Interference contrast

The interest in vesicles as models for cell biomembranes has led to much work on the interactions within and between lipid layers. The primary contributions to vesicle stability and curvature include those familiar to us already, the electrostatic interactions between charged head groups (Chapter V) and the van der Waals interaction between layers (Chapter VI). An additional force due to thermal fluctuations in membranes produces a steric repulsion between membranes known as the Helfrich or undulation interaction. This force has been quantified by Sackmann and co-workers using reflection interference contrast microscopy to monitor vesicles weakly adhering to a solid substrate [78]. Membrane fluctuation forces may influence the interactions between proteins embedded in them [79]. Finally, in balance with these forces, bending elasticity helps determine shape transitions [80], interactions between inclusions [81], aggregation of membrane junctions [82], and unbinding of pinched membranes [83]. Specific interactions between membrane embedded receptors add an additional complication to biomembrane behavior. These have been stud-... 

Figure Bl.17.4. Visualization of image contrast fomiation methods (a) scattering contrast and (b) interference contrast (weak phase/weak amplitude contrast).

Fig. 2. Differential interference contrast (Nomarski) microscope, showing exaggerated light path (12).

The second term corresponds to a simple delay and can be generated by air propagation. The third and higher terms are specific of propagation through material. They induce pulse spreading for optical telecommunications and degradation of the interferences contrast in the frame of interferometry. 

In video microscopy, for instance, background is normally subtracted using differential interference contrast (DIC) [18]. This technique, which requires a number of manipulations from the user, may now be automated using a new method called polarization-modulated (PMDIC) [19,20], It requires the introduction of a liquid crystal electro-optic modulator and of a software module to handle difference images. PMDIC has been shown to bring improvements in imaging moving cells, which show a low contrast, as well as thick tissue samples. 

FIGURE 2-11 Video-enhanced Differential Interference Contrast (DIC) images of gold-labeled p opioid GPCR on the surface of a GPCR-transfected fibroblast. The white trace is the trajectory of one particle over 2 minutes at 25frames/s. The black trace is the mean square displacement of the particle as a function of time. Reproduced from Figure 1 of [30], with permission. 

Contrast. See also Differential interference contrast (DIC) computer-assisted, 16 487 in microscopy, 16 474 techniques for improving, 16 474-487... 

Differential centrifugation, 5 531 Differential contacting, 10 760-762 Differential display, 13 354 Differential equations, 11 736 of motion, 11 738-739 Differential interference contrast (DIC), 16 480-483... 

Reflected light differential interference contrast (DIC), 16 482 Reflection correction algorithms, 24 456 Reflection high-energy electron diffraction (RHEED), 24 74 Reflection indexing... 

Figure 7.5 An interference contrast photograph of a white adipose tissue celt Note the spherical lipid droplet fills most of the cell.

Li, J. H., Guiltinan, M. J., and Thompson, D. B. 2006. The use of laser differential interference contrast microscopy for the characterization of starch granule ring structure. Starch-Starke 58 1-5. 

This latter application is the key to the broadband femtosecond approach to nonlinear microspectroscopy presented here. From the point of view of coherent control, it becomes clear that high spectral bandwidths are needed providing a hnge nnmber of photon energies and, as such, interfering pathways is necessary to be able to achieve high interference contrast, and thus good controllability of optical processes. 

Choice of Substrate Material to Reach Maximal Interference Contrast... 

A new optical microscopy method which enables interference contrast imaging of biological cells has been developed. The method is based on a well known physical phenomenon, white light interference on a thin transparent film. 

The colour interference contrast image is achieved via special experimental conditions, which comprise the angle of the incident light, wavelength of the light of the reflected ray, chemical composition, thickness and refractive index of a sample, and refractive index and chemical composition of a substrate. 

Optical microscopy, such as phase contrast or differential interference contrast. 

Powerful methods that have been developed more recently, and are currently used to observe surface micro topographs of crystal faces, include scanning tunnel microscopy (STM), atomic force microscopy (AFM), and phase shifting microscopy (PSM). Both STM and AFM use microscopes that (i) are able to detect and measure the differences in levels of nanometer order (ii) can increase two-dimensional magnification, and (iii) will increase the detection of the horizontal limit beyond that achievable with phase contrast or differential interference contrast microscopy. The presence of two-dimensional nuclei on terraced surfaces between steps, which were not observable under optical microscopes, has been successfully detected by these methods [8], [9]. In situ observation of the movement of steps of nanometer order in height is also made possible by these techniques. However, it is possible to observe step movement in situ, and to measure the surface driving force using optical microscopy. The latter measurement is not possible by STM and AFM. 

Figure 5.6. Differential interference contrast photomicrographs showing the morphology of growth spirals observed on (a) (0001), (b) (2131), and (c) (1010) faces of synthetic emerald.

---