|
We demonstrate control of terahertz (THz) waves developing novel
devices in the THz regime: THz pulse shapers. THz technology is a
relatively unexplored subject, yet the importance of THz wave
manipulation cannot be emphasized enough considering its potential
application to THz imaging systems, ultrafast optical signal
processing, ultrahigh-speed computing, quantum information
science, nanotechnology, and chemical reaction dynamics among
other areas. THz time-domain spectroscopy (THz-TDS) can assess the
performance of the THz pulse shapers monitoring time-dependent THz
wave propagation. THz-TDS permits precise measurements not only of
the amplitude but also of the phase of THz waves, thus a
comprehensive assessment of the THz devices can be achieved. The
phase sensitivity is also vital to many applications such as
high-contrast THz imaging and quantum control of semiconductor
nanostructures. We develop arbitrary THz pulse generators
synthesizing THz waveforms via optical rectification in
pre-engineered domain structures of poled nonlinear crystals using
femtosecond lasers. The terahertz waveforms coincide with the
crystal domain structures. The one dimensional nonlinear wave
equation simulates the experimental results with a good
qualitative agreement. The ratio of the domain length to the
optical pulse length in the crystal turns out to be the crucial
limiting factor to generating optimum terahertz fields and
preventing waveform distortion. Optical pulse shaping techniques
is integrated into the THz pulse generators to extend the scope of
THz pulse shaping control. Continuously tunable narrow-band THz
pulses are generated in a fanned-out periodically-poled lithium
niobate crystal. We measure the free induction decay of rotational
transitions in gas-phase HCl molecules using the narrow-band THz
pulses. The shape of the multi-cycle THz pulses is controlled by
adjusting the relative time delay and intensity between the two
optical pulses.
|
