Gratings grating order

Imperfections that are inherent to all of the discussed test structures are minimized partially in case of application of porous anodic alumina. It is known that anodic alumina has sharp pore edges [4]. Therefore it may be used as tiplike grating. In order to combine the benefits of porous anodic alumina and a nanoscale tip array a one-step electrochemical approach is used to fabricate nanoscale alumina tips (tip-like anodic alumina) [5]. However, a curvature radius of pore edges or alumina nanotips of these structures is too high for ultrasharp SPM tip characterization. 

This type of echelle grating and order separation gives rise to the most sensitive analytical line(s) that can be chosen for any element. High spectral efficiencies can be obtained across the entire wavelength due to the use of multiple orders. 

Obviously the gain in coherence has to be paid for by a dramatic drop in the count rate because the signal decreases quadratically with the distance from the source and linearly with the size of each collimation slit. Although the first collimating slit alone already provides coherence, we still have to introduce a second collimating slit - in our case also 7 pm wide and about 1 m downstream from the first slit. The reason for this is the requirement that the collimated beam width needs to be significantly smaller than the separation between the diffraction orders behind the grating in order to clearly resolve the diffraction peaks in Fig. 2. 

CHIO REFLECTION, REFRACTION AND DIFFRACHON GRATING ORDERS... 

Figure 10.18 Illustration of a ruled diffraction grating. Top grating orders, with m = 0 indicating the non-dispersive specular reflection. Bottom principle of obtaining increased (blazed) grating efficiency...

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