METHODS OF AND APPARATUS FOR RECORDING ACOUSTIC OR MICROWAVE HOLOGRAMS

摘要

1422802 Holograms SIEMENS AG 10 Jan 1973 [21 Feb 1972] 1335/73 Heading G2J [Also in Division H4] In a method of recording acoustic or microwave holograms, wave-distribution signals are transformed into parallel rows of light signals which are recorded on a light-sensitive medium, each row being recorded twice and each second recorded row being displaced both parallel to and perpendicular to the direction of the rows. The displacement results in efficient spatial separation of the non-diffracted (unwanted) light from the image-forming first-order diffracted light when the recorded hologram is reconstructed using a convergent laser beam. The double recording avoids a halving of the image field of view which would otherwise occur during reconstruction if only a single recording with alternate rows displaced were made. In the acoustic embodiment described the wavedistribution signals, representing a wave field as modified by a test object, are derived from a mechanically-scanned transducer or electricallyscanned transducer array. They are mixed with a coherent electrical reference signal and the mixed signal is applied directly to a double-beam or beam-switched oscilloscope to provide a double display which is photographed to form the hologram, the row displacement being effected by control of the beam deflection. Alternatively the mixed signal is passed through a doubling and/or delay circuit to the oscilloscope so that the circuit effects the displacement.