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

Focus: Atomic Impersonator
Optics

Focus: Atomic Impersonator

Calculations show that a carefully engineered laser pulse can induce an atom to emit light as if it were a different atom. Read More »

Viewpoint: Transportable Clocks Move with the Times
Optics

Viewpoint: Transportable Clocks Move with the Times

Transportable atomic clocks are now operating with fractional-frequency uncertainties below one part in 1016, opening up new applications. Read More »

Viewpoint: Trapped Ions Stopped Cold
Optics

Viewpoint: Trapped Ions Stopped Cold

A novel method for cooling trapped ions could boost the accuracy of atomic clocks. Read More »

More Articles