Optical image correlation

Degenerate four-wave-mixing (DFWM, Section 10.2.3) in conjugated polymers has also been explored. Its use in optical image correlation has been demonstrated using Durham-route PAc and similar polymers. The very large optical non-linearity of PAc, Table 9.3, and the fast electronic response allow correlation to be performed with sub-picosecond laser pulses. The poor stability of PAc prevented this laboratory demonstration being turned into a practical device. 

The specificity of the detection scheme was demonstrated by correlating optical images of the nanowire barcodes acquired with and without fluorescence excitation. In this manner, multiple probes could be used simultaneously for the detection of a diverse set of analytes. 

Hamann et al. were among the first to use the apertureless near-field approach to greatly enhance optical processes in the near-field region. One important result of this investigation is that the spatial resolution of this approach is correlated with the radius of the tip apex, while the high cross section arises from an anteima enhancement provided by the tip volume [118]. This illustrates the high potential of this approach for local spectroscopy and optical imaging on the nanometer scale. 

Fig. 4 Seed-based Hb02 correlation maps for four mice. One control session and one post-4-AP injection session are displayed for each mouse. (F frontal cortex, M motor cortex, C cingulate cortex, S somatosensory cortex R retrosplenial cortex, V visual cortex subscripts L and R refer to left or right hemisphere, respectively.) The scale for all correlation maps is from r = -1 to 1. Maps are shown overlaid on the anatomical image of the brain, acquired with green light. Seeds placement and sizes are indicated with black circles. (From Guevara, E., et ah, Optical imaging of acute epileptic networks in mice. Journal of Biomedical Optics, 2013. 18(7) p. 076021-076021 with permission) [106].

Non-contact strain measuring methods are generally based on optical principles. The principal methods addressed in the literature include MI or SI (moire or speckle interferometry), and DIG (digital image correlation). Amongst their advantages, whole-field, non-contact or remote measurement... 

Moire interferometry and digital image correlation are the most popular non-contact strain-measuring methods. Both are based on optical principles. 

Key words elastic modulus, orthotropic, micromechanics, classical lamination theory, digital image correlation, optical methods. 

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