Single Mode Resonant Applicators

Another useful but less versatile single mode resonant applicator is shown in Figure 26. It consists of a circular waveguide operating in the transverse magnetic or TMq.]q mode and is shortened at both ends. This fixes the overall dimensions which restrictions the operation to a given narrow frequency band for a given ceramic. 

By far a very efficient applicator, particularly for the syntheses on a small scale (< 50 ml), is a single-mode resonant cavity, in which only one mode of microwave propagation is permitted and hence the field pattern is well defined so the material can be positioned accordingly (Fig. 3.6). 

The contents of Chap. 4, which covers spectroscopic instrumentation and its application to wavelength and intensity measurements, are essential for the experimental realization of laser spectroscopy. Although spectrographs and monochromators, which played a major rule in classical spectroscopy, may be abandoned for many experiments in laser spectroscopy, there are still numerous applications where these instruments are indispensible. Of major importance for laser spectroscopists are the different kinds of interferometers. They are used not only in laser resonators to realize single-mode operation, but also for line-profile measurements of spectral lines and for very precise wavelength measurements. Since the determination of wavelength is a central problem in spectroscopy, a whole section discusses some modern techniques for precise wavelength measurements and their accuracy. 

In the previous sections we have seen that the frequency fluctuations of singlemode lasers caused by fluctuations of the product nd of the refractive index n and the resonator length d can be greatly reduced by appropriate stabilization techniques. The output beam of such a single-mode laser can be regarded for most applications as a monochromatic wave with a radial Gaussian amplitude profile, see (5.32). 

Figure 25 A single mode TE. Qj, resonant applicator, permission of Peter Peregrinus Ltd).

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