Calculation Of Harmonic Generation Research Articles

Pulse-shape control of two-color interference in high-order-harmonic generation

We report on calculations of harmonic generation by neon in a mixed (800-nm + time-delayed 400-nm) laser pulse scheme. In contrast with previous studies we employ a short (few-cycle) 400-nm pulse, finding that this affords control of the interference between electron trajectories contributing to the cutoff harmonics. The inclusion of the 400-nm pulse enhances the yield and cutoff energy, both of which exhibit a strong dependence on the time delay between the two pulses. Using a combination of time-dependent $R$-matrix theory and a classical trajectory model, we assess the mechanisms leading to these effects.

Minor hysteresis loops and harmonic generation calculations in a generalized critical-state model.

We present analytic calculations of minor hysteresis loops obtained when a sample is subjected to a time-varying field B(t)=${\mathit{B}}_{\mathrm{dc}}$+${\mathit{B}}_{\mathrm{ac}}$ cos\ensuremath{\omega}t. We enumerate eight classes of minor hysteresis loops, and calculations are done within the critical-state model but for an arbitrary field dependence of the critical current density ${\mathit{J}}_{\mathit{c}}$(B). The sample shapes considered are the zero-demagnetization factor cases of a circular cylinder, and of a slab, in a longitudinal field. Harmonic components of the magnetization (${\mathit{M}}_{\mathit{n}}$) are numerically obtained for various forms of ${\mathit{J}}_{\mathit{c}}$(B). Our results bring out the importance of the sample shape used in the calculation and also point out the features in ${\mathit{M}}_{\mathit{n}}$ vs ${\mathit{B}}_{\mathrm{dc}}$ that clearly reflect the details of the field dependence in ${\mathit{J}}_{\mathit{c}}$(B).

Calculation of harmonic generation during the multiphoton ionization of the hydrogen atom

The response of a hydrogen atom to an intense nonresonant laser field is investigated by direct numerical solution of the time-dependent Schrodinger equation. This calculation is nonperturbative and does not involve the eigenstates of the field-free atom. An ionization rate for three-photon ionization is calculated and found to be in excellent agreement with previous values. The time-dependent electric dipole moment is calculated; its Fourier transform yields the spectrum of scattered light. Odd-order harmonic peaks through at least the 25th order are present in the spectrum.