Nanosecond Nd-YAG Laser Research Articles

10B-based films grown by pulsed laser deposition for neutron conversion applications

Solid-state neutron detectors exploit nuclear interactions producing energetic charged particles within a converter layer embedding nuclei with high neutron capture cross section and with thickness compatible with the charged particle range. Recently, boron-10 (10B) is being considered as a valid alternative to the expensive and decreasingly available 3He gas thanks to its large neutron absorption cross section and high-energy reaction products. Minimized amounts of impurities, films with optimal and well-controlled thickness, good uniformity over large areas and good adhesion to the substrates are essential to achieve efficient neutron detection performance. In this study, we present well-adherent 1-µm-thick 10B-enriched boron coatings, deposited over a large area by off-axis pulsed laser deposition (PLD) using a nanosecond Nd-YAG laser beam operating at 1064 nm and high fluence (~ 10 J/cm2), onto 1-mm-thick Al substrate as well as smooth and rough C substrates. By combining plasma plume divergence and peaked profile under off-axis deposition geometry, uniform10B films were obtained over an area of a 3.4 × 3.4 cm2. We discuss the morphological characteristics of our deposits as related to the mechanisms of nanosecond laser ablation and present energy dispersive spectroscopy (EDS) elemental analysis of the film, paying attention to the different surface features. Negligible presence of O, N and C contaminants was achieved by controlled vacuum conditions. Moreover, we present encouraging neutron detection performances of our film deposited onto Al.

Luminescent MoS2 quantum dots with reverse saturable absorption prepared by pulsed laser ablation

Effects of quantum confinement, focusing on upconversion and downconversion photoluminescence and reverse saturable absorption, on MoS2 quantum dots produced by nanosecond UV laser ablations is not widely reported. The effect of wavelength and pulse energy of ablating laser on the size, colloidal stability, upconversion and downconversion photoluminescence and non-linear properties of MoS2 quantum dots (QDs) are reported here. MoS2 QDs are grown by pulsed laser ablation (PLA) from bulk MoS2 pellets in deionized (DI) water with UV (355 nm), visible (532 nm) and IR (1064 nm) laser beams from a nanosecond Nd-YAG laser source and ablation is repeated with varying pulse energy. The target MoS2 pellet prepared for ablation was sintered at 800 °C in nitrogen ambience for 8 h. Hexagonal structure of MoS2 pellet is confirmed by XRD and Raman spectroscopy before and after sintering. The exfoliated MoS2 QDs dispersion show appreciable photon upconversion (UPC) and down conversion (DC) photoluminescence (PL). The downconversion PL emission shows multiple peaks. QDs size is found to vary with the wavelength of the ablating laser beam. The mean particle size, measured by dynamic light scattering measurements and TEM analysis, is in the range of 2–30 nm. Absorbance measurement shows high energy peaks around 5.88 eV (211 nm) with shoulder peak at 3.79 eV (327 nm) corresponding to MoS2 QDs. MoS2 QDs dispersion show moderate dispersion stability as per zeta potential analysis. Raman analysis of spin coated few layer MoS2 QDs shows characteristic in-plane (E12g) and out-of-plane (A1g) vibrational modes of MoS2. Nonlinear optical studies of colloidal MoS2 show reverse saturable absorption (RSA) due to two photon absorption (TPA) process.

Third-order optical nonlinearity of N-doped graphene oxide nanocomposites at different GO ratios

In the present work, the influence of GO ratios on the structural, linear and nonlinear optical properties of nitrogen-doped graphene oxide nanocomposites (N-GO NCs) has been studied. N-GO NCs were synthesized by hydrothermal method. The XRD, FTIR, SEM, and TEM results confirmed the reduction of GO by nitrogen doping. The energy band gaps of N-GO NCs calculated from UV–Vis analyzed by using Tauc plot. To obtain further insight into potential optical changes in the N-GO NCs by increasing GO contents, Z-scan analysis was performed with nanosecond Nd-YAG laser at 532 nm. The nonlinear absorption coefficient, β, and nonlinear refractive index, n2, for N-GO NCs at the laser intensity of 113 MW/cm were measured and an increase was observed in both parameters after addition of nitrogen to GO. The third-order nonlinear optical susceptibilities of N-GO NCs were measured in the order of 10−9 esu. The results showed that N-GO NCs have negative nonlinearity which can be controlled by GO contents to obtain the highest values for nonlinear optical parameters. The nonlinear optical results not only imply that N-GO NCs can serve as an important material in the advancing of optoelectronics but also open new possibilities for the design of new graphene-based materials by variation of N and GO ratios as well as manufacturing conditions.

Nonlinear optical response of Mg/MgO structures prepared by laser ablation method

BackgroundInvestigation of new materials plays an important role in advancing the field of optoelectronics.MethodsIn this work, Mg/MgO microstructures were prepared by Nd-YAG laser (λ= 1064 nm) ablation of magnesium target in acetone. For the first time, the nonlinear optical properties of square Mg/MgO microstructures were investigated by using the Z-scan technique with nanosecond Nd-YAG laser at 532 nm.ResultsThe XRD analysis approved the formation of Mg/MgO microstructures. The energy band gap of Mg/MgO microstructures was calculated to equal 2.3 eV from UV-Vis spectrum. The ablated materials were ejected into acetone as structures with an average size of 1-1.5 μm. The nonlinear absorption coefficient, β, and nonlinear refractive index, n2, for Mg/MgO microstructures at the laser intensity of 1.1 × 108 W/cm2 were measured to be 1.15 × 10–8 cm/W and 8.2 × 10-13 cm2/W, respectively. In order to investigate size particles and liquid medium effects, the nonlinear optical parameters, β and n2 of Mg/MgO nanostructures synthesized by laser ablation of magnesium target in isopropanol also were calculated and it was found these parameters are an order of magnitude larger than the values for the β and n2 of Mg/MgO microstructures synthesized in acetone. The third-order nonlinear optical susceptibility, χ(3), of Mg/MgO microstructures and nanostructures were measured in order of 10-6 and 10-5 esu, respectively.ConclusionsThe results show that Mg/MgO structures synthesized in acetone and isopropanol have negative nonlinearity as well as good nonlinear absorption at 532 nm and these magnesium-based structures have the potential applications in the nonlinear optical devices.

Inducing bioactivity of dental ceramic/bioactive glass composites by Nd:YAG laser

ObjectivesAims of this study were to investigate the optimal conditions of laser irradiation of a novel Bioactive Glass/Dental Ceramic-BP67 composite for acceleration of hydroxyapatite-HA formation and to assess cellular responses on the precipitated HA region. MethodsBP67 (Bioactive Glass: 33.3%, Dental Ceramic: 66.7%) was fabricated by the sol–gel method. A laser assisted biomimetic-LAB process was applied to BP67 sintered specimens immersed in 1.5-times concentrated simulated body fluid-1.5×-SBF. The effect of various energy densities of pulsed nanosecond Nd-YAG (1064nm) laser and irradiation exposure times (30min, 1 and 3h) were evaluated for HA precipitation. The HA film was characterized by FTIR, XRD, SEM and micro Raman techniques. ICP-AES was used for revealing changes in chemical composition of the 1.5×-SBF during irradiation. Cell viability and morphological characteristics of periodontal ligament fibroblasts-PDLFs, human gingival fibroblasts-HGFs and SAOS-2 osteoblasts on the HA surface were evaluated by MTT assays and SEM. ResultsAt optimal energy fluence of 1.52J/cm2 and irradiation time for 3h followed by immersion in 1.5×-SBF at 60°C, a dense HA layer was formed on laser-irradiated BP67 within 7 days. The resulting HA film was tightly bonded to the underlying substrate and had mineral composition similar to cementum. MTT assay showed a consistent reduction of cell proliferation on the HA layer in comparison to conventional control ceramic and BP67 for all 3 cell lines studied. SignificanceThese findings suggest LAB is an effective method for acceleration of HA formation on materials with low bioactivity, while cellular responses need further investigation.

Synthesis of uranium-di-oxide nanoparticles by pulsed laser ablation in ethanol and their characterisation

The importance of actinide based nano-structures is well known in the area of biology, nuclear medicine and nuclear industry. Pulsed laser ablation in liquid is recognised as an attractive technique for production of nano-structures of different metals and metal oxides with high purity. In this paper, we report synthesis of uranium-di-oxide nanoparticles by pulsed laser ablation in ethanol. The second harmonic emission of an electro-optically Q-switched nano-second Nd-YAG laser was used as the coherent source here. The structural and optical properties of the fabricated uranium-di-oxide nanoparticles were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive analysis of X-rays (EDX) and UV–Vis–NIR spectrophotometry. The mean size of the particles was found to be dependent on the laser ablation parameters in particular with laser fluence. XRD and TEM analysis confirmed the phase of the synthesised material as pure crystalline uranium-di-oxide with face centred cubic structure. UV–Vis–NIR absorption spectra of the colloidal solution revealed high absorption in the UV regime.

Evidence of feasible hardness test on Mars using ratio of ionic/neutral emission intensities measured with laser-induced breakdown spectroscopy in low pressure CO2 ambient gas

An experimental study is conducted on the possibility and viability of performing hardness measurement of the various stone and chert samples in low pressure (600 Pa) CO2 ambient gas, a condition that is encountered in the Mars atmosphere. For this study, a nanosecond Nd-YAG laser is employed to generate plasma emission from the samples with different degrees of hardness. This technique is developed in light of the role of the shock wave in the generation of a laser-induced plasma. It was previously shown that the speed of the shock front depends on the hardness of the sample, and a positive relationship was found between the speed of the shock front and the ionization rate of the ablated atoms. Hence, the ratio of the intensity between the Mg II 279.5 nm and Mg I 285.2 nm emission lines detected from the laser-induced plasma can be used to estimate the hardness of a material. In fact, it is shown that the ratio changes linearly with respect to changes of sample hardness. The result has thus demonstrated the feasibility and viability of using LIBS for non contact hardness measurement on Mars.

Optical Limiting Studies on Chalcone Doped PMMA Polymer Film

An organic nonlinear optical (NLO) material (2E)-1-(3-chlorophenyl)-3-(3,4-dimethoxyphenyl)prop-2-en-1-one (CPDP) with molecular formula C17H15ClO3has been synthesized and crystallised in methanol solution. The crystals of CPDP were characterised by FTIR spectral technique. The various functional groups present in the crystal are identified. The thermal characteristics of the crystal were determined from the thermo gravimetric analysis (TGA) and differential scanning calorimetry(DSC) technique. CPDP crystals are thermally stable up to 115°C.Thin films of poly(methylmethacrylate) (PMMA) doped with CPDP were prepared on a clean corning glass substrate using a spin coater unit. N, N-dimethylformamide (DMF) is used as solvent. The surface characteristics of the film is studied using scanning electron microscope (SEM).Direct and indirect band gap energy of CPDP doped PMMA is determined using UV–Vis spectral response in the wavelength range 200-1100nm. Single beam Z-scan technique is used to study the nonlinear optical properties like nonlinear absorption coefficient and optical power limiting of the film using a nanosecond Nd-YAG laser operating at 532nm. The results of optical limiting studies show that the film possesses reverse saturable absorption (RSA) due to excited state absorption. The nonlinear optical properties of CPDP have been retained in the presence of PMMA making it a good candidate for optical power limiting applications.

Nonlinear optical studies of inorganic nanoparticles–polymer nanocomposite coatings fabricated by electron beam curing

The optical nonlinearity of metal nanoparticles in dielectrics is of special interest because of their high polarizability and ultrafast response that can be utilized in potential device applications. In this study nanocomposite thin films containing in situ generated Ag nanoparticles dispersed in an aliphatic urethane acrylate (AUA) matrix were synthesized using electron beam curing technique, in presence of an optimized concentration of diluent Trimethylolpropanetriacrylate (TMPTA). The metal nanocomposite films were characterized using UV–visible spectrophotometry, transmission electron microscope (TEM) and field emission scanning electron microscope (FE-SEM) techniques. Ag nanoparticle impregnated films demonstrated an absorption peak at ∼420nm whose intensity increased with increase in the Ag concentration. The optical limiting property of the coatings was tested using a nanosecond Nd-YAG laser operated at third harmonic wavelength of 355nm. For a 25ns pulse and 10Hz cycle, Ag-polymer coatings showed good optical limiting property and the threshold fluence for optical limiting was found to be ∼3.8×10–2J/cm2 while the transmission decreased to 82%. The nonlinear optical coefficients were also determined using the standard Z-scan technique with picosecond (∼2ps, 1kHz) and femtosecond (∼150fs, 100MHz) pulses. Open aperture Z-scan data clearly suggested two-photon absorption as the dominant nonlinear absorption mechanism. Our detailed studies suggest these composites are potential candidates for optical limiting applications.

Nanosecond Nd-YAG laser induced plasma emission characteristics in low pressure CO2 ambient gas for spectrochemical application on Mars

An experimental study is conducted on the possibility and viability of performing spectrochemical analysis of carbon and other elements in trace amount in Mars, in particular, the clean detection of C, which is indispensible for tracking the sign of life in Mars. For this study, a nanosecond Nd-YAG laser is employed to generate plasma emission from a pure copper target in CO2 ambient gas of reduced pressure simulating the atmospheric condition of Mars. It is shown that the same shock wave excitation mechanism also works this case while exhibiting remarkably long cooling stage. The highest Cu emission intensities induced by 4 mJ laser ablation energy is attained in 600 Pa CO2 ambient gas. Meanwhile the considerably weaker carbon emission from the CO2 gas appears relatively featureless over the entire range of pressure variation, posing a serious problem for sensitive trace analysis of C contained in a solid sample. Our time resolved intensity measurement nevertheless reveals earlier appearance of C emission from the CO2 gas with a limited duration from 50 ns to 400 ns after the laser irradiation, well before the initial appearance of the long lasting C emission from the solid target at about 1 μs, due to the different C-releasing processes from their different host materials. The unwanted C emission from the ambient gas can thus be eliminated from the detected spectrum by a proper time gated detection window. The excellent spectra of carbon, aluminum, calcium, sodium, hydrogen, and oxygen obtained from an agate sample are presented to further demonstrate and verify merit of this special time gated LIBS using CO2 ambient gas and suggesting its viability for broad ranging in-situ applications in Mars.

Anti-bacterial selenium nanoparticles produced by UV/VIS/NIR pulsed nanosecond laser ablation in liquids

The ability to produce nanoparticles free of any surface contamination is very challenging especially for bio-medical applications. Using a pulsed nanosecond Nd-YAG laser, pure selenium nanoparticles have been synthesized by irradiating selenium powder (99.999%) immerged in de-ionized water and ethanol. The wavelength of the laser beam has been varied from the UV to NIR (355, 532 and 1064 nm) and its effect on the particle size distribution has been studied by dynamic light scattering (DLS) and transmission electronic microscopy (TEM), revealing then the production of selenium quantum dots (size < 4 nm) by photo-fragmentation. It has been found that the crystallinity of the nanoparticles depends on their size. The zeta-potential measurement reveals that the colloidal solutions produced in de-ionized water were stable while the ones synthesized in ethanol agglomerate. The concentration of selenium has been measured using inductively coupled plasma mass spectrometry (ICP-MS). The anti-bacterial effect of selenium nanostructures has been analyzed on E. Coli bacteria. Finally, selenium quantum dots produced by this method can also be useful for quantum dot solar cells.

A comparative study on reflection of nanosecond Nd-YAG laser pulses in ablation of metals in air and in vacuum

A comparative study on reflection of nanosecond Nd-YAG laser pulses in ablation of aluminum in air and in vacuum under the same other experimental conditions is performed. We find that, hemispherical total reflectivity of aluminum undergoes a sharp drop at the plasma formation threshold both in the air and in vacuum. The initial large value (0.8) of aluminum reflectivity decreases to a level of about 0.14 and 0.24 for ablation in the air and in vacuum, respectively. These decreased reflectivity values remain virtually unchanged with further increasing laser fluence. The reflectivity drop in the air is observed to be sharper than in vacuum. Our study indicates that the reflectivity drop is predominantly caused by absorption of the laser light in plasma. Nano/micro-structural defects present on practical sample surfaces play the important role in the plasma formation, especially for the ablation in the air, where the plasma formation threshold is found to be by a factor of 3 smaller than in vacuum.

Expansion and backscattering of laser produced Fe plasma plume

Forward and backward moving atoms within the laser produced plasma plume were studied by means of a cavity ringdown spectroscopy. The plume was produced using a nanosecond Nd-YAG laser pulse illuminating stainless steel target in a vacuum or helium background gas. Measurements were done at pressures ranging from 10−5 to 1mbar. Atomic absorption line shapes of iron around 388nm were measured above and below the target at different times after the ablation initiation. Changes in absorption line shapes were used to estimate kinetic parameters of the plasma plume. The observations were interpreted through modeling which takes into account the angular and velocity distributions of atoms in the expanding plume. The amount of backward scattered atoms was about 10% of the total number of particles.

Pulsed repetition rate nanosecond laser heating and ablation of the tokamak graphite tile deposited layers

Laser heating and ablation of the plasma-facing surface of a graphite tile from TEXTOR tokamak that was covered by a deposited carbon layer has been studied. Laser heating measurements were performed with a pulsed nanosecond Nd-YAG laser (2nd harmonic, 10 kHz repetition rate, 100 ns pulse duration). Surface temperature measurements were recorded with a home-made pyrometer having a response time of 15 μs ( t 99%). The experimental results are simulated with an analytical model of laser heating of a surface covered by a deposited layer and heated repeatedly by laser pulses. The comparison between experimental and theoretical data of the observed temperature excursions enables us to assess the deposited carbon layer physical parameters (thermal conductivity, porosity, etc.) if the thermal and optical properties of the graphite substrate are known. Laser ablation measurements were performed with two pulsed nanosecond Nd-YAG lasers (20 Hz and 10 kHz repetition rate with 5 ns and 100 ns pulse duration, respectively). For a plasma-facing graphite surface covered by a thick (∼30–50 μm) deposited carbon layer, the ablation threshold is 4.5 ± 1 kJ/m 2 regardless of the pulse duration. The obtained ablation threshold is significantly lower than the one measured for a virgin tokamak graphite sample. The comparison of the experimental results and theoretical data demonstrated that the laser ablation mechanisms for tokamak graphite and thick carbon layers deposited on plasma-facing surface are different.

Cluster-assisted generation of multicharged ions in nanosecond laser ionization of carbon bisulfide clusters at 1064 nm

The photoionization of seeded carbon bisulfide molecular beam by a 1064nm nanosecond Nd-YAG laser with intensities varying from 0.8 × 1011 to 5.6 × 1011 W/cm2 have been studied by time-of-flight mass spectrometry. Multiply charged ions of Sq+ (q = 2-6) and Cq+ (q = 2-4) with kinetic energy of hundreds of electron volts have been observed, and there are strong experimental evidences indicating that those multicharged ions originate from the ionization of CS2 neat clusters in the beam. An electron recolliding ionization model is proposed to explain the appearance of those multiply charged atomic ions under such low laser intensities.

Cluster assistant multiply ionization of benzene by nanosecond laser: wavelength dependence of the production of highly charged carbon ions

The multicharged carbon ions are produced in the laser ionization of molecular benzene beam seeded in noble gas by a nanosecond Nd-YAG laser with intensities of ∼10 11 W cm −2 at 1064 and 532 nm. The He-like C 4+ ions are the dominant carbon ions at 1064 nm, while C 2+ ions are the main multicharged ions at 532 nm. When the laser wavelength is changed to 355 and 266 nm, only singly charged ions are observed. The multicharged atomic ions are probably produced in Coulomb explosion of highly charged benzene ions.

Characteristics and thermal behavior of W/Si multilayers with well-defined interfaces

Multilayers consisting of alternating thin bilayers of W and Si (period: 1.5&amp;lt;d&amp;lt;9 nm) have been analyzed by x-ray scattering (absolute reflectivity, period, mosaicity, interface roughness, crystallinity, and density) and by cross-sectional transmission electron microscopy observations (periodicity, crystalline phase, and damaged area). Our purpose was to determine the thermal properties of the multilayers with respect to the period value under pulsed laser heating (with a nanosecond Nd-YAG laser at different energy densities up to 1 J/cm2 and at a wavelength λ=0.53 μm) and by furnace annealing (250&amp;lt;T&amp;lt;1000 °C under 10−7 Torr pressure). We propose that two distinct diffusion mechanisms are involved in annealings: first, interdiffusion in the amorphous phase and then crystallization into WSi2, the latter related to a period contraction of about 5–10%. The diffusion coefficients and the crystallization temperature depend drastically on the period value. Simulations of small-angle x-ray scattering curves take well into account this thermal evolution. Extinctions and modulations of the intensities of the Bragg peaks are well fitted by thickness and roughness variations.

Continuous wave (CW) and pulsed laser effects on vascular tissues and occlusive disease in vitro

Human arterial segments with occlusive defects and acute dog hearts were exposed, in vitro, to high-energy pulsed and continuous wave (CW) laser beams at argon (514 nm) and Nd-YAG (1,064 nm) wavelengths, using various pulse powers, durations and pulse repetition rates. The laser effects included vaporization of plaques in the arterial segments and penetration of the pericardial sac, evaporation of pericardial fluid, and discoloration of tissue with crater-like lesions in the impact zone, all as a result of vaporization of heart muscle tissues. The areas affected and depth of penetration depended on the wavelength, power, pulse duration, and mode of energy deposition. Focused nanosecond Nd-YAG laser pulses at repetition rates of 40-50 Hz caused ablation or vaporization of hard plaques and kidney stones in air and saline. Picosecond (mode-locked) argon laser pulses at repetition rates of 3.8 MHz--average power 6.5 W, peak power of 230 W--caused effective vaporization of hard plaques and kidney stones in air and saline. Picosecond argon laser pulses--average power 1 W, peak power 250 W--were not effective in vaporization. Transmission characteristics of the various types of laser pulses through fiber optic waveguides were determined. The energy and power density required to vaporize fatty and hard plaques and kidney stones were tabulated as a function of laser wavelength, pulse energy, duration, and repetition rates.