Potential performance loss and compensation techniques of a lens under ionizing radiations

Our goal is to design a radiation resistant camera lens for color imaging capable to withstand ionizing radiations up to total doses of a few MGy. The latter cause damages in the internal structure of glass which can affect its optical transmission and refractive index (RI). On the one hand, the radiation-induced attenuation (RIA) mainly causes the glass darkening and image signal-to-noise ratio degradation and can be partially handled by choosing the most appropriate materials. On the other hand, the radiationinduced RI change (RIRIC) causes the blurring of the image which can be more harmful to the viewing applications. Indeed, typical RIRIC magnitudes of 10−4 to 10−3 mainly induce defocus on the image. Yet, no motorized elements have been shown to be resistant to radiations at the aimed dose levels. Similarly to thermal defocus in non-cooled thermal imaging, the impact of the RIRIC has to be studied during the design step of the camera lens. However, until comprehensive measurements on different glasses and under different types of radiations, the easiest way to foresee the lens behavior with respect to the RIRIC is to perform a parametric study of its response. We studied RIA and RIRIC effects on a dummy lens and show that a self-compensation of the lenses RI changes appears as possible. As this problem is very similar to the constraint of increased depth of field, we also studied the technique of wavefront coding to increase the lens tolerance to RIRIC.