| 摘要 |
1,254,357. Sound diffraction. INTERNATIONAL BUSINESS MACHINES CORP. 27 Oct., 1969 [25 Nov., 1968], No. 52460/69. Heading H4X. [Also in Division G2] An image 26 is generated in an image plane by first constructing an object 25 having controlled phase retarding areas and then illuminating the object by electromagnetic waves 24 which are selectively retarded by the object and produce in the image plane resultant interference in the pattern of the image 26, there being no diffraction into other than a predetermined order. The object 25 is a kinoform and is formed by calculating on a computer the phase distribution required to produce a desired 3-D image assuming a constant amplitude. This follows the steps of (a) specifying the desired amplitude T R [a,b], (b) multiplying a random phase factor exp. [i#(a,b)] on the image amplitude whereby T R =T - TR exp. [i#], (c) computing the backward propagation of the complex wave amplitude T from the image plane by means of a Fresnel transformation T*F = | h | exp. [i#(x,y)], (d) plotting the phase distribution #(x,y) as amplitude on a multi-level gray level plotter, (e) photographically reducing this plot and (f) bleaching the photoreduction to provide a complex amplitude transmittance exp. [i#(x,y)]. The phase distributing object is preferably transmissive and of varying thickness. The phase factors preferably approximate a collection of discrete point apertures which may be 3-D with each aperture assigned a value of between 0 and 1, where 0 implies no light transmittance and 1 implies an open aperture and the values between represent relative transmittance. The illumination may be coherent light, ultrasonic waves or microwaves. Each area of object 25 contains the total information necessary to reconstruct the imaage.
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