Dr. Sivakumar M. currently serves as Associate Professor in Physics, Department of Sciences, School of Engineering, Coimbatore. His areas of research include Laser Materials Processing  






Publication Type: Journal Article
Year of Publication Publication Type Title
2015 Journal Article E. R. Mohan, Sivakumar, M., and Sreelatha, K. S., “Modelling evanescent field components in metal-oxide core waveguides for nonlinear applications”, Materials Research Bulletin, vol. 69, pp. 131-137, 2015.[Abstract]

In a thin film planar geometry, the guiding effect due to the linear index results in light confinement in the thin film layer, at the same time causing evanescent waves to decay into the outer substrate or cladding layers. The magnitude of the field in the cladding is dependent on the characteristics of the waveguide and the wavelength of the wave. In this paper, we have modelled four metal-oxide core waveguides with prime focus on the evanescent field as light propagates through these optical structures. ZnO waveguide structure is taken as the benchmark. The evanescent path resembles a soliton consistent with the input soliton solution. A comparison is also carried out with a lower metal oxide core, MgO and a higher index TiO2. The variation in refractive index with input wavelength induces second order nonlinearity in these waveguide structures. For the simulated structures, mode field distributions are plotted against the refractive index. The magnitude of evanescent field also reduces with an increase in the input wavelength for the structures. The nature of the soliton path is insightful for the development of evanescent field based sensors. Optical waveguides with metal-oxide cores can act as a cheaper substitution to nanophotonic devices and integrated optics applications. With the study of evanescent phenomena in such structures, a minimally invasive manufacturing method without disturbance to the core may be made beneficial. © 2015 Elsevier Ltd. All rights reserved.

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2015 Journal Article Ra Jagdheesh, Valarmathi, Ab, and Sivakumar, M., “Influence of laser beam polarization on micromachining of crystalline silicon using ultrafast laser pulses”, Lasers in Engineering, vol. 32, pp. 19-35, 2015.[Abstract]

Ultrafast laser machining is a unique technique to fabricate nano- and microscale structures with limited distortion to substrate materials. In the present work the influence of laser beam polarization direction on micromachining of crystalline Si with ultrafast laser pulses has been reported. The geometry of hole, ablation depth, machined features, kerf width and edge quality are studied with respect to the state of polarization. In terms of hole geometry, machining with S-polarized beam generates nearly circular holes as compared to asymmetrical stretching of the holes machined with P-polarization. Moreover, the depth of holes and channels machined with P-polarized beam is higher when compared to the depths of features machined with S-polarized beam. In multi-pulse, ultrafast laser machining, absorption of incident radiation is highly dependent on state of laser polarization and angle of incidence after first few pulses. The absorption is significantly higher for P-polarized beam resulting greater ablation depths. It is apparent from the experimental results that state of laser polarization is an important parameter in micromachining of semiconductors with ultrafast laser pulses under ambient condition. © 2015 Old City Publishing, Inc.

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2010 Journal Article M. Sivakumar, Venkatakrishnan, K., and Tan, B., “Study of Metallic Fibrous Nanoparticle Aggregate Produced Using Femtosecond Laser Radiation Under Ambient Conditions”, Nanotechnology, vol. 21, p. 225601, 2010.[Abstract]

In this study, we report formation of weblike fibrous nanoparticle aggregate due to irradiation of bulk iron, aluminium and titanium samples using femtosecond laser radiation at MHz pulse repetition frequency in air at atmospheric pressure. Electron microscopy analysis revealed that the nanostructure is formed due to aggregation of polycrystalline nanoparticles of the respective constituent materials. The nanoparticle diameter varies between 5 and 40 nm and they are covered with an oxide layer of a few nanometres thick. X-ray diffraction and micro-Raman analysis revealed metallic and oxide phases in the nanostructure. The formation of a nanoparticle aggregate is explained by nucleation and condensation of vapour in the plasma plume and by phase explosion. Moreover the laser interaction time plays a significant role in the generation of nanostructure from bulk metals. This study provides evidence that femtosecond laser irradiation can be an ambient condition physical method for metallic fibrous nanoparticle aggregate generation.

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2010 Journal Article M. Sivakumar, Tan, B., and Venkatakrishnan, K., “Enhancement of Silicon Nanostructures Generation Using Dual Wavelength Double Pulse Femtosecond Laser Under Ambient Condition”, Journal of Applied Physics, vol. 107, p. 044307, 2010.[Abstract]

In this study we propose a unique method to increase the weblike silicon nanofibrous structures formation using dual wavelength double pulse femtosecond laser radiation under ambient condition. The augmentation of nanostructures is evidenced from the difference in nanofibrous structure layer thickness. Enhancement in generation is explained through the increase in excited state electrons with double pulse as compared to single pulse. Moreover the absorption characteristic of irradiated surface undergoes significant changes after the first pulse (515 nm) which enhances absorption for the second pulse (1030 nm) and consequently results in an increase in nanostructures. More »»
2009 Journal Article M. Sivakumar, Oliveira, V., Vilar, R., and Oliveira, S., “Shear Bond Stress of Composite Bonded to Excimer Laser Treated Dentin”, Journal of Laser Applications, vol. 21, pp. 129–132, 2009.[Abstract]

The aim of this work was to study the bond strength of resin composite bonded to dentin surfacestreated with KrF excimer laser radiation, untreated surfaces, and acid-etched surfaces using a single-plane shear method. Dentin specimens cut from freshly extracted permanent molar teeth were subjected to laser treatment with a KrF excimer laser (248 nm) using a fluence of 1 J/cm2. The bond strength was greater for acid-etched specimens than for laser treated or untreated specimens. The low strength of the bond to laser treatedsurfaces is probably due to a shift from a mixed to a cohesive rupture mechanism. It was concluded from this study that surface treatment of dentin surfaces with KrF excimer laser under the conditions described does not significantly improve the shear bond strength to composites. More »»
2006 Journal Article M. Sivakumar, Oliveira, V., Oliveira, S., Leitão, J., and Vilar, R., “Influence of Tubule Orientation on Cone-Shaped Texture Development in Laser-Ablated Dentin”, Lasers in medical science, vol. 21, pp. 160–164, 2006.[Abstract]

In the present paper, the influence of tubule orientation on surface texture development was studied. Specimens of dentin with a wide range of tubule orientations were extracted from caries-free human teeth, processed using KrF laser radiation, and analyzed by scanning electron microscopy. When a transverse cross section of dentin cut perpendicularly to the tooth axis is processed with KrF laser radiation, a cone-like topography develops in the inner dentin where tubules are parallel to the laser beam. When laser processing is carried out in the outer dentin, because tubules are significantly tilted with respect to the laser beam, flat surfaces are achieved. The surface texture after laser processing depends effectively on the angle between the tubules and the laser beam. The dependency of cone growth on tubule orientation was confirmed using a simple differential ablation model. More »»
Publication Type: Conference Paper
Year of Publication Publication Type Title
2008 Conference Paper M. Sivakumar, Oliveira, V., Vilar, R., and Rego, A. M. Botelho do, “KrF Excimer Laser Ablation of Human Enamel”, in Materials Science Forum, 2008.[Abstract]

Laser treatment is a promising technique for dental applications such as caries prevention, dental hypersensitivity reduction and improvement of bond strength of restoration materials. In this study the morphological, structural and chemical changes of enamel surface due to treatment with KrF excimer laser radiation were evaluated using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. For radiation fluences near 1 J/cm², laser processing originates a relatively porous surface due to preferential removal of material in the enamel prism sheaths. Increasing the fluence leads to a relatively flat surface with clear evidence of surface melting. The X-ray diffractograms of both treated and untreated enamel are similar and correspond to hydroxyapatite. The only modification due to the laser treatment is a slight shift of the peaks, probably, due to a loss of the structural water of hydroxyapatite. X-ray photoelectron spectroscopy confirmed that organic matter is removed from the irradiated surface but no significant changes in the mineral phase occur. More »»
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