Pulse Shot Research Articles

Generation of nanopore structures in yttria-stabilized zirconia by femtosecond pulsed laser irradiation

Femtosecond pulsed laser irradiation of yttria-stabilized zirconia (YSZ) was performed to investigate the feasibility and fundamental characteristics of nanopore structure fabrication. Numerous nanopores were successfully generated on the YSZ surface with only a single laser pulse shot by controlling laser power near the ablation threshold. The nanopore generation mechanism involves light focusing by the convex shape of a crystal grain and ablation inside the grain. By increasing laser power, the number of nanopores increased. Cross-sectional observation revealed that the depth of nanopores was about 500 nm, and nanopores were generated inside the YSZ grains of the top layer while keeping the grains' shapes unchanged. It was found that higher scanning speed and a small number of scans enabled nanopores fabrication without changing the original surface shape, avoiding the removal of the surface layer. Laser-irradiated surfaces of YSZ were characterized by Raman spectroscopy, and it was found that there was no significant phase change in the specimen after nanopore generation compared with the original YSZ surface, confirming that there was no thermal damage to the bulk material. The surface with nanopores showed an enhancement in surface hydrophilicity. These findings demonstrated the possibility of selectively generating nanopores in the top surface of YSZ for use in functional surfaces without serious thermal damage to the workpiece. It is expected that the nanopore generation will lead to new applications of YSZ.

Large temporal window and high-resolution single-shot cross-correlator with two separate measurement channels

Abstract In strong-field physics experiments with ultraintense lasers, a single-shot cross-correlator (SSCC) is essential for fast optimization of the pulse contrast and meaningful comparison with theory for each pulse shot. To simultaneously characterize an ultrashort pulse and its long pedestal, the SSCC device must have both a high resolution and a large temporal window. However, the resolution and window in all kinds of single-shot measurement contradict each other in principle. Here we propose and demonstrate a novel SSCC device with two separate measurement channels: channel-1 for the large-window pedestal measurement has a moderate resolution but a large window, while channel-2 for the ultrashort pulse measurement has a small window but a high resolution; this allows the accurate characterization of the pulse contrast in a single shot. A two-channel SSCC device with a 200-fs resolution and 114-ps window has been developed and tested for its application in ultraintense lasers at 800 nm.

Demonstration of Single‐Shot Measurements of 1013 Ultrahigh‐Contrast Pulses by Manipulating Cross‐Correlation

In strong‐field physics experiments with high‐intensity lasers, single‐shot characterization of the temporal contrast between the laser pulse peak and its temporal pedestal is important; this allows fast optimization of the pulse contrast and meaningful comparison with theory for each pulse shot. To date, high contrast ratios of 1010 have been demonstrated in single‐shot measurements for petawatt (PW) lasers. However, ultrahigh contrast ratios of ≈1013, as required for the planned 200 PW lasers, pose challenges to high‐intensity laser technologies and have thus far remained open for investigation. This article reports a pilot demonstration of ultrahigh‐contrast measurements by adapting a single‐shot cross‐correlator (SSCC). An evaluation method for the SSCC detection limit is introduced. The strategy mimics the test beam with known spatial contrast, whose cross‐correlation is equivalent to that of a test pulse with ultrahigh temporal contrast. The ultimate contrast measurement limit of 1013 is achieved, which corresponds to the highest pulse intensity by optical damage and the lowest temporal pedestal by single‐photon detection. The photon noise of the detector is observed and becomes dominant as the temporal pedestal of the optical pulse decreases. The demonstrated detection ability is applied to a high‐contrast laser system, suggesting the accessibility of ultrahigh‐contrast measurements.

Tunable surface plasmon resonance of Al-Cu bimetallic nanoparticles thin films induced by pulsed-laser

Al-Cu bimetallic nanoparticles (NPs) thin film was fabricated by Nd:YAG fiber pulsed-laser irradiation of Al/Cu bilayers at ambient conditions. The effects of laser irradiation on the morphology, structure, composition and optical properties of the samples were investigated. The tunability of both localized surface plasmon resonance (LSPR) wavelength and intensity were realized by varying the pulse shot or relative thickness of Al/Cu bilayers. The SEM analysis with EDS results further revealed that the obtained particles consisted of a mean diameter of 36–80 nm bimetallic NPs system, being dependent on the Cu proportion. In addition, Surface-enhanced Raman spectroscopy (SERS) measurement and corresponding finite-difference time-domain (FDTD) simulation of before and after laser irradiation samples were discussed to verify the LSPR properties.

Thermal Analysis in Electromagnetic Rail Launcher Taking Friction Heat into Account Under Active Cooling Condition

A high-efficiency thermal management system is one of the key points in the practical application of electromagnetic rail launcher (ERL). In this paper, the thermal characteristics in ERL with the section of rectangle, convex, and concave rails by active cooling under different friction coefficient condition are investigated. By two cooling approaches, at two launch rates, with four friction coefficients, peak temperature in convex rails at the same moment is minimum in three types rails. Joule heat dominates in three shapes rail by channel or surface/channel cooling approach, but friction heat is a nonnegligible part under multiple launching mode. The spatial and temporal distribution features of peak temperature of three shapes rail with different friction coefficient under active cooling condition are compared. The mathematical relations between friction coefficient, time and temperature rising caused by friction at pulse end time and shot end moment in ERL with the three types rail are obtained, respectively. In terms of obtaining lower maximal temperature in rail, the ERL with convex rails is the best one.

Cleaning contactor pins by laser

In semiconductor final electrical testing manufacturing, the contactor pin is very important component as to make a contact between leads of devices to test hardware circuits. The contactor pins are made from metal alloy material which provide a good electrical conductive. In daily test manufacturing, the contactor pins may be up to several thousand contacting insertions, which will collect of many dust at their tips of contactor pins. The classic traditional cleaning of the contactor pins typically use abrasive cleaning, such as brush. In this research, we present the using of laser application to clean the contactor pins with Laser cleaning machine IMT model 600MV with Nd:YAG laser type. The optimized parameter setting up on the laser cleaning machine are studied with varies of number of pulse shot between 2-4 pulses, distance between the tip of contactor between 2-4 inches and energy of the Laser beam between 15-250 mJ/pulse. The cantilever contact pin type of majority used in one of IC Test manufacturing have been put into the evaluation. The testing of the cleaning effects is performed by optical power scope and scanning electron microscopy, including the analysis of metallic pin surface impacted was done by the EDX analyses. The parameters for cleaning effectiveness and safe cleaning of pins corrosion in metallic surface were determined.

Picosecond laser lift-off method for fracture and debonding of copper oxide layer grown on copper substrate

The objective of this work is to investigate the ablative removal behavior of copper oxide under the picosecond laser (pulse duration 12 ps and wavelength 1064 nm) irradiation. For this purpose, a thin CuO layer with a thickness of about 750 nm is synthesized on a pure copper substrate by the dipping method to serve as the target samples for experimental tests. It is shown that, unlike the pure ablation behavior, the removal process of the CuO layer is mainly based on the nonthermal lift-off effect, by which the stripping of the whole piece of oxide films from the substrate can be achieved with a single pulse shot. A minimum fluence required for peeling off the layer is determined to be about 0.11 J/cm2. Further analyses demonstrate that the entire pop-off of the CuO layer caused by the confined ablation at the interface occurs only if the laser fluences are applied below 0.62 J/cm2. However, when it comes to the cases at higher fluences, a thin residual layer can be observed remaining on the substrate. To explain this phenomenon, a plausible interpretation with respect to the ablation induced by nonlinear absorption and impact ionization is proposed, which declares that it is the combination of direct ablation and the interface lift-off that ultimately causes such special removal features. In addition, the influence of the oxide film thickness on the debonding threshold and the removal behavior are additionally assessed.

Integrated simulation of magnetic-field-assist fast ignition laser fusion

To enhance the core heating efficiency in fast ignition laser fusion, the concept of relativistic electron beam guiding by external magnetic fields was evaluated by integrated simulations for FIREX class targets. For the cone-attached shell target case, the core heating performance deteriorates by applying magnetic fields since the core is considerably deformed and most of the fast electrons are reflected due to the magnetic mirror formed through the implosion. On the other hand, in the case of a cone-attached solid ball target, the implosion is more stable under the kilo-tesla-class magnetic field. In addition, feasible magnetic field configuration is formed through the implosion. As a result, the core heating efficiency doubles by magnetic guiding. The dependence of core heating properties on the heating pulse shot timing was also investigated for the solid ball target.

Detection of picometer-order atomic displacements in drift-compensated HAADF-STEM images of gold nanorods.

Cs-corrected atomic resolution scanning transmission electron microscopy under a drift-compensated operation enabled us to acquire high-angle annular dark-field (HAADF) images of entire gold nanorods without distortion induced by specimen drift. The precision in locating the atomic columns was evaluated to be ±5 pm in the images thus obtained, which is comparable to the image pixel size. A high-precision HAADF image of a single-crystalline gold nanorod revealed that the tip portions at both ends tended to undergo outward displacements along the rod axis and inward contraction along the perpendicular direction. A single nanosecond pulse shot of laser light with a wavelength of 1064 nm and an average intensity of 7.3 kJ/m2 pulse deformed the nanorods into spherical shapes. Simultaneously, the particle interior was completely changed into a multiple twin structure. Substantial displacements of atomic columns on the order of several tens of picometers were confirmed to be localized in the corners of domains at multiple twin junctions. Both the magnitude and direction of displacements were linearly relaxed with increasing distance from a multiple junction.

Operation of SST-1 TF power supply during SST-1 campaigns

SST-1 TF power supply provides the direct current for the required magnetic field of TF coil. TF power supply includes transformer, 12-pulse converter, bus bar, water-cooled cable, protection and measuring equipments, and isolator, VME DAC system and GUI software. TF power supply is operated through GUI software built in TCL/Tk. VME DAC system monitors the parameters, provides On/Off commands, voltage and current references and initiates predefined reference to emergency shutdown. The emergency shutdown is hardwired to TF power supply from central control. During quench power supply converter opens DCCB and dump resistor is connected in the circuit and VME DAC system acquires bus bar voltage, dump voltage and dump current. Operation of TF power supply also requires monitoring of SCR and transformer temperature and water flow rate of water-cooled cable during high current long pulse shot. Before start up of TF power supply a quench simulation is performed to check the readiness of protection. This paper describes pre startup operation, normal shot operation, emergency and quench process, dynamic control and complete shutdown operation of TF power supply.

Effect of Pulse Number on Dopant Activation in Silicon during Shallow p+/n Junction Formation by Non-Melt Excimer Laser Annealing

Shallow p+/njunctions were formed using Ge-PAI and low-energy/high-dose boron-ion implantation, followed by thermal annealing involving nanosecondnon-melt excimer laser annealingandrapidthermal annealing. The effect of laser pulse number on dopant activation and regrowth of a-Si layer are discussed.We found that laser annealing aloneis insufficient to regrow a-Si layer and activate dopant. In contrast, activationwas observed in the samples that were subjected to preannealingrapid thermal annealing followed by non-melt laser annealing; with slight increase of sheet resistance valuewhen the number of laser pulse shot was increased. This is considered due to the interaction of dopant and supersaturated defect in the remaining a-Si layer.The percentage of defect-dopant interaction increased with the pulse shot numbers which contributed to the decrease in activation level.

1201 Machining quality controls in ultrashort pulse laser micromachining on lithium niobate substrates

The physical relations between the machining conditions and the surface qualities of machined surfaces are investigated in laser micromachining (direct drawing) on ferroelectric lithium niobate (LN), for high quality fabrication of microstructures on the functional material with brittle nature, as a future manufacturing technology of advanced MEMS devices. Pico second pulsed laser with the wavelength of 1064nm was used, then multiphoton process dominants the laser-matter energy coupling for material removal and generating heat. Quantity of heat was controlled by the energy density ρ(0.1-10 J/cm^2), the pulse shot number N(1-1000), the pulse interval t(0.5-10 msec), the kurtosis of laser spot k(14-22), and the environment (air or water). Heat energy is increased exponentially by ρ, and additively by the pulse shot number N. Hence high quality surfaces are obtained by conditions as low ρ-high N of laser irradiations even the same laser fluence ρ×N. Also, longer t(as cooling periods), lower k(as uniform laser power in the spot) and underwater processing (as hear dissipative medium) are effective for high machining quality.

Mechanism of original damage of thin optical components induced by surface particle contamination

Based on the optical transmission theory, the reason why front-surface particle contamination may induce the original damage of thin optical components is considered, and a damage mechanism is put forward: The localized thermal deformation of an optical element induced by the thermal effect of particle contamination together with the shading effect of it can disturb the laser beams. Simulated results show that for a high power laser, the localized thermal deformation of thin optical components, which disturbs the laser beam, is an important cause to produce strong light intensity modulations. The surface shape, phase delay, and thermal diffusion length of a localized thermal deformation are constantly changing with the increase of laser pulse shot number, so the highest light intensity modulation will be produced at different positions in the thickness direction or the xy direction on the rear-surface of an optical element. This not only can easily induce some damages on the rear-surface of the optical element, but also cause the interior damages scattered in the thickness direction.

A Parameters Optimization of the CO<sub>2</sub> Laser Drilling Process for HDI Microvia Fabrication

The blind via holes formation by laser drilling is one of the key technologies for demanding high density interconnect printed circuit boards. In this paper , the drilling conditions of drilling the blind via holes and the quality of the drilled holes are examined using a CO2 laser source against the FR4 board without copper foil.We chose laser energy,pulse shot,pulse width and diameter of beam as the experimental parameter . The results showed that laser energy and beam diameter played a more important role on changing the blind vias’ diameter than pulse shot and pulse width .While the pulse shot and pulse width take more important role in changing the depth of vias.

Surface Modifications of Metals Induced by Soft X-Ray Laser Pulse Irradiations

We irradiated the soft x-ray laser (SXRL) pulses having a wavelength of 13.9 nm, the duration time of 7 ps to aluminum (Al), copper (Cu) and gold (Au) surfaces. After the irradiation processes of SXRL beam with laser flux of ~14 mJ/cm 2 for Al case and of ~21 mJ/cm 2 for Cu and Au cases, the modified surfaces were observed with the visible microscope, the scanning electron microscope, and the atomic force microscope. The surface modifications caused by the SXRL irradiations were clearly seen on the surfaces, and it was found that the conical structures having around 100 nm in diameters were formed on the Al surface under a single pulse shot. The conical structures were formed in the features with the average depth of about 40 nm, and this value was in accordance with the attenuation length of the SXRL beam for Al. The modified structure on Al surface induced by SXRL pulse irradiations is different from those of Cu and Au surfaces. The modified structure formed on Al surface induced by the SXRL pulse exposure is interesting as the newly structure. Hence, the SXRL beam would be a candidate for a tool of micromachining, which enable to fabricate of three dimensional structures with nano-meter size on Al surface.

Maskless laser tailoring of conical pillar arrays for antireflective biomimetic surfaces

Herein, we report a facile approach for rapid and maskless production of subwavelength structured antireflective surfaces with high and broadband transmittance-direct laser interference ablation. The interfered laser beams were introduced into the surface of a bare optical substrate, where structured surfaces consisting of a micropillar array were produced by two-step laser irradiation in the time frame of seconds. A multiple exposure of the two-beam interference approach was proposed instead of multiple-beam interference to simply realize planar patterns of a high aspect ratio. Tall sinusoidal pillars were created and shaped by pulse shot number control. As an example of the application, zinc sulfide substrates were processed with the technology, from which high transmission at an infrared wavelength, over 92%, at normal incidence was experimentally achieved.

Role of the rise rate of beam current in the microwave radiation of vircator

In this paper, the effect of the rise rate of beam current on the microwave radiation of a virtual cathode oscillator (vircator) is presented. Interestingly, it was observed that the rise rate of the beam current increased as the pulse shot proceeded, which is accompanied by the decrease in microwave power. By comparing the experimental results of two cathode materials (carbon fiber and stainless steel), it was found that the above behavior is independent of the cathode materials. The ion flow, induced by the repetitive action of beam electrons with the anode grid, directly affects the development of beam current. A twice-increased process of ion flow was observed, and there are two factors involved in this process, namely, the reflection of electrons between the cathode and virtual cathode and the effect of one-time bombardment of electron beam. After the irradiation of pulsed electron beam, some microprotrusions toward the cathode appeared on the anode surface, with a quasiperiodic structure. The appearance of ion flow, as the anode plasma forms, increases the beam current and enhances the beam current density. The anode plasma is generated relatively easily as the shot test proceeds, due to the aging of anode grid, which allows the possibility of the decrease in the microwave power. As the pulse shot proceeds, the changes in the rise rate of beam current are closely related to the aging process of anode surface. Therefore, the further enhancement of vircator efficiency needs to lengthen the lifetime of anode, besides the optimization of explosive emission cathodes.

Nanoscale surface modifications and formation of conical structures at aluminum surface induced by single shot exposure of soft x-ray laser pulse

We irradiated the soft x-ray laser (SXRL) pulses having a wavelength of 13.9 nm, a duration time of 7 ps, and fluences of up to 27 mJ/cm2 to aluminum (Al) surface. After the irradiation process, the modified surface was observed with the visible microscope, the scanning electron microscope, and the atomic force microscope. The surface modifications caused by the SXRL pulses were clearly seen, and it was found that the conical structures having about 70–150 nm in diameters were formed under a single pulse shot. The conical structures were formed in the features with the average depth of about 40 nm, and this value was in accordance with the attenuation length of the SXRL beam for Al. However, those conical structures were deconstructed under the multiple pulse shots exposure. Thermomechanical modeling of SXRL laser interaction with Al surface, which explains nanostructure surface modification, was provided.

Excimer Laser Crystallization Processes of Amorphous Silicon Thin Films by Using Molecular-dynamics Simulations

Crystallization processes of amorphous Si during the excimer laser annealing in the complete-melting and near-complete-melting conditions have been investigated by using molecular-dynamics simulations. The initial amorphous Si MD cell was prepared by quenching a liquid Si layer with 18666 atoms. KrF excimer laser annealing processes of amorphous Si were calculated by taking account of the change in the optical constant upon melting during a Gaussian-shape laser pulse shot with full width at half maximum (FWHM) of 25 ns. The simulated results well reproduced the observed melting rate and the near-complete-melting and complete-melting conditions were obtained for 160 and 180 mJ/cm2 fluence, respectively. It was found that larger grains were obtained in the near-complete-melting condition. Our MD simulations also suggest that the nucleation occur from unmelted amorphous Si region during laser irradiation and crystal growth proceeds toward supercooled l-Si region in the near-complete-melting condition.

Robust, easily shaped, and epoxy-free carbon-fiber-aluminum cathodes for generating high-current electron beams

This paper presents the construction of carbon-fiber-aluminum (CFA) cathode by squeezing casting and its applications for generating high-current electron beams to drive high-power microwave sources. The fabrication process avoided using epoxy, a volatile deteriorating the vacuum system. These cathodes had a higher hardness than conventional aluminum, facilitating machining. After surface treatment, carbon fibers became the dominator determining emission property. A multineedle CFA cathode was utilized in a triode virtual cathode oscillator (vircator), powered by a approximately 450 kV, approximately 400 ns pulse. It was found that 300-400 MW, approximately 250 ns microwave was radiated at a dominant frequency of 2.6 GHz. Further, this cathode can endure high-current-density emission without detectable degradation in performance as the pulse shot proceeded, showing the robust nature of carbon fibers as explosive emitters. Overall, this new class of cold cathodes offers a potential prospect of developing high-current electron beam sources.