Let us consider a concave grating of principal curvatures 1/Rs, 1/Rt in sagittal (x, z) and tangential (y, z) sections respectively, where the line projections on the tangent plane (x, y) at the grating vertex O are parallel to the y-axis and have a constant spacing. Let (x,y, z) be the coordinates of G; 5 and 8' the y-distances of P and P' to the (x,z) plane; r and r' the lengths OP and OP'; and a, a' the incidence and diffraction angles of the principal ray projection in the (x, z) plane. The first terms of the optical path length £ = GP + GP' are

r + r— (sin a + sina ) x +— —7 sin a +—7 sin a

0 0

Post a comment