The generation of broadband terahertz radiation in quadratically nonlinear crystals containing additional resonant impurities having a permanent dipole moment has been theoretically analyzed. It has been shown that the contributions to the intensity of the generated radiation from resonance and nonresonance mechanisms of optical rectification are nonadditive. In semiconductor nanostructures and systems of organic molecules, the energy efficiency of generation due to the resonance mechanism can reach about 0.001, which is much higher than the corresponding efficiencies of the currently widespread tilted front technique. The spectra of the input optical pulses exhibit a noticeable red shift due to the resonance-nonresonance rectification.

Theoretical approaches to the formation and propagation of soliton-like broadband electromagnetic and acoustic pulses with terahertz frequencies in condensed media are reviewed. Solitons of...

The nonlinear generation of an acoustic supercontinuum in a solid doped with impurity paramagnetic ions is studied theoretically. It is shown that generation can be the most efficient at two certain carrier frequencies of input pulses lying above the resonance spin-phonon absorption line and determined by the time and spatial dispersions, respectively. The generated supercontinuum lies well below the resonance absorption line. Generation of the supercontinuum in the single-frequency regime is accompanied by a shift of the input pulse spectrum mainly to the red. In the two-frequency regime, cross scattering is possible when a higher-frequency pulse is scattered by the powerful supercontinuum generated by a pulse with a different, lower carrier frequency. As a result, the spectrum of the high-frequency pulse experiences a strong modulation and broadening both to the red and blue. The efficiency of supercontinuum generation both in the single-frequency and two-frequency regimes can be on the order of 1%.

Microtubules are the basic components of the eukaryotic cytoskeleton. We discuss a class of nonlinear waves traveling in microtubules. The waves are obtained on the basis of a kind of z-model. The model used is extended to account for (i) the possibility for nonlinear interaction between neighboring dimers and (ii) the possibility of asymmetry in the double-well potential connected to the external electric field caused by the interaction of a dimer with all the other dimers. The model equation obtained is solved by means of the specific case of the Simple Equations Method. This specific case is denoted by SEsM(1,1), and the equation of Riccati is used as a simple equation. We obtain three kinds of waves with respect to the relation of their velocity with the specific wave velocity $v_c$ determined by the parameters of the dimer: (i) waves with $v>v_c$, which occur when there is nonlinearity in the interaction between neighboring dimers; (ii) waves with $v<v_c$ (they occur when the interaction between neighboring dimers is described by Hooke’s law); and (iii) waves with $v=v_c$. We devote special attention to the last kind of waves. In addition, we discuss several waves which travel in the case of the absence of friction in a microtubule system.