Aperturing, redundant

Redundant aperturing overcomes these problems and ensures high-quality data from free-standing polymer films, from small inclusions in polymer films, and from laminates composed of thin films. 

Redundant aperturing involves placing remote apertures at image places located above and below the sample. The effect is to square the integral of the function describing the diffraction at the aperture, resulting in much improved spatial resolution. This can only be successfully implemented when an on-axis lens system is used. 

Redundant apertures A pair of apertures can reduce the diffraction of light caused when the light passing through and aperture is of a wavelength close to the size of the aperture. A second aperture matched to the first aperture can reduce or eliminate the spurious energy due to diffraction. Use of a second aperture (termed the redundant aperture) allows a single sample layer less than 50 laa to be measured on a routine basis. 

Optical effects such as stray light or scattering are treated by placing one or more apertures in the optical train of the infrared microscope. For transmission measurements, one aperture is placed between the condenser and the sample and another is placed between the objective and the image plane. The two apertures are matched in size in order to optimize the signal. For reflectance measurements, only one aperture is used. This type of arrangement is widely employed in infrared spectroscopy, and is known as redundant aperturing . 

Fenimore, E.E. k, Cannon, T.M. 1978 Coded aperture imaging with uniformly redundant arrays. Applied Optics 17, 337... 

During the past decade a nmnber of flown space-bome experiments definitely demonstrated the ability of the coded aperture technique (Caroli et al., 1987) to perform efficient and reliable observations over the whole X-ray energy band. Two main classes of coded mask instruments have been recognized, one comprising the so called optimum or cyclic systems, in which an optimized mask design is obtained by cyclically shifted repetition of a Uniformly Redundant Array (URA) pattern (Fenimore and Cannon, 1978), and the box-camera or simple system, in which the mask and detector useful areas have the same dimensions (Brinkmann et al., 1985). 

Coded arrays were originally conceived for applications in X-ray imaging (Mertz and Young 1961 and Dicke 1968). A coded array is defined to be a pattern on a periodic two-dimensional lattice which associates with each lattice point a 0 or a 1 indicating whether the lattice point is open or closed . In coded-aperture imaging, the open and closed lattice points become open and closed cells in an opaque mask which casts a shadow of the photon source on a position-sensitive detector. For a review see Caroli et al. (1987). A uniformly redundant array, or URA (Fenimore and Cannon 1978), is a particular form of coded array. For a URA, each possible vector displacement between pairs of inequivalent open lattice points occurs a uniform number of times. (Equivalent lattice points are separated by a period of the array.)... 

Spatial resolution can be inaeased by introducing a dual aperturing (Redundant, Spectra-Tech). In this case, two apertures of identical size are placed at the source and sample images. This technique reduces the stray light by a factor of 3 [183] by reducing the illuminated spot at the sample. 

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. 

To outline an integrated documentation and retrieval system ranging (for the sake of completeness) over all scales of matter leaving no gaps and without redundancies, and in which the user could choose and continuously adjust the target range, aperture and resolution. 

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