A Numerical Investigation of Sidebands in High Harmonic Spectra

A Numerical Investigation of Sidebands in High Harmonic Spectra When an atom is subjected to coherent electromagnetic radiation, it is possible for its electrons to be excited by the electric field that is inherent to this radiation. A commonly used source for coherent electromagnetic radiation is a laser, which delivers an electric field that oscillates in time. High harmonic generation (HHG) is the process of applying a strong laser field to a material, such that one of its electrons is accelerated away from the atom, only to be driven back toward it by the oscillating laser field. As the electron is repeatedly accelerated away from and back to this ion, it emits photons that are of odd-integer harmonics of the driving field. In other words, light is emitted at frequencies that are odd integer multiples of the laser frequency. When a second, weaker field is applied to the system, the trajectory of the electron is perturbed at its maximum distance from the ion. This process causes a signal to occur in the harmonic spectrum that is characteristic of the perturbing field energy. This signal is referred to as sidebands due to their shape and the way they appear on either side of the even harmonics. These sidebands have been shown to contain valuable information regarding the optical free-induction decay of complex biomolecules, which can be used to spectroscopically identify these molecules. Numerical simulations of this physical process were performed using the split-step Fourier method of solving the time-dependent Schrödinger equation. The results of these simulations provide insights on how to optimize the signal of the sidebands in future laboratory experiments