Toshiharu Sugiura

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.

Broad-spectrum frequency comb generation and carrier-envelope offset frequency measurement by second-harmonic generation of a mode-locked fiber laser

Frequency comb spanning more than one octave has been achieved by injecting the second harmonic generation (780 nm) of a mode-locked fiber laser (1.56 /spl mu/m) into a photonic crystal fiber. We propose and realize a novel interferometric scheme for observing the carrier-envelope offset frequency.

Broadband and high power terahertz pulse generation beyond excitation bandwidth limitation via χ (2) cascaded processes in LiNbO 3

We proposed a novel THz generation technique beyond the limitation of the input optical pulse width, based on phase modulation via cascaded chi((2)) process. When intense THz electric field generated by optical rectification lies in electro-optic (EO) crystal, emitted THz field gives phase modulation to the optical excitation pulse. The phase modulation causes excitation pulse narrowing and consequently gives rise to the enhancement of conversion efficiency and THz wave bandwidth broadening. We experimentally realize this generation technique with high chi((2)) EO crystal LiNbO(3) and with subpicosecond pulse from Yb-doped fiber laser. It opens new concept of THz technologies.

1.0–1.7-

A widely wavelength-tunable ultrashort-pulse fiber-laser source has been demonstrated using a high-power mode-locked ytterbium (Yb)-doped fiber laser and a highly nonlinear photonic crystal fiber (PCF). The Yb-doped fiber laser produces 66-fs ultrashort pulse at the wavelength of 1.05 mum. The pulse energy and the peak-power are 2 nJ and 20 kW, respectively. By injecting this pulse into the highly nonlinear PCF, soliton and anti-Stokes pulses are generated in the wavelength regions of 1.05-1.69 and 0.6-0.7 mum, respectively. The generated soliton pulse is 100-150-fs transform-limited sech2-shaped pulse

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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.

m Wavelength-Tunable Ultrashort-Pulse Generation Using Femtosecond Yb-Doped Fiber Laser and Photonic Crystal Fiber

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.

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

We present an all-fiber system for generating pedestal-free 22-fs ultrashort pulses with a single-peak spectrum. High-power Raman soliton pulses and a normally dispersive highly nonlinear fiber are used to generate a smooth, broadened single-peak spectrum. Then, the higher order dispersion is compensated for using a hybrid fiber composed of a reverse-dispersion fiber and a standard single-mode fiber, which allows pedestal-free ultrashort pulses to be successfully generated. To our knowledge, this is the first demonstration of pedestal-free 20-fs-class ultrashort pulse generation without spectral distortion using an all-fiber configuration.

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

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.

Generation of pedestal-free 22-fs ultrashort pulse using highly nonlinear fiber and reverse-dispersion fiber

We propose a novel technique for the generation of high power monocycle terahertz pulse beyond the excitation pulse width limitation. Optical pulse may get modulated by emitted intense THz electric field. This causes excitation pulse compression and consequently gives rise to the enhancement of generation efficiency and its bandwidth. We experimentally demonstrate this χ(2) cascaded processes using tilted wavefront excitation beam by LiNbO3 from Ti:Sapphire and Yb doped fiber laser.

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

We propose a novel technique for the generation of high power monocycle terahertz (THz) pulse beyond excitation pulse width limitation. When intense THz electric field generated by optical rectification lies in EO crystal, optical pulse itself gets modulated by emitted THz electric field. It causes excitation pulse compression and consequently gives rise to the enhancement of generation efficiency and its bandwidth. We experimentally demonstrate it using tilted wavefront excitation beam by LiNbO3 from Yb doped fiber laser.