Microscopy, optical embedding

In condensed-phase CARS, the effects of the nonresonant susceptibility x(3)nr are most profound when a sample with weak Raman modes is embedded in a nonlinear medium. The nonresonant background of the latter can be easily comparable to or larger than the resonant contribution from the sample of interest. This is a situation commonly encountered in biological applications of CARS microscopy. Depending on the experimental situation, the CARS detection sensitivity to weak resonances can then be restricted either by the nonresonant background or by the photon shot-noise [62]. To maximize either the relative or the absolute CARS intensity, nonresonant background suppression schemes [44, 60, 61, 63, 64] and optical heterodyne detection (OHD) techniques [65-67] have been developed during recent years. 

Surface profllometry showed that the average thickness of the CaCOj films was 1 pm. Optical microscopy, FT-IR and SEM all demonstrated that the films were amorphous with few embedded crystalline spherulites. Upon standing, the film... 

The samples have been prepared by e-beam evaporation of a dielectric layer followed by thermal evaporation of the silver fraction, which builds the island film, while the sandwich is completed by a further dielectric film. In every sample, intentionally the same amount of silver (corresponding to an average thickness of 4 nm, as recorded by quartz monitoring) has been embedded in a 6 nm thick dielectric film, formed from either Mgp2, LaFs, Si02, or AI2O3. The optical transmittance T and reflectance R of all films have been measured by a Perkin Elmer Lambda 19 spectrophotometer. To correlate the optical properties with the sample morphology, transmission electron microscopy (TEM) has been applied. 

In recent years, a new approach to condensed-phase spectroscopy has emerged, that focuses on the spectral properties of a single molecule (SM) embedded in a condensed phase [14], Thanks to experimental advances made in optics and microscopy [5], it is now possible to perform single molecule spectroscopy (SMS) in many different systems. Motivations for SMS arise from a fundamental point of view (e.g., the investigation of the field-matter interaction at the level of a SM and the verification of statistical assumptions made in ensemble spectroscopy) and from the possibility of applications (e.g., the use of SMS as a probe for large biomolecules for which a SM is attached as a fluorescent marker). 

Specimens sufficiently small to be examined entire may also be examined alive, contrast being provided by optical devices such as phase contrast or interference contrast microscopy, or occasionally by means of vital dyes - nontoxic stains that have an affinity for certain components of cells. However, most organisms, their organs and tissues, and even their cells, are too large to provide high-resolution information with the conventional light microscope, and they must be killed and then (usually) dehydrated, embedded, sectioned, stained, and movmted before microscopical examination. 

Figure 17.10 Optical microscopy photograph showing part of three repeating units in one embedded stack cross-section parallel to gas channels.

Figure 17.11 Optical microscopy photograph showing five repeating units of one embedded stack cross-section perpendicular to gas channels the inset at the top shows a higher magnification.

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