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Madhukar Y.K.,Indian Institute of Technology Kharagpur | Mullick S.,Indian Institute of Technology Kharagpur | Shukla D.K.,Reactor Operation Division | Kumar S.,Laser and Plasma Technology Division | Nath A.K.,Indian Institute of Technology Kharagpur
Applied Surface Science

The laser paint removal behavior with the continuous wave (CW) beam and repetitive pulses has been investigated using an Yb:fiber laser. The specific energy, which is defined as the amount of laser energy needed to remove unit volume of paint prior to the onset of substrate damage and is a measure of the process efficiency, was found to be dependent on the laser processing parameters. In CW mode the specific energy reduced with the increase of laser scan speed and corresponding increase of laser power. In case of repetitive pulsed mode the specific energy was found to depend on the pulse on-time as well as on the time interval between two successive pulses. At 1 kHz repetition rate, the specific energy reduced with the increase of duty cycle and corresponding increase in scanning speed, but at relatively low frequencies of 50-150 Hz and 50% overlap between two pulses specific energy was found to increase with increasing duty cycle. Irrespective of the mode of operation specific energy increased with the increase of average line energy. During the laser paint irradiation a plume of burning fume was formed over the surface and the variation in specific energy with laser processing parameters has been attributed to the absorption of laser radiation in the plume. Since the dimension of plume and fume particle density in it will depend on the laser energy absorbed in paint, the absorption loss in plume will depend on the laser parameters. This was confirmed by measuring the plume temperature for different laser processing conditions. Based on this and considering that the actual specific energy absorbed by paint should be constant, the absorption characteristic of plume was modeled applying Beer Lambert's law. © 2012 Elsevier B.V. All rights reserved. Source

Mullick S.,Indian Institute of Technology Kharagpur | Madhukar Y.K.,Indian Institute of Technology Kharagpur | Kumar S.,Laser and Plasma Technology Division | Shukla D.K.,Reactor Operation Divisions | Nath A.K.,Indian Institute of Technology Kharagpur
Applied Optics

Absorption of CW Yb-fiber laser light of 1.07μm wavelength in water has been measured at different water temperatures and laser intensities. The absorption coefficient was estimated to be 0.135 cm-1 at 25°C water temperature, and this was found to decrease with temperature at a rate of 5.7 × 10-4 cm-1 °C-1. The absorption coefficient increased significantly when the laser beam was focused in water, and the increase depended on the distance of the focal point from the water surface. This has been attributed to the absorption and scattering losses of laser radiation in a cavity formed in water by the focused beam at laser intensities in the megawatts per square centimeter and higher range. © 2011 Optical Society of America. Source

Mullick S.,Indian Institute of Technology Kharagpur | Madhukar Y.K.,Indian Institute of Technology Kharagpur | Roy S.,Indian Institute of Technology Kharagpur | Kumar S.,Laser and Plasma Technology Division | And 2 more authors.
International Journal of Machine Tools and Manufacture

The conventional underwater laser cutting process usually utilizes a high pressure gas jet along with the laser beam to create a dry condition in the cutting zone and eject out the molten material. This causes a lot of gas bubbles and turbulence in water, and produces aerosols and waste gas. This may cause contamination in the surrounding atmosphere, while cutting the radioactive components. In order to minimize this effect, a water-jet assisted underwater laser cutting technique has been developed using a high power fiber laser. A high velocity coaxial water-jet has been employed in place of gas-jet to remove the molten material through the kerf. Some amount of water vapour bubbles is formed at the laser-metal-water interface; however, they tend to condense as they rise up through the surrounding water. AISI 304 stainless steel sheet of maximum 1.5 mm thickness was cut at 1.4 m/min cutting speed with the present setup at 1800 W CW laser power, and the resulting average kerf-width was about 0.75 mm. The heat convection by water jet and the scattering of laser beam by vapour were found to influence significantly the energy efficiency of the cutting process. The effects of various processing parameters on the cutting performance were investigated. The energy efficiency improved at higher cutting speeds. An energy balance model with various loss mechanisms included has been also developed. © 2013 Elsevier Ltd. Source

Suri B.M.,Laser and Plasma Technology Division
Springer Proceedings in Physics

Classical high-resolution spectroscopy had been of interest for the sake of studies related to isotope shifts and hyperfine interactions and for resolving complex spectra associated with heavy elements like lanthanides and actinides. In this chapter, some of the history of classical high-resolution spectroscopy has been described. The highest-resolution laser spectroscopy is usually performed with CW lasers which have inherent ultra-narrow linewidths. Pulsed dye lasers though have relatively large linewidth because of Fourier transform limit but can still be usefully employed for multicolor laser spectroscopy of various elements with complex spectra. We have demonstrated the utility of pulsed dye lasers for studying lanthanides and actinides by employing techniques like multicolor optogalvanic spectroscopy in hollow cathode discharges, multicolor laser-induced fluorescence, and resonance ionization spectroscopy in atomic beams. We have for the first time utilized ICCD-based spectrograph for some of the measurements. These techniques have yielded excellent new information on atomic parameters like radiative lifetimes, branching ratios, and absolute transition probabilities of singly or multiply excited atomic levels. These techniques have inherent simplicity and may offer themselves as excellent alternative to conventional techniques and have universal applications of interest to wide cross section of atomic spectroscopists. © Springer India 2015. Source

Panda A.B.,Birla Institute of Technology | Mahapatra S.K.,Birla Institute of Technology | Barhai P.K.,Birla Institute of Technology | Das A.K.,Laser and Plasma Technology Division | And 2 more authors.
Applied Surface Science

Nanostructured TiO 2 thin films were deposited using RF reactive magnetron sputtering at different O 2 flow rates (20, 30, 50 and 60 sccm) and constant RF power of 200 W. In situ investigation of the nucleation and growth of the films was made by Optical Emission Spectroscopy (OES). The nano amorphous nature as revealed from X-ray diffraction (XRD) of the as deposited films and abundance of the Ti 3+ surface oxidation states and surface hydroxyl group (OH -) in the films deposited at 50 sccm as determined from X-ray photo electron spectroscopy (XPS) was explained on the basis of emission spectra studies. The increase in band gap and decrease in particle size with O 2 flow rate was observed from transmission spectra of UV-vis spectroscopy. Photoinduced hydrophilicity has been studied using Optical Contact Angle (OCA) measurement. The post irradiated films showed improved hydrophilicity. The bactericidal efficiency of these films was investigated taking Escherichia coli as model bacteria. The films deposited at 50 sccm shows better bactericidal activity as revealed from the optical density (OD) measurement. The qualitative analysis of the bactericidal efficiency was depicted from Scanning Electron Microscope images. A correlation between bactericidal efficiency and the deposited film has been established and explained on the basis of nucleation growth, band gap and hydrophilicity of the films. © 2012 Elsevier B.V. Source

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