LASER DAMAGE TESTING OF CVD-GROWN DIAMOND WINDOWS

Laser-induced damage threshold (LIDT) measurements have been made on b ulk polycrystalline (BP) CVD diamond plates using 0.532, 1.06 and 10.6 mum radiation and compared with measurements on natural type IIa diam ond samples. Using 10.6 mum radiation, damage thresholds for BP CVD di amond have been measured as 5.6-12.7 MW mm-2 (29-66 J cm-2) using a 50 ns laser spike. These values compare with measurements in type IIa di amond of 12.5-18.5 MW mm-2 made in this study, and values of 3.5-40 MW mm-2 reported elsewhere. The LIDTs measured show a strong correlation with bulk absorption, which is significant at 0.532 mum, and with sam ple surface finish, but poor correlation with the carbonaceous inclusi ons found in the samples. Extrapolation from the d.c. dielectric break down threshold to the time domain of interest would suggest that, in b oth current CVD diamond and type IIa single-crystal natural diamond, t he damage threshold is being substantially reduced by material or samp le imperfections.