Image-contrasting optics

As was discussed above, the image contrast is significantly affected by the aberrations of the electron-optical... 

In effect, the phase contrast technique employs an optical mechanism to translate minute variations in phase into corresponding changes in amplitude, which can be visualized as differences in image contrast. Light waves that are diffracted and shifted in phase by the specimen (termed a phase object) are transformed into amplitude differences that are observable in the eyepieces. 

The chemical specificity of CARS microscopy is readily combined with other nonlinear optical image contrast mechanisms, such as two-photon fluorescence (TPF), SHG, and THG, resulting in a multimodal CARS microscopy [88, 118, 117, 43]. In multimodal nonlinear optical imaging, TPF, SHG, and THG signals all benefit from the use of femtosecond laser pulses of high peak intensities, whereas the contrast and chemical selectivity of CARS benefits from the use of picosecond (narrow-bandwidth) pulses (see discussion in Sect. 6.2.3). As demonstrated by Pegoraro et al. [43], this apparent... 

Shown herein are the first 2D multiple-pulse NMR images following a chemical reaction for which the image contrast is Ti rather than T2. A multiple pulse line narrowing sequence is critical to efficient image acquisition where broad lines are expected. The gas-solid reaction between ammonia and a crystal of 4-bromobenzoic acid was monitored optically and by NMR imaging. Some anisotropy in the reaction... 

Fig. 12. Phase-contrast optical microscopy images after mixing phosphatidyl-cholesterol based liposomes bearing the complementary guanidinium and phosphate moieties...

The overall resolution in HRTEM is governed partly by the electron wavelength and partly by the optical characteristics of the objective lens. The most important effect of the latter arises from spherical aberration. This aberration introduces a phase difference into the individual diffracted beams and when the real image is synthesized by the lens from these diffracted beams this can give rise to considerable confusion in the image contrast. 

Focus can be controlled by monitoring the image contrast with the two-dimensional CCD camera while using the AF actuator to move the objective lens back and forth along the optical axis. Very clear images can be obtained with this simple focus control. 

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