Spatial resolution compared

The introduction of multidetector row computed tomographic (MDCT) scanners in late 1998 opened a new era for CT in general and CTC in particular (Berland and Smith 1998). The use of multiple detector arrays along the z-axis offers substantial benefits related to anatomic coverage, scanning time and longitudinal spatial resolution compared with single-slice spiral CT (SSCT) (Beaulieu et al. 1998 Fenlon et al. 1999 Kara et al. 2001). 

The above remarks point out the interest of direct measurements of the boundary condition (BC) for the fluid velocity at a fluid solid interface. To obtain reliable information on the flow velocity BC of a fluid, with a spatial resolution from the wall down to molecular sizes, is a particularly difficult challenge. Conventional velocimetry techniques (even laser velocimetry) are far from such a resolution. We have developed a near field laser velocimetry technique which allows to increase significantly the spatial resolution compared to more conventional velocimetry techniques. This technique has been used to characterize the friction between a polymer melt and a solid wall and to understand how surface modifications weakening the interactions between a solid and a given simple fluid affected the fluid -- wall friction. 

The ability to focus the extremely small incident wavelengths of energetic electrons results in an unprecedented spatial resolution compared to optical based microscopy techniques (Figure 7.3). Since the resolution of our eyes is on the order of 0.1 mm, in order for us to observe these features, an appropriate level of magnification must be used. That is, for the increasingly greater resolution capabilities of modem scanning electron microscope (SEM) and transmission electron... 

One way to try and compensate for the very low excitation intensities currently inherent in the RSNOM technique is to enhance the Raman signal from the sample. A number of reports have been published in which surface-enhanced Raman SNOM measurements have been made [34,42,44]. This is particularly interesting as the surface topography of a substrate for surface-enhanced Raman spectroscopy (SERS) plays a critical role in the SERS enhancement process. RSNOM provides both a Raman map with spatial resolution comparable to the surface roughness and also a simultaneous topographic image of the SERS substrate. 

It is clear that the experimentally measured degree of mixing depends on the spatial resolution (compared to Lg) and on the time resolution (compared to Tg) of the probe used to estimate local concentrations in the mixture. The mixture appears as uniform if the scale of concentration fluctuations is smaller than the resolution of the probe. Generally, it is admitted that micromixing takes place in the range between molecular dimensions up to the scale where non-uniformities can be detected by usual means of ob-... 

In order to enhance spatial resolution, it is necessary to make the NA of the objective larger, as is clear from Equation (17.3) that is, either n or 6, or both of them should be increased. Due to the optical geometry of a microscope, there is an upper limit for 0. On the other hand, it is possible practically to increase n by introducing an attenuated total reflection (ATR) accessory into a microscope (see Chapter 13 for the ATR method this is a frequently used accessory for many recent infrared microspectroscopy absorption measurements). The refractive index n of Ge, which is a commonly used material for an internal reflection element (IRE) in the ATR method, is about 4, and the NA when using a Ge IRE exceeds 2. This means that, if an ATR accessory with a Ge IRE is combined with a microscope, the theoretical spatial resolution is enhanced about four times that of the conventional reflection measurement. In fact, in the FT-IR microspectroscopic imaging measurement with a Ge ATR accessory, it has been confirmed that a spatial resolution comparable to the infrared wavelength used for the measurement is realized, and thus a higher spatial resolution may be attainable. 

Image plates have a spatial resolution comparable to film with a much larger dynamic range. However, they still suffer from the need for scanning which, even with ingenious online carousels and dedicated scanners, still makes it impossible to conduct genuinely real-time interactive experiments. The examples of diffraction data included in this review illustrate the use of the various types of detector. 

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