Picosecond Pulsed Laser Irradiation Research Articles

Synergy of Nd:YAG Picosecond Pulsed Laser Irradiation and Electrochemical Anodization in the Formation of TiO2 Nanostructures for the Photocatalytic Degradation of Pesticide Carbofuran

This study proposes a simple and controlled method for producing TiO2 with phase junction, oxygen vacancies, and Ti3+ by combining picosecond pulsed laser irradiation and electrochemical anodization. Ti mesh was pretreated by irradiating with a picosecond pulsed laser technique using an Nd:YAG laser (1064 nm) at two fluencies, 15 J/cm2 and 30 J/cm2. The samples were then subjected to electrochemical anodization to form TiO2 nanotube arrays on the previously laser-treated surface. This study will investigate the possibility of forming TiO2 nanotube arrays on a pre-laser-treated Ti substrate and determine their physicochemical and photocatalytic properties. The samples were characterized by FESEM, XRD, Raman, XPS, and UV-Vis DRS. UV-Vis spectroscopy was used to observe the progress of photocatalytic degradation for all samples, and degradation products were determined using GC-MS. With the synergistic effects of phase junction, oxygen vacancies, and Ti3+, the laser-treated TiO2 with 30 J/cm2 showed a higher photocatalytic degradation rate (85.1%) of the pesticide carbofuran compared to non-laser-treated TiO2 (54.8%), remaining stable during successive degradation cycles, which has promising practical applications.

Efficient Combination of Surface Texturing and Functional Coating for Very Low Secondary Electron Yield Surfaces and Rough Nonevaporable Getter Films

AbstractThe formation of a fissured copper surface by picosecond pulsed laser irradiation is combined with functional coatings consisting of Ti and amorphous carbon layers or a Ti–Zr–V compound film to fabricate surfaces with the maximum of the secondary electron yield being as low as 0.4. By structural and spectroscopic analysis of the formed surfaces it is demonstrated that both coatings enclose the nanostructures generated by redeposition of metal structures from the laser‐induced plasma plume, keeping the initial topography intact. This allows an efficient elimination of secondary electron emission by combining the benefits from structural surface modification and adaption of electronic surface properties to efficiently dissipate the energy of impinging electrons. Thermal activation tests of the Ti–Zr–V nonevaporable getter films revealed that for films on nanostructured substrates, which have a much higher effective surface, a slight diminution of surface activation occurs at 160 and 200 °C, while this effect is completely compensated when heating up to 250 °C indicating promising pumping capabilities. Both examples highlight the benefits from combining 3D substrate patterning with classical 2D deposition technologies.

Plasmon-enhanced photoemission from Au nanoparticles covered with cesiated film

The quantum efficiency (QE) and thermal emittance are two main parameters for photocathode, especially for the emission source of free electron laser (FEL) accelerator. It is in challenge how to reduce the rigorous fabrication of cathode and how to enhance the quantum efficiency for photocathode. Facing to the issues in our case, we have investigated plasmon-enhanced photoemission from Au nanoparticles (NPs) covered with Cs film in the microwave electron gun of free electron laser. The large-area preparation and low-cost photocathode are formed by rapid thermal annealing of thin Au films. Cs film covered is found to effectively excite photoelectrons from Au NPs under the visible light (at the 532 nm). The quantum efficiency (QE) of the Au NPs-Cs increases to 2.3 × 10−4 with the pico-second pulsed laser irradiation, and the normalized root mean square (RMS) thermal emittance of the electron beam is about 1.89 mm mrad. It confirms the feasibility for the proposed metallic nanoparticles to be applied to the high brightness electron sources.

Multiscale Surface Patterning of Zirconia by Picosecond Pulsed Laser Irradiation

Abstract Irradiation of yttria-stabilized zirconia (YSZ) was performed by a picosecond pulsed laser to investigate the possibility for multiscale surface patterning. Nanoscale laser-induced periodic surface structures (LIPSS) were successfully generated inside microscale grooves over a large surface area under specific conditions. A thermally induced phase transformation of YSZ was identified after laser irradiation, and this phase transformation was restrained by reducing the laser power or the number of irradiations. Moreover, it was found that the generation of LIPSS greatly changed the surface wettability of YSZ. These results demonstrated the possibility of creating zirconia hybrid patterns with high functionality, which may expand the applications of YSZ in industry.

Formation behavior of laser-induced periodic surface structures on stainless tool steel in various media

The formation of laser-induced periodic surface structure (LIPSS) has been observed on various materials. As LIPSS can be used for modifying various surface properties such as wettability, tribology and optical performance, the control of the period and topography of LIPSS is an important issue. In this study, picosecond pulsed laser irradiation was performed on a stainless tool steel in various types of media including the air, water, sugar syrup (water and sucrose (C12H22O11)), decane (C10H22), and ethanol (C2H5OH). Different surface morphologies were observed on the steel surface after laser irradiation, depending on the types of media. A strong relationship was identified between the period of LIPSS and the refractive index of liquid. In addition to the change of LIPSS period, complicated mesh patterns were formed on the surface irradiated in decane and ethanol, indicating the significant effect of thermal conductivity of the liquids on surface formation mechanisms. This study demonstrated the possibility of controlling the period and topography of LIPSS by using different media.

Nonlinear optical characteristics of DADP crystals with different deuterium

DADP crystals with different deuterium as 0%, 30%, 50%, and 70% were grown via traditional temperature reduction method and the samples were gained from the as-grown crystals in the directions of Ι-type (θ = 90°,φ = 45°). The transmittance spectrum, UV absorption spectrum, and Raman spectrum were implemented to describe the properties of DADP crystals, and the deuteration of ADP crystals makes a difference on the absorption peaks in these spectrums. Particularly, the optical band gap Eg decreases with the accretion of deuterium content. The third-order nonlinear optical characteristics were systematically represented and tested by means of Z-scan measurements with Pico-second pulse laser irradiation at λ = 355 nm, with the results listing the reverse saturable absorption and self-focusing effect. The investigations may contribute to replenish and elucidate the application and laser-induced damage of DADP crystals.

Micro-nano scale surface patterning of zirconia by picosecond pulsed laser irradiation

Micro-nano scale surface patterning of zirconia by picosecond pulsed laser irradiation

Very long laser-induced graphitic pillars buried in single-crystal CVD-diamond for 3D detectors realization

The morphology, optical, spectroscopic and electrical characterization of mm-long graphite pillars created by picosecond pulsed laser irradiation (λ = 800 nm and 1 kHz of repetition rate), buried in single crystal CVD diamond to be employed as electrodes in a 3D diamond detector, is reported. The array of graphitized columns – 2.5 mm-long, with a diameter of ≈ 10 μm – consisted of two rows spaced by 110 μm with 12 pillars in each, which formed an interdigitated electrode structure embedded in the diamond crystal bulk. The presence of stressed regions along and between pillars were clearly shown with optical polarized microscopy, in a black field configuration. Confocal micro-Raman and photoluminescence analysis has been employed to scan local stresses, both generated around the graphitic wires and also developed on the pillars' plane. Defected/stressed regions with diameter of the order of 10 μm surrounding the individual pillars was measured, and paired carbon interstitials (3H defects) were also revealed. For the investigated structure, detrimental effects induced by such structural defects, clearly produced by laser-induced diamond-graphite transition, as well as the presence of a relatively high voltage drop along the graphitized pillars related to their own geometry have been reflected on the charge carriers collection performances evaluated under MeV β-particles. The creation of electronic active states within the diamond bandgap, as emphasized by spectral photoconductivity characterization, would play a fundamental role in lowering lifetime of generated carriers and then the detector collection efficiency. Indeed, states located in the middle of the diamond bandgap, acting as efficient recombination centers and decreasing the lifetime of generated carriers, drastically reduce the mean drift path of carriers and then the overall detector collection efficiency, as evaluated in the examined structure even at the highest applied voltages (up to 600 V).

Surface Flattening and Nanostructuring of Steel by Picosecond Pulsed Laser Irradiation

Steel is used as a mold material for press/injection molding of plastic products. High accuracy and releasing ability are required for a steel mold surface. This paper proposes a surface finishing method for steel molds by using picosecond pulsed laser irradiation. The process involves two steps: one is surface flattening by removing the surface asperity through laser ablation, and the other is forming nanoscale laser-induced periodic surface structures (LIPSS) on the flattened surface. The two steps are realized by using the same laser at controlled laser fluence and focus position. Experimental results showed that LIPSS was successfully formed after surface flattening under specific ranges of laser fluence and defocus length. Furthermore, plastic forming experiments demonstrated that a steel surface with LIPSS significantly decreased the effective contact area and, in turn, reduced the mold releasing force. These findings provide the possibility of fabricating high-performance steel molds by picosecond pulsed laser irradiation.

Nonlinear optical characteristics of an ADP crystal grown in a defined direction

Samples in the crystal directions of Z, X(ab) and the non-critical phase matching angle (θ = 90°,φ = 45°) were gained from high-quality ammonium dihydrogen phosphate (NH4H2PO4, ADP) crystals grown in the Z direction and in defined crystallographic direction (θ = 90°, φ = 45°) via the rapid growth method. Z-scan measurements with pico-second pulse laser irradiation at λ = 355nm were implemented to systematically investigate their nonlinear characters, such as the nonlinear absorption coefficient β, nonlinear refractive index n2 and the third order nonlinear susceptibility χ(3). The results displayed the nonlinear absorption and nonlinear refraction, and the ADP crystals exhibit the reverse saturable absorption and self-focusing effect (n2>0). The nonlinear absorption and refraction were anisotropic in the crystal directions of Z, X, and the non-critical phase matching angle (θ = 90°, φ = 45°) sorted as: [110] < X < Z. The remarkable NLA behaviors at 355 nm are identified to the co-existence of 2PA and 3PA, while 2PA is dominant and the occurrence probability of 3PA is rather low. The anisotropy of the NLA of ADP crystals is closely bound up with the damage anisotropy in our experiments.

Picosecond pulsed laser irradiation of silver nanowire films coated on the polyethylene terephthalate substrates

ABSTRACTWe investigated the effect of picosecond pulsed laser irradiation on the sheet resistance and microstructure of the silver nanowire films coated on PET substrates. The sheet resistance of the silver nanowire film abruptly increases from ∼102 to ∼108 ohm/square at a certain range of laser power. The sheet resistance of the picosecond laser annealed silver nanowire film strongly depends on the microstructure. The silver nanowires are ablated from the substrate and the surface of the substrate are seriously damaged above certain range of laser power. We analyzed the abrupt increase of sheet resistance and the damage of substrate surface in terms of temperature rising during the laser irradiation.

Adjusting the catalytic properties of cobalt ferrite nanoparticles by pulsed laser fragmentation in water with defined energy dose

Highly active, structurally disordered CoFe2O4/CoO electrocatalysts are synthesized by pulsed laser fragmentation in liquid (PLFL) of a commercial CoFe2O4 powder dispersed in water. A partial transformation of the CoFe2O4 educt to CoO is observed and proposed to be a thermal decomposition process induced by the picosecond pulsed laser irradiation. The overpotential in the OER in aqueous alkaline media at 10 mA cm−2 is reduced by 23% compared to the educt down to 0.32 V with a Tafel slope of 71 mV dec−1. Importantly, the catalytic activity is systematically adjustable by the number of PLFL treatment cycles. The occurrence of thermal melting and decomposition during one PLFL cycle is verified by modelling the laser beam energy distribution within the irradiated colloid volume and comparing the by single particles absorbed part to threshold energies. Thermal decomposition leads to a massive reduction in particle size and crystal transformations towards crystalline CoO and amorphous CoFe2O4. Subsequently, thermal melting forms multi-phase spherical and network-like particles. Additionally, Fe-based layered double hydroxides at higher process cycle repetitions emerge as a byproduct. The results show that PLFL is a promising method that allows modification of the structural order in oxides and thus access to catalytically interesting materials.

Pseudo-topotactic conversion of carbon nanotubes to T-carbon nanowires under picosecond laser irradiation in methanol

Pseudo-topotactic conversion of carbon nanotubes into one-dimensional carbon nanowires is a challenging but feasible path to obtain desired diameters and morphologies. Here, a previously predicted but experimentally unobserved carbon allotrope, T-carbon, has been produced from pseudo-topotactic conversion of a multi-walled carbon nanotube suspension in methanol by picosecond pulsed-laser irradiation. The as-grown T-carbon nanowires have the same diameter distribution as pristine carbon nanotubes, and have been characterized by high-resolution transmission electron microscopy, fast Fourier transform, electron energy loss, ultraviolet–visible, and photoluminescence spectroscopies to possess a diamond-like lattice, where each carbon is replaced by a carbon tetrahedron, and a lattice constant of 7.80 Å. The change in entropy from carbon nanotubes to T-carbon reveals the phase transformation to be first order in nature. The computed electronic band structures and projected density of states are in good agreement with the optical absorption and photoluminescence spectra of the T-carbon nanowires.

Effect of Fe3+on third-order optical nonlinearity of KDP single crystals

A series of trace Fe3+-doped KH2PO4 single crystals were grown using the conventional temperature cooling method. The Fe3+ ion content in the as-grown crystals and the corresponding transmission spectrum were measured, respectively. With an increase of Fe3+ ion concentration, the transmittance of the crystal gradually decreases within the wavelength range of 200 nm to 370 nm. Under picosecond pulse laser irradiation, third-order nonlinear optical characteristics were systematically measured at λ = 532 nm. The existence of nonlinear absorption and nonlinear refraction was demonstrated. The results show that the nonlinear refractive index n2 is positive, indicating the presence of a self-focusing effect for the as-grown crystals. Specially, nonlinear absorption and refraction have a heavy dependence on the Fe3+ ion content and crystal directions (II and z). With increasing Fe3+ ion concentration, a significant variation has been observed with respect to the nonlinear absorption coefficient β, nonlinear refractive index n2 and third-order nonlinear susceptibility χ(3). A similar pattern for II < z has been presented for nonlinear absorption and refraction. The investigations suggest that nonlinear absorption and refraction caused by distortion of the electron cloud might be associated with the H2PO4− and (FeO4)2− groups.

Radially and azimuthally polarized laser induced shape transformation of embedded metallic nanoparticles in glass.

Radially and azimuthally polarized picosecond (~10 ps) pulsed laser irradiation at 532 nm wavelength led to the permanent reshaping of spherical silver nanoparticles (~30 - 40 nm in diameter) embedded in a thin layer of soda-lime glass. The observed peculiar shape modifications consist of a number of different orientations of nano-ellipsoids in the cross-section of each written line by laser. A Second Harmonic Generation cross-sectional scan method from silver nanoparticles in transmission geometry was adopted for characterization of the samples after laser modification. The presented approach may lead to sophisticated marking of information in metal-glass nanocomposites.

Generation of silver nanoparticles with controlled size and spatial distribution by pulsed laser irradiation of silver ion-doped glass

Silver ions were driven into glass by a direct current electric field-assisted ion exchange technique. The silver ion exchanged glass was then irradiated by laser pulses of 10 ns and 10 ps in length at 355 nm for comparison purposes. In both cases, laser irradiation led to the formation of a metallic-like film at the surface of the ion exchange glass. Scanning electron microscopy showed that the films consist of a very dense single layer of silver nanoparticles with similar particle sizes and separation. Irradiation with different laser parameters shows no significant difference in transmission spectra and modification width between ps- and ns-pulsed lasers. Particle sizes and separation at the surface are increasing with increasing laser power, and are larger for picosecond pulsed laser irradiation. It is also shown that the film formation is a thermal process.

Picosecond pulsed laser induced optical dichroism in glass with embedded metallic nanoparticles

Picosecond (~10 ps) pulsed laser irradiation at 532 nm led to the efficient and scalable fabrication of dichroic areas in glass with spherical silver nanoparticles of ~30 - 40 nm in diameter embedded in a surface layer of thickness ~20 μm. The observed dichroism is due to the uniform and permanent shape transformation of the nanoparticles - from spherical to spheroidal shapes - throughout the irradiated areas and along the laser polarization direction, paving the way for affordable manufacture of polarization-selective diffractive optical elements. The shape modification threshold and the dichroism as a result of Surface Plasmon Resonance band separation were identified. The process was then studied as a function of the laser polarization, repetition rate and the number of pulses fired per spot.

Phase change and stress wave in picosecond laser–material interaction with shock wave formation

When background gas is present in pulsed laser–material interaction, a shock wave down to the nanoscale will emerge. The background gas will affect the phase change and explosion in the target. This study is focused on the void dynamics and stress wave in a model material (argon crystal) under picosecond pulsed laser irradiation. Our results show that existence of ambient gas and the shock wave significantly suppresses the void formation and their lifetime. Void dynamics, including their growing rate, lifetime, and size under the influence of ambient gas are studied in detail. All the voids undergo an accelerating and decelerating process in the growth. The collapsing process is almost symmetrical to the growing process. Higher laser fluence is found to induce an obvious foamy structure. Stress wave formation and propagation, temperature contour, and target and gas atom number densities are studied to reveal the underlying physical processes. Although the interaction of the plume with ambient gas significantly suppresses the void formation and phase explosion, no obvious effect is found on the stress wave within the target. Very interestingly, secondary stress waves resulting from re-deposition of ablated atoms and void collapse are observed, although their magnitude is much smaller than the directly laser-induced stress wave.

Reduction of graphite oxide to graphene with laser irradiation

Reduction of graphite oxide (GO) to graphene induced by picosecond pulsed laser irradiation has been studied by Raman spectroscopy, scanning electron microscopy together with modeling of temperature dynamics in the materials. Dependence of the D, G, and 2D Raman band parameters on the laser pulse energy and the irradiation dose was evaluated. The exponential decline of the full width at half maximum of the Raman lines with increasing product of the pulse energy and irradiation dose was observed indicating ordering in the film and reduction in the number of graphene layers during the laser treatment. The minimum concentration of structural defects and the largest relative intensity of the 2D peak were found for the 50mW mean laser power and the 30mm/s scanning speed. Modeling of temperature dynamics revealed that the temperature of the GO film irradiated with a single laser pulse at a fluence of 0.04J/cm2 (50mW) increased up to 1400°C for a few nanoseconds, which was sufficient for the effective reduction of GO to graphene with successive laser pulses.

Third-Order Nonlinear Optical Properties of a Series of Polythiophenes

The third-order nonlinear optical properties of a series of polythiophenes are investigated with the Z-scan method under picosecond pulse laser irradiation at 532 nm. The copolymers exhibit a good nonlinear response: large nonlinear refraction coefficients without nonlinear absorption. The signs of nonlinear refraction coefficients are positive, which are opposite to the negative signs of the polythiophene reported before. The mechanism accounting for the process of nonlinear refraction under pulse laser excitation is analyzed from the viewpoint of the electron-donor/acceptor units of polythiophenes. Moreover, changes of nonlinearity according to the lengths of main chains in polythiophene molecules are discussed.