GOALI: Exploring the Potential of Fluorescent Materials to Detect Subsurface Damage (SSD) and Plastic Deformation Induced by Polishing Processes

University Of North Carolina At Charlotte, Charlotte NC

Investigators

Abstract

The research objective of this Grant Opportunity for Academic Liaison with Industry (GOALI) award is to study polishing removal mechanisms and to determine if fluorescent materials can be used to detect the extent subsurface damage remaining in laser crystals after polishing. Fluorescent dyes and quantum dots (nano-sized cadmium selenium crystals with diameters less than 6.8nm) fluoresce when excited and are observable with confocal microscopes up to depths of 100um beneath a surface. Polishing slurries used to polish the laser crystals will be tagged with suitable fluorescent materials. During the polishing process it is thought that the fluorescent materials will be drawn into facture lines and cracks by capillary action or favorable surface charges. Subsequent detection of the fluorescent material will validate this methodology and reveal the extent of subsurface damage remaining in the polished material. Verification of this detection method will primarily be achieved through etching. As the fluorescent material will be present during the actual polishing process, this method also has the potential to capture dynamic polishing events and provide answers to long standing questions regarding material removal mechanisms in polishing. For example, will the localized compressive and tensile zones on abrasive particle leading and trailing edges widen preexisting fractures? Or, will the surface material plastically deform to 'cover' over sub micron sized scratches and pits? Successful completion of this research will greatly assist the project's industrial partner, Northrop Grumman, in characterizing and optimizing their laser crystal polishing processes. Minimizing subsurface damage in laser crystals increases the laser damage threshold, that is, the amount of power that can be pumped into the crystal without causing crystal damage. Fast, economical polishing of laser materials with guaranteed low to zero subsurface damage is essential in ensuring the continued manufacture in the United States of critical components for key military and medical applications.