Resolution elements

Gc/ms is an example of a hyphenated instmment consisting of two techniques that provide orthogonal (independent) information. If two independent techniques are linked in tandem, a large number of data resolution elements is obtained from each. The more dimensions present, and the higher the available resolution along each dimension, the greater is the obtainable information (19). Because hyphenated systems generate an immense... 

Adaptive optics (AO) undoubtedly constitutes the most daring challenge. It is also absolutely essential seeing-limited observations with a 100-m class telescope would imply impossibly short focal ratio of the instrumentation, and immediate saturation by sky background. A smaller on-sky resolution element is the only way out, which implies at least some degree of adaptive compensation for atmospheric turbulence. 

Analytical electron microscopy (AEM) can use several signals from the specimen to analyze volumes of catalyst material about a thousand times smaller than conventional techniques. X-ray emission spectroscopy (XES) is the most quantitative mode of chemical analyse in the AEM and is now also useful as a high resolution elemental mapping technique. Electron energy loss spectroscopy (EELS) vftiile not as well developed for quantitative analysis gives additional chemical information in the fine structure of the elemental absorption edges. EELS avoids the problem of spurious x-rays generated from areas of the spectrum remote from the analysis area. 

The net result of these considerations is that, for a spectrum of Gaussian lines, one should sample 10 times per resolution element ( FWHM of isolated lines) and that the scan rate should be adjusted to yield a scan rate of 10 times constants to scan one resolution element (Blass, 1976a). 

Preparation of data for deconvolution must begin prior to the acquisition of the first data point. Once the resolution of the system is set (in a dispersive spectrometer this is equivalent to setting the slit width), the density of data points per resolution element must be chosen as discussed in Sections III.D and III.E. There are some subtle factors that must be taken into account. For example, for continuous scanning, approximately 10 data points per resolution element are recommended (Blass, 1976a) to capture all of the information required by the data and the noise. On the other hand, the data-point density must be great enough to characterize the spectral lines after... 

Under less restrictive noise/bandwidth considerations, one might drop the density to 6 points per resolution element at the risk of some minor noise aliasing. However, deconvolution by a factor of 3 would leave only two points per FWHM of a Gaussian spectrum-a number sufficient to characterize the spectrum, although display and measurement are difficult. 

Returning to the mainstream discussion of data preparation, we note that, for a 6-dB-per-octave-rolloff RC filter network in a lock-in amplifier, the continuous scan rate amounts to approximately one time constant per data point or 10 time constants per resolution element (Blass, 1976a). Some time is saved if only six data points are taken per resolution element. We have tried acquiring in this fashion, with no visible negative effects. 

SNMS ions neutrals ZZ sputtered neutrals (post ionized by e-beam or laser) > 3 nm 5 pm (+) > P gg-1 high depth resolution elemental information poor sensitivity... 

The imager provides a technique for achieving a small scale pre-multiplexing of the detector array while retaining a photovoltaic structure. By cycling the potentials on the control lines to selectively create field induced junctions, the effective collection area for incoming radiation will cycle about the unit cell. Consequently, the number of resolution elements on the focal plane is multiplied. 

In the IR spectral region the noise characteristics, typical of the measurement system, have led to the development of multiplex detectors whose operation is based on the use of mathematical transformations such as the Fourier and the Hadamad. With these detection systems, an appropriate encoding (transformation) of the raw spectral signal is performed, which permits simultaneous monitoring of a wide spectral window with a single-channel sensor. A SNR (multiplex) advantage is achieved that is typically proportional to the square root of either the observation time or the number of spectral-resolution elements contained in that spectral window. 

F a (N) N number of individual spectral resolution elements simultaneously monitored by the TV detector... 

Fa (AA)" AA, spectral coverage of a single resolution element (during time t)... 

The evolution of detection systems suitable for multielement determinations has proceeded along two basic lines of development as indicated in Figure 1. One line of development is based upon dispersive systems. Dispersive systems are all multichannel devices which may be further classified as temporal or spatial devices. In the temporal approach, the measurement of intensities in different resolution elements is separated in time. The spatial approach uses detectors which are separated in space. 

Temporal Devices. A temporal dispersive device uses a single channel which is scanned as a function or time to yield information on the intensities present in various resolution elements. Two basic approaches are possible (1) the detector may be scanned across a fixed spectrum or (2) the spectrum may be scanned across a fixed detector. In addition, these systems may be further differentiated on the basis of the manner in which the spectrum is scanned. Thus, linear-scan systems scan the spectrum at a constant, fixed rate. In contrast, programmed-scan systems have the capability of momentarily stopping at wavelengths of analytical interest, while spectral regions of little interest are rapidly scanned. For a complete review of the area of rapid-scanning spectrometry up to 1968, the interested reader should consult Volume T of Applied Optics which was entirely devoted to this subject. 

Because most of the imaging detectors have only 100 to 500 independent resolution elements along one axis, if one is to achieve 1 A resolution, then the total spectral range that can be covered with a single experiment is 100 to 500 A. 

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