We present a detailed theoretical study of the odd–even harmonics generated from the polar molecule CO by the method based on numerically solving the time-dependent Schrödinger equation within the single-active-electron approximation.

The effects of vibrational motions on dynamic Stark-induced π-electron rotations in a low-symmetry aromatic ring molecule are theoretically studied in the adiabatic approximation. We adopt a simplified three-electronic state model with a few vibronic states. A pair of the lowest vibronic states in two electronic excited states is set degenerate by irradiation of two linearly polarized UV lasers. The resultant degenerate state is named the dynamic Stark-induced degenerate vibronic state (DSIDVS). The laser parameters (intensities and central frequencies) are determined under the conditions of DSIDVS formation. The aromatic ring molecules of interest are supposed to belong to the weak coupling case. The analytical expressions for the DSIDVS and coherent angular momentum L Z (t) are derived in the displaced harmonic oscillator (DHO) model. Two horizontal potential displacements (δ α , δ β ) between the two electronic excited states (α and β) and the ground state are the parameters in the DHO model. The L Z (t) calculated with δ α = δ β is characterized by a regular sequence of the angular momentum pulses with a positive (or negative) constant. For a more general case with δ α ≠ δ β , the regular sequence is broken down because of the contribution of the first excited vibronic state in each electronic state to L Z (t).

We consider in a simple and general way elastic waves in isotropic and anisotropic media, their polarization, speeds, reflection from interfaces with mode conversion, and surface waves. Reflection of quasi transverse waves in anisotropic media from a free surface is shown to be characterized by three critical angles.

The peculiarities of elastic wave propagation in a bilayer medium are studied theoretically and experimentally. One (isotropic) layer was an acrylic glass plate, and the other (anisotropic) was a quartz sin gle crystal. In experiments, the elastic waves were generated by a piezoelectric transmitter and received by a piezoelectric transducer contacting the surface of the model medium. The propagation time of a quasi lon gitudinal wave was determined using high order statistics. In the general case, the incident elastic waves are split at the interface between the layers: beams undergo double reflection and triple refraction. The measured dependences of the propagation times of quasi longitudinal split waves on the angles of refraction are in sat isfactory agreement with the calculated ones. The calculation was performed by solving the Christoffel equa tion with allowance for the boundary conditions.

Recently, the pure-even high-order harmonic generation (HHG) has theoretically found by the ab initio methods for CO molecules interacting with an intense laser. An examination of this phenomenon using the analytical approach such as the Lewenstein model, and for another polar molecular with other symmetry is needed. In this study, we theoretically investigate the odd-even harmonic generation from the CO and NO molecules in the linearly polarized laser field by using the Lewenstein model. Firstly, we confirm entirely the pure-odd and pure-even emission from CO whose molecular axis is perpendicular to the polarization direction of the laser. Secondly, we show that the odd-even behavior of the HHG spectra from NO is similar to that from the CO molecule. The HOMO’s symmetricity of the linear molecule does not change the odd-even property of the HHG spectra.

Abstract. By numerically solving the time-dependent Schrödinger equation, we calculate the ionization probability of a vibrating H + 2 exposed to ultrashort intense laser fields. The results show that the ionization probability increases by time and gets a saturation value. We also find that with some first vibration levels, the ionization probability from a higher vibration level is larger than that from a lower one. However, with higher vibration levels, at a certain level the ionization probability will take maximum and decrease with next levels.

Atom in a coherent superposition state reveals an advantage in the enhancement conversion efficiency of high-order harmonic generation (HHG), which is meaningful in producing attosecond pulses. In this study, we expand to investigate a more complicated system, H\(_2^+\) molecule in the superposition of the ground and second excited states, exposed to an ultrashort intense laser pulse by numerically solving the time-dependent Schrödinger equation. Firstly, we examine the enhancement of HHG from this system. Then, we study the depletion effect on the cutoff energy of HHG spectra with the coherent superposition state. We found that these effects on the HHG from molecules are similar to those from atoms. Finally, we study the signature of the interesting effect, which is absent for atoms -- two-center interference effect in the HHG from H\(_2^+\) in the coherent superposition state. We recognize that the minimum positions in HHG from molecules in the superposition state, and in the pure ground state are the same. Especially, for weak laser intensity, in the HHG with the superposition state, the minimum due to the interference effect is apparent, while it is invisible in the HHG from pure ground state. As a result, in comparison with the ground-state molecule, the coherent molecule can be used as a more accurate tool to determine the internuclear distance of molecule.

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