Orienting CO molecules with an optimal combination of THz and laser pulses: Optimal control simulation with specified pulse amplitude and fluence

Abstract

Pulse-amplitude and fluence-specified optimal control simulation with linear (dipole) and nonlinear (polarizability) interactions is applied to find the best way to orient CO molecules with a combination of THz and laser pulses. The optimal pulses are numerically designed with a specified maximum amplitude of the THz pulse and a specified fluence of the laser pulse within the ranges of E max = 50 MV/m ∼ 150 MV/m and f 0 = 2.5 J/cm 2 ∼ 4.5 J/cm 2 at temperature T = 0 K ∼ 10 K. The optimal pulse almost always consists of a near-single-cycle THz pulse of zero area and a laser pulse that is mainly composed of three subpulses. There is no temporal overlap between the THz pulse and the laser subpulses. The THz pulse, which virtually contains no dc components, induces rotational transitions in a resonant way, whereas the three laser subpulses efficiently induce multiple rotational transitions through Raman scattering. Comparing the optimal control simulations with and without laser pulses, the laser pulses effectively increase the degrees of orientation by approximately half through the polarizability interaction with inversion symmetry.

Unified parameter for localization in isotope-selective rotational excitation of diatomic molecules using a train of optical pulses

“…The rotation of small molecules has been studied from the viewpoint of non-adiabatic molecular alignment [1][2][3] or molecular orientation [4][5][6][7][8][9][10]. Non-adiabatic molecular alignment has been experimentally realized using non-resonant broadband optical pulses [11,12].…”

Control of molecular orientation with combined near-single-cycle THz and optimally designed non-resonant laser pulses: Carrier-envelope phase effects

“…The purpose of the present study is to examine CEP effects on the hybrid control scheme that combines a fixed nearsingle-cycle THz pulse and an optimal non-resonant laser pulse. As it would be meaningful to compare the present results with the full-optimization results in our previous study [37], we use CO molecules as the target molecule.…”

“…The positive constant, , represents the instantaneous penalty, and will be used to adjust the pulse fluence in the optimal control simulation [12,37].…”

“…In our previous study [37], we have adopted a full-optimization approach that numerically designs both THz and laser pulses with the aim of orienting CO molecules. We have proposed a pulse-amplitude-and pulse-fluence-specified optimal control simulation to quantitatively compare the results in several ranges of the peak amplitudes of the THz pulses, the laser pulse fluence, and temperature.…”

“…A recent topic of the hybrid approach is to use the combination of near-single-cycle THz and laser pulses [34][35][36][37][38] because of the development of the THz pulse generation techniques [26,27]. Some studies have introduced a pre-laser pulse to prepare an aligned superposition state and applied a near-single-cycle THz pulse to this state with a suitable time delay [34][35][36].…”