Immersion optics

Fig. 2. (a) Discrete isotropic coke, anisotropic coke, and inertinite particles in fly ash from an eastern US bituminous coal (reflected light, oil immersion optics, 250 pm on long axis of photographs) (b) Anisotropic coke attached to inertinite in fly ash from an eastern US bituminous coal - the coke develops from vitrinite in the feed coal and the inertinite is an original, essentially unaltered, constituent of the coal (c) Massive and fine spinel in bottom ash from an eastern US bituminous coal (d) Spinel (light-coloured rods) in spherical glass in fly ash from an eastern US bituminous coal. 

The observations are performed with a Leitz Ortholux polarizing microscope equipped with the ftOpak illuminator, lamps for reflected and transmitted light, immersion objectives, and verniers. Characteristics of the polished thin sections and of the nuclear emulsion plates are observed in transmitted light with the same immersion optics after removing the Berek prism. 

Fix a second clean coverslip onto the specimen using DePex. Unless the labelling is heavy it is usually necessary to use oil immersion optics. 

The refractive index of the medium between the objective and coverslip There is more light collected with oil immersion optics than with dry optics (Fig. 3). 

In many heated applications the presence of an object at a lower temperature will cause material to condense on it. Therefore, dual-wall immersion optic designs exist which heat the probe by using the same steam chasing that keep the process pipes hot. In Fig. 38a, a schematic of a steam-jacketed immersion optic is shown, with a photograph of a commercially available probe shown in Fig. 38b (including the probe head enclosure). In Fig. 38c, a schematic of a similar probe head enclosure is shown which includes an optional air-purge system for cooling the probe head. 

Figure 38 Steam-jacketed immersion optic (a) Schematic of a steam-jacket immersion optic for use with an imaging probe head suitable for interfacing to a production chemical reactor. The external focusing drive assembly allows the focal position of the probe optic to be varied by adjusting the distance between the internal moveable lens and the sapphire window, (b) Photograph of a commercial steam-jacketed immersion optic, (c) Schematic of a similar probe head enclosure showing the location of an optional air-purge system for cooling the probe head. (Reproduced with permission from Kaiser Optical Systems, Inc.)...

In other process installations, it may not be possible to use an immersion optic due to the lack of an appropriate opening. In these cases, if available, a standard sight glass... 

An example of an immersion optic designed for a filtered probe is given in Fig. 6. The immersion optic can be interfaced to the process via either direct crimping onto the outer tube or a flange interface. Internal to this is a second tube with a lens mounted on... 

Figure 7 Effect of window position on the observed optic background for an opaque latex sample. Raman spectra of latex obtained with (a) a X10 objective, (b) an immersion optic focused close to the window surface, and (c) an immersion optic focused into the sample, and (d) the Raman spectrum of the sapphire window 785-nm excitation. Note that bands marked with an asterisk originate from the sapphire window. 

For a permanent process installation, it may be preferable to avoid the use of O-ring seals and use either a brazed in or a tapered push fit window due to the maintenance cycle required to service the O-ring. It should be noted that all of the materials shown in Fig. 5 can all be used as window materials for immersion probes depending on the process conditions however, the most commonly employed window material is sapphire. For both process developments in the laboratory or trials under less challenging conditions, it may be possible to employ an O-ring-sealed immersion optic. The advantage of this optic is that it can be reconfigured with different window materials to allow for optic optimization where the refractive indices of the process and the standard window are different. 

The installation of Raman for online process monitoring can either be by immersion optics or in a noncontact fashion through a sapphire or diamond window. The laser excitation source can be hazardous. Low voltage lasers are required to avoid sparks or ignition when hitting black particles and must be located outside of a production area unless well shielded and conforms to safety requirements. Additionally, laser power will deteriorate with time requiring periodic replacement. 

The immersion optical clearing concept and technology is applicable not only to soft tissues and blood, but also to hard tissues, at present cartilage [43,44], tendon [61], cranial bones [152], and tooth [153] were tested. 

V.V. Tuchin, DXl. Zhestkov, A.N. Bashkatov, and E.A. Genina, Theoretical Study of Immersion Optical Clearing of Blood in Vessels at Local Hemolysis, Optics Express, voL 12, 2004, pp. 2966-2971. 

A.N. Bashkatov, D.M. Zhestkov, E.A. Genina, and V.V. Tuchin, Immersion Optical Clearing of Human Blood in the Visible and Near Infrared Spectral Range, Opt Spectrosc. (submitted). 

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