The quantum control (or coherent control) has been extensively investigated, which has a potential to control the properties and functions of matter through the direct manipulation of the quantum state and its quantum dynamics by using a coherent nature of laser fields. I have investigated the quantum control concerning molecular orientation by the phase-controlled two-color laser fields consisting of a fundamental light and its second-harmonic light.

The total electric field of the linearly polarized laser fields of the two frequencies, the fundamental (ω) and its second harmonic (2ω), is given by E(t) = E 1 cos(ωt) + E 2 cos(2ωt + φ ), where E 1 and E 2 are the amplitudes of the electric fields and φ is the relative phase difference between the fundamental light and the second harmonic light. The phase-controlled ω+2ω field has a characteristic asymmetry: the amplitude of the electric field in the negative direction is twice that in the positive direction. The effects regarding molecular orientation include two main contributions: (1) dynamic molecular orientation? m olecules can be dynamically oriented along the laser polarization direction by the torque generated by the interaction between nonresonant laser fields and the dipole moment (induced dipole or permanent dipole) of molecules; (2) selective ionization of oriented molecules ?molecules initially oriented in a certain direction with respect to the laser polarization have larger ionization rates, resulting in selective ionization of oriented molecules among randomly oriented molecular ensembles.

The phase-controlled two-color laser fields have a potential to open the door for exploring a new type of phase-dependent quantum phenomena in the light-matter interaction, and to propose a new method for molecular manipulation. Especially, quantum control of molecular orientation may lead to precision spectroscopy, nanoscale design, or chemical reaction control because the orientational averaging that leads to loss of information or disturbs the homogeneous molecular manipulation can be eliminated.