www.elsevier.com/locate/optlastec Optics & Laser Technology 37 (2005) 348–356 Processing of concretes with a high power CO 2 laser B. Tirumala Rao*, Harish Kumar, A.K. Nath Industrial CO 2 Laser Section, Centre for Advanced Technology, Indore 452013, India Received 9 January 2004; received in revised form 26 April 2004; accepted 10 May 2004 Abstract Laser material processing, being a non-contact process, minimizes many of the complexities involved in the decontamination and decommissioning of nuclear facilities. A high power laser beam incident on a concrete surface can produce spalling, glazing or vaporization, depending upon the laser power density and scan speed. This paper presents effect of various laser processing parametersontheefficiencyofmaterialremovalbysurfacespallingandglazing.Thesizeoflaserbeamatconstantfluenceorenergy density had significantly different effect on the spalling process. In thick concrete block cutting the flow or removal of molten material limits the cutting depth. By employing repeated laser glazing followed by mechanical scrubbing process cutting of 150 mm thick concrete block was carried out. Gravitation force was utilized for molten materials to flow out while drilling holes on vertical concrete walls. The dependence of the incident laser beam angle on drilling time was experimentally studied. r 2004 Elsevier Ltd. All rights reserved. Keywords: Spalling; Glazing; Drilling; Laser cutting 1. Introduction In the development of various advanced technologies for the decontamination and decommissioning of nuclear facilities high power lasers are being evaluated in many laboratories [1–4]. Decontamination and decommissioning with lasers has several advantages over other techniques. It includes remote and non- contact nature of processing (minimizing occupational exposure of personnel), no requirement of secondary media (like abrasive or chemicals) to assist the process (significantlyreducingvolumeofradioactivewastetobe disposed off), absence of reaction forces eliminating engineering complexity and low levels of noise, vibra- tions and dust. In many instances radioactive contam- ination in the concrete lies within a few millimeter thick surface layer and removal of this layer would greatly reduce the volume of the concrete to be disposed as a nuclear waste during decommissioning of a nuclear facility. In addition to surface decontamination, decom- missioning of a nuclear facility often involves cutting anddrillingofthethickconcretestructures.Highpower NdYAG, diode and CO 2 lasers have been used [2,5,6] for surface decontamination and also for cutting and drilling of concrete blocks. CO 2 lasers, because of their high power capability and efficiency, are more attractive for these applications. Present experimental work has been undertaken with the objectives: (1) to study the effect of different process parameters like laser power density, size and shape of the laser beam, direction of scanning, laser operation mode (CW or pulsed), composition of the concrete etc. on the efficiency of material removal during CO 2 laser beam induced spalling and glazing of concrete surface; (2) to extend the process of surface glazing (with the optimized parameters) for cutting of 6 inch thick ground concrete block and (3) to study the effect of process parameters on the efficiency of laser beam drilling of a vertical concrete wall. 2. Background When a concrete surface is irradiated with a high power laser beam, depending upon the laser power density and scan rate, material is removed via spalling, glazing and vaporization. Usually concrete contains ARTICLE IN PRESS *Corresponding author. E-mail address: trao@cat.ernet.in (B.T. Rao). 0030-3992/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlastec.2004.05.001