ABSTRACT: Stainless steel as a welded joint has very important applications in industry. In this project, laser welding of stainless steel was studied at different values of laser power, pulse width and frequency, and keeping beam diameter as constant. A 9.9 kW ALPHA LASER AL200 Nd:YAG laser was used. The experiments were carried out in two sets on an SS430 ferritic stainless steel plate (100 x 100 x2.5 mm). Metallurgical and mechanical characterizations were carried to evaluate the weld beads. Macro and micro structural analysis is carried done to evaluate the bead profile and microstructures. Mechanical properties of the welded seam were evaluated by hardness and tensile strength testing. Durable joining was achieved only when the laser power is 2.2KW, Pulse width is 3.6 µs and Frequency is 14Hz. The Percentage of contribution found in ANOVA for each Process parameters were result of maximum tensile strength is based on the pulse width-41 percent and result of minimum hardness is based on the Power- 80 percent. The results of the various tests and examinations enabled definition of the best position for the incident laser beam with respect to the joint, for welding together the stainless steels. Microstructure revels that, it contains coarser ferrite grains with randomly distributed carbides. Due to laser beam welding and fast solidification. It forms dendritic grain structure in the outer portion of the weld, and equiaxed axial grains in the central regions of the weld
The critical quantifiable parameter in welding procedure is process productivity. It relies on handling and working parameters, thermo mechanical and compound properties of the material, surface conditions and laser control source. The welding rate is altogether influencing on a wide range of efficiencies. It has been found that the measure of force required for liquefying the material is higher and warm diverted by conduction is lower at a welding rate of 7mm/s or more. The semi exact technique exhibited in this work predicts higher productivity than every other model. The effectiveness got by utilizing the model in light of reflection gives essentially bring down esteem than the material-free model. The deformity free welds have been seen inside the scope of chose welding speeds. The effect of pulse duration, gas flow rate and focal position on process efficiency can also be tried and effective methods can be devised to measure efficiencies.
Ultraviolet (UV) lasers have been employed for many applications such as in the food industry, medicine and dentistry. The use of laser and other pulsed light systems for phototherapy and other microbial disinfections are based on spectral characteristics and configuration of the light used. The objective of this study was to use a flash lamp-pumped passive Q-switched Nd:YAG laser for inactivation two pathogenic bacteria, namely Escherichia coli and Listeria monocytogenes. A 1064 nm pulsed infrared (IR) laser and its 2 nd and 3 rd harmonics were used to irradiate Escherichia coli at various values of fluence. A 350 nm continuous wave (CW) UV lamp was also used in the inactivation process for the purpose of comparison with the 3 rd harmonic (355 nm) pulsed laser. The result indicates that there is a statistical significant difference between mean log 10 reductions for the three
It is concluded from preliminary in vivo tests that Nd: YAGlaser can induce a desirable surface modification on Ti6Al4V alloy. In order to achieve the best experimental results, the irradiation process must be optimized in terms of optical parameters. The SEM, corrosion test, EDXA, contact angle measurement together with the in vivo experiment confirm that a noble and biocompatible Ti alloy with better physio-chemical properties can be obtained under suitable physical conditions. Finally, we believe that more investigations are needed to further clarify the fundamentals of cell adhesivity on smooth surfaces and cell attachment onto rough surfaces.
Although pulsed Nd:YAG laser micro welding has become widely used in microelectronics and photonics packaging industry, a full understanding of various phenomena involved is still a matter of trials and speculations (Nowakowski, 2005; Fadhali, 2008). Laser micro welding is a very complex process which involves variability in shape and properties of welds. Until today, researchers are still finding ways to produce optimum laser micro welding conditions for specific applications. To facilitate pulse Nd:YAG laser spot weld development, it is a common practice to adjust the laser peak power, pulse duration and laser spot size. These physical parameters need to be optimized numerically and experimentally to obtain the desired weld dimensions and microstructure with minimum defects. A strong weld joint is needed to produce reliable and stable attachment. An accurate understanding of the effect of these parameters on melting, weld appearance and heat input is thus required.
Photo-disrupter laser is the major class of ophthalmic lasers. It is a non-invasive method of performing posterior capsulotomy on an out-patient basis.  This solid state laser source emits an infra-red (IR) light invisible to the eye of 1064 nm wavelength. A red Helium-Neon(He-Ne) laser aiming beam is therefore incorporated into the instrument,  is aligned through the same optical pathway in the slit-lamp to allow accurate aiming of the beam.  The He-Ne laser is a low power gas laser producing a red beam.  The tissue disruption occurs at the focal point of the two laser beams.  The Nd-Yag L is a powerful continuous wave(CW) laser which is usually used Q-switched when treating the eye. Neodymium(Nd) ions produce the laser light and they are contained as impurity ions within an optically pure Yag crystal.  Solid crystals are usually pumped by incoherent light such as the Xenon arc flash lamp.  In this way a much higher concentration of active laserNd ions can be achieved than in a gas laser medium.  Photo-disruption is a physical process known as optical breakdown, were by focused emitted laser energy of extreme intensity can be used to create such a strong electro-magnetic field that leads to molecular break-up. A strong local shock-wave results, which can be used in surgery to disrupt tissues.  If a large amount of energy is rapidly delivered into a tiny focal volume in a very short time, the constituent atoms of the target material will be ionized and disintegrate into a collection of electrons, ions and unionized atoms called a plasma at the focal point of Nd-Yag L with explosive expansion. This rapidly expands causing acoustic and shock waves which can disrupt tissue in the immediate neighborhood of the blast. The Q-switched Nd-Yag L is used in this way to disrupt posterior capsule.  A similar process occurs when lightning is followed by thunder in a storm and the atmosphere becomes ionized to a plasma state. Lightning occur as electrons rejoin their atoms. Thunder represents the resultant shock-wave created by this sudden energy release.  In Q-switched Nd-Yag L the duration of each laser pulse reduces to 10-20 nanoseconds,  this allow fierce ionization of the target tissue in the eye with creation of a flash, then a shock- wave results in photo-disruption of the molecules.  Laser releases a giant pulses of energy, when this pulse is focused to a 15-20 Mm spot, so that the nearly instantaneous light pulse exceeds a critical level of
Nd:YAG lasers can be operated in both pulsed and continuous mode. The pulsed lasers are typically operated using Q-switching mechanism: In Q-switched mode, the laser output powers of 20 megawatts scale and pulse durations of less than 100 nanoseconds are commonly available. The high-intensity pulses may be required to convert light from 1064 to become 532 nm through the process of frequency doubler, or even higher order harmonics generation can be achieved at 355 and 266 nm . A high quality beam is desired to pump another high power laser such terawatt class Ti:Sapphire amplifiers .
I-V characteristics of i-Ge samples before and after ir- radiation by Nd:YAG laser with a wavelength of 266 nm and different laser intensities are shown in Figure 3. The I-V characteristic of the non-irradiated sample is linear. It means, I-V characteristics obey Ohm’s law, and there- fore, there are no potential barrier between the electric contacts and the sample. After irradiation by the laser, I-V characteristics become diode like. Moreover, this process takes place in threshold manner, it means, RR is non-monotonic function on laser radiation intensity.
As we know, Q-switching is a widely used laser technique to obtain intense and short bursts of laser oscillation. A simple picture of Q-switching is that the cavity feedback or the cavity losses, or in other words, the quality factor Q of the optical resonator, is switched by some means from an initial high loss (low Q) state to a low loss (high Q) state. In the low Q state the gain or population inversion AN can build up to a very high value without oscillation. In the high Q state the threshold drops down to a low value and the intracavity photons thus experience an extremely high net gain, which results in a very short, intense burst of laser output (a giant pulse [1-3]). The second process dumps most of the energy stored in the pumped atoms, ions or molecules into the optical field. The final effect of Q-switching is just like a cw laser output being compressed tightly in the time domain but with the same amount of output energy. The typical Q-switched pulse duration is few tens of nanoseconds and depends on the pump power.
The combination of both technologies offers different strategies for machining. While the laser can be applied de-focused for heating up the sur- face, a focused laser application enables a defined processing of the surface. The de-focused laser pre- vents a cooling down of the workpiece. The higher temperature increases the thermal shock when the dry-ice particles hit the surface and the efficiency is improved. Therefore, the wavelength has to be cho- sen according to the absorptance of the surface of the substrate. A focused laser application enables a defined surface structuring or smoothing of the workpiece. Thus, a preliminary purification by dry- ice blasting can be followed by a final laser-process- ing cleaning step. It, furthermore, makes it possible to combine the cleaning process with a potential following pre-treatment process (i.e., to realize a de- fined roughness). Both technologies can be applied at the same focal point or at different focal points. Two different focal points allows a repeatable quick change of separate processing by each single tech- nology while using the same focal point for both technology is easier to realize.
The research of acoustic wave had been widely explored for many years and still being study until now. An acoustic wave can be utilised as a non-contact method to characterising and monitoring process of liquids in chemical or pharmaceutical industries. Other than that the acoustic wave also had been demonstrated for other applications, such as in physics, engineering, biology and medicine.
Naonosecond Nd:YAG laser was utilized as a part of the vast majority of tests achieved up today. Aside from the vitality of laser pulse energy, the aftereffects of laser removal in fluid stage rely on upon numerous other test parameters: laser wavelength, time of removal investigation, blending conditions and centering conditions. The Exact impact of a significant number of these components is not clear up today. In the event that most of the takes a shot at laser removal of fluid was performed in immaculate water (the fundamental inspiration for these works is SERS application or in watery arrangements, a few specialists made their trials in various natural solvents. Silver (Ag) nanoparticles (NPs) were synthesized by pulsed (Q-switched, 1064 doubled frequency- Nd: YAG). The laser ablation of silver metal plates has been performed by immersing these metal plates in deionised water DDW and NaCL solvent. The pulsed laser ablation in liquids (PLAL) process preformed with different laser shots such as 15 and 30 pulses and laser pulse energy of(600-900) mJ and liquid depth is 8 mm. The formation efficiency of PLAL process was quantified in term of the absorption spectrum peaks. The absorption spectra Ag shows a sharp and single peak around 412 nm indicates the production of pure and spherical Ag NPs with an average size in the range of (5- 20) nm. There is a simultaneous possibility of on-line observation of the nanoparticles formation via measuring the variation in nanoparticles absorption at the peaks observed. Changing the way of the fluid environment is a simple and flexible way to control the size appropriation and strength of silver colloidal nanoparticles.
And Hori’s nevus shows multiple brown to gray macules or patches on the face but the hyperpigmentation does not involve the neck(Serrano,1989;Wang,2014 and Hur,2017). RM is a pigmented contact dermatitis or photocontact dermatitis resulting from contact sensitivity related to chemicals, particularly, fragrances including aniline dye(orange II),formaldehyde, geraniol and lemon oil(Serrano,1989). Although the pathogenesis of RM is unknown, some authors think that the sensitizing chemicals in cosmetics produce a type IV cytolytic reaction at the epidermal basal layer and subsequent damage to the basement membrane leads to leakage of melanin from the damaged cells into the papillary dermis, which is engulfed by dermal melanophages. Therefore, this process may provoke the hyperpigmentation in RM (Nakayama, 1984 and Imokawa, 1987). Traditional laser treatments for RM had been used widely for many years.
Conventional annealing normally expensive and desires long period to process. This is because the process involves the application of high quality substrate like quartz or BK7 to stand with high temperature environment and long period of heat treatment in the furnace. An alternative way is needed to solve this problem. Laser annealing has offered a superior technique because of its low fabrication cost and high efficiency.
Crystal of Yttrium Aluminum garnet doped with elements such as Nd, Ce, or Cr where Nd is often applied in steady state lasers emotions. Ce and Cr ions are used for increasing the crystal efficiency of arc lamp pumping. These ions takes up the greatest part of pump radiation and transfer it to generating ions. Another method that improves laser characteristics of different crystals is their annealing at high temperature (near melting point). During annealing process a partial removal of growth defects (e.g. oxygen vacancies) takes place. This method is time-consuming.
up to their end. The omission of cascade ionization (curve 2) showed only a slight decrease of the electron density during the second half of the laser pulse. This result supports the important role played by multiphoton ionization process to the breakdown of distilled water at the ultra short laser pulse (100 fs). This figure clarifies the important role played by the cascade ionization proc- ess in enhancing the electron density to reach the break- down limits. Moreover, it showed also that for infra red wavelengths most free electrons are produced by cascade ionization even for the short pulse duration. Recombina- tion losses occur near the end of the laser pulse (where a high electron density is achieved) as shown by the slow drop of the electron density illustrated by curve (1) Fig- ure 2(a) for nanosecond pulses. Its influence becomes negligible for the ultra short pulses Figures 2(b) and (c) since its rate becomes slower compared to the laser pulse length.
ABSTRACT – A Q-Switched Nd: YAG (neodymium yttrium aluminium garnet) infrared laser can be used to clean micropalaeontological specimens, particularly those coated in gold–palladium for SEM studies. Variable pressure SEM images taken of uncoated specimens before and after laser treatment show that the laser does not have a detrimental a ﬀ ect on micropalaeontological specimens composed of phosphate, silica or calcite in a number of wall structural forms. The laser has no e ﬀ ect on the textural surface of the specimen but flakes and crinkles water-soluble mounting glues used to fix specimens to the stub. Sticky carbon tabs (Reference Agar Scientific) were found to be the best mounting medium for holding specimens in place during treatment but microfossils were prone to become detached during the process if not attached firmly. Laser cleaning has a number of advantages over traditional methods of gold removal using sodium cyanide, which is toxic, slow and does not e ﬀ ectively remove gold–palladium coatings due to the insolubility of palladium in the reagent. This laser removal method has potential for removing matrix from specimens as well as other types of coating and mounting media including aluminium, carbon and wax. Safe removal of coatings releases important scientific information from gold–palladium coated museum micropalaeontological specimens. J. Micropalaeontol. 23(2): 165–169, November 2004.
Studies on the fabrication of efficient PDs are constantly expanding given the urgent need for more advanced and better devices with high stability, speed, sensitivity, selectivity, and large signal to noise ratio. [11-13]. PSi based PDs have been fabricated using different methods [14, 15]. particularly the PECE method, which has produced excellent and high quality PDs . However, the optimum method for the growth of PSi with controlled pore size distribution has not been realized despite the many efforts to do so. This is imperative as controlling the structure, morphology, optical and electrical properties (I-V curves, rise time, recovery time, sensitivity and responsivity) of ZnO based PDs will enhance their overall gain and reduce their loss rate. Moreover, the influence of laser annealing (varied fluences, laser energy, pulses, repetition time, etc.) on the structure, morphology, optical and electrical properties of grown n-PSi/ZnO NCs based MSM PDs has not been examined systematically. Thus, it is expected that coupling the established PECE method with pulse laser annealing process will lead to the synthesis of better quality n-PSi and n-PSi/ZnO NCs under optimum conditions. In this view, this thesis attempts to combine the PECE technique with Nd:YAG laser annealing to improve the optical, electrical and morphological properties of grown n-PSi and n-PSi/ZnO NCs samples (at optimum growth condition), resulting in the fabrication of high performing and efficient MSM UV PDs. Such modifications in the overall behavior of n-PSi samples are anticipated to produce an optimized MSM UVPD characterized by large surfaces and high-quality structures needed for diverse applications. The optimally synthesized n-PSi and n-PSi/ZnO NCs samples can further be used to fabricate MSM PDs of high efficiency and fast response.
used for the treatment of superficial epidermal pigmented lesions [6,8]. Their wavelengths are absorbed by both intra- and extracellular water of the epidermis and dermis, which results in a non-specific destruction [8-10]. There is a relatively narrow margin of safety when treating epidermal nevi; if the treatment is too superficial with removal of the epidermis only, the nevus will recur and if it goes too deeply into the reticular dermis, hypertrophic scaring may develop . In Previous studies, 585-nm Pulsed dye laser (PDL) has been used successfully in treatment of inflammatory linear verrucous nevus (ILVEN), which is a variant of epidermal nevi, by destructing the dilated blood vessels and decreasing the inflammatory process [12,13]. Based on the postulation that oxyhemoglobin in blood vessels has strong absorption peaks at wavelengths ranging from 585 to 595 nm of PDL and moreover has a significant, albeit more modest, absorption peak between 800 and 1,100 nm, long pulsed Nd -YAGlaser (1064nm) have been used in the treatment of vascular defects as telangiectasia, portwine stains,
In the present investigation a mathematical model, by using response surface methodology (RSM) and an artificial neural network (ANN) model  has been generated to predict the relationship between the process parameter of Nd: YAGlaser drilling and the surface roughness of the specimens. Also a comparison has been done with between the result obtained through response surface methodology (RSM) and artificial neural network (ANN).