• Volume 11, Issue 2-3

      November 1988,   pages  87-268

    • Foreword

      C N R Rao D D Bhawalkar

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    • Editorial note

      C N R Rao S B Ogale

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    • Laser processing of III–V compound semiconductors

      A S Vengurlekar

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      Lasers have found an increasingly important role in semiconductor processing technology. While they are now widely used in some of the silicon-based device fabrication processes, their applications in III–V compound semiconductor processing are not equally well established. Considerable research work has been carried out to find ways to overcome some of the technical difficulties in their usage in technologies based mainly on GaAs. In this paper, we review these developments and mention possible future directions that will help establish the use of lasers in this very active field.

    • Laser annealing of silicon

      V P Godbole S M Chaudhari

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      In recent years laser processing has attracted much attention in view of its potential use in basic solid-state and material science research as well as in new processing technologies. The dominant feature of laser processing being the deposition of large amounts of energy (a few J/cm2) over very short time scales (a few tens of nanoseconds), it leads to melting of surface layers of solid followed by rapid resolidification. In this article, a few basic consequences of such laser-induced phenomena in silicon are reviewed.

    • Modelling of laser-induced effects in materials

      Animesh K Jain

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      Progress made in modelling laser-induced effects in materials is reviewed. Calculation of the thermal history of a material treated with a high power laser pulse is described in detail. Variation of thermophysical properties with temperature, and phase changes such as melting, vaporization and resolidification are incorporated into the calculations. Typical results for laser treatment of iron are presented. The melt parameters obtained from the heating calculations are used to predict the solute depth profiles in surface alloys produced by pulsed laser treatment. Non-equilibrium segregation effects, arising from extremely high resolidification velocities of several metres per second, are discussed and incorporated into calculations of the solute depth profiles. Departures from expected profiles due to convection in the melt are briefly discussed.

    • Laser chemical vapour deposition

      S K Roy

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      The special role of lasers in material processing is outlined in this article. In the background of the various chemical vapour deposition processes, the laser-induced chemical vapour deposition processes have been described. The unique aspects of pyrolytic and photolytic laser chemical vapour deposition have been stressed. Some of the recent experimental results on thin film deposition by laser have been reviewed. The problems and future of laser deposition processes have also been mentioned.

    • Laser-induced synthesis, deposition and etching of materials

      S B Ogale

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      The field of laser-induced synthesis, deposition and etching of materials is reviewed with an emphasis on the emerging trends and novel adaptations of the basic laser processing concepts. A number of examples are cited to illustrate the issues involved. These include rapid synthesis of titanium nitride by pulsed laser induced reactive quenching at Ti:liquid NH3 interface, laser deposition of good quality thin films of such materials as hot oxide superconductors, zinc ferrite, iron oxide, stainless steel, etc. and laser etching of superconductor films.

    • Laser etching and dry processing

      A K Nath

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      Controlled, anisotropic etching of different materials commonly used in microelectronics is an important processing step in microfabrications. During recent years it has been demonstrated that lasers can be used for initiating and enhancing the etching process in many gas-solid (dry processing) and liquid-solid (wet processing) systems. The laser-induced reaction could be either photochemical or thermochemical. Using laser etching technique a variety of materials such as Al, Ta, Ni/Fe, GaAs, InP, Si, SiO2 mylar, different polymers and superconducting materials have been processed. In this paper we briefly review these laser etching experiments.

    • Pulsed laser reactive quenching at liquid-solid interface

      S M Kanetkar S B Ogale

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      Recent results on high-power pulsed-laser-induced transformations at liquid-solid interface are described in the context of synthesis of new metastable phases of materials. Specifically two types of problems are reported: (i) laser-induced synthesis of compound film at liquid solid interface, this process being termed “reactive quenching”, and (ii) laser-induced alloying of layered structure under liquid medium wherein the reactive aspect plays the minimal role. So far the reactive quenching process has been studied for different metals, compounds and thin film sandwiches in various liquid ambients such as H2O, liquid ammonia (NH3), liquid N2 and benzene (C6H6). The identification of the metastable phases and the microstructural transformations therein subsequent to laser processing and thermal annealing have been brought out by employing a range of techniques such as conversion electron Mössbauer spectroscopy (CEMS), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), etc. Laser-induced alloying of layered structure in liquid ambient has been investigated in case of Fe/Al and Fe/B systems. The possible mechanism which could be responsible for the observed effects is discussed on the basis of time-resolved reflectivity measurements.

    • Laser welding

      Arvind Bharti

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      A brief state-of-the-art review of laser welding has been presented. Results of our experimental studies on laser welding of Ti-6Al-4V have been reported. Results of weld evaluation including microstructure, mechanical properties and microchemistry have also been presented.

    • Laser materials processing

      G L Goswami Dilip Kumar

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      The ability of the laser to produce a controlled and intense source of heat is the key characteristic which has led to its recent emergence as an important manufacturing tool. In this paper we have discussed the different techniques of laser materials processing and have given a brief description of their important applications.

    • Laser processing of polymers: an overview

      Lalit Mohan Kukreja

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      A review of the author’s work on laser processing of polymers and others’ work on photo-etching in polymers is presented. Processes based on laser-induced volatile decomposition like cutting, engraving, etc. are investigated in thermoset and thermopolymers using a continuous wave CO2 laser. Dependence of geometrical parameters and gross thermal effects on parameters of the laser beam for these processes are discussed. It is shown that a highly combustible polymer like cellulose nitrate can be processed with a CO2 laser in air because of the faster kinetics of the volatile decomposition than that of the combustion. It is found that irreversible surface softening can be achieved in a thermoset polymer of allyl diglycol carbonate by treating it with a CO2 laser. Basic parametric relations of this phenomenon are established. Mechanism of laser softening in the surface of a thermoset polymer is discussed. Finally, the process of fine etching based on photodecomposition in polymers is presented and various theories proposed to explain this phenomenon are discussed in brief.

    • Laser-tissue interaction studies for medicine

      G R Kulkarni

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      A brief review of laser-tissue interactions is given in this article. The choice of a laser system for therapeutic use is based on laser-tissue interaction reports. Knowledge of specific molecular events that follow laser irradiation of biological materials is very important.

    • Gas lasers

      A K Nath

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      The important gas lasers which find wide applications in material processing are the CO2 laser, the argon-ion laser and the excimer lasers. This paper briefly describes the basic concepts and the technology of these lasers.

    • Prospects of solid state lasers for material processing

      T P S Nathan M P Kamath

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      Since the invention of LASER in 1960, lasers have made a great impact in a wide range of scientific and technological applications. The first half of this paper discusses the basic differences between lasers and conventional heat sources and the second half is devoted to solid state lasers with specific reference to ‘high average power’ solid state lasers used in material processing. The various physical processes that influence their operation and the role of focusing optics are also discussed.

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