Characterization of laser noise in free-free beam structures using a Scanning Laser Doppler Vibrometer

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Virginia Tech


The advent of the laser has yielded many applications in modern science. One which has recently gained popularity in the area of structural dynamics is the use of a Scanning Laser Doppler Vibrometer (SLDV) to measure the dynamic response of vibrating structures. Essential in the optimal use of such a device is an understanding of the idiosyncrasies and operating parameters which may affect the quality of the experimental data. Specifically, the quality of the data taken with an SLDV system may contain noise which, for the purpose of this investigation, will be defined as "laser noise". It is the purpose of this thesis to characterize the laser noise, and investigate its potential sources.

Characterization of laser noise as a function of the range of velocities is presented. An investigation of the speckle pattern motions which correspond to the areas prone to the laser noise and the effect of increased retroreflective surface treatments are explored. Additionally, the effect of three user defined parameters of the SLDV system are examined. In order to quantify the effect of the above on the experimental data, a statistical representation of the quality of the scan data is introduced.

The work presented in this thesis provides insight into the physical mechanisms and phenomenon which contribute to the occurrence of laser noise. Additionally, some guidelines which will help the experimentalist use the SLDV system more optimally are presented. Also, some recommendations on future improvements of the SLDV are made, along with proposals for future research.