Abstract
When a molecule is placed in a nonresonant laser field, the Stark interactions between the laser field and the induced molecular dipole result in a mechanical force on the molecule. This nonresonant dipole force is proportional to the intensity gradient of the laser, thus requiring a strong and focused pulsed laser for a sizable impact on the molecule. 36.4 mJ pulses of a 1064 nm Nd:YAG laser focused with a 17.5 cm focal length convex lens produced a 6.4 m/s change in the transverse velocity of a CS2 molecular beam. Using spherical mirrors with shorter focal lengths such as 10.0, 7.5, and 5.0 cm, dipole forces of similar magnitude were obtained with laser pulses of much lower energies. In particular the 5.0-cm focal length spherical mirror provided an 11.3 m/s change in the transverse velocity using 3.6 mJ laser pulses. This corresponds to 18-fold increase in the deflection efficiency, the ratio between the maximum velocity change and the pulse energy. From the improved efficiency, the nonresonant dipole force can be exerted with ease.
Highlights
Molecule optics that controls the molecular external degrees of freedom using optical forces from light-matter interactions has grown into a major branch of physics [1, 2]
Using focusing units of different focal lengths, pulses from a 1064 nm Nd:YAG laser were focused on a CS2 molecular beam to compare the nonresonant dipole force efficiency
Using a short focal length mirror, we demonstrated that a low energy laser pulse could exert a nonresonant dipole force on the molecule to yield a sizable impact on the molecular motion
Summary
Molecule optics that controls the molecular external degrees of freedom using optical forces from light-matter interactions has grown into a major branch of physics [1, 2]. Some examples include a molecule lens focusing a molecular beam [3–5], a molecule prism spatially separating a molecular mixture beam [6], a moving periodic optical potential slowing down or accelerating molecules [7–9], and correlated rotational alignment spectroscopy with aligning molecules non-adiabatically [10] Ideas such as deflection of pre-aligned molecules were proposed [11, 12]. One practical difficulty in molecule optics is the use of a high energy laser which causes issues with molecular ionization and optical component damages. We solved these problems by tight focusing of a laser exerting dipole forces. The deflection efficiency, given as the ratio of the maximum velocity change and the pulse energy, was improved 18 times greater with a tighter focusing of the IR laser
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