Depth discrimination

Fig. 2. Depth discrimination (z-axis resolution) properties of a confocal microscope. The illumination and detection images in a confocal microscope are diffraction-limited and confined to a small region of the specimen (1). Only light emitted in the plane of focus and on the optical axis will pass the detector pinhole and form an image. Light emitted from other areas of the specimen does not enter the detector pinhole.

Laser scanning confocal microscope A fluorescence microscope achieving improved depth discrimination and contrast by blocking fluorescence that originates outside the plane of focus by use of a confocal pinhole. 

To date, the Raman method has been used with commercial Raman probes and microscopes, predominantly in the backscattering collection mode (see Figure 12.1), although in a number of specialist laboratories a 90° collection geometry is also used [1]. While the backscattering mode is used mainly for its instrumental simplicity and ease of use, this approach permits the effective depth discrimination of Raman signals in these media only at shallow depths [1]. Consequently, as... 

As a result of extreme depth discrimination (optical sectioning), the resolution is considerably improved (by up to 40% compared to optical microscopy). The CLSM technique acquires images by laser scanning or uses computer software to subtract out-of-focus details from the in-focus image. The images are stored as the sample is advanced through the focal plane in increments as small as 50 nm. Three-dimensional images can be constructed to show the shape of the particles. 

To determine the water resources of the subsoil (free water quantification and depth discrimination of water-tables), geologists can base their investigations upon H NMR signals submittted to the low ambient Earth s field by using a suitably adapted equipment (the Larmor frequency is a few hundreds Hz). 

PAS has been found to be an ideal technique for the study of surfaces and adsorbed species. In studies of optically thin samples, pulsed laser excitation has been shown to enable sensitivities of 10 to be obtained. The degree of chemical modiflcation of silica gel surfaces has been monitored by PAS. A linear relationship between the photoacoustic signal and the amount of carbon or nitrogen adsorbed on the surface was found. PAS has also been used to study the photoinduced transient formed when eosine Y was adsorbed onto ZnO powder, and the thin oxide layers (<4nm thick) on a copper electrode. An investigation of layered samples has shown that PAS may be capable of depth discrimination. ... 

One way to measure the axial response of a confocal microscope is to record light intensity from a thin layer with infinite lateral extension. In a conventional microscope, no difference—and therefore no depth discrimination—are obtained. However, in confocal microscopy, a strong falloff occurs if the object is out of focus. The free width at half maximum (FWHM) of such a function is propoitional to the optical section thickness [64], [67]. The optical section thickness also depends on the diameter of the pinhole. The optimum pinhole size D with a maximum deterioration of 10% in reflection is given by [63]... 

Figure 4 Principle of confocal microscopy and depth discrimination. (From Ref. 68.)...

Mei, E. and D. A. Higgins (2000). "Nanometer-scale resolution and depth discrimination in near-field optical microscopy studies of electric-field-induced molecular reorientation dynamics." Journal of Chemical Physics 112(18) mS-UAl. 

Danger, M.S., Biilthoff, H.H. Depth discrimination from shading under diffuse fighting. Perception 29(6), 649-660 (2000). http //www.ncbi.nlm.nih.gov/pubmed/ 1040949... 

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