GB1422801A - Methods of and apparatus for recording acoustic or microwave holograms - Google Patents

Abstract

1422801 Holograms SIEMENS AG 10 Jan 1973 [16 Feb 1972] 1334/73 Heading G2J [Also in Division H4] In a method of recording acoustic or micro-wave holograms, wave-distribution signals are transformed into hologram light signals which are recorded in parallel rows on a light-sensitive medium with alternate rows displaced parallel to the direction of the rows. The displacement has the effect that, when the hologram image is reconstructed optically, the non-diffracted light is spatially separated from the image-forming firstorder diffracted light and so can be readily blocked by a diaphragm. The wave-distribution signals, in the acoustic embodiment described, are obtained from a physically-scanned transducer or from an electrically scanned transducer array and represent a wave field as modified by a test object. The signals are mixed with a coherent electrical reference signal and the mixed signal energizes an incandescent lamp scanned linearly in synchronizm with the transducer(s). The lamp is photographed and its thermal inertia effectively causes the alternate row displacement. Alternatively, the mixed signal is fed to an oscilloscope for display, a rectangular waveform signal is added to one of the oscilloscope deflection signals and has half the frequency of the deflection signal, and the display is recorded. In a third method the mixed signal is delayed briefly in a delay line during alternate rows of the recording. The recorded hologram is reconstructed using a convergent laser beam.