Grating Replicas

The sizes and shapes are determined using transmission electron microscopy (TEM) over a diffraction grating replica. Dynamic light scattering can also be used to obtain the dimensions (see Chapter 8). 

Monochromators. Replica gratings and narrow band-pass filters are used commonly, more so than quartz prisms. Computer control of the monochromator is available in some instruments, so that optimum intensity at the desired wavelength or maximum absorption by the examined substance can be obtained. 

Replica grating An impression of a master grating used as the dispersing element in most grating instruments, owing to the high cost of a master grating. 

We thank F. Gaill for the use of the facilities of her laboratory. We are indebted to J.P. Lechaire and G. Frebourg for their excellent work with the preparation of the replicas. We are also grateful for the provision of the High Pressure Equipment by the Region Ile-de-France. 

Replica gratings arc formed front a master grating by a liquid-resin casting process that preserves virtually perfectly the optical accuracy of the original master grating on a clear rosin surface. This surface is usually made reflective by a coating of aluminum, or sometimes gold or platinum. 

Replicas of gratings can be made successfully and can provide excellent resolution and high reflection efficiency and definition. They usually have somewhat higher scattered light properties than do originals. Most producers of replica gratings do not make the details of their processes available. One method, however, is to prepare a collodion solution, flow it over a grating, allow it to set, strip it off, and mount it on a permanent base. 

The principle of this method is depected in Fig. 6.85. The signal pulse at the frequency co and its frequency-shifted replica 2A(o + Sa> pass with a time delay x through a beam of noble gas atoms. The high harmonics at and n(concave grating and reach the detector. 

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