Microscope light

It is interesting to note the analogy of developments in light microscopy during the last few decades. The confocal microscope as a scaiming beam microscope exceeds by far the nomial fluorescence light microscope in resolution and detection level. Very recent advances in evanescent wave and interference microscopy seem to promise to provide even higher resolution (B1.18). 

EM instmments can be distinguished by the way the infonnation, i.e. the interacting electrons, is detected. Figure Bl.17.2 shows the typical situations for TEM, STEM, and SEM. For TEM the transmitted electron beam of the brightfield illumination is imaged simply as in an light microscope, using the objective and... 

Light microscope Scanning electron microscope Transmission electron microscope Scanning probe microscope... 

Shaw S L, Salmon E D and Quatrano R S 1995 Digital photography for the light microscope results with a gated, video-rate CCD camera and NIFI-image software BioTechniques 19 946-55... 

A principal advantage of the Raman microprobe is that the optics are those of a conventional light microscope a wide variety of special-purpose objectives developed for materials and biological microscopy are available. The Raman microprobe also offers the advantage of fluorescence reduction owing to the high spatial resolution of the microscope if a region of low fluorescence can be chosen for observation. 

A confocal microscope using ultraviolet light and a 1.30-NA objective is expected to produce a resolution of about 0.07 p.m (70 nm), but no such instmment has been developed. There are confocal attachments that fit on almost any compound microscope. If one of the eady twentieth century ultraviolet microscopes or a Burch reflected optics scope can be found, the shorter wavelength and improved contrast would make possible better resolution than any compound light microscope. 

Nc.ar-Fi ld Scanning Optical Microscope.. The near-field scanning optical microscope (NSOM) should, strictiy speaking, be NSLM for near-field scanning light microscopy because "optical" includes electron optical as well as light optical and NSOM is a light microscope. 

A cathodoluminescence stage for a polarized light microscope that will take advantage of the x-rays generated by the electrons to detect the elements excited from single small (10—20-p.m) particles (EDS) is under development (see Luminescentmaterials,chemiluminescence). 

The two most useful supplementary techniques for the light microscope are EDS and FTIR microscopy. Energy dispersed x-ray systems (EDS) and Eourier-transform infrared absorption (ETIR) are used by chemical microscopists for elemental analyses (EDS) of inorganic compounds and for organic function group analyses (ETIR) of organic compounds. Insofar as they are able to characterize a tiny sample microscopically by PLM, EDS and ETIR ensure rapid and dependable identification when appHed by a trained chemical microscopist. 

Fluorescence Microscope. A useful light microscope utilizes UV light to induce fluorescence in microscopic samples (40). Because fluorescence is often the result of trace components in a given sample rather than intrinsic fluorescence of the principal component, it is useful in the crime laboratory for the comparison of particles and fibers from suspect and crime scene. Particles of the same substance from different sources almost certainly show a different group of trace elements. It is also very useful in biology where fluorescent compounds can be absorbed on (and therefore locate and identify) components of a tissue section. 

Laser Raman Microprobe. A more sophisticated microscope is the Laser Raman Microprobe, sometimes referred to as MOLE (the molecular orbital laser examiner). This instmment is designed around a light microscope to yield a Raman spectmm (45) on selected areas or particles, often <1 ia volume. The data are related, at least distantly, to iafrared absorption, siace the difference between the frequency of the exciting laser and the observed Raman frequency is the frequency of one of the IR absorption peaks. Both, however, result from rotational and vibrational states. Unfortunately, strong IR absorption bands are weak Raman scatterers and vice versa hence there is no exact correspondence between the two. 

A whole science, called metallography, is devoted to this. The oldest method is to cut the alloy in half, polish the cut faces, etch them in acid to colour the phases differently, and look at them in the light microscope. But you don t even need a microscope to see some grains. Look at any galvanised steel fire-escape or cast brass door knob and you will see the grains, etched by acid rain or the salts from people s hands. 

Fig. 6.2. The solidification of salol can be followed very easily on a temperature-gradient microscope stage. This can be made up from standard laboratory equipment and is mounted on an ordinary transmission light microscope.

Sketch the structures that you would expect to see if you looked at polished sections of the samples under a reflecting light microscope. Label the phases, and any other features of interest. You may assume that each specimen has been cooled moderately slowly from a temperature of 1100°C. 

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