Spreading, beam

A1 Calibration Block was also used to examine the beam spread of surface SH Wave... 

The beam spread for surfece SH Wave probes was examined by STB-Al Calibration Block in comparisonwith the edge echo and lower comer echo height as shown in Fig. 5. 

Evaluation of Beam Spread for Surface SH Wave Probes by STB- A1 Calibration Block... 

By using a laser with less power and the beam spread over a larger area, it is possible to sample a surface. In this approach, after each laser shot, the laser is directed onto a new area of surface, a technique known as surface profiling (Figure 2.4c). At the low power used, only the top few nanometers of surface are removed, and the method is suited to investigate surface contamination. The normal surface yields characteristic ions but, where there are impurities on the surface, additional ions appear. 

In most ultrasonic tests, the significant echo signal often is the one having the maximum ampHtude. This ampHtude is affected by the selection of the beam angle, and the position and direction from which it interrogates the flaw. The depth of flaws is often deterrnined to considerable precision by the transit time of the pulses within the test material. The relative reflecting power of discontinuities is deterrnined by comparison of the test signal with echoes from artificial discontinuities such as flat-bottomed holes, side-drilled holes, and notches in reference test blocks. This technique provides some standardized tests for sound beam attenuation and ultrasonic equipment beam spread. 

The simulations were carried out on a Silicon Graphics Iris Indigo workstation using the CERIUS molecular modeling and the associated HRTEM module. The multislice simulation technique was applied using the following parameters electron energy 400 kV (lambda = 0.016 A) (aberration coefficient) = 2.7 mm focus value delta/ = 66 nm beam spread = 0.30 mrad. 

Usually the beam spread can be neglected, since it is much smaller than the energy resolution of the detectors. 

The spatial resolution of X-ray analysis carried out in the EPMA is limited to the size of the sampling volume, which is around 1 pm3. There may be many important features of a specimen which are smaller than 1 pm, and one way of overcoming the problem is by the use of thin specimens. We have seen (Figure 5.7) that the lateral spread of the electron beam increases with depth of penetration, so that in a sufficiently thin specimen the beam spread is much less. We will therefore next consider the analysis of thin foil specimens in the TEM. 

If the sampling volume is now treated as a truncated cone, and if the specimen thickness is t nm, then the lateral beam spread B (in nm) for thin specimens is given by ... 

The nearly parallel laser beam furthermore allows absorption spectroscopy experiments which realize a long light path at low pressures in the absorption cell without loss in intensity due to beam spread effects it also eliminates disturbing reflections from cell walls. 

Fig. 7. In an effort to improve tlie performance of the basic semiconductor laser, researchers developed tlie buried-heterostructure laser. In this configuration, the p-n junction is reduced to a tube that runs the length of the semiconductor crystal. This tube is surrounded by layers of semiconductor whose wide band gap raises the electrical barrier confining charge earner s within the tube. The wide-band-gap material also confines the. photons produced at the junction. The laser beam spreads because of diffraction occurring where the beam emerges from tlie face of tire device...

Note that the point analyses shown in Figures 6, 7, 8 and 10 represent average compositions through the thickness of the particle or thin section. At each analysis point the composition was sampled in a cylindrical volume of material whose diameter is roughly lOnm, beam diameter plus beam spreading ), and whose height is the specimen thickness. Thus, for the particle... 

Beam-spreading effects in thin foils, particularly, elastic and inelastic scattering of the incident beam implies that, for even the smallest probes focused, say, on the uppermost (entry) surface of a sample, beam spreading during transmission through the foil may limit the attainable resolution. 

What is not known, however, is whether image deconvolution can eliminate beam spreading as a contributor to the line scan shape. One would expect that beam spreading from a dense array of sources like the aggregates would obscure features beyond the resolution capabilities of the microscope. In this instance, deconvolution would provide only a modicum of aid in image interpretation. The authors of this entry however believe that beam spreading is a minimal contributor to the image. 

Finally, a comparison of the experimental and theoretical velocity contour plots for the reaction D+(HD, H)D2 is given in Fig. 7. It will be noted that exact detailed agreement of such plots can not be expected because of instrumental beam spread and energy resolution. To within such limitations the agreement in Fig. 7 is good. It will be noted that the large barycentric... 

In order to have a uniform exposure to electrons over the entire wafer, a standard transmission microscope (RCA EMV-3) was used. The apertures were opened and the 40 kv beam spread out over a circle larger than the wafer itself. The coated wafer was introduced into the microscope via the film cassette drawer (below the fluorescent screen). Charge density was measured with a Faraday Cup. Each polymer was irradiated at doses of 2, 5, 10, and 20 yC/cm. The radiation chemical yield was measured from plots of 1/Mjj versus the incident dose. A sample plot is shown in Figure 1, in this case for itaconic acid-MMA copolymers. The slope of such a plot is given by ... 

Laser Divergence. The divergence of a laser is a description of how fast the beam spreads out over distance. It is expressed as an angle and given in milliradians. For a typical military laser, the laser beam is 1 meter in diameter at a distance of 1 kilometer, and 2 meters in diameter at a distance of 2 kilometers. The divergence of such a laser would be 1 milliradian (see Figure 6-D). 

A laser beam spreads (diverges) over distance. 

Divergence - A description of how fast a laser beam spreads over distance. 

EELS and detector aperture function For analysis by electron energy loss, however, the situation is rather different. Here, the detector is usually limited by a collector aperture in order to reduce energy resolution degradation. This has two effects firstly, only beams spread by an amount t are collected, where fc is the solid angle subtended by the collector aperture. Thus an estimate of A, the resolution obtainable by EELS, is... 

The electron beam spreads out as the primary electrons strike the surface. This means that the spatial resolution is limited by how much the beam spreads within the material ( 2 pm). The probability of X-ray emission reduces with atomic number, so elements with low atomic number are difficult to detect and helium and hydrogen have never been detected using EPMA. The depth of penetration of the electron beam into the material is 2 pm. This means that EPMA is not a truly surface sensitive technique but is more sensitive to the bulk. 

All these effects are important, but beam spreading due to large thicknesses of some samples is the chief factor limiting the spatial resolution of the CBED and which frequently makes it difficult to obtain good results. Similarly, thermal conductivity of specimens, such as poor thermal conductors can increase the temperature to above 300° C for larger beam currents [21]. 

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