Detector collection

Figure 18. Cross section of an InSb pixel. This detector collects holes and amplifies the signal. The charge is collected in the vertical (z) direction by the p-n junction, and is separated in the X- and /-directions by the fields of the p-n junction.

Optical System. As shown in Figure 11, the optical section of the instrument consists of a beamsplitter, two optical wedge mirrors and a detector section with associated detector collection mirror. This is basically the Michelson interferometer technique except that the end mirrors have been replaced by optical wedges mirrored on the back side. The two windows are necessary only to maintain an ambient pressure in the Interferometer section, and a vacuum in the detector section. The window on the detector can be replaced with an optical filter if only a selected spectral region is to be investigated. 

Figure 4.3 Two examples of a 27t-spectrometer collecting electrons within a plane, (a) Suggested set-up with full rotational symmetry around the symmetry axis z. The electric field is supplied by conical bodies, and the detector collects simultaneously all electrons emitted from the source Q into the plane perpendicular to the z-axis (for directional information of electron emission using a discretised detector, see below). From [Kuy68]. (b) Spatial view of a toroidal analyser. The outer and inner toroids which again possess axial symmetry provide the electric field. The detector is a position-sensitive detector (see Section 4.3.2) which records directional information about the electron emission. Hence, the angle dependence of electron emission from the source Q into the plane perpendicular to the symmetry axis is preserved. See also [EBM81, Hue93]. Part (b) reprinted from Nucl. Instr. Meth. B12, Toffoletto et al, 282 (1985) with kind permission of Elsevier Science - NL, Sara Burgerhartstraat 25, 1085 KV Amsterdam, The Netherlands.

Destructive versus Nondestructive. Nondestructive-type detectors are necessary if the separated analytes are to be reclaimed for further analysis, as, for example, when identifications are to be performed using auxiliary instruments. One way to utilize destructive detectors in this situation is to split the effluent stream and send only part of it to the detector, collecting the rest for analysis. 

Though a typical XPS detector collects all emitted photons, regardless of their ejection angles, it should be noted that angle-resolved XPS (ARPES) and UPS (ARUPS) may also be carried out. By detecting photoelectrons emitted from a surface at different emission angles, one obtains the energy of the electrons as a function... 

Now, the big difference between multichannel and multiplex techniques arises because a single detector in FT-Raman is collecting all the modulated wavelengths at once. Consider a single data acquisition in an FT experiment, with the interferometer at a fixed position. The detector collects light from... 

Fig. 9 Z -contrast imaging and EELS. The electron probe is scanned across the sample. For each scan position, the HAADF detector collects the high-angle scattering intensity. The intensity of one scan-position is represented as the corresponding pixel intensity in the STEM image. The forward scattered beam is not affected by the detector and can be used for EELS. (View this art in color at www.dekker. com.)...

Another problem with RS measurements is that the corresponding thermometry is subject to calibration. This implies careful evaluation of the experimental parameters (quantum efficiency of the detector, collection efficiency, laser energy, total number density, solid angle of the collection optics, optical path length, and so on), but a typical procedure relies on the ratio between the measured RS signal and a reference signal obtained from a gas of known RS cross section and temperature. 

The basic pXRF measurement is a spot analysis where the beam is positioned on the area of interest and a fluorescence spectrum is accumulated. Efforts must be made to optimize the detector configuration for a particular measurement. In particular, with a synchrotron excitation source, it is common for a solid-state detector to be easily saturated by fluorescence from major elements in the sample as well as from scattered radiation. Consequently, the count rate in the detector needs to be optimized by varying one or more of the following incident beam intensity, detector collection solid angle... 

If high precision is required (1 part in ten thousand), an isotope-ratio mass spectrometer is used. These instruments are normal magnetic-sector instruments with dual inlets and dual collectors. The ion containing one isotope is focused on one collector ( Ar) and an adjoining detector collects the other peak ( Ar). The signals are accurately compared using precision resistors and null detection. 

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