Half-spheric mirror

Figure 3.5-10 Scanning micro arrangements for Raman spectroscopy a normal sample arrangement b arrangement using a microscope and fiber optics c scanning of surfaces with liber optics and half-spheric mirror, which reflects the part of the exciting and Raman radiation back to the sample which is not directly collected by the fiber bundle (Schrader, 1990).

Fig. 3.5-10 c shows another sample arrangement which makes use of a fiber-optical connection from the laser to the sample and back to the spectrometer. It is specially designed for the scanning of surface layers, e.g., of precious prints or paintings. The half spheric concave mirror reflects the portion of exciting radiation and Raman radiation back to the sample which has been. scattered by the sample and is not collected by the optical fiber. Thus the mirror as a component of a multiple reflection system enhances the observed intensity of the Raman lines by a factor of 2 to 8, depending on the properties of the sample. 

Fig. 49. The Polytec FIR 30 Fourier spectrometer (No. 5c in Tables 2, 3, 4) Optical diagram (lower part) and the possibilities of using the sample chamber (upper half). M 2, M 3, M 5, M 6 plane mirrors M 1, M 4 paraboloid mirrors M 7 spherical mirror M8 elliptical mirror C Chopper S high pressure Hg-lamp BS beamsplitter D mirror drive IS Moird system G Golay detector S sample...

Besides the above two most frequently used back-scattering modes, another kind of configuration is specially designed for higher collection efficiencies [14], see Fig. 9. It consists of an elliptical mirror with a higher eccentricity, to which an electrochemical cell is attached from the back. The cell has a half-spherical window... 

Fig. 9 Diagram of specially designed collecting optics and cell. An elliptic mirror attached to an electrochemical cell having a half-spherical window. (Reproduced with permission from Ref [14]. Copyright 1992.)...

If the spherical anode is situated at a finite depth, f, the resistance is higher than for t and lower than for t = 0 (hemisphere at the surface of the electrolyte). Its value is obtained by the mirror image of the anode at the surface (f = 0), so that the sectional view gives an equipotential line distribution similar to that shown in Fig. 24-4 for the current distribution around a pipeline. This remains unchanged if the upper half is removed (i.e., only the half space is considered). 

A spherical concave mirror of radius R — CP = CQ reflects an object at O (mirror-object distance OP = u) into image at / (mirror-image distance IP= v). If object moves to infinity (u = oo), then all rays from that object will converge at the principal focus point F f—FP = (1/2) CP—RI2] that is, the principal focal length f is half of the radius of curvature. 

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