Thin films: a survey as of April 1975.

This report appeared in the ICO Bulletin for June 1975, an intermittent publication of the International Commission for Optics. O. S. Heavens is the ICO rapporteur for thin films. A report by A. Vasko on the ICO-10 Congress held in Prague in August 1975 will appear in an early 1976 issue of Applied Optics.

Thin film research today.

Improved methods of study have contributed to a great advance in thin film research in the past twenty years. A brief survey shows that applications have spread to many advances of electronics and optics.

Cell studies of total internal reflection fluorescence: effect of lipid membranes.

The intensity of the fluorescence generated when cell-substratum contacts are studied by total internal reflection fluorescence is calculated. In previous work, some approximations were made in respect of the effect of the lipid membranes. These approximations are removed in the present treatment.

Elimination of the effects of stray light in measurements by total internal reflection aqueous fluorescence (TIRAF).

Total internal reflection aqueous fluorescence has been shown to be capable of achieving spatial resolution in surface contours of about 1 nm. When used with highly structured objects, errors in measurements can arise from light scattered either by the object or within the body of the microscope. We describe how these errors can be eliminated when studying surface contours of human platelets.

Staggered broad-band reflecting multilayers.

Considerable broadening of the reflectance band of a multilayer stack may be obtained by staggering the layer thicknesses in such a way that they form either an arithmetic or geometric progression. Results are shown for asymmetric and symmetric filters of 15, 25, and 35 layers. The presence of the narrowband transmission peaks exhibited by the symmetric filters is explained, and the advantages of the use of this type of filter as an interference filter is discussed.

General electromagnetic theory of total internal reflection fluorescence: the quantitative basis for mapping cell-substratum topography.

Total internal reflection fluorescence (TIRF) has recently been used to look at the contacts made between cells and a glass surface on which they are spread. Our method utilizes the fluorescence of a water-soluble dye that acts as an extracellular aqueous volume marker. Fluorescence is stimulated by the short-range electric field near the glass surface that exists under conditions of total internal reflection. Since fluorescence is normally generated beneath a spread cell and not beyond it, the fluorescence of the image is related to the size of the cell-glass water gap. The images obtained are remarkable for their detail, contrast and the absence of confusing granularity due to cytoplasmic heterogeneity, which is commonly seen in interference reflection (IRM) images. We here develop a rigorous electromagnetic theory of total internal reflection in layered structures appropriate for cell contacts and apply it to quantitative TIRF. We show that: (1) TIRF, unlike IRM, can report cell-glass gaps in a way that is practically independent of the detailed physical properties of the cell; (2) TIRF is also far more sensitive than IRM for measuring cell-glass water gaps up to approximately equal to 100nm. These striking results explain the image quality seen by TIRF. As the initial step towards verifying our theory we show that measurement of the fluorescence stimulated by total internal reflection at a simple glass-water interface matches theoretical predictions.