"Snapshots" of ultrafast rotating nitrogen
molecules at a hundred billion per second (femtosecond = a quadrillionth
part of one second).
Credit: IMS/NINS
Can you imagine how subnano-scale molecules
make an ultrafast rotation at a hundred billion per second? Do the
ultrafast rotating subnano-scale molecules show a wave-like nature
rather than particle-like behavior? The Japanese research team led by
Professor Yasuhiro Ohshima at the Tokyo Institute of Technology, and Dr
Kenta Mizuse at the Institute for Molecular Science, National Institutes
of Natural Sciences, successfully took sequential "snapshots" of
ultrafast unidirectionally rotating molecules at a hundred billion per
second.
To visualize such an ultrafast molecular rotation, the team developed
a Coulomb explosion imaging setup with regulating rotational direction
by a pair of time-delayed, polarization-skewed laser pulses. In the
sequential "snapshots," the team successfully reported high-resolution
direct imaging of direction-controlled rotational wave packets (RWPs) in
nitrogen molecules, and the quantum wave-like nature was successfully
observed. The result will guide more sophisticated molecular
manipulations, such as an ultrafast molecular "stopwatch." This result
is published in Science Advances.
Rotational wave packets (RWPs) are time-varying states of motion of
rotating microscopic objects like molecules, and they change shapes in
an ultrafast time scale, typically some parts in a trillion second. More
importantly, because RWPs are governed by the fundamental microscopic
physical laws, quantum mechanics, they show a wave-like nature, much
different from what macroscopic things exhibit. So, RWPs are one of the
ideal play grounds for examining the connection between quantum and
classical worlds.
In the present study, the RWPs were created by using a pair of
ultrafast laser pulses, of which mutual delay and polarization were
properly adjusted. In addition, by using a specially designed
ion-imaging setup, the team got images of unidirectional RWPs at a
viewing angle that the previous 2D imaging studies could not adopt. As a
result, the team succeeded in recording a series of images of
time-varying molecular angular distribution with high-spatial
resolution, which is nothing but a "movie" on the RWPs with a defined
sense of rotation. The movie clearly shows the wave-like nature of the
RWPs. Multiple running waves get together at some time to give a highly
concentrated spatial orientation and split after a while into parts
having different angular velocities, while the overall movement keeps
rotating in one direction. This propagation of wave packets may well be
expected as a pedantic example of a simple quantum system like rotating
molecules in free space, for which mutual interaction is essentially
inoperative. Nevertheless, it has never been visualized experimentally
so far.
There have been many proposals for novel application of
unidirectional RWPs. For instance, unidirectionally rotating molecular
gas ensembles are expected to make sophisticated polarization shaping of
ultrafast light pulses. In addition, unidirectional RWPs exhibiting
cogwheel like motion are expected to be used as a "stopwatch" to measure
the precise time difference between pulses from two independent
ultrafast laser systems.
In a purely fundamental point of view, on the other hand, it is so
challenging to experimentalists to explore how the wave-like nature of
RWPs is approaching the particle-like behavior for a macroscopic object.
It is also of great interest to experimentally track the loss of the
wave-like character by a mutual or external interaction. Professor
Ohshima said, "We hope our high-resolution RWP imaging to be applicable
in making a movie on such crossovers from quantum to classical worlds."
Story Source:
The above post is reprinted from
materials provided by
National Institutes of Natural Sciences.
Note: Materials may be edited for content and length.
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