The liquid impact resistance of CVD diamond and other infrared materials

The high velocity environment endured by infrared (IR) domes often results in strength and transmission loss due, in part, to rain erosion. The Multiple Impact Jet Apparatus (MIJA) has proven, over a number of years, to be an accurate and rapid means of simulating this erosion phenomenon on many conventional IR materials in the laboratory and obtaining quantitative data on damage threshold velocities and transmission loss. Recent years have seen a rapid development of good optical grade CVD diamond with the eventual achievement of full hemispherical IR domes. Samples of CVD diamond from different sources and of differing thicknesses have been rigorously investigated on MIJA. Due to the low shock wave attenuation and the high shock wave velocity (approximate to 18 mm mu s(-1)) a number of damaging mechanisms are additional to other than the typical liquid impact pattern, with the relative importance of the damage mechanisms depending upon the thickness of the sample, the surface (i.e. growth or nucleation) and location of the impact. The results in this paper include initial tests on full hemispherical diamond domes, comparison with natural diamond and high temperature and high pressure (HTHP) diamond and discussion of the minimum thickness of a proposed CVD diamond dome. These data are compared with those obtained on other IR transmitting materials.