Traveling-wave excitation

The traveling-wave excitation described by Eq. (21) affects the dielectric tensor, as described by Eq. (15). The effects can be detected by a variably delayed probe pulse that is phase matched for coherent scattering, that is, collinear (in practice, nearly collinear) with the excitation pulse and the vibrational wave vector. Since the probe pulse follows the excitation pulse through the sample at the same speed c/n (neglecting dispersion), it surfs along a crest or null of the vibrational wave. The probe pulse therefore encounters each region of the sample with identical coherent vibrational distortion. 

Use of traveling wave tube (TWT) amplifiers at power levels of hundreds of watts has been proposed (54) for power appHcations, at least when the heating chamber is well shielded. The potential advantage is an improved uniformity of heating when a broad band of frequency is used, ie, excitation of many modes. Disadvantages are high cost and lower (<50%) efficiency of the TWT. 

Kadar, S., Wang, J. and Showalter, K. (1998) Noise-supported travelling waves in sub-excitable media. Nature, 391,... 

I he notation 0e indicates that this is the dielectric function at frequencies low i ompared with electronic excitation frequencies. We have also replaced co0 with l (, the frequency of the transverse optical mode in an ionic crystal microscopic theory shows that only this type of traveling wave will be readily excited bv a photon. Note that co2 in (9.20) corresponds to 01 e2/me0 for the lattice vibrations (ionic oscillators) rather than for the electrons. The mass of an electron is some thousands of times less than that of an ion thus, the plasma liequency for lattice vibrations is correspondingly reduced compared with that lor electrons. 

Tyson, J. J. and Keener, J. P. (1988). Singular perturbation theory of traveling waves in excitable media (a review). Physica, D 32, 327-61. (December)... 

The next important step in the study of the regularities of the autowave modes of cryochemical conversion was to perform a series of experiments with thin-film samples of reactants. The changeover to such objects, characterized by the most intense heat absorption, allowed the realization of quasi-isothermal conditions of the process development and thus favored the manifestation of the abovementioned isothermal mechanism of wave excitation, which involves autodispersing the sample layer by layer due to the density difference between the initial and final reaction products. The new conditions not only not suppressed the phenomenon, but made it possible to reveal some details of the traveling-wave-front structure, which will be discussed here and also in Section X. 

The use of heterodyne detection to monitor vibrational oscillations even after traveling wave propagation out of the excitation region has also been demonstrated in the case of acoustic modes in bulk and thin... 

S. Kadar, J. Wang, and K. Showalter. Noise-supported traveling waves in suh-excitable media. Nature, 391 770, 1998. 

Under normal one-photon excitation conditions, no selective excitation is possible. For two-photon excitation, the moving particle sees each photon of frequency a> as a travelling wave of different frequencies w kv, depending on the direction of motion of the particle. If the particle absorbs both photons from a single travelling wave, then the resonance condition is ... 

---