Eur. Phys. J. D (2013) 67: 227
https://doi.org/10.1140/epjd/e2013-40383-y

Regular Article

Efficient field-free orientation of CO molecules using a three-step excitation scheme

School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024, P.R. China

^a e-mail: shlcong@dlut.edu.cn

Received: 30 June 2013
Received in final form: 16 August 2013
Published online: 1 November 2013

Abstract

An efficient three-step excitation scheme is proposed to achieve the strong molecular orientation. By taking the CO molecule for example, via the Raman excitation by the femtosecond pulse L₁ and subsequently resonant excitations by a single-cycle THz pulse L₂, the high degree of the field-free orientation of |⟨ cosθ ⟩ |_max = 0.8921 can be obtained at the rotational temperature T = 0 K. An additional single-cycle THz pulse L₃ is introduced to further regulate the population distribution on rotational states and decrease the reduction of the orientation originating from the offset phase. With the increase of the central frequency ω₃ of L₃, the optimal |⟨ cosθ ⟩ |_max increases monotonically. When ω₃ = 1.0 THz, the degree of the field-free orientation reaches |⟨ cosθ ⟩ |_max = 0.9401. Moreover, our scheme is robust against the rotational temperature. Although the molecular orientation weakens with the rise of rotational temperature, |⟨  ⟨ cosθ ⟩  ⟩ | > 0.5 is still obtained until T = 22.8 K.