Strong oscillator

The spectra from strong oscillators have special features which are different from those from metallic and dielectric substrates. Different structures in tanf and A are observed on a metallic substrate, dependent on the thickness of the film (Fig. 4.65). For very thin films up to approximately 100 nm the Berreman effect is found near the position of n = k and n < 1 with a shift to higher wavenumbers in relation to the oscillator frequency. This effect decreases with increasing thickness (d > approx. 100 nm) and is replaced by excitation of a surface wave at the boundary of the dielectric film and metal. The oscillator frequency (TO mode) can now also be observed. On metallic substrates for thin films (d < approx. 2 pm) only the 2-component of the electric field is relevant. With thin films on a dielectric substrate the oscillator frequency and the Berreman effect are always observed simultaneously, because in these circumstances all three components of the electric field are possible (Fig. 4.66). 

It is usually possible to investigate very thin films (up to the subnanometer range) by use of infrared wavelengths, which are much greater than the thickness of the film (a factor of 10000) because of the interference optics of the strong oscillator (Berreman effect). 

Elsworth et al. (1983) report experiments performed in an open-topped channel 52 m long x 5 m high whose width was variable from 1 to 3 m. Experiments were performed with propane, both premixed as vapor and after a realistic spill of liquid within the channel. In some of the premixed combustion tests, baffles 1-2 m high were inserted into the bottom of the channel. Ignition of the propane-air mixtures revealed typical flame speeds of 4 m/s for the spill tests, and maximum flame speeds of 12.3 m/s in the premixed combustion tests. Pressure transducers recorded strong oscillations, but no quasi-static ovetpressure. 

Due to the high coherence of electron source in an FEG electron microscope, the information resolution limit of an image can reach the atomic level, much higher than the point resolution. However, the stmcture information, especially those in the high-resolution region, is seriously distorted due to the strong oscillation of the CTF. The distortion can be removed by the image deconvolution technique. 

Fig. 5.5. (A) Strong oscillations in the stimulated emission signal at 470 nm due to wave-...

Figure 6.4-5 Simulated spectra of a strong oscillator (strength/ = 200 10 cm with resonance at t> real and imaginary part of the dielectric function = s + k", refractive index n and absorption index k, ellipsometric parameters A and ip, as well as reflectance R for the angles of incidence and the polarization states stated.

For the strong oscillator the n and k spectra are asymmetric. The shift of the k maximum away from the resonance frequency is particularly obvious. In such a case a reliable representation of the vibrational structure cannot be derived from transmittance spectra and thus, from the absorption index k alone. Another peculiarity of the strong oscillator is the spectral range where the (real) refractive index is below unity. This renders... 

The ellipsometric parameters xl> and A experimentally determined with a homogeneous thick sample, are algebraically related with the components of the dielectric function, which in turn define the refractive index and the absorption index (Bom and Wolf, 1980). The parameters for the strong oscillator used to simulate the spectra shown in Fig. 6.4-5 were chosen to resemble the strong infrared resonance of quartz glass. Radiation reflected from such a sample was measured ellipsometrically the evaluation led to the results presented In Fig. 6.4-14. For weaker absorbers such as many molecular compounds. 

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