Mfg. of solar concentrator with prism

A concentrator has a prism with input, reflection and output faces. It is manufactured by depositing a light-sensitive layer (5) on the input face (2), placing a substance (8) with refractive index close to that of the layer between the layer and an auxiliary prism (9), and recording an interference pattern to obtain a three-dimensional hologram in the layer. A ref. laser beam (6) is passed through the auxiliary prism and substance in the direction of solar radiation when in use, and an object laser beam (7) is passed via the auxiliary prism at an angle to the layer so that fringe planes are formed to diffract incident radiation at the angle. The auxiliary prism and substance are removed and the layer is developed. The angular relationship between the reflection and input faces and the angle are selected to preclude diffraction of a beam reflected from the reflection face.