Junichi Nishizawa

Frequency-tunable high-power terahertz wave generation from GaP

A frequency-tunable terahertz wave was generated from GaP crystals using an optical parametric oscillator as the pump source and a YAG laser (1.064 μm) as the signal source. By tuning the very small angle, θin, between the pump and signal light beam directions, tunable terahertz waves over the frequency range from 0.5 to 3 THz were obtained. The THz frequency changed almost linearly with the angle θin. The precise noncollinear phase matching condition is discussed. The pulsed peak power of the THz wave was as high as 480 mW at 1.3 THz.

Terahertz-wave generation by GaP rib waveguides via collinear phase-matched difference-frequency mixing of near-infrared lasers

We constructed rib waveguides from GaP material using an inductively coupled plasma reactive ion etching technique based on Ar/Cl2 gas application. We obtained a waveguide with a rib height of 200 μm. Terahertz-wave generation from the GaP-crystal rib waveguides was demonstrated via collinear phase-matched difference-frequency mixing of near-infrared light. The terahertz output peak corresponding to the fundamental modes appeared around 0.75 THz for a 1-mm-wide rib waveguide. The position of the fundamental mode shifted to 1.32 THz for a 200-μm-wide waveguide, which is attributable to the two-dimensional confinement of the terahertz waves in the waveguide. The conversion efficiency was enhanced in the rib waveguide compared to that in both slab waveguides and bulk GaP crystals.

Two-Directional CW THz Wave Generation System by Pumping With a Single Fiber Amplifier of Near-IR Lasers

We constructed a two-directional continuous-wave (CW) terahertz (THz) wave generation system with laser diode pumping. The generation method is based on difference frequency generation (DFG) of two near-infrared (NIR) lasers by excitation of phonon polaritons in a GaP crystal. The two NIR lasers for DFG are amplified simultaneously using one ytterbium-doped fiber amplifier (FA). Efficient beam overlapping of the NIR lasers was achieved on the GaP crystal surface. This system consists of a simple optical design with a single FA. Narrow linewidth CW THz waves, which are generated in two directions, can be applied to high-resolution spectroscopy.

Terahertz wave generation and Raman amplification in semiconductors

History and recent developments of terahertz devices utilizing lattice and molecular vibration are presented. In particular, semiconductor Raman oscillator and amplifier, parametric generation of terahertz wave using polariton-phonons in dielectrics and semiconductors are discussed, together with future important applications in the field of medicine, biology, and pharmacy.

Developments of Terahertz wave generation technologies

Recent developments of terahertz wave generation devices utilizing lattice and molecular vibration are introduced. They are semiconductor Raman laser and amplifier, parametric generation of terahertz wave using phonon-polaritons in semiconductors and dielectrics, together with electronic devices: TUNNETT diode and ISIT. Future important applications will be in the field of medicine, biology, and pharmacy.

CW THz-wave generation from GaP pumped with semiconductor lasers and its applications for high-resolution spectroscopy

We have developed a continuous wave (CW) terahertz (THz) wave generation by near infrared laser diode (NIR-LD) pumping based on non-collinear phase-matched difference frequency generation (DFG) in a GaP crystal. The THz output power is improved at suitable length of GaP and NIR beam spot size. By using this generator, we measured spectra with high resolution.

Low-frequency dynamics of hydrogen-bonding small organic molecules

Single frequency coherent terahertz-wave generation method is used to obtain low-frequency spectra of the hydrogen bonding organic small molecules. Transmission spectrum of each sample show several peaks in this region. On the other hand, ab initio frequency calculations are performed for each molecule by CRYSTAL06 package. Both experimental results and theoretical calculations are compared each other.

Observation of room temperature THz emission based on photoluminescence from Ge

Room temperature Terahertz (THz) emissions were observed from a single crystalline germanium (Ge) by photoluminescence mechanism. The emission mechanism can be explained by intracenter transition of antimony impurities in n-Ge. The emission spectrum contains two peaks corresponding to the 2P± →1S (T,A) (about 8.28 meV; 149.6µm), and 3P0 →1S (T,A) (about 7.45 meV; 166.3 µm) intra-center antimony transitions in n-Ge 1

Experimental and calculated terahertz spectra of naphthalene and 1,4-dihydroxynaphthalene in the 0.5 - 6 terahertz region

Far infrared (IR) spectra of naphthalene and 1,4-dihydroxynaphthalene (1,4-naphthol) were measured in the region from 0.5 to 6.3 THz at room temperature using a GaP THz wave generator. Quantum chemical calculations were performed to obtain normal mode coordinates and frequencies for an isolated molecule case of naphthalene and 1,4-naphthol.

Stimulated Raman gain spectroscopy of solutions by nanosecond pulsed and CW probe IR laser

Coherent Raman spectra of solutions have been studied with a stimulated Raman gain technique using a pump pulse with narrow bandwidth (3 GHz) and CW laser probe around 1 /spl mu/m. The spectra of benzene, toluene, CCl/sub 4/ and trehalose solute in water are presented and discussed in terahertz region.