Research Index / Ultrafast Science Group
People:
Faculty:
Theodore Norris
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Jing Yong Ye
Graduate Students:
Guoqing (Noah) Chang
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Hyunyong Choi
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Chuck Divin
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Kim Jackson
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Tim Meade
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Mon Myaing
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Zong-kwei (John) Wu
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Cheng (Frank) Zhong
Postdoctoral Research Assistants:
Takashi Buma
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Brian Daly
More information about the Ultrafast Science Group
Research Overview:
The research in our group centers on the propagation and applications
of ultrashort optical pulses. We have developed very-high-repetition-rate,
broadly tunable femtosecond amplifiers, and used these novel laser sources in a
wide variety of applications. We are interested in studying the dynamics of
high-speed carrier transport in semiconductors, including ballistic transport
and overshoot phenomena. Transport and relaxation processes in self-organized
quantum dots (which are being used for novel semiconductor lasers and infrared
detectors) are under active study using femtosecond spectroscopy; we have made
the first observation of the phonon bottleneck in quantum dot relaxation, and
recently have performed a comprehensive study of the gain dynamics in inverted
quantum dots. We are also investigating the dynamics of quantum well excitons in
semiconductor microcavities, including the use of coherent control of exciton
populations as a way to generate new quantum optical states in semiconductors,
and as a potential mechanism for high-speed optical switching. Femtosecond
pulses are being used for the generation and detection of coherent terahertz
radiation. Recently we have demonstrated a new technique for generating
narrowband (or even arbitrarily shaped) THz waveforms using poled lithium
niobate. Our research in semiconductor device physics is carried out in
collaboration with the Solid State Electronics Lab here at Michigan, as well as
with other groups fabricating state-of-the-art devices around the world.
The second major theme in our research is the coupling of ultrafast optics with
novel imaging techniques. By coupling femtosecond spectroscopy with near-field
scanning optical microscopy (NSOM), we were able to obtain subwavelength spatial
resolution simultaneously with 100-fs temporal resolution. In confocal
microscopy, we demonstrated real-time confocal imaging using our amplified
Ti:sapphire system. More recently, we have applied the techniques of adaptive
optics and learning algorithms to provide aberration correction in multiphoton
confocal microscopy. In a collaboration with the Center for Biologic
Nanotechnology in the Medical School, we are applying short pulse lasers to
imaging and triggering of dendrimer complexes, which are being developed as a
novel cancer therapeutic. We have recently used an optical fiber probe to
observe the targeted uptake of the dendrimers in cancer cells. Finally, we are
also applying THz techniques to imaging. We have demonstrated that, by measuring
scattered single-cycle THz fields scattered from objects, we can reconstruct an
image of the objects by time-reversing the measured waveforms and applying the
time-domain Huygens-Fresnel diffraction integral. We are presently investigating
the possibilities for applying the time-reversal technique using picosecond
acoustic pulses generated by ultrafast lasers.
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