Atomic Physics Division
- The strategy of the Atomic Physics Division is to develop and apply
atomic-physics research methods to achieve fundamental advances in measurement
science relevant to industry and the technical community, and to produce and
critically compile physical reference data.
|
GOAL: To determine
atomic properties
and explore their
applications |
| Strategic Focus Areas: |
| |
First |
Light-Matter
Interactions and Atom Optics - to advance the physics of
electromagnetic-matter interactions and to explore new applications for laser
cooled and trapped atoms. |
| Second |
Plasma and X-Ray
Measurement Methods - to develop advanced optical and x-ray
measurement techniques for applications involving laboratory and space plasmas,
thin-film structures, and nanoscale devices. |
| Third |
Nanoscale and
Quantum Metrology - to advance measurement science at the
atomic and nanometer scale, focusing on ultraprecise length-displacement
measurements, x-ray and gamma-ray precision metrology, and nanooptics and
nanosystems modeling. |
| Fourth |
Critically Evaluated
Atomic Data - to produce reference data on atomic structure and
to critically compile reference data for scientific and technological
applications. |
Nanoscale and Quantum Metrology:
to advance measurement science at the atomic and
nanometer scale, focusing on ultraprecise length-displacement measurements,
x-ray and gamma-ray precision metrology, and nanooptics and nanosystems
modeling.
INTENDED OUTCOME AND
BACKGROUND
Optical and x-ray interferometry is being used to complete the
intercomparison phase in displacement interferometry. We are measuring the
effect of diffraction on interferometric measurements through comparison of
Michelson and Fabry-Perot interferometry. We are evaluating a hybrid
positioning system in which long-range positioning over 50 mm is provided
by a high-quality commercial translation stage, and guiding errors are
compensated by a fine positioning stage incorporating a multichannel
closed-loop servo system. We are also working on the direct link of a
displacement measurement to a cesium clock by means of a frequency comb. The
goal is to provide the first measurement of a displacement directly related to
the definition of the meter, without the intervention of a calibrated reference
laser.
The wavelengths and energies of x- and gamma-ray transitions are determined
for applications in crystallography and x-ray astronomy, for fundamental
studies of the properties of matter, and for the fundamental constants. Crystal
diffraction is the principal measurement tool, and the lattice spacings of
nearly perfect crystals are determined by comparison to standard crystals.
Diffraction angles are measured interferometrically or with well-calibrated
encoders. For lower-precision measurements, curved crystals are used with
position-sensitive detectors.
Accomplishments
Optical Fiber Tapering System for Supercontinuum Generation
| |
Figure 7. Tapered optical fiber shifts the frequency spectrum of
mode-locked femtosecond laser output from 850 nm to cover most of the
visible spectrum. The vertical scale is linear; the scales for input and output
are different. |
The frequency comb produced by a mode-locked femtosecond laser has
revolutionized optical-frequency metrology and is now being applied to
displacement metrology. In order to relate the visible wavelengths used for
interferometry with an infrared femtosecond laser, we shift the spectrum of the
femtosecond laser by means of nonlinear optics in a fiber that is tapered to
such a small diameter that the light propagates in the exterior of the cladding
rather than the core.
We have constructed a facility to taper optical fibers to a well-controlled
geometry. The facility consists of four steppermotor-driven stages that
simultaneously pull the fiber as it is being heated by a very small, traveling
flame. By controlling the oscillatory motion of the flame as the fiber is
pulled, we can force the fiber to adopt almost any arbitrary shape.
Figure 7 shows the spectrum from a fiber whose diameter had been reduced from
125 µm to 2.7 µm and which was pumped at 850 nm. We have
successfully observed the beat from such a fiber and a helium-neon laser at
633 nm.
Designing the Nanoworld: Atomic-Scale Simulations of Nanostructures and
Nanodevices
| |
Figure 8. Schematic of a self-assembled pyramidal quantum dot. Atomic
positions used in the modeling are indicated. |
Atomic-scale simulations of the electronic and optical properties of complex
nanosystems at the meso/molecular interface are being carried out. These
systems include nanocrystals, self-assembled dots (as shown in Fig. 8),
nanodot arrays and solids, molecular electronics, biomolecules, and
bio/nanohybrids.
Atomic-scale variations in geometry, size, shape, and composition critically
impact the functionality of these nanosystems. For example, our simulations
show that the optical response of arrays of nanodots can be turned on or off
simply by changing the number of atoms between the dots. Our studies of doped
fullerenes show that dopants exist for p- and n-type doping, that these doped
fullerenes can be combined to form molecular rectifiers, and that their
properties can be tailored as dopant atoms are added one-by-one.
These simulations provide benchmarks for precision experimental tests of the
atomic-scale sensitivity of nanosystems. The work is providing the foundation
needed to build design tools for engineering nanolasers, detectors, biomarkers
and sensors, quantum devices, and nanomaterials.
First strategic focus |
Second strategic focus |
Third strategic focus |
Fourth strategic focus
"Technical Activities 2002" - Table of Contents |
|
