Compact, low power consumption, solid-state, continuous wave (CW) and room
temperature operating THz sources are required for practical applications,
such as
imaging, remote sensing, solid state spectroscopy and medical. Oyama laborator
demonstrates THz emissions at room temperature from Ge:Sb as a
photoluminescence induced by an LED. Proposed emission mechanism is based
on transitions between excited states and the ground state of the hydrogen-like
shallow emptied donor in the recombination process of optically excited
electrons
to the conduction band from the valence band (inter-band pumping) of Ge.
The stoichiometry-controlled solution growth (TDM-CVP) was successfully applied
for GaSe at constant and low growth temperature. The grown crystals have shown
ε-type monocrystalline phase, and NIR and THz absorption characteristics are
improved by applying Se vapor pressure during growth. By using the GaSe crystal,
wide frequency tunable THz wave generation was successfully achieved via DFG of
two NIR parallel beams under the collinear phase matching conditions. Stoichiometry
-controlled growth or heat-treatment of GaSe under Se vapor should be effective for
increasing the THz intensity and tunable frequency ranges.
We constructed two types of THz spectrometers with automatic scanning control
based on the difference frequency generation method by the excitation of the
phonon-polariton mode in GaP. The pulsed THz wave spectroscopic systems were
based on an optical parametric oscillator and Nd: YAG laser sources having a
frequency resolution of 1.5 GHz, and on Cr:fosterite sources with a resolution of 20
GHz. Furthermore, a 30 cm-long portable THz-wave generator is constructed
using
two Cr:Forsterite lasers pumped using a single Nd:YAG laser. In case of THz wave
generation from a waveguide-designed GaP, the waveguide effect has function of
a high-efficient generation and an elliptically polarized THz wave generation.
Following these, we recently constructed a continuous wave (CW) THz wave
spectroscopic system with laser diode excitation. The linewidth is about
4 MHz.
GaAs tunnel injection transit time (TUNNETT) diode is one of the noblest THz
wave
source with low noise and low power consumption. All these advantages enable
the
GaAs TUNNETT diode to come up with a sensitive and compact THz inspection
system.
The first operating device using the TUNNETT diode was demonstrated by
Nishizawa in 1958. The recent development of this device is realized by
molecular
layer epitaxy (MLE) for nano-structure fabrication. The TUNNETT chips fabricated
with the MLE method can work in the CW mode with fundamental oscillation
frequencies from 60 to 720 GHz. The estimated oscillation frequency limitation
is as
high as 1 THz.
TUNNETT diode oscillation is induced on the basis of the tunnel injection
transit time
effect, which is controlled by the thickness of the transit region. The
GaAs-layered
structure is fabricated by the MLE method with the precision of atomic accuracy.
Based on the tunneling phenomenon, TUNNETT can work with high frequency,
low
noise and low bias voltage compared to the other high-frequency oscillation
diodes.
The temperature stability is also very good.
 |
 |
 |
 |
 |
Y. Oyama, T. Tanabe, F. Sato, A. Kenmochi, J. Nishizawa, T. Sasaki, K. Suto
“Liquid-phase epitaxy of GaSe and potential application for wide frequency-tunable coherent terahertz-wave generation”
Journal of Crystal Growth 310 (2008) 1923-1928.
A. Kenmochi, T. Tanabe, Y. Oyama, K. Suto, J. Nishizawa
“Terahertz wave generation from GaSe crystals and effects of crystallinity”
Journal of Physics and Chemistry of Solids 69 (2008) 605-607.
J. Nishizawa, T. Sasaki, Y. Oyama, T. Tanabe
“Aspects of Point Defects in Coherent Terahertz-Wave Spectroscopy”
Physica B 401-402 (2007) 677-681.
S. Balasekaran, T. Tanabe, Y. Oyama, M. Kimura, J. Shibata, J. Nishizawa
“Spontaneous THz emission from Ge at Room temperature”
The International Workshop on Terahertz Technology 2009, Nov 30-Dec 3, 2009, Osaka University, Osaka, Japan
S. Balasekaran, T. Tanabe, Y. Oyama, M. Kimura, J. Shibata, J. Nishizawa
“Observation of room temperature THz emission based on photoluminescence from Ge”
The 34th International Conference on Infrared, Millimeter, and Terahertz Waves, September 22, 2009, Paradise Hotel, Busan Korea
S. Balasekaran, K. Endo, T. Tanabe, Y. Oyama
“Patch antenna Coupled 0.2 THz TUNNETT Oscillators”Accepted to Solid State Electronics
Y. Oyama, L. Zhen, T. Tanabe, M. Kagaya
“Sub-Terahertz Imaging of Defects in Building Blocks”NDT & E International 42 (2009) 28-33.
T. Tanabe, S. Ragam, Y. Oyama
“CW THz wave spectrometer based on diode laser pumping: Potential applications in high resolution spectroscopy”
Review of Scientific Instruments 80 (2009) 113105.
S. Ragam, T. Tanabe, K. Saito, Y. Oyama, J. Nishizawa
“Enhancement of CW THz wave power under non-collinear phase-matching conditions in DFG”
Journal of Lightwave Technology 27 (2009) 3057-3061.
K. Saito, T. Tanabe, Y. Oyama, K. Suto, J. Nishizawa
“Terahertz-wave generation by GaP rib waveguides via collinear phase-matched difference-frequency mixing of near-infrared lasers”
Journal of Applied Physics 105 (2009) 063102.
T. Tanabe, S. Ragam, Y. Oyama, T. Sasaki, J. Nishizawa, M. Ohkado N. Yamada
“Two-directional CW THz wave generation system by pumping with a single fiber amplifier of near-IR lasers”
IEEE Photonics Technology Letters 21 (2009) 260-262.
J. Nishizawa, T. Sasaki, T. Tanabe, N. Hozumi, Y. Oyama, Ken Suto
“Single-frequency coherent terahertz-wave generation using two Cr:forsterite lasers pumped using one Nd:YAG laser”
Review of Scientific Instruments 79 (2008) 036101.
K. Saito, T. Tanabe, Y. Oyama, K. Suto, T. Kimura, J. Nishizawa
“Terahertz-wave absorption in GaP crystals with different carrier densities”
Journal of Physics and Chemistry of Solids 69 (2008) 597-600.
K. Saito, K. Nozawa, T. Tanabe, Y. Oyama, K. Suto, J. Nishizawa, T. Sasaki, T. Kimura
“Fabrication and characterization of GaP photonic crystals for terahertz wave application”
Materials Transactions 48 (2007) 2340-2342.
T. Tanabe, J. Nishizawa, K. Suto, Y. Watanabe, T. Sasaki, Y. Oyama
“Terahertz Wave Generation from GaP with Continuous Wave and Pulse Pumping in the 1-1.2 μm region”
Materials Transactions 48 (2007) 980-983.
J. Nishizawa, K. Suto, T. Tanabe, K. Saito, T. Kimura, Y. Oyama
“THz Generation From GaP Rod-Type Waveguides”
IEEE Photonics Technology Letters 19 (2007) 143-145.
