Lens space

The effect of varying the distance between the lens and the transducer is to vary the illumination of the lens, and this in turn affects the point-spread function of the lens (Chou et al. 1988). Figure 4.3 shows the point-spread function calculated for three values of the transducer-lens spacing for the same lens with a radius of curvature r0 = 47Ao, where Ao is the wavelength... 

If we assume that the integral f on Q has more than one minimal and maximal circles, the assertion concerning infinity of the group Hi Q,Z) becomes invalid. We will give an example lens spaces obtained by gluing two full tori along the boundary torus. On such spaces one may set a function with exactly two critical circles, minimal and maximal. 

Shifting the origin in the Fourier space by uci, we obtain the wave-function FT[0(r)]e > , from which the lens aberration term can be eliminated in principle by multiplication with the inverse of the aberration phase factor e . The inverse Fourier transform gives finally the amplitude and phase of the true object wave 0 (f). 

The vitreous is a transparent extracellular matrix occupying the space between the posterior lens and the retina and, in the majority of vertebrate species, constitutes the major f)art of the volume of the eye. Embryo-logically it can be considered as the basement membrane of the retina. It provides a mechanical support for surrounding tissues and acts as a shock absorber by virtue of its viscoelastic properties (Balzas and Delinger, 1984). Vitreous consists mainly of water (98%) and colloids (0.1%) with ions and low molecular weight solutes making up the remainder. It is not fully developed at birth, and changes in both volume and chemical composition occur postnatally. 

The experimental apparatus is illustrated schematically in Figure 1.8. Monochromatic light emitted from the point source S is focused by a lens L onto a detection or observation screen D. Between L and D is an opaque screen with two closely spaced slits A and B, each of which may be independently opened or closed. 

Figure 5. Front end of triple a quadrupole mass spectrometer with an ion source and reaction chamber (see Figure 4) mounted in front of an evacuated space containing skimmer cone CB, AC only quadrupole lens Qo, and first quadrupole Qi. The second and third quadrupoles, Q2 and Q3, are not shown. CR denotes cryopumping surfaces. IQ is an interquad lens.

Consequently, mirror optics are more common, in particular in the mid-IR. The mirrors used are usually aluminium- or gold-coated flat or curved substrates. While near-IR mirrors are usually protected by thin SiO-layers, in the mid-IR unprotected mirrors have to be used. Disadvantages of mirror optics are the elevated space consumption and the higher prices in comparison to refractive optics, especially comparing non-standard mirrors against non-standard lens. In total, mirror optics are so preferable to fibres and refractive optics, at least in the mid-IR, that in some technical applications they are used to replace waveguides to transport IR radiation between source, sensor head and spectrometer. 

The phase shift induced by the aberration function, can be understood geometrically in terms of the path length difference between a diffracted beam in an ideal lens and in a lens affected by aberrations. This path length difference is a function of the diffraction angle 0 Ag, which is the reason why it is more convenient to describe the imaging process in Fourier space. 

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