Tomoya Hirosumi

Generation and detection of terahertz radiation by electro-optical process in GaAs using 1.56μm fiber laser pulses

We report the generation and detection of a terahertz wave with a nonresonant electro-optical crystal using 1.56μm femtosecond laser pulses. Using a 0.5-mm-thick (110)-oriented GaAs wafer for optical rectification and electro-optical modulation, we detected spectral sensitivity below 3THz. We also estimated the availability of GaAs from the viewpoint of an electro-optical coefficient and phase match condition.

Excitation wavelength dependence of terahertz emission from semiconductor surface

The authors have measured terahertz radiation from InSb, InAs, and InGaAs excited by femtosecond optical pulses at wavelengths of 1560, 1050, and 780nm. The amplitude of the terahertz field strongly depends on the pump wavelengths. Among the materials, the InSb emitter shows the largest terahertz emission amplitude at high power 1560nm excitation, whereas 780nm excitation provides the weakest. With increasing photon energy, the increase in emission amplitude from InAs is less as compared to that from InGaAs. The decrease from InSb and InAs originates in low mobilities of L or X valley carriers generated by intervalley scatterings.

Significant enhancement of terahertz radiation from InSb by use of a compact fiber laser and an external magnetic field

We investigated the magnetic-field dependence of terahertz (THz) radiation power from InSb. Significant enhancement of THz-radiation power is observed by using a compact fiber laser that delivered 100 fs optical pulses at a center wavelength of 1560 nm. Additionally, applying external magnetic fields dramatically enhanced the THz-radiation power. THz-radiation power reaches a maximum value at around 1.2 T, and its enhancement factor exceeds 100. From an applications viewpoint, this is a significant finding for practical light source design, since it is easily achieved by using a compact fiber laser and a conventional magnet.

Evaluation of a terahertz wave spectrum and construction of a terahertz wave-sensing system using a Yb-doped fiber laser

We experimentally evaluated a cadmium-telluride (CdTe) crystal as the nonlinear crystal for generation and detection of terahertz (THz) radiation by using a femtosecond-pulse laser. Numerical simulations based on the nonlinear Maxwell equations, including third-order optical dispersion within the spectral width of an optical pulse and absorption in the THz frequency region, well reproduce both the amplitude and phase spectra of the emitted THz wave. Excitation wavelength dependences of the THz radiation from the CdTe crystal indicate that the phase-matched condition is satisfied at a wavelength of 1000 nm. We also experimentally demonstrated a THz generation and detection system using a 1045 nm Yb-doped ultrashort-pulse fiber laser, and we verified that CdTe is one of the most suitable nonlinear crystals for a Yb-doped fiber laser.

Simultaneous measurement of thickness and water content of thin black ink films for the printing using THz radiation

Using THz radiation, a simple, noncontact, simultaneous method is applied to measure thickness and water content of black ink films independently from frequency-dependent and frequency-independent absorption characteristics of black ink films.

Generation and detection of terahertz radiation by non-resonant nonlinear process in GaAs using 1.56 /spl mu/m fiber laser pulses

We demonstrate the generation and detection of a terahertz wave by non-resonant electro-optical processes with femtosecond 1.56 /spl mu/m laser pulses. Using a 0.5 mm-thick [110]-oriented GaAs wafer for optical rectification and electro-optical modulation, we achieve spectral sensitivity up to 3 THz. For high net efficiency of nonlinear process, it is important to evaluate the phase matching condition in electro-optical crystals.

Visualization of carbon black distribution in rubber vulcanizates by terahertz time-domain spectroscopy

The distribution of carbon black (CB) in rubber vulcanizates containing several additives such as carbon black, zinc oxide, etc. was estimated by terahertz time-domain spectroscopy. It was found that the CB distribution could be clearly visualized by this method and the THz measurements indicated high reproducibility.

Distribution variation of carbon black in tensile-tested rubbers estimated by terahertz time-domain spectroscopy

The dependence of a carbon black (CB) dispersion in a tensile-tested specimen of a vulcanized rubber on the compounding ratio of CB was evaluated by terahertz time-domain spectroscopy (THz-TDS). The near broken-out section of the specimens were investigated by THz-TDS, and the distribution of the absorbance in the THz regime, which directly affected by the CB dispersion, was investigated. It was found that the THz image of the CB dispersion in the samples showed a biased distribution between the fixed side and the pulled side of the tensile-tested specimens. It was also found that the difference of the CB dispersion of the both sides was decreased with the CB ratio.

THz Wave Generation and Detection System using ∼1000 nm Yb-doped Fiber Laser

The THz generation and detection system using ∼1000 nm Yb-doped ultrashort pulse fiber laser has been constructed. We compared three binary zinc blende semiconductors CdTe, GaAs, and ZnTe as the nonlinear optical crystals for THz radiation. The phase matching condition of THz generation is satisfied in CdTe at the pumping wavelength of ∼1000 nm. At the condition, the intensity of THz wave becomes very high and its spectrum spreads widely. This behavior agrees with our simulation based on phase-matching condition.

Terahertz emissions from semiconductors excited by femtosecond pulses at wavelengths of 1560, 1050 and 780 nm

THz emissions from semiconductor surfaces excited by laser pulses at 780, 1050 and 1560 nm wavelengths have been investigated. InSb is the most efficient emitter for 1560 nm excitation in the other emitters.