Imaging of the wave field of surface acoustic wave devices

An optical measurement technique for the phase preserving imaging of elastical wave fields of surface acoustic wave devices was developed. This technique uses short pulses from a mode-locked picosecond laser, harmonic mixing, and coherent detection to achieve a measurement bandwidth beyond 1 GHz. It is therefore well suited to perform measurements on surface acoustic wave devices of even the highest frequencies where modeling becomes increasingly difficult. The detection capability for surface displacements of 1 pm/ square root Hz allows a minimum dynamic range of about 40 dB for the determination of amplitude profiles of surface acoustic wave devices. As an example of a practical application, results of measurements on a bandpass filter are presented. The generated wave profiles have been determined at several different distances from the transducer both in the passband and in the stopband of the device. The measurements are in excellent agreement with computer simulations obtained with an angular spectrum of waves model.<
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