二層球レンズの構成とその集束特性

抄録

This paper describes the possibility of spherical lenses with two concentric layers having constant refractive indices smaller than 2. The phase distribution in the reference plane which is taken in front of the lens is calculated as functions of the refractive index and radius. The lens parameters for the two-layer lenses are obtained under the condition that this phase distribution in the reference plane is uniform and the lenses of two types are obtained. The validity of this method is proved by the calculation and the measurement of the pressure gain. The lens used for the measurement consists of mixture of RTV silicon rubber and zinc powder. Although the pressure gain of these lenses undergose a small change as the k_0 a varies, the average pressure gains are comparable to the level of Luneburg lens.