Cassegrain

Figure 10. Gregorian (left) and Cassegrain (right) solutions.

Special thanks are due to the staff of the Institut d Etudes Scientifiques de Cargfese for the warm hospitality and for the continuous and patient assistance, in particular Mme B. Cassegrain,... and not forgetting the kitchen staff ... 

Table 1 shows some approximate r values calculated for frequently used absorptions. NA values are assumed for customary Cassegrain objectives (for transmission and ATR, respectively). 

Case materials, in electronic materials packaging, 77 837-840 Case nitrided steels, properties of, 76 207 Case polymers, uses for, 25 481 82 Cash flows, 9 540-542 CASLINK software, 73 250 Caspian Sea, 5 784 CAS Registry, 73 242, 246 Cassegrain condenser, reflective, 74 233 Cassia, 23 165-166 Cassie-Baxter equation, 22 112, 113 Cassiterite, 24 783, 791 Casson-Asbeck plots, 27 709 Casson fluid flow model, 27 705 CASS test, 9 790... 

In vitro measurements of native chemical concentrations in whole blood were first reported for a 69-sample data set by Berger et al. using the same Cassegrain-based reflective geometry that was designed originally for serum [1], Enejder et al. subsequently optimized the collection optics for whole blood... 

As Raman scattering is a weak process, photons are precious and high collection efficiency is desired for a higher signal-to-noise ratio. Specialized optics such as Cassegrain microscope objectives and nonimaging paraboloidal mirrors have been employed to increase both the collection spot size and the effective numerical aperture of the optical system.10... 

In practice more sophisticated double focussing arrangements are usually used, several of which are shown in figure 10.23. The Cassegrain, Gregory and Nasmyth systems are in common use, and the offset Cassegrain system has the advantage that the secondary reflector does not block the field of view of the primary dish... 

Figure 10.23. Geometry of different focusing systems and detector positions with parabolic radio telescope reflector dishes, (a) Cassegrain, (b) Gregory, (c) Nasmyth, (d) offset Cassegrain [36]. 

R is approximately between 4 and 30/mi in the mid-IR range (2.5-20//m) when NA = 0.70. Sometimes it is possible to obtain IR spectra of good quality for samples with dimensions below the theoretical limits. The high diffraction effects of Cassegrain objectives may require the use of two apertures, one below and the other above the sample, to minimize the diffraction in the transmission mode. 

New developments in spectroscopic techniques have made it possible to obtain Raman spectra and more recently also FTIR spectra of oligomer crystals. The crystal area used for FTIR studies with all reflecting Cassegrain type microscopes is about 30 x 30 um, while the laser beam focused through the microscope covers about 5 j,m in diameter. Several examples of IR and Raman crystal studies, some of them correlating with X-ray crystal diffraction studies, are listed in Sec. 4.7.1.3.5. 

Figure 9.25 Optical paths of FTIR microscope with IR radiation (a) transmittance and (b) reflectance. M, mirror C, Cassegrain lens. (Reproduced by permission of PerkinElmer Inc.)...

The condenser goes by two names some call it a Cassegrain, while others call it a Schwarzschild objective. The present author has always been rather confused about the difference between a Cassegrain and a Schwarzschild objective but, aiming to resolve such confusion, contacted one of the designers of the first FT-IR microscopes. Bob Messerschmidt (now with Rare Light, Inc.), as to their difference. His reply to this question was as follows ... 

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