Achieving high molecular alignment and orientation for CH$$_3$$F through manipulation of rotational states with varying optical and THz laser pulse parameters

Abstract

AbstractIncreasing interest in the fields of high-harmonics generation, laser-induced chemical reactions, and molecular imaging of gaseous targets demands high molecular “alignment” and “orientation” (A&O). In this work, we examine the critical role of different pulse parameters on the field-free A&O dynamics of the CH$$_3$$ 3 F molecule, and identify experimentally feasible optical and THz range laser parameters that ensure maximal A&O for such molecules. Herein, apart from rotational temperature, we investigate effects of varying pulse parameters such as, pulse duration, intensity, frequency, and carrier envelop phase (CEP). By analyzing the interplay between laser pulse parameters and the resulting rotational population distribution, the origin of specific A&O dynamics was addressed. We could identify two qualitatively different A&O behaviors and revealed their connection with the pulse parameters and the population of excited rotational states. We report here the highest alignment of $$\langle {\mathrm{cos}^2\theta }\rangle = 0.843$$ ⟨ cos 2 θ ⟩ = 0.843 and orientation of $$\langle {\mathrm{cos}(\theta )}\rangle = 0.886$$ ⟨ cos ( θ ) ⟩ = 0.886 for CH$$_3$$ 3 F molecule at 2 K using a single pulse. Our study should be useful to understand different aspects of laser-induced unidirectional rotation in heteronuclear molecules, and in understanding routes to tune/enhance A&O in laboratory conditions for advanced applications.