Beam, zero order

Apart from using the grating in zero order so that it works like a mirror, maintaining a (compact) round beam at the camera (A = 1) requires that the spectrograph adopt the Littrow configuration for which Tf = 0 and the incident and diffracted rays are parallel. From equations 6 and 9, the resolving power at blaze in the Littrow configuration is... 

The dynamic calculations include all beams with interplanar distances dhki larger than 0.75 A at 120 kV acceleration voltage and thickness between 100 A and 300 A for the different zones. The structure factors have been calculated on the basis of the relativistic Hartree - Fock electron scattering factors [14]. The thermal difiuse scattering is calculated with the Debye temperature of a-PbO 481 K [15] at 293 K with mean-square vibrational amplitude

= 0.0013 A following the techniques of Radi [16]. The inelastic scattering due to single-electron excitation (SEE) is introduced on the base of real space SEE atomic absorption potentials [17]. All calculations are carried out in zero order Laue zone approximation (ZOLZ). 

Suppose first that, in addition to the direct (zero-order) beam, only... 

To study the orientational relaxation of the excited HDO molecules, we rotated the polarization of the probe pulse by 45 degrees with respect to the pump polarization using a zero-order A/2 plate. After the sample the probe is split in two beams, and using two polarizers and two detectors, the transmission changes of the probe parallel to the pump (ln(T/7o) ) and perpendicular to the pump (ln(T/7o)j ) are measured simultaneously. 

Concentration effects are important in some photochemical reactions as they are in ordinary thermal reactions, but in other photochemical reactions they are unimportant. In reactions involving only the primary photo-process concentration should have no effect, provided that the concentration is sufficiently great so that all the light that enters the reaction chamber is absorbed. Each photon absorbed produces one activated molecule and the speed of this process depends not on the concentration of molecules but only on the concentration of photons, i.e., on the intensity of the beam of light. Such a reaction, whose rate is independent of concentration, is known as a zero order reaction. This type is fairly common among photochemical reactions. We have seen that in... 

When the grating is illuminated with one of the two original waves, some of the wave will be scattered into a reconstruction of the other wave, some of the wave will pass through the grating unaffected (the zero-order beam), and some of the beam may be scattered into other directions corresponding to the other various orders of the grating (Fig. 2b). 



Figure 7 Phase-contrast two-beam STEM lattice image for Au(lOO) crystal using zero-order and 200 reflexions. Lattice spacing is 2.04 A...

Figure 6. Schematic drawing of the spectral and polarization imaging experiment using one of the two-transducer AOTFs with three cameras to image the two diffracted and one of the undiffracted beams. The two cameras on the side, image orthogonally polarized spectral images from the two diffracted beams and the middle camera with a linear polarization filter in front, acquires a broadband image from one of the zero order...

The AOTF was water-cooled for safety purposes. The first and zero order beams are almost collinear. Hence, a polarizer and an analyzer comprising of linear polarizers placed at right angles relative to each other, one before and one after the AOTF are required for beam separation. In the above table, spectral resolution is measured with collimated output. Diffraction efficiency refers to the laser line. The expected efficiency at the edges is around 10% of the peak value. Further characterization of this AOTF is planned with deep-UV wavelengths in coming days... 



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