Imaging stigmatic

The choice of mass spectrometer for a particular analysis depends on the namre of the sample and the desired results. For low detection limits, high mass resolution, or stigmatic imaging, a magnetic sector-based instrument should be used. The analysis of dielectric materials (in many cases) or a need for ultrahigh depth resolution requires the use of a quadrupole instrument. 

Fig. 3.19. Basic set-up of a direct imaging magnetic sector instrument. The stigmatic secondary ion optics consists of an electrostatic analyzer (ESA) and a magnet sector field.

The direct imaging magnetic sector mass analyzer (Fig. 3.19) has the unique property that all parts (lenses, electrostatic analyzer and magnetic sector field) of the secondary ion optics are stigmatic (comparable with light microscopes). This means that all points of the surface are simultaneously projected into the analyzer. 

There are two basic types of detectors used to measure ion signals, current detectors and ion counters. Each type has different implementations. A third type of detector is an imaging detector. In some SIMS instruments, the mass spectrometer is also an ion microscope, which transmits a stigmatic image of the sample to a detector plane. 

Figure 12 Stigmatic imaging time-of-flight instrument of Schueler et al. (From Ref. 55.)...

In the United States today, the indoctrination to help—actually, to judge, condemn, report, and stigmatize—other people s behavior, from relatives to schoolmates, begins in early childhood and never ceases. The view that certain disapproved or disliked behaviors are not necessarily problems and might not be the business of others is considered heresy. The individual as informant— helping others with their health problems —has become our ideal of the responsible person and model citizen. The fact that many such persons are unwilling or unable to assume responsibility for their own behavior only enhances their image. 

Solving the equations Ai = Aq = 0 for and My, we find that there is a pair of object planes for which the image is stigmatic though not free of distortion. 

In stigmatic spectrometers the height and width of the slit are imaged in the same plane. Several mountings (Fig. 9) are used with a plane gratings. 

Diffraction astigmatism It is also called intermediate lens astigmatism. Use the largest condenser aperture and spread the beam with brightness fully clockwise. In the diffraction mode, a caustic image can be obtained. Adjust the intermediate lens stigmator to obtain a caustic triangle (similar to the one as shown in Fig. 5.2). Finally adjust the diffraction focus to obtain a very small and distinctly visible spot. 

KPJ Williams, GD Pitt, JE Smith, A Whitley, DN Batchelder, IP Haywood. Use of a Rapid scanning stigmatic Raman imaging spectrograph in the industrial environment. J Raman Spectrosc 25 131-138, 1994. 

If the sample is transparent and very thin, less than hi, then the combination of lenses LI and L2 and the intermediate slit in Fig. 2 are redundant. The stigmatic quality of the microscope ensures that a diffraction-limited image will be focused on the CCD. In this case, the Raman microscope is intrinsically confocal without the need for a slit or other aperture. 

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