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The focus of this paper is to disclose sources of measurement error in laser Doppler vibrometers (LDV) and to suggest specifications, suitable to describe their impact on measurement uncertainty. Measurement errors may be caused by both the optics and electronics sections of an LDV, caused by non-ideal measurement conditions or imperfect technical realisation. While the contribution of the optics part can be neglected in most cases, the subsequent signal processing chain may cause significant errors. Measurement error due to non-ideal behaviour of the interferometer has been observed mainly at very low vibration amplitudes and depending on the optical arrangement. The paper is organized as follows: Electronic signal processing blocks, beginning with the photo detector, are analyzed with respect to their contribution to measurement uncertainty. A set of specifications is suggested, adopting vocabulary and definitions known from traditional vibration measurement equipment. Finally a measurement setup is introduced, suitable for determination of most specifications utilizing standard electronic measurement equipment.

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The new international standard 16063-41:2011 provides well-defined rules for the calibration of laser-Doppler vibrometers up to 50 kHz. Recent research work addresses the enhancement of the methods defined by the standard to the frequency range up to a few hundreds of kilohertz. However, the newest generation of vibrometers can measure frequencies up to the GHz range which requires completely new approaches for calibration. Here, we demonstrate the overall characterization of the photodetector, connection cable, and analog-digital (A/D) converter transfer characteristics. This is an important step towards calibration of high-frequency vibrometers up to the GHz range.