



TECHNICAL ACTIVITIES 1998 -
NISTIR 6268
MISSION
ORGANIZATION
CURRENT DIRECTIONS
TECHNICAL HIGHLIGHTS
FUTURE DIRECTIONS
FUTURE DIRECTIONS
- Ultrafast Soft X-Rays. A table top soft x-ray laser operating at
1000 Hz has been developed to study time-resolved x-ray photoelectron
spectroscopy of dissociating and reacting systems. An ultrafast laser system
operating on Ti:sapphire at 800 nm produces 2.5 mJ at 1000 Hz,
with 75 fs pulse duration. The ultrafast laser is focused into a jet of
neon rare gas, also pulsed at 1000 Hz. High harmonics are generated up to
about 90 eV photons. The harmonics are separated with a grazing incidence
grating and approximately 3 billion photons per sec are estimated thus far
at 80 eV. In new experiments, these photons will be used to probe the core
level x-ray photoelectron spectra of atoms in dissociating molecules and
clusters. (S.R. Leone).
- Single Molecule and Single Quantum Dot Confocal Microscopy. In close
conjunction with the NSOM efforts, we are developing new capabilities in high
sensitivity detection and spectroscopic characterization of single molecules.
This is based on laser excitation and fluorescence detection via scanning
confocal microscopy, coupled with a high sensitivity, CCD array spectrometer.
Most recently, we have been using this new capability to investigate the
photobleaching dynamics of individual dye molecules, green fluorescence
protein, and CdSe quantum dots. Our long-range interest is in developing
methods to optically tag biomolecules at single molecule sensitivity and high
spatial resolution for probing physical properties of biopolymers. Particularly
interesting is the observation of multiple time scales for fluorescence from
individual quantum dots, ranging from the fast radiative and nonradiative
recovery on the ns time scale to so called "blinking" fluorescence
intermittency due to multiphoton ionization of single quantum dots on the
millisecond to second time scale. (For example, see cover figure for this
section.) (D.J. Nesbitt).
- Coherent Phenomena in Optically Dense Material. Coherent phenomena
in semiconductors have been the subject of significant research during the last
decade due to the development of lasers capable of producing pulses with widths
below 1 ps. The general understanding of coherent phenomena is derived
from extensive work in dilute atomic vapors. Semiconductors display new
phenomena and modifications to well known phenomena. Some of these are due to
the large optical density; others are unique to the many-body interactions
among mobile carriers. Coherent phenomena are not well understood in dense
atomic vapors either. Experiments are being set up to explore coherent
phenomena in semiconductors and dense atomic vapors. Comparison of the
phenomena in the two media should yield interesting insights.
(S.T. Cundiff).
- Nonlinear Spectroscopy of Mixed-Valent Materials. Mixed valent
materials have a band of strongly localized f-electrons energetically
overlapping a conduction band of itinerant d-electrons. The interaction results
in strong electron correlation and the opening of an energy gap. Electron
correlation is important in many solids of current interest, including high
Tc superconductors, colossal magneto-resistance materials, Mott
insulators and Kondo insulators. Recent theoretical results predict that
electron pairing should occur, leading to ferroelectric behavior and a breaking
of the inversion symmetry present in the crystal structure. This will imbue the
material with a second order, nonlinear, optical response. The nonlinear
optical response will be resonantly enhanced near the gap energy, which is
about 10 meV. Experiments are being set up to search for this nonlinearity
using intense pulses of THz radiation. The THz pulses are generated using
photoconductive emitters excited by ultrashort optical pulses.
(S.T. Cundiff).
- Guided-Atom Optics. A new generation of atom-guiding technology is
currently in development. Atoms will be guided by the magnetic fields generated
by the electrical currents in a pair of lithographically patterned wires. The
atoms will "fly" just a few microns above the substrate, much like
the cars of a miniature, magnetically levitated train. This work is an offshoot
of the ongoing QPD experiments in which atoms are optically guided inside of
hollow glass fibers. The lithographic method used to pattern the "train
tracks" will be readily extended to create "switches" (i.e.,
atomic beam splitters) and "loop-the-loops" (i.e., Sagnac-type
circular atom interferometers.) Initial experiments will inject laser-cooled
atoms into the guide; second generation experiments will couple-in
Bose-Einstein condensates. Ultimately the technology will enable the
construction of robust, large-area, atom-interferometers with enormous
sensitivity to electric, magnetic, and gravitational fields and to various
spatial and temporal gradients of those fields. (E.A. Cornell).
- W.M. Keck Optical Measurement Laboratory. JILA has received a grant
from the W.M. Keck foundation to establish an Optical Measurement Laboratory.
It will support ongoing NIST research in many areas, including that on
Bose-Einstein condensation, ultrafast optical processes, optical nano-material
science, and near field scanning microscopy. This state-of-the-art facility
will encompass three main areas: optical materials preparation,
nanofabrication, and laser characterization. A clean area is being constructed
and a suite of instrumentation is being assembled to provide the required new
capabilities.
Mission | Organization | Current Directions | Technical Highlights |
Future Directions
TECHNICAL ACTIVITIES 1998 - Contents

Pages designed and maintained by the Office of ECSED.
Inquiries or comments: Feedback.
Online: April 1999