Round beam

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... 

Lanthanum hexaboride cathodes fall short of the required brightness for a round beam to compete with a shaped beam only producing lxl06 A/cm2.ster. (25 kV) with adequate reliability for unattended production applications (40). In summary, highest throughput in production is obtained with shaped beams. 

In vectorscan systems, the beam is only directed to those areas of the chip that require exposure. With round beams, the beam diameter must be less than or equal to one quarter of the minimum linewidth, and to obtain adequate pattern fidelity, the beam must be incremented to at least sixteen positions to write a single minimum image square. Chip writing time can be estimated from the beam incrementing rate, and the average fraction of the chip area that needs to... 

EBES-like systems are used extensively for mask making. They can make masks with dimensions as small as 0.5 jxm, and 3a overlay accuracy approaching 0.1 jam. They generally use a small round beam, although shaped beam versions have also been described (40). 

In electron-beam direct-write lithography, the scanning electron beam of the exposure systems is focused to a small spot that is controlled [i.e., deflected and turned on and off (blanked)] by a computer as it is scanned across the surface of the resist film. Masks are not used in this exposure process. Two beam-forming approaches are employed. The first uses a Gausssian round beam. The second... 

Slotted beam or U-contacts describe a versatile design for the termination of soHd wire and require that the wire be pushed into a narrow slot between two moderately rigid tines, or beams, at the back end of the separable contact (Fig. 8). The edges of the beams displace the insulation, squee2e the wire, and keep it in compression for the life of the connection. This termination method was developed for terminating conductors in a gang using flexible flat cables with round conductors (5). 

An example of a serial-recording EEL spectrometer is shown in Eig. 2.33 it features a magnetic prism system which was constructed for a TEM/STEM of the type JEOL JEM lOOS [2.199, 2.200]. Its second-order aberrations are corrected by curved pole-piece boundaries, an additional field clamp, and two extra hexapoles acting as stig-mators. The electron beam can be adjusted relative to the optical axis by use of several deflection coils. A magnetic round lens is positioned just in front of the prism to... 

The apparatus used, as described previously (7), has modifications as described by Maier (16). A description also appears in this volume (15). A mass spectrometer of special design with 2-inch round poles, using 90° deflection with 1-inch magnetic radius, provides momentum-selected beams of low energy ions. These ions proceed at full energy... 

The projector chosen for Keck is an afocal Gregorian telescope (see Ch. 3) which expands the beam to a full 50-cm round profile. The final lens is placed with the plane surface facing the sky and the aspheric surface ground to give a 1/10 wave (rms) transmitted wave front. A back reflection from the last surface is used to monitor the quality of the wave front as it leaves the dome. 

Let us first consider the case where the laser beam is emitted through the telescope. The outgoing beam undergoes a tilt deflection through the turbulent atmosphere as does the backscattered light. The round trip time to the mesosphere is 0.6 ms at zenith. It is much shorter than the tilt coherence time ... 

A simple Michelson interferometer. If we place two mirrors at the end of two orthogonal arms of length L oriented along the x and y directions, a beamsplitter plate at the origin of our coordinate system and send photons in both arms trough the beamsplitter. Photons that were sent simultaneously will return on the beamsplitter with a time delay which will depend on which arm they propagated in. The round trip time difference, measured at the beamsplitter location, between photons that went in the a -arm (a -beam) and photons that went in the y arm (y-beam) is... 

A typical plate is shown in Figure 11.22. The plate sections are supported on a ring welded round the vessel wall, and on beams. The beams and ring are about 50 mm wide, with the beams set at around 0.6 m spacing. The beams are usually angle or channel sections, constructed from folded sheet. Special fasteners are used so the sections can be assembled from one side only. One section is designed to be removable to act as a manway. This reduces the number of manways needed on the vessel, which reduces the vessel cost. 

---