum ring under external probes: intense laser-field radiation and static electric fields were carried out. The corresponding Schrödinger equation for these two coupled donors system was numerically solved by using the finite element method within the effective mass approximation. The effects of the donor angular and radial positions on the entropy, heat capacity and internal energy were analysed. Results show that the entropy of the system is maintained low as long as the molecule preserves its integrity but if the molecule is fragmented, the randomness of the system is substantially increased. Nevertheless, applying an intense laser or an external electric field can reduce this property in real time. [ABSTRACT FROM AUTHOR]

In order to obtain the high performance output of DBR semiconductor laser, the grating pattern is photolithographed by electron beam exposure technique, and the grating structure is fabricated by combining inductively coupled plasma etching and other processes. By controlling the exposure dose of electron beam lithography and optimizing the graphic line width, a grating shape that meets the device fabrication requirements is finally obtained. The test results show that the grating line width meets the experimental requirements and the grating sidewall steepness is good; the reflectivity and other indicators meet the device fabrication requirements, laying the foundation for the performance optimization of high-power semiconductor lasers. [ABSTRACT FROM AUTHOR]

In this study, a novel narrowband perfect absorber (NPA) with dual band resonance frequencies is presented. The proposed NPA absorbs over 99% of the incident laser beam in both resonance modes and it indicates high quality factor (Q = 135.2) resonance which is the highest for a perfect absorber performing in the mid-infrared region. In this work, the charge and current distributions for the corresponding resonance modes are investigated. The absorbance spectrum of the electric and magnetic field distributions is also obtained for the corresponding resonance modes. Furthermore, the detecting performance of the NPA is analyzed by covering the proposed device with a cladding layer. The figure of merit (FOM) and refractive index sensitivity (RIS) of the structure are calculated. Due to its high quality factor, enhanced electric and magnetic field responses, near unity absorbance for both resonance modes and tunable detecting characteristics the proposed NPA can be used in spectroscopy applications. [ABSTRACT FROM AUTHOR]

In many applications of joining and reinforcing timber elements with self-tapping fully threaded screws, the exact positioning of the screws becomes difficult as the screws tend to "stray" from their designated axis during insertion in wood and wooden semi-products. Experimental investigations show that besides natural local discontinuities like knots or resin inclusions, the screw-to-grain angle and the screws stiffness have an influence on the insertion process and thus can be identified as factors to a deviation of fully threaded screws. Mechanical predrilling cannot solve this problem, as the drills also stray during the predrilling process. As an alternative, a pyrolytic method of predrilling based on laser radiation proved suitable for obtaining guide holes with adequate straightness. This paper includes a description of the developed drilling processes using different lasers beam sources. The resulted borehole geometries of a QCW fiber laser, as well as an ultrashort pulsed laser, show satisfying results. Furthermore, the short- and long-term bond behavior of fully-threaded screws in a glued-laminated timber matrix, installed in laser predrilled guide holes, was tested and evaluated. The results show that with the new innovative wood processing method an exact positioning of fully-threaded screws is possible, almost without loss of withdrawal resistance of the screws. [ABSTRACT FROM AUTHOR]

AlSi10Mg is often used to fabricate functional parts by Laser Beam Powder Bed (LBPB) fusion but is limited by the residual stresses formed during the process. Conventional methods of stress relief of AlSi10Mg often compromise the mechanical properties due to the high-temperature used. This paper solves the dilemma by using a novel method of residual stress relief without compromising its mechanical properties. This process uses a lower temperature for treatment followed by uneven cooling, inducing thermal stress during the cooling process such that it cancels out the existing residual stress that remains. The compressive strength of the part was not compromised after this treatment, verified by microstructure images. From electron backscatter diffraction (EBSD) analysis, the change in density of low angle grain boundaries (LAGB) and magnitude of residual stress relieved via this method followed the same trend, indicating the induction of dislocations from the stress-induced during uneven cooling. [ABSTRACT FROM AUTHOR]

This study demonstrated that the gas flow direction in the laser beam powder bed fusion (PBF-LB) significantly affects the crystallographic texture evolved in the products. The effect on texture is attributed to the difference in the melt pool depth, which depends on gas flow direction. The melt pool was shallower when the laser scanning and gas flow directions were parallel than when they were perpendicular. This phenomenon should be of particular concern when applying Scan Strategy_XY wherein the laser was scanned with a 90° rotation in each layer, which is often used in PBF-LB. The asymmetry in the melt pool depth generated by laser scanning in the x- and y-directions can lead to unintended variations in the crystallographic texture. The gas phase would interact with a part being manufactured immediately beneath the gas and affect the crystallographic feature of the product. [ABSTRACT FROM AUTHOR]

The study of corneal stiffness in vivo has numerous clinical applications such as the measurement of intraocular pressure, the preoperative screening for iatrogenic ectasia after laser vision correction surgery and the diagnosis and treatment of corneal ectatic diseases such as keratoconus. The localised aspect of the microstructure deterioration in keratoconus leading to local biomechanical softening, corneal bulging, irregular astigmatism and ultimately loss of vision boosted the need to map the corneal stiffness to identify the regional biomechanical failure. Currently, two methods to map the corneal stiffness in vivo are integrated into devices that are either already commercially available or about to be commercialised: the stress-strain index (SSI) maps and the Brillouin Microscopy (BM). The former method produces 2D map of stiffness across the corneal surface, developed through numerical simulations using the corneal shape, its microstructure content, and the deformation behaviour under air-puff excitation. It estimates the whole stress-strain behaviour, making it possible to obtain the material tangent modulus under different intraocular pressure levels. On the other hand, BM produces a 3D map of the corneal longitudinal modulus across the corneal surface and thickness. It uses a low-power near-infrared laser beam and through a spectral analysis of the returned signal, it assesses the mechanical compressibility of the tissue as measured by the longitudinal modulus. In this paper, these two techniques are reviewed, and their advantages and limitations discussed. [ABSTRACT FROM AUTHOR]

A general theory is presented describing the photo-excitation dynamics of transient, paramagnetic triplet states of aromatic molecules including their absorption properties in a molecular host crystal when irradiated by a pulsed laser beam. It is applied to the system of a pentacene doped naphthalene single crystal, where the photo-excitation of pentacene results in a highly non-equilibrium population of intermediate electronic triplet states. These paramagnetic states can be addressed to align the proton spins of the naphthalene host at moderate experimental conditions using dynamic nuclear polarisation (DNP). The photo-excitation profile and the resulting triplet state distribution, which is determined by the material and the laser parameters, leads to a corresponding proton polarisation profile. Measurements of the resulting polarisation inhomogeneity by spatially resolved neutron transmission confirm the theory. The theoretical model then allows the extraction of crucial parameters that enable quantitative investigations of the dynamics of spin systems. For applications of triplet DNP with pentacene-doped naphthalene crystals, polarisation maximum, homogeneity and buildup rate are key factors, and the theory allows the identification of optimal experimental parameters depending on the priorities placed on these factors. [ABSTRACT FROM AUTHOR]

The performance of electro-optics (EO) beam steering systems relies on the EO effect exhibited by certain crystals which is a refractive index change with an applied electric field. The very high EO coefficient and transparency, high optical damage limit, low conductivity, and comparatively low Curie temperature of SrxBa1-xNb2O6 (SBN) make this EO crystal very attractive for EO beam steering applications. In this study, an EO laser beam steering device based on a bulk Sr0.75Ba0.25Nb2O6 (SBN75) crystal grown at Teledyne Scientific was designed1. The SBN beam steerer was tested under different scenarios and the first and second EO effects and all linear EO coefficients of the SBN75 ( r 13 , r 33 , r 51 ) were measured based on the laser beam's deflection angles and compared with the values reported in the literature. The results showed that Teledyne's SBN75 crystal exhibited a primary EO effect of about 4 to 6% more than the value reported in the literature at the room temperature, the share of the secondary EO effect is less than 8% and the linear EO effect disappeared at 58 °C. [ABSTRACT FROM AUTHOR]

In the present work, we used the ex situ casting technique to synthesize a nanocomposite (NC) of polyvinyl alcohol (PVA) and nanosize palladium (Pd). The Pd has a particle size in the range from 2 to 22 nm with 10 nm on average. Samples from the synthesized NC have been irradiated with different fluences ranging from 2 to 20 J/cm2 from GaAs infrared pulsed laser (5-watt power, 904 nm wavelength, 200 ns pulse duration, 1200 Hz frequency and 0.28 cm2 spot area). Nonisothermal crystallization kinetics of the synthesized NC was investigated using differential scanning calorimetry (DSC) with different cooling rates. The Jeziorny and Mo approaches were applied to describe the nonisothermal analysis. Several nonisothermal kinetic parameters, such as the crystallization peak temperature (Tc), the enthalpy of crystallization (ΔHc), the degree of crystallinity (Xc), the crystallization halftime (t1/2), the Avrami exponent (n) and the activation of crystallization (Ea) were evaluated and interpreted as a function of laser fluences. The results indicated that the incorporation Pd nanoparticles into the PVA matrix accelerate the crystallization process, while the laser radiation causes chain crosslinking that reduces the crystallinity. [ABSTRACT FROM AUTHOR]

Monochromatic hard X-rays with high brightness are desired for medical applications including Auger therapy. One can generate such X-rays through laser-Compton scattering (LCS) by allowing photons from a compact laser system to interact with electrons accelerated by a compact electron accelerator. In this paper, after a brief description of laser-Compton X-ray sources, a scheme called crab crossing to enhance the X-ray intensity is proposed. The effect of crab crossing is evaluated, and we report our dedicated laser system for the crab crossing LCS research. The luminosity enhancement factor by crab crossing is evaluated. For the electron beam, a rf deflector will be used to generate a tilted electron beam. For the laser system, chirped pulsed amplification is adopted. Yb-doped optical fibers and a Yb:YAG thin-disk is used for the laser gain media. The luminosity enhancement factor by crab crossing is expected to be 3.8 when the crossing angle is 45 degrees. 10mJ pulse energy was achieved by thin-disk regenerative amplifier. The pulse duration after the pulse compressor was about 1.5 ps. We are going to demonstrate the LCS X-ray enhancement by crab crossing of electron beam and laser pulse. The expected enhancement factor is 3.8. We have successfully finished the laser development and the proof-of-principle experiment will be conducted soon. [ABSTRACT FROM AUTHOR]

In this study, the silk fabrics mordanted at the ratio of 1%, 5%, 10%, 20% of aluminum potassium sulfate (KAl(SO4)2·12H2O) and 0.1%, 0.5%, 1%, 3%, of iron sulfate (FeSO₄) were separately dyed 50% weld (Reseda luteola L.). Then firstly, laser radiation was used on un-mordanted silk fabrics and as a second step, silk samples with different ratios mordanted and dyed with weld were irradiated to investigate the laser radiation effects on color using several combinations of the two main laser parameters namely energy density and number of pulses. Nd:YAG laser device was used two different wavelengths of 1064 nm and 532 nm, and it was found that the laser wavelength of 532 nm is most appropriate to all dyed fabrics, while 1064 nm wavelength causes damages such as discoloration and burning in the iron sulfate mordanted fabrics. Colorimetric analysis was performed to examine surface alterations of silk samples. The CIEL*a*b* color values of the silk fabrics were measured and compared with each other. In general, the use of iron sulfate (FeSO₄) as a mordant increased the color difference (ΔE*) of dyed fabrics at 1064 nm. The color coordinates and fastness values of rubbing and light were investigated. Morphological analysis was performed using optical and scanning electron microscopy. Elemental analysis was performed using SEM-EDX (scanning electron microscopy–energy-dispersive X-ray spectroscopy) to identify mordants. A reserved phase high-performance liquid chromatography (RP-HPLC) with the diode-array detection (DAD) method was utilized for the identification of the components of dyes present in the silk samples. [ABSTRACT FROM AUTHOR]

The problem of heating a non-homogeneous thermoelastic layer induced by absorbing a penetrating laser radiation throughout its volume is solved by employing the dual-phase-lag theory of thermoelasticity. The surfaces of the layer are taken insulated and traction free. Using the Laplace integral transform technique, a solution to the considered problem is obtained. The results presented graphically for the distributions of the upper surface temperature, temperature, displacement, and normal stress. [ABSTRACT FROM AUTHOR]

A promising laser cooling candidate molecule is essential for laser cooling experiments. In this study, the possibility of laser cooling an 88Sr35Cl molecule is investigated using an ab initio method. Seven low-lying Λ-S and six Ω electronic states of the 88Sr35Cl molecule are calculated at a multi-reference configuration interaction level of theory. Spectral constants of bound states of fitted values are in good agreement with experimental values, which are better than the previously obtained theoretical data for higher excitation states. The resulting permanent and transition dipole moments near the equilibrium bond length are close to the theoretical values. Potential energy curves and transition dipole moments are used for obtaining highly diagonally distributed Franck-Condon factors for the A2Π → X2Σ+ transition using the LEVEL program. A short radiative lifetime of the A2Π state is determined; a laser cooling scheme is designed in the vibration level that requires a cooling main laser beam and two repumping laser beams. Transition spectral data of hyperfine energy levels with errors relative to the experimental data do not exceed −0.25∼0.19 MHz when using a quantum effective Hamiltonian approach. This study provides a helpful reference for experimental observation and operation of laser cooling the 88Sr35Cl molecule. [ABSTRACT FROM AUTHOR]

The relationship between the magnetic susceptibility and degree of polymerization of liquid polydimethylsiloxane (PDMS) was studied experimentally. The magnetic susceptibility of the liquid PDMS was established with the Moses effect, i.e., study of the shape of the near-surface well (the well created near the surface-vapor interface) created in the liquid by a permanent magnetic field. The study of the shape of the near-surface well was carried out under experimental registration of the laser beam reflected from the PDMS/air interface. The broad range of available molecular weights of PDMS made it suitable for the study. The diamagnetic susceptibility, χ , of PDMS was measured for a broad range of molecular weights. The plot of magnetic susceptibility, χ, against the number of repeating units in the chain, n, was linear. The result was compared with the magnetic susceptibility predicted by the Pascal law. The volume magnetic susceptibility χ v of the liquid PDMS was established as χ v = (−7.77 ± 0.06) · 10−6. The magnetic susceptibility of the PDMS monomer was established as χexp(n = 1) = (60.3 ± 0.32) · 10−11, which is in a satisfactory agreement with the Pascal empirical rule. [ABSTRACT FROM AUTHOR]

Laser-induced periodic surface structures (LIPSS) on biomedical stainless steel in air and water were systematically studied. The LIPSS exhibit in-plane curves near the ripple centres in the individual tracks of laser scan and the curving was opposite to the laser scan direction. The collective in-plane curving of LIPSS, a hitherto unknown feature for single train pulsed laser processing, is attributed to the accumulative effect of laser ablation and redeposition, which modifies the interference between the surface scattered wave and the incident laser beam. Combinations of media, scan-speed, and laser fluence, showed that the roughness can be increased by slowing the scan-speed. Ripples fabricated in the flowing water with slow scan-speed and high laser power are helpful for the hydrophilicity of biomaterials. A contact angle as low as 47.00 ± 9.35° is obtained towards high surface hydrophilicity. The results provide new insights on LIPSS about their formation and biomedical applications. [ABSTRACT FROM AUTHOR]

In underwater turbulent medium, field correlations are found when the incidence is a laser beam array. Variations of the field correlations against the variations in the ring radius of laser array beam, number of beamlets composing the laser array, source size, underwater turbulence parameters, i.e. the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of mean-squared temperature and rate of dissipation of kinetic energy per unit mass of fluid, are investigated. Field correlations of laser arrays are found to be larger than the field correlations of the single beams. The effect of underwater turbulence is to reduce the field correlation of laser arrays. [ABSTRACT FROM AUTHOR]

Kinetic investigations of titanium-containing interpenetrating polymer networks (Ti-IPNs) formation based on cross-linked polyurethane and Ti-containing copolymer (Ti-CP) were carried out using differential calorimetry method. Analysis by the SAXS method revealed that the systems possessed nanosized regions of heterogeneity. The increase of (–TiO2–) fragments content led to increase of both overall level of heterogeneity and of Tg of Ti-СP component. Ti-IPNs are optically transparent with optical transparency coefficient value up to 90–91% at 650 nm. The reverse visible darkening at UV-irradiation was observed for Ti-IPNs, thereby allowing their application in optical data recording on exposure to laser radiation. [ABSTRACT FROM AUTHOR]

The propagation properties of a circular cosh-Gaussian beam (CiChGB) in a fractional Fourier transform (FRFT) optical system are investigated theoretically. The analytical expressions for a CiChGB propagating through apertured and unapertured FRFT systems are derived based on the Collins formula and the expansion of the hard-aperture function into a finite sum of Gaussian functions. From the obtained expressions, the evolution of the intensity distribution at the output plane is analysed with illustrative numerical examples. It is shown that the intensity distribution of the CiChGB propagating in FRFT is closely dependent on the decentred beam parameter and the aperture size besides the fractional order of the FRFT system. The results obtained may be beneficial to applications in laser beam shaping, optical trapping, and micro-particle manipulation. [ABSTRACT FROM AUTHOR]

The present study is concerned with the investigation of the transient responses of a half-space medium with the variable material properties in the context of dual phase lag thermo-elasticity. The boundary of the medium is subjected to thermal shock. Further, the bounding surface is considered to be heated by a non-Gaussian laser beam. Kirchhoff transformation and the Laplace transform technique have been adopted to obtain the analytical solutions. Graphical results of the field components such as non-dimensional conductive temperature, non-dimensional displacement as well as non-dimensional stress have been achieved and illustrated for the different values of time and variable thermal conductivity. Significant results are obtained and it is believed that these results may support in designing the structures heated by a non-Gaussian laser beam in engineering. [ABSTRACT FROM AUTHOR]

Due to the excellent comprehensive properties, Si3N4 ceramics have been widely studied and applied in the field of engineering structures. Conventional processing of Si3N4 ceramics faces a series of challenges, and laser processing has become an effective processing technology for hard and brittle materials. In this paper, a new type of dual-beam coupled nanosecond pulsed laser was used to carry out a series of ablation experiments on Si3N4 ceramic at various powers, and the laser ablation mechanism was analyzed. The equivalent diameter method and the equivalent area method were used to calculate the corresponding laser ablation threshold, and influence of laser power on surface roughness of the ablation hole edge, hole depth, removal volume and hole taper were explored. The results show that when the repetition frequency f = 10 kHz, wavelength λ = 532 nm and ablation time t = 6 s, the laser ablation thresholds of Si3N4 ceramic calculated by the equivalent diameter method and the equivalent area method are 0.55 J/cm2 and 0.59 J/cm2, respectively. In a certain power range, surface roughness of the ablation hole edge, hole depth and removal volume increase with the increase of laser power, while the ablation hole taper decreases with the increasing laser power. This innovative work is helpful to expand the scope of laser processing technology for hard and brittle materials, and has guiding significance for the optimization of laser processing technology parameters of Si3N4 ceramics. [ABSTRACT FROM AUTHOR]

A method that combines Lucy-Richardson deconvolution algorithm (LRA) with a multiview projection setup to improve imaging reconstruction of objects embedded in scattering media is presented. In the first step, the medium was illuminated with a laser beam and single-shot multiple images of the object were obtained from different viewpoints. Next, the above procedure was performed under the same conditions but only the medium, without the object, was illuminated by a light point source to obtain the system PSF. Third, each sub-image of the object was digitally cropped, extracted from the array, and deconvolved with the average PSF image following the LRA. Finally, all the sub-deconvolved images were shifted to a common point and superimposed to reveal the shape of the hidden object. Various setup conditions including medium turbidity, thickness, target shape, and illumination state were tested and compared. Results indicate an effective performance of the proposed method. [ABSTRACT FROM AUTHOR]

The integrated bubbly wake strength of two ship models with different scales is investigated in this paper. The laser spot video recording technique is implemented to measure the light scattering properties of laser beams transmitted through the wake. The bubbly wake is generated by the movement of two geometrically similar models towed at constant velocities in a towing tank. The effect of the model's velocity and scale are investigated using data provided by the multiple laser emitter and detectors. Results show the dominance of small bubbles on the persistence of the wake. Also, the effects of wetness of the stern on the vertical distribution of the wake are evident. Comparing the wake of two scale models shows a stronger wake for the bigger model in similar conditions. Moreover, the importance of Froude and Weber numbers on the scaling of major features of the bubbly wake of ship models is prominent. [ABSTRACT FROM AUTHOR]

This paper presents a vision system designed for an underwater robot to facilitate measuring the distance to an inspected surface and its orientation with respect to the robot. The system uses a set of laser modules to project a rectangular dot pattern on the inspected surface. The vision system is used to measure the dots' locations in the 3D space and calculate the distance to the surface, together with the pitch angle and the yaw angle of the camera. A novel calibration procedure is presented, which allows for constructing high resolution camera-laser systems, without requiring a perfect alignment of laser beams and camera optical axis. An underwater vision system simulation environment, based on open-source software, is also introduced and extensively used to test the developed algorithms. The experimental results, obtained in a laboratory tank and a pool, confirm high performance of the system. [ABSTRACT FROM AUTHOR]

Scintillation index of multimode laser beams used for communication systems in vertical paths of weak atmospheric turbulent medium are examined by employing the Rytov method. On-axis scintillation index is examined versus the source size, propagation distance and zenith angle for vertical link including uplink and downlink. At the selected values of source sizes and propagation distances, scintillation responses of multimode laser beams are evaluated. In general, it is found for both uplink and downlink that the laser beam with multimode content has larger scintillation noise as compared to a Gaussian laser beam. However, for the downlink at L=700 km, at the chosen parameters, the multimode beam possessing larger mode content, is found to attain slightly smaller scintillations. [ABSTRACT FROM AUTHOR]