Lamp Pulse Research Articles

Optimization of Nd:YAG Laser Parameters for Microdrilling of Alumina with Multiquality Characteristics via Grey–Taguchi Method

In laser microdrilling, the formation of taper and the dimension of the heat-affected zone (HAZ) are important attributes that greatly influence the quality of a drilled hole. In this article, an experimental investigation into Nd:YAG laser microdrilling of alumina is carried out to produce desired high-quality microdrill. Four independently controllable process variables viz. lamp current, pulse frequency, air pressure, and pulse width are considered as input parameters, while hole taper and HAZ width are considered the output parameters. The Taguchi method combined with the grey relational analysis is used as a statistical design of experiment technique to set the optimal process parameters. The objective is set to minimize both quality characteristics, simultaneously. Grey relational analysis is applied to convert the multiple quality characteristics to a single performance characteristic, called grey relational grade. Optimal process parameters are then determined by the Taguchi method using grey relational grade as the quality index. Both of the quality characteristics of drilled holes are improved markedly at the optimal process condition, as verified by an additional confirmation test. This indicates the application feasibility of the grey-based Taguchi technique for continuous improvement of laser microdrilling quality in the manufacturing industry.

Laser micro-drilling of alumina: parametric modelling and sensitivity analysis

In the present research, laser micro-drilling of alumina has been investigated experimentally. The laser used is Nd:YAG, having a wavelength of 1.06 μm. The process parameters investigated are: lamp current, pulse frequency, air pressure and pulse width. The quality of micro-holes is evaluated by measuring the hole taper and HAZ width. Response surface methodology is adopted to perform the experimental design and also to develop the mathematical relationships relating the input process parameters and output qualities. The adequacy of the models is tested by statistical measures. Finally, the developed mathematical models are used for sensitivity analysis to identify the critical parameters and their tendencies.

Experimental Investigation into Pulsed Nd:YAG Laser Micro-Turning of Engineering Ceramics

Laser beam machining (LBM) is the most exciting thermal energy based non-contact type advanced material machining method to process almost whole range of materials. The laser microturning of ceramics are highly demanded in the present industries because of its wide and potential uses in various engineering fields such as automobile, electronics, aerospace, biomedical applications etc. The present paper addresses the basic experimental study of Nd:YAG laser microturning of advanced engineering cylindrical shaped ceramic material to explore the desired laser output responses i.e. depth of cut and surface roughness by varying laser micro-turning process parameters such as lamp current, pulse frequency and rotational speed of workpiece etc.

Parametric analysis of Nd:YAG laser marking on ceramics

Laser marking is an elegant, clean, fast and non-contact permanent marking method with high durability. The present paper deals with the analysis of laser marking process parameters like lamp current, laser scanning speed, pulse frequency, average and peak power of laser beam using Nd: YAG laser on various laser marking characteristics like the mark width, mark depth and mark contrast are studied during pulsed Nd: YAG laser marking on zirconia ceramic material. Analysis based on optical photographs has also been performed. The present study shows that high pulse frequency and lamp current with low scanning speed has more effect to achieve the minimum mark width, maximum mark depth and mark contrast. In addition to it, a multi objective optimisation has also been performed.

Gamma-Ray Responses of Pr:LuYAP and Pr:YAP Scintillators

Pr3+ doped LuYAP crystal was grown by the Czochralski method with 1 inch diameter and 10 cm length. In order to compare scintillation characteristics, Pr3+ doped YAP crystal was also grown by the micro-pulling-down method. Absorption spectra of them were measured and Pr3+ 4f → 4f5d and 4f2 → 4f absorption lines were observed at 230,470, and 600 nm, respectively. In photoluminescence measurements, here excited by Xe lamp pulse of wavelength around 223,250 and 280 nm emission lines due to Pr3+ 4f5d → 4f transition were detected. When coupled with PMT R7600 and irradiated by gamma-rays, gamma-ray induced light yields were estimated as 1900 ph/MeV for Pr: LuYAP and 5600 ph/MeV for Pr: YAP. In both crystals, light yield non-proportionality and energy resolution were investigated by individual lines in the gamma-ray energy range from 59.5 keV to 1408 keV. The gamma-ray excited decay time constants turned out to be 9.8 ns for Pr:LuYAP and 9.0 ns for Pr:YAP.

Effects of Process Parameters on Hole Circularity and Taper in Pulsed Nd:YAG Laser Microdrilling of Tin-Al2O3 Composites

This study investigates the effect of five parameters on circularity and taper of drilled holes in pulsed Nd:YAG laser microdrilling process. The effect of various process parameters like lamp current, pulse frequency, pulse width, air pressure, and focal length of Nd:YAG laser microdrilling on hole circularity at entry, exit, and taper has been investigated through response surface methodology (RSM)–based experimental study. The significant parameters have been selected based on the analysis of variance (ANOVA). The parametric combination for optimal hole circularity and hole taper has also been evaluated. In micromanufacturing, circularity of a drilled hole at entry, exit, and taper are important attributes which greatly influence the quality of a drilled hole. The drilling operation has been carried out on titanium nitride-alumina (TiN-Al2O3) composite, an important electroconductive ceramic suitable for wear and heating applications.

Characterization of hole circularity in pulsed Nd:YAG laser micro-drilling of TiN–Al2O3 composites

In micro-manufacturing, circularity of a drilled hole at entry and exit are important attributes which greatly influence the quality of a drilled hole. This study investigates the effect of five parameters in the circularity of drilled holes in pulsed Nd:YAG laser micro-drilling process. The drilling operation has been carried out on titanium nitride–alumina (TiN–Al2O3) composite, an important electroconductive ceramics suitable for wear and heating applications. The effect of various process parameters like lamp current, pulse frequency, pulse width, air pressure, and focal length of Nd:YAG laser micro-drilling on hole circularity at entry and exit has been investigated through response-surface-methodology-based experimental study. The parametric combination for optimal hole circularity at entry and exit has also been evaluated.

Experimental analysis on Nd:YAG laser micro-turning of alumina ceramic

Laser micro-turning is a micro-machining strategy to machine cylindrical workpiece of hard-to-process materials such as ceramics. Laser micro-turning method is in high demand in the present high-precision manufacturing industries because of its wide and potential uses in various engineering fields such as automobile, electronics, aerospace, and biomedical applications, etc. In the present research, the experimental analysis of Nd:YAG laser micro-turning of cylindrical-shaped ceramic material has been made to explore the desired laser output responses, i.e., depth of cut and surface roughness by varying laser micro-turning process parameters such as lamp current, pulse frequency, and laser beam scanning speed. Single laser beam has been utilized for successful micro-turning operation. Experimental results revealed that the laser machining process parameters have great influences for achieving desired laser micro-turned depth and surface roughness characteristics during laser micro-turning of alumina ceramics. SEM and optical photographs have also been analyzed for better understanding of the laser micro-turning process for different parametric settings.

Heat generation by optically and thermally interacting aggregates of gold nanoparticlesunder illumination

The generation of heat by clusters and arrays of gold nanoparticles under illumination isinvestigated theoretically. The nanoparticles are embedded in a homogeneous dielectric medium,and the finite thermal resistance at the interface between the nanoparticle and the medium istaken into account. An analytic solution is derived for the case of a single nanoparticle. TheT-matrix method is used to calculate the energy absorption efficiency of groups ofnanoparticles, taking into account their optical interactions. Heat transfer equations aredeveloped that take into account thermal interactions between nanoparticles. Theequations are solved numerically using the finite element software COMSOL. Periodicboundary conditions are applied to treat the thermal interactions between thenanoparticles for arrays of nanoparticles. Results are presented for illumination by astandard xenon flash lamp. The thermal resistance at the nanoparticle–medium interface isfound to strongly influence the nanoparticle temperature, but to have negligible influenceon the temperature of the dielectric medium after a few tens of nanoseconds of exposure tothe flash lamp pulse. Optical interactions are found to be important if particle centres areseparated by about twice the particle diameter or less. Thermal interactions betweennanoparticles via the medium are found to be the dominant factor in determiningthe temperature increase in the dielectric medium. The maximum temperatureincrease is proportional to the volume fraction of the nanoparticles in the medium.

A parametric study of pulsed Nd:YAG laser micro-drilling of gamma-titanium aluminide

In the present research, Nd:YAG laser micro-drilling of gamma-titanium aluminide, a new material which has performed well in laboratory tests as well as in different fields of engineering, is studied. The effect of different process parameters in the optimization of the process is investigated. The aspects considered are the hole circularity at exit and the hole taper of the drilled hole. Lamp current, pulse frequency, air pressure and thickness of the job are selected as independent process variables. The central composite design (CCD) technique based on response surface methodology (RSM) is employed to plan the experiments to achieve optimum responses with a reduced number of experiments.

Low Frequency Architecture for Multi-Lamp CCFL Systems With Capacitive Ignition

A low frequency architecture is proposed for driving parallel cold cathode fluorescent lamps (CCFLs) in large screen liquid crystal display (LCD) TV backlighting applications. Key to the architecture is a proposed capacitive coupling approach for aiding lamp ignition. A dc voltage is applied to the lamp electrodes while an ac voltage is applied to an external plate for capacitive coupling. The result is reliable, simultaneous ignition of parallel lamps with a required applied dc voltage near the lamp steady-state operating voltage. The complete system architecture includes a single high voltage converter, a pulse lamp ignition circuit, current control circuits and a single backlight controller. The topology is capable of driving a large number of parallel lamps with independent lamp current regulation, while avoiding ac coupling losses in steady-state operation and achieving significant reduction in reactive components when compared to typical high frequency ac ballast designs. Experimental results are presented for a system of four parallel 250 mm length lamps, demonstrating simultaneous parallel lamp ignition and dc current regulation.

Preparation and optical properties of Ag/PPy composite colloids

Ag/PPy (polypyrrole) composite colloids were prepared through the reaction of silver nitrate with pyrrole solution in DMF either in the dark, or under the irradiation of femtosecond laser (fs) pulse or UV lamp. The UV–vis spectra of the nanocomposite colloid display an intense absorption band around 620 nm, accompanied by a weak one around 470 nm. The colors and optical absorption spectra of as-synthesized colloids can be reversibly tuned between blue and red, corresponding to absorption band of 620 nm and 526 nm, within few seconds by adding base and acid solutions or gases in turn into the composite colloid suspension. In addition, excess of H + solution enhanced the absorption band around 470 nm and, at the same time, depressed that around 620 nm. The possible mechanism for the formation and optical absorption properties of the Ag/PPy composite colloid was proposed.

Effect of the Crystallization Conditions on the Epitaxial Relationship of Si Deposited on 3C-SiC(100)

The epitaxial relationship of Si deposited on 3C-SiC was studied using both free standing 3C-SiC(100) material from Hoya and 3C-SiC thin layers deposited on Si(100) as substrates. The conditions of Si growth were varied depending on the substrate. When Si is deposited at 1000°C on (001) 3C-SiC, it is in perfect epitaxial relation with the SiC layer [100]Si//[100]SiC and [001]Si//[001]SiC. After a 20 ms flash lamp pulse on the same sample, which has the effect of fast melting of the Si top layer only, the defects in the Si are eliminated. Using free standing 3C-SiC, the deposition temperature was not limited by the Si melting point so that it was fixed at 1500°C in order to form a set of Si liquid droplets on the surface with diameters ranging from 5 to 20 μm. Surprisingly more than 60% of the Si droplets exhibit the epitaxial relation [110]Si//[001]SiC and [111]Si//[110]SiC after crystallization. The occurrence of this epitaxial relationship can be understood in terms of lattice mismatch reduction from 20% to 18.3%. The conditions of crystallization, most probably the cooling rate, seem to have a strong effect on Si orientation.

Experimental investigations on Nd:YAG laser cutting of silicon nitride

A laser beam has great ability to machine very hard conductive as well as non-conductive materials such as high speed steel, ceramics, and diamonds, etc. The present paper includes the parametric analysis on performance of CNC pulsed Nd:YAG laser cutting operation on silicon nitride ceramics. The present experimental investigations reveal that the saw cutting operation on silicon nitride can be successfully performed with a better surface finish after proper setting of the machining parameters. The cut quality of the job surface has been presented and analysed through microscopic views. Better quality of the cutting edge can be achieved during the Nd:YAG laser cutting operation when the lamp current, cutting speed and pulse frequency are set at moderate values.

Annual ring-like grain growth in Ni-mediated crystallization of amorphous silicon by pulse annealing

We studied annual ringlike grain growth in Ni-mediated crystallization of amorphous silicon (a-Si). Ni particles were sputtered onto a-Si and then the sample was crystallized in a pulse lamp annealing system. The crystallization of a-Si proceeds circularly from the seed at the center of a grain. The Ni atoms on the a-Si aggregate together and then from a NiSi2 crystallite, which is a seed for inducing crystallization. The crystallization proceeds from these nuclei, and then the diskshaped grain grow laterally with increasing the number of heating cycles. An annual ring appears after Secco etch of a disklike grain even though the crystallization temperature is fixed. The explosive crystallization over 1μm results in annual ring, which is more clear when pulse heating is used for crystallization. Polycrystalline silicon with a grain size of 103μm was achieved in the present work.

Transmission Electron Microscopic Study of the Morphology of Oxygen Precipitates and of Chromium Precipitation during Intrinsic Gettering in Czochralski‐Grown Silicon: Influence of Lamp Pulse Annealings

The specific effects of lamp pulse annealings on the oxygen precipitates morphology and on the chromium precipitate formation during intrinsic gettering in Czochralski‐grown silicon were investigated by transmission electron microscopy. High‐low‐high gettering treatments were carried out after deposition of a chromium film onto the silicon substrates and a subsequent in‐diffusion anneal. In order to test the effect of a lamp pulse on the gettering effects, the chromium diffusion (980°C for 30 nm) has been performed either in a cold wall lamp furnace or in a classical quartz tube furnace. The effect of a shorter lamp pulse at a higher temperature (1200°C for 5 s) applied prior to the chromium diffusion was also tested. When no lamp pulse was used, the oxygen has precipitated into two forms, i.e. platelets and polyhedra, depending on the gettering cycle. However, chromium precipitates were observable only in the presence of the polyhedra and in that case the phase was unambiguously identified. Moreover, it was observed that the lamp pulse annealings used in this work, applied prior to the gettering sequence, produced a significant retardation of the oxygen precipitation together with the impediment of chromium precipitate growth.

A Deep Level Transient Spectroscopy Study of the Internal Gettering of Cr in Czochralski‐Grown Silicon: Efficiency and Reversibility upon Lamp Pulse Annealings

The interaction of lamp pulses with the internal gettering of chromium (Cr) in Czochralski‐grown silicon (Si) has been studied by deep level transient spectroscopy profiling of the electrically active Cr concentration on beveled samples. B‐doped Si wafers were submitted to various sequences of thermal treatments consisting in different combinations of Cr diffusion, gettering treatments (high‐low‐high or high‐low), and lamp pulse annealings. An inhibition of the internal gettering mechanism was observed whenever Cr was diffused in a lamp furnace before gettering, or when a lamp pulse was applied before Cr diffusion in a quartz tube furnace. In addition, the stability of the Cr precipitates, formed inside the wafer after internal gettering, was found to depend significantly on the gettering temperature. These results were consistently explained in the framework of the “oxygen precipitation” gettering model, taking into account the two basic requirements of efficient denuded zone formation by oxygen nucleation, and further oxygen precipitate growth rate enhancement of the metal precipitation.

Effects of Lamp Pulses on the Oxygen - Precipitation - Gettering of Cr in Czochralski Grown Si

ABSTRACTExperiments on the intrinsic gettering of Cr in p-type Czochralski-grown Si including lamp pulse annealings have been carried out. Transmission Electron Microscopy observations of both oxide and metallic precipitates on cross-sectional specimens, as well as quantitative results about the electrically active metal depth-profiles, using Deep Level Transient Spectroscopy measurements, are presented. We have observed that a lamp pulse (1200 °C/5 s) applied prior to a three-step gettering cycle produced a strong retardation of the oxygen precipitation, and consequently an inhibition of the Cr bulk precipitation during the nucleation step. Besides, it was observed that the Cr-precipitates formed in the bulk during the oxygen nucleation step were highly unstable upon a post-gettering 2–4 s lamp pulse at 1000 °C, whereas the same lamp pulse did not produce a significant re-dissolution of Cr-precipitates formed during the oxide precipitate growth step. The reversibility of the intrinsic gettering of Cr upon a post-gettering lamp pulse thus critically depends on the oxide precipitate growth rate during the gettering process.

Opto-optical modulation in nematic liquid crystals

A new type of opto-optical modulation effect in nematic liquid crystals is experimentally observed. The transmitted intensity of a He-Ne laser beam passing through a liquid crystal sample while applying a dc voltage is modulated by illuminating the sample with a xenon flash lamp pulse. The response time is fast, of the order of several milliseconds. The modulated state lasts for about 500 ms. A modulated intensity of light as large as ten times the unmodulated one is obtained. The physical origin of this effect is also discussed.

Continuous wave and Q-switched infrared erbium laser

Upconversion pumping has been demonstrated both experimentally and theoretically to be important in the 2.8-μm 4I11/2–4I13/2 lasing transition in a CaF2 (Er3+) system. A minimum pump threshold of only 2.8 J with a 1-ms Xe lamp pulse has been achieved in CaF2 rods containing 5 mol % of Er3+ ions. A simple theory has been developed to show that upconversion pumping makes possible cw lasing between the 4I11/2 and 4I13/2 states even when the lifetime of the terminal 4I13/2 state is much longer than that of the upper 4I11/2 state. Semi-cw lasing has been experimentally demonstrated by pumping with six ganged photographic flash bulbs fired in sequence, with each bulb having a duration of 15–20 ms. Lasing at 2.8 μm lasted for 80 ms, well beyond 10 and 20 ms lifetimes of the 4I11/2 and 4I13/2 states. The 2.8-μm CaF2 (Er3+) laser has also been Q switched, using a 100-nm thin graphite foil as a shutter.