Color changesDarkening as a measure of fluenceCarbonization of the surface layerRaman spectroscopy analysis of the modified layerElectron spin resonance spectroscopy analysis of structural changesFourier-transform infrared spectroscopy analysis of structural changesChanges in surface energyX-ray photoemission spectroscopy analysis of structural changesX-ray diffraction for crystalline fractionsAnalysis of cross-linking by gel-fraction measurementsEffects of structural changes on mechanical propertiesSummaryReferences