ESPI-characterization of online deformations of CVD-diamond output coupler windows in high-power IR lasers

Synthetic diamond, deposited by Chemical Vapour Deposition (CVD), is becoming an interesting alternative for ZnSe as a window material for high power CO lasers. Although the infrared absorption of CVD-dianiond is higher than of ZnSe, this drawback is largely overruled by its better thermal conductivity, leading to smaller temperature gradients in the window and hence a less distorted laser beam. Electronic Speckle Pattern Interferometry (ESPI) is applied to study the on-line deformation of ZnSe and CVD-diamond anti-reflective coated output coupler windows exposed to a high power CO laser beam. It is seen that a ZnSe window already starts deforming at moderate beam power (100 W), while a diamond window does not deform considerably up to a beam power of 700 W.