DD Duncan, SJ Kirkpatrick, FF Mark, LW Hunter. Transform method of processing for speckle strain-rate measurements. Appl Opt 33:5177-5186, 1994.

We have developed a highly sensitive method for measuring thermal expansion, mechanical strain, and creep rates. We use the well-known technique of observing laser speckle with a pair of linear array cameras, but we employ a data-processing approach based on a two-dimensional transform of the speckle histories from each camera. This technique can effect large gauge sizes, which are important in the assessment of the spatial statistics of creep. Further, the algorithm provides simultaneous global estimates of the srain rates at both small- and large-scale sizes. This feature may be of value in the investigation of materials with different short- and long-range orders. General advantages of our techniques are compact design, modest resolution requirements, insensitivity to slow surface microstructure changes (as seen with oxidation), and insensitivity to zero-mean-noise processes such as turbulence experiments. These tests are intended to demonstrate the performance advantages and limitations of the transform method of processing speckle strain-rate data. Keywords: Creep, thermal expansion, strain rates, speckle metrology.

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