Beam-shape

Fig. 39. Schematic showing the basics of cell projection. The desired beam shape is selected by steering the electron beam through the appropriate pattern in the aperture plate. By using a rectangular aperture the system can operate like a conventional direct-write e-beam tool, so any shape of pattern can be...

The discussion of diffraction so far has made no reference to the size of the 2D grating. It has been assumed that the grating is infinite. In analogy with optical or X-ray diffraction, finite sizes of the ordered regions on the surface (finite-sized gratings) broaden the diffracted beams. From an analysis of the diffracted-beam shapes, the types of structural disorder in the surface region can be identified and quantified. - ... 

A very important characteristic of laser radiation is the beam shape. So far most LA experiments have been performed with Gaussian laser beams. Lasers with uniform distribution of the beam cross-section have been used only recently to achieve high lateral and depth resolution. Specially designed beam homogenizers must be used for this purpose [4.226-4.228]. The Cetac LSX-200 system has a flat-top distribution of the laser beam. 

Flexural strength is determined using beam-shaped specimens that are supported longways between two rollers. The load is then applied by either one or two rollers. These variants are called the three-point bend test and the four-point bend test, respectively. The stresses set up in the beam are complex and include compressive, shear and tensile forces. However, at the convex surface of the beam, where maximum tension exists, the material is in a state of pure tension (Berenbaum Brodie, 1959). The disadvantage of the method appears to be one of sensitivity to the condition of the surface, which is not surprising since the maximum tensile forces occur in the convex surface layer. 

Auger analysis of small features. The primary electron beam column is similar to that in electron microscopes, and it may contain both electrostatic and magnetic lenses for beam focussing as well as quadrupole deflectors for beam steering and octopole lenses for beam shaping. 

Since powerful X-ray sources and sophisticated beam shaping have generally become available, point-collimated setups for the study of X-ray scattering have lost their former handicap of low intensity. Today they benefit from their simple and versatile geometry. This section is devoted to an overview of modern apparatus -beginning with the source of X-radiation and ending with the detector and the data acquisition system. 

Figure 4.2. Sketch of a laboratory setup comprising a rotating anode, conventional beam shaping optics, and an X-ray camera with the sample in normal-transmission geometry...

Optical devices are placed in the light path in order to shape the primary beam. Beam-position monitors, shutters, slits, monochromators, stabilizers, absorbers, and mirrors are utilized for this purpose. The effective beam shape and its flux are defined by these components. In particular, if mirrors are cooled, vibration must be avoided and thermal expansion should be compensated. 

Figure 4.7. Microfocus beam shaping by means of a capillary used as a waveguide (ESRF, ID13) (courtesy C. RlEKEL)... 

Some experimental techniques require the sample to be studied in very well-defined orientations and positions with respect to the X-ray beam. In the corresponding experiments the structure of the samples is, in general, not changed. A synchrotron beamline is required, because it would take too much time to record the respective data with laboratory equipment or because a special beam shape (microbeam) is essential for scanning the part with high spatial resolution. 

Laser Beam Shaping, Fred M. Dickey and Scott C. Holswade... 

Laser Beam Shaping Applications, edited by Fred M. Dickey, Scott C. Holswade and David L. Shealy... 

Keywords Radar sensor scheduling waveform beam-shape control detection tracking revisit time myopic non-myopic. 

Here, the proportionality constant Kd is a function of the geometry of the calorimeter and other instrument parameters (e.g., laser beam shape and its position relative to the transducer). 

A. Larsson, N. Eriksson, S. Kristjansson, P. Modh, M. Uemukai, T. Suhara, and H. Nishihara, Grating coupled surface emitters integrated lasers, amplifiers, and beam shaping outcouplers, SPIE 3626, 190-200 (1999). 

LINEWIDTH CONTROL Lens imperfections Source stability Mask dimensions Beam shape Mechanical stability Developing Etching Baking Plasma descum Film thickness Film uniformity Swelling... 

ION BEAM Particles cm eV cm Ion mass and charge Accelerating voltage Beam size Beam shape Flash (dwell) time... 

Whereas special beam-shapes can be employed to highlight axial edges, the same interface can be accentuated with a lateral phase step. This somewhat fortuitous... 

Written by an international panel of experts, this volume begins with a comparison of nonlinear optical spectroscopy and x-ray crystallography. The text examines the use of multiphoton fluorescence to study chemical phenomena in the skin, the use of nonlinear optics to enhance traditional optical spectroscopy, and the multimodal approach, which incorporates several spectroscopic techniques in one instrument. Later chapters explore Raman microscopy, third-harmonic generation microscopy, and nonlinear Raman microspectroscopy. The text explores the promise of beam shaping and the use of a broadband laser pulse generated through continuum generation and an optical pulse shaper. 

Entropy and Information Optics, FrancisT. S. Yu Computational Methods for Electromagnetic and Optical Systems, John M. Jarem and Partha P. Banerjee Laser Beam Shaping, Fred M. Dickey and Scott C. Holswade Rare-Earth-Doped Fiber Lasers and Amplifiers Second Edition, Revised and Expanded, edited by Michel J. F. Digonnet Lens Design Third Edition, Revised and Expanded, Milton Laikin Handbook of Optical Engineering, edited by Daniel Malacara and Brian J. Thompson... 

Potma and Krishnamachari (Chapter 9) explore the effects of spatial beam shaping on the generated nonlinear Raman signals in a tightly focused geometry, demonstrating its enhanced ability to image chemical interfaces. 

The required beam shape is typically generated using a conical lens (axicon)... 

Fig. 5.6. A block diagram of an optical coherence tomography/Raman spectroscopy system C, circulator RSOD, rapid scanning optical delay BP, 785 bandpass BSO, beam shaping optics DM1, dichroic mirror at 990 nm DM2, dichroic mirror at 800-950 nm LP, long pass at 808 nm GP, galvanometer pair BD, balanced detector BPF, electronic band-pass filter AI-AO DAQ, analog input-output data acquisition (reprinted with permission from [34]. Copyright 2008 Optical Society of America)...

Both the pulsed and cw lasers were used for photodissociation of gaseous ions produced by laser desorption. The cw laser had a maximum output power of 50 watts at 10.61 micrometers and a beam diameter of 6 mm. The pulsed laser produced 2.6 joules in a pulse of 1 microsecond duration at 10.61 micrometers and had a 2 x 3 cm rectangular beam shape. Modifications of the FTICR vacuum chamber that facilitate ion irradiation have been reported previously (13). 

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