Synopsis: Orientation without perturbation

Femtosecond light pulses at two different frequencies are effective in aligning and orienting molecules without the need for a strong static field.
Synopsis figure
Illustration: S. De et al., Phys. Rev. Lett. (2009)

Analyzing the structure of molecules in a gas or liquid is akin to x raying a classroom of unruly kids randomly jostling and changing their positions and orientations. Getting a handle on the detailed structure of molecules requires some means of lining them up to avoid orientational averaging and smearing. Researchers have developed techniques for orienting molecules, but so far they have relied on strong electric fields, which may perturb the molecules or interfere with some other aspect of the analysis. Taking advantage of femtosecond laser technology, Sankar De and colleagues from Kansas State University, US, and the Max Planck Institute in Garching, Germany, report in Physical Review Letters their success in achieving field-free orientation of carbon monoxide molecules.

De et al. used overlapping femtosecond pulses at 800nm and 400nm to excite odd and even angular momentum states of the CO molecules, enabling net macroscopic orientation. Changing the optical phase between the two pulses enabled the group to not only align the carbon monoxide molecules (i.e., with their molecular axes pointing the same direction) but orient them as well (i.e., all the carbons pointing in the same direction). Another 800nm pulse striking the molecules caused a “Coulomb explosion” and ejection of carbon ions that were detected to confirm the molecular orientation. By grabbing hold of molecules and orienting them neatly without strong fields, researchers should be able to carry out improved ultrafast structural imaging and molecular tomography. – David Voss


Features

More Features »

Announcements

More Announcements »

Subject Areas

Atomic and Molecular Physics

Previous Synopsis

Nanophysics

Small-scale hydraulics

Read More »

Next Synopsis

Particles and Fields

The shortest known photon pulses

Read More »

Related Articles

Viewpoint: Sharpening the Features of Optical Lattices
Atomic and Molecular Physics

Viewpoint: Sharpening the Features of Optical Lattices

Lasers trap cold atoms in a lattice of potential barriers much narrower than the lasers’ wavelength. Read More »

Focus: <i>Video</i>—Condensate Duo Puts on a Show
Atomic and Molecular Physics

Focus: Video—Condensate Duo Puts on a Show

Simulations of the mixing of two oppositely polarized Bose-Einstein condensates produce fingering patterns that look like those of classical fluids. Read More »

Viewpoint: Atoms Oscillate Collectively in Large Optical Lattice
Atomic and Molecular Physics

Viewpoint: Atoms Oscillate Collectively in Large Optical Lattice

By coupling atoms in an optical lattice to a thin elastic membrane, researchers have demonstrated a dynamic instability that is evidence of collective atomic motion. Read More »

More Articles