Junichi Hamazaki

Broadband frequency-chirped terahertz-wave signal generation using periodically-poled lithium niobate for frequency-modulated continuous-wave radar application

We have proposed a method by using a nonlinear optical technique to generate frequency-modulated (FM) signals in the terahertz (THz) band with much broader bandwidth. Periodically-poled lithium niobates (PPLNs) are excited by ultrashort pulses, and linearly frequency-chirped THz pulses are obtained by changing the periodicity of the PPLN gradually. The bandwidth achieved is approximately 1 THz at a center frequency of 1.5 THz. Using this wave in a FM continuous (CW) radar system is expected to result in a range resolution of ~150 μm. This FM-THz signal generation technique will thus be useful in or future civil safety applications requiring high-resolution ranging or imaging.

Effects of chirp of pump pulses on broadband terahertz pulse spectra generated by optical rectification

The effects of the chirp of the pump pulse in broadband terahertz (THz) pulse generation by optical rectification (OR) in GaP were systematically investigated. It was found that the pre-compensation for the dispersion of GaP is important for obtaining smooth and single-peaked THz spectra as well as high power-conversion efficiency. It was also found that an excessive amount of chirp leads to distortions in THz spectra, which can be quantitatively analyzed by using a simple model. Our results highlight the importance of accurate control over the chirp of the pump pulse for generating broadband THz pulses by OR.

High power THz radiation using double-clad Yb-doped fiber amplifier

Using a double-clad Yb-doped fiber amplifier system, optical pulses with a power of >3 W and a width of 110 fs is obtained. Using this amplified pulse, THz generation emitted from DAST is measured by pyroelectric detector. A square-law dependence of the THz power on the pump power is observed.

High-power ultrashort pulse amplifier using double-clad Yb-doped fiber for high-power high-efficiency THz pulse generation

Optimizing high-power ultrashort pulse amplifier using double-clad Yb-doped fiber, maximum output power of >3 W with a pulse width of 110 fs without pedestal component is obtained. Using this pulse, high-power THz pulse generation is measured by a pyroelectric detector with a low sensitivity.

Blue and green cooperative luminescence of highly Yb-doped optical fiber

Blue luminescence emitted from ytterbium-doped fiber under infrared excitation was observed, along with well-known green cooperated luminescence. We suggest blue luminescence is due to higher-order cooperated luminescence related three excited ytterbium ions.

Characterization of absorption spectrum of ethanol gas for use as terahertz alcohol sensor

The absorption spectra of pure ethanol gas and ethanol gas mixed with air were characterized for examining the use of ethanol gas as a terahertz alcohol sensor. A comparison of the spectra of both gases showed that the absorbance of the latter was ~1.3 times greater than that of the former.

Fast and accurate broadband THz time domain spectroscopy using rapid scanning delay line

To produce accurate broadband THz time-domain spectroscopy system, we employ a rapid scanning delay line. Then, measurement time was reduced to ~1 minute, and intensity stability of THz spectrum was well improved.