High degree of molecular orientation by a combination of THz and femtosecond laser pulses

Abstract

We propose a method for achieving molecular orientation by two-step excitation with intense femtosecond laser and terahertz (THz) pulses. First, the femtosecond laser pulse induces off-resonant impulsive Raman excitation to create rotational wave packets. Next, a delayed intense THz pulse effectively induces resonant dipole transition between neighboring rotational states. By controlling the intensities of both the pulses and the time delay, we can create rotational wave packets consisting of states with different parities in order to achieve a high degree of molecular orientation under a field-free condition. We numerically demonstrate that the highest degree of orientation of cos θ > 0.8 in HBr molecules is feasible under experimentally available conditions.

Observation of the field-free orientation of a symmetric-top molecule by terahertz laser pulses at high temperature

“…Note that a larger degree of orientation can be achieved with the two-color mechanisms through ionization depletion [53]. In this second regime, molecular orientation has been recently addressed experimentally for linear molecules using only a THz field [54] or its combination with a laser field [55], and in [56,57] for an excitation process with two-color laser fields.…”

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

“…One numerical study reported a high degree of orientation (>0. 8) (low-temperature limit) [34] with experimentally available conditions. In the recent experiment by Egodapitiya et al [36], the effectiveness of the introduction of a pre-laser pulse prior to a near-single-cycle THz pulse was confirmed, in which the degree of orientation is similar in value to that achieved by the two-color scheme but is obtained with avoiding ionization.…”

“…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]. One numerical study reported a high degree of orientation (>0.…”

“…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].…”

Phase Evolution and THz Emission from a Femtosecond Laser Filament in Air

“…Recent investigations show that waveform-controlled THz radiation is of great importance due to its potential application in THz imaging and coherent control of molecular dynamics [25,26]. Can we control the waveform of femtosecond laser filament based THz radiation?…”