Beams illumination

The history of EM (for an overview see table Bl.17,1) can be interpreted as the development of two concepts the electron beam either illuminates a large area of tire sample ( flood-beam illumination , as in the typical transmission electron microscope (TEM) imaging using a spread-out beam) or just one point, i.e. focused to the smallest spot possible, which is then scaimed across the sample (scaiming transmission electron microscopy (STEM) or scaiming electron microscopy (SEM)). In both situations the electron beam is considered as a matter wave interacting with the sample and microscopy simply studies the interaction of the scattered electrons. 

When a grating is used to excite the modes, usually the waveguide film is periodically modulated at the film/cover or film/substrate (or at both) interface (Fig. 15.4b). The incident beam illuminates this grating and one of the diffraction orders will excite the modes. The mode s effective refractive index can be calculated from the so-called grating equation10,30. 

The apparatus for recording photobleaching has been described in previous publications (10,15,16). Briefly, an argon ion laser (364,476,514nm, or all visible lines) or a He-Cd laser (442 nm) with greatly expanded beam illuminated the sample (fused silica wafer) while its spectrum was recorded by an HP8450A spectrometer. 

The advantage of being able to record diffraction intensities over a range of incident beam directions makes CBED readily accessible for comparison with simulations. Thus, CBED is a quantitative diffraction technique. In past 15 years, CBED has evolved from a tool primarily for crystal symmetry determination to the most accurate technique for strain and structure factor measurement [16]. For defects, large angle CBED technique can characterize individual dislocations, stacking faults and interfaces. For applications to defect structures and structure without three-dimensional periodicity, parallel-beam illumination with a very small beam convergence is required. 

A force that is as large as the gravitational force can be used to suspend a particle against gravity, provided that it can be controlled and directed upward to balance gravity. One such force is the radiation pressure force or radiometric force. Ashkin and Dziedzic (1977), whose work is discussed in the next section, were the first to use the radiation pressure to levitate a microsphere stably. It was demonstrated by Allen et ai (1991) that the radiometric force can be measured with the electrodynamic balance, and they used the technique to determine the absolute intensity of the laser beam illuminating a suspended particle. This was accomplished in the apparatus displayed in Fig. 13. The laser illuminated the microparticle from below, and... 

Ashkin and Dziedzic (1977) used the radiation pressure force of a laser beam to levitate microdroplets with the apparatus presented in Fig. 15. A polarized and electro-optically modulated laser beam illuminated the particle from below. The vertical position of the particle was detected using the lens and split photodiode system shown. When the particle moved up or down a difference signal was generated then a voltage proportional to the difference and its derivative were added, and the summed signal used to control an electro-optic modulator to alter the laser beam intensity. Derivative control serves to damp particle oscillations, while the proportional control maintains the particle at the null point. 

Figure 6. A photograph of an aqueous thin film formed between two droplets of n-tetradecane. The laser beam illuminating the thin film (misaligned for clarity) can be used to measure lateral diffusion in the adsorbed layer or film thickness.

This section is based on the description published in reference [40], The geometry of the data acquisition for XRDCT is shown in Fig. 18. A fan beam illuminates the object, and the transmitted fan (in the plane of the drawing) reaches the 2-D detector at its central row. These data can be used for attenuation correction and also for a conventional transmission-CT image. The detector columns are indexed by the variable t, whereas the relative angle between measurement system (source, detector, etc.) and suitcase is described by the variable 4>. In conventional CT, a 2-D data set, I(f, ), is measured for many angular positions, 4>, of the object with respect to the device. 

For testing convenience the device was mounted on a microscope stage in which the recording laser beam is focused from below through the glass substrate, as shown in Fig. 20a. This allows the recording surface to be directly observed from above. Since both the polymer and the top conductor are semitransparent, the performance is comparable to that obtained if the laser beam illuminates the photoconductor from the top surface. 

The ratio of the polarized light intensity scattered from two different coaxial beams illuminating a particle can be used to determine particle size. Azzizy and Hess [191] used two coaxial beams of different wavelengths at 30° from the forward axis polarized in different directions. The ratio of these two parameters gives a unique curve that is a function only of particle size. They found errors of a similar magnitude to those found with intensity ratio methods. 

When either of the two writing beams illuminates the material after the seeding process is stopped (Figures 11.18 and 11.19), the relaxation dynamics of the induced susceptibility is much faster than for the dark relaxation dynamics case. Then again, as shown in Figure 11.19, no relaxation of the... 

In their mode of operation a monochromatic neutron beam, of wavevector k, is selected fi om the white incident beam, using Bragg reflection firom a single crystal, the monochromator. This beam illuminates the sample. In a selected direction from the sample a second single crystal, the analyser, is oriented such that only a given final wavevector, kf, is reflected onto a single detector. The choice of monochromator and analyser crystals depend on the energy transfer... 

In contrast to the other listed single molecule techniques, measurements based on fluorescence correlation spectroscopy (FCS) can already be performed both routinely and rapidly. Moreover, FCS is applied in many scientific disciplines and the number of applications of this technique is growing very rapidly. Thus, its principles will be briefly outlined Usually, a sharply focused laser beam illuminates a volume element of about 10 1 by using confocal or multi-photon microscopy. 

A photorefractive polymer consisting of DMNPAA, TNF, ECZ, and PVK has been used for erasable/rewritable three dimensional bit optical data storage under two-photon excitation. A three dimensional bit density of 5 Gbits/cm(3) is achieved by pulsed beam illumination at an infrared wavelength of 800 nm in the recording process. 

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