GB1478362A - Acousto-optic light deflecting system - Google Patents

Abstract

1478362 Controlling light EASTMAN KODAK CO 29 July 1974 [30 July 1973] 33427/74 Heading G2F An acousto-optic deflector of the type comprising a stepped array of Piezo-electric transducers, whereby the acoustic beam is automatically steered as its frequency is changed to maintain the Bragg diffraction condition over an extended frequency range, is operated only over a predetermined bandwidth having a centre frequency less than the transducer resonant frequency to counteract the reduction of the electro-acoustic conversion efficiency at higher frequencies due for example to losses in the transducer bonding and to compensate for the shift in the resonant frequency of the transducer from its free air value when it is bonded to the elasto-optic medium, whereby a flatter response, diffraction intensity against electrical input, is obtained. The resonant frequency is preferably 30% higher than the centre frequency. The angle of optical incidence may be greater or less than that giving peak response at the centre frequency whereby resolution and diffraction efficiency may be traded one against the other. By closing an angle giving 3dB less response at the centre frequency, the overall 3dB bandwidth can be increased by #2. Design critica, e.g. aperture width, cross-sectional distribution of the optical beam and dimensions of the deflector, are discussed in detail. The step height of the transducer array is an integral number of acoustic half-wavelengths at the centre frequency, with series electrical connections appropriately poled depending on whether the integer is odd or even. Acoustic absorbers are disposed on the surface opposite the transducer array e.g. lead, aluminium or epoxy loaded with tungsten powder, for a lead molybdate elasto-optic mediam and on two sides of the elasto-optic medium, the latter acting also as heat sinks e.g. Al or Cu covered with insulating layers. Finned heat sinks may also be provided for the transducers.