Molecular Orientation-Induced Second-Harmonic Generation: Deciphering Different Contributions Apart

Abstract

We demonstrate and explore an all-optical technique for direct monitoring of the orientation dynamics in gas-phase molecular ensembles. The technique termed “MOISH” utilizes the transiently lifted inversion symmetry of polar gas media and provides a sensitive and spatially localized probing of the second-harmonic generation signal that is directly correlated with the orientation of the gas. Our experimental results reveal selective electronic and nuclear dynamical contributions to the overall nonlinear optical signal and decipher them apart using the “reporter gas” approach. “MOISH” provides new crucial means for implementing advanced coherent rotational control via concerted excitation by both terahertz and optical fields.

Full control of the orientation of non-symmetric molecules using weak and moderate electric fields

“…Regarding molecular orientation control, the Krotov algorithm 31,37,38 is used to design terahertz laser pulses, 39 or to manipulate the permanent dipole orientation of molecular ensembles, as reported in various studies. [40][41][42][43] In addition, this algorithm has been used to optimize alignment of molecules immersed in a thermal bath. 44,45 In this work, we consider a non-symmetric molecule, and apply the QOC algorithm to optimize the orientation along several molecular directions.…”

Quantum control of field-free molecular orientation

“…Quantum control of molecular rotation is an active research field within atomic, molecular, and optical physics, given its fundamental significance in physics, chemistry, and quantum information science. [1][2][3][4][5] Apart from its impact on chemical reactivity, [6][7][8] this technique has found numerous applications, including molecular phase modulation, 9 ultrashort pulse compression, 10 nanoscale design, 11 high-order harmonic generation, [12][13][14] molecular rotational echoing, 15,16 and ultrafast X-ray diffraction. 17,18 Significant experimental and theoretical efforts have been devoted to achieve desired rotational motions of molecules, resulting in molecular alignment or orientation in space.…”

Echo-enhanced molecular orientation at high temperatures

“…For chiral molecules, it is possible to induce orientation by using laser pulses with twisted polarization [32][33][34][35][36][37][38]. With the advance in terahertz (THz) technology, it has become possible to orient polar molecules using single-or half-cycle THz pulses through coupling to the permanent molecular dipole moment [39][40][41][42][43][44][45][46][47][48][49].…”