Differential phase-contrast detector

The sample is then raster scanned through the focus spot, and the transmission in each image pixel is recorded. Among the variety of soft X-ray detectors are proportional counters and phosphors with photomultipliers. A recent development is a silicon detector with a segmented chip (Feser et al., 2003) allowing for dark and bright field as well as differential phase contrast imaging. 

Differential Phase-Contrast Microscope with a Split Detector... 

An alternative readout system is a scanning differential phase-contrast microscope with a split detector as shown in Figure 16.5. The optical configuration is compact and easy to align. The memory medium, in which the data bits have been recorded, is located at the focus of an objective lens. The band limit of the optical transfer function (OTF) is the same as that of a conventional microscope with incoherent illumination. The resolution, especially the axial resolution of the phase-contrast microscope, is similar to that obtained by Zemike s phase-contrast microscope. The contrast of the image is much improved compared to that of Zernike s phase-contrast microscope, however, because the nondiffracted components are completely eliminated by the subtraction of signals between two detectors. The readout system is therefore sensitive to small phase changes. 

The fringes contrasts are subject to degradation resulting from dissymmetry in the interferometer. The optical fields to be mixed are characterized by a broadband spectrum so that differential dispersion may induce a variation of the differential phase over the spectrum. Detectors are sensitive to the superposition of the different spectral contributions. If differential dispersion shifts the fringes patterns for the different frequency, the global interferogramme is blurred and the contrast decreases. Fig. 5 shows corresponding experimental results. 

Photometric detection has been used for the determination of PG and other antioxidants such as BHA [53,54] and BHT [55] using flow injection systems and a diode array detector (DAD), which allows the measurement of the intrinsic absorbance of each analyte at its individual wavelength. Thus, a flow sensor for the determination of PG and BHA has been described using the differential transient retention of the analytes in a solid phase packed in a flow-through cell [53]. The use of hydrophilic adsorbents, such as Sephadex G-15 and G-25, resulted in low retention of the antioxidants, and similar residence times. In contrast, the use of Cig-bonded silica as adsorbent with average particle sizes of 55-105 pm produced good retention and elution of both antioxidants. PG experienced a faster transient retention than BHA, which allowed the separation and determination of both analytes. PG was determined at 40 s from injection, measuring at 272 nm, and BHA... 

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