Hiroshi Shimosato

Ultrabroadband terahertz generation using 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate single crystals

Ultrabroadband terahertz generation up to 200 THz has been demonstrated using a 5 fs Ti:sapphire laser and a 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) crystal. The high-frequency components beyond 100 THz are much stronger than those generated using conventional electro-optic crystals such as GaSe. A simple simulation of the difference frequency generation in the DAST crystal by considering the refractive index dispersion can reproduce the broadband generation of the terahertz wave and its chirp dependence. Because the generated terahertz wave is coherent and has a broad bandwidth, it can serve as a suitable light source for ultrabroadband terahertz time-domain spectroscopy of a material.

Hardening of the ferroelectric soft mode in SrTiO3 thin films

We have studied the origin of soft-mode hardening in SrTiO3 thin films using broadband terahertz time-domain spectroscopy. We measured the dielectric dispersions in the terahertz region of as-deposited, O2 annealed, and high-temperature annealed SrTiO3 thin films deposited on MgO and La0.3Sr0.7Al0.65Ta0.35O3 substrates. The results show that the ferroelectric soft mode softens dramatically by the high-temperature annealing. We also measure x-ray diffractions and atomic force microscope images and conclude that the hardening of the ferroelectric soft mode in the thin films is determined by the grain size of each crystalline domain which is enlarged by the high-temperature annealing due to remelting.

Ultrabroadband Detection of Terahertz Radiation from 0.1 to 100 THz with Photoconductive Antenna

We demonstrate ultrabroadband detection of terahertz electric field from 0.1 up to 100 THz with a dipole-type photoconductive antenna using an ultrashort pulse laser whose pulse width is approximately 10 fs. Ultrabroadband terahertz pulses are generated with a thin GaSe crystal and a low-temperature grown GaAs photoconductive antenna. The sensitivity of the photoconductive antenna is examined in mid-infrared region.

Ultrabroadband THz field detection beyond 170THz with a photoconductive antenna

We demonstrate ultrabroadband THz field detection with a photoconductive antenna using a combination of ultrashort laser pulses of 6 fs duration and a DAST crystal. We successfully observed ultra-high frequency component beyond 170 THz in near-infrared region.

Ultrabroadband THz wave detection using photoconductive antenna

We demonstrate ultrabroadband THz wave detection using a photoconductive antenna with a combination of an ultrashort pulsed laser with 5 fs pulse duration and a DAST crystal. We successfully detected an extremely wide frequency range from 0.5 to 170 THz.

Electric Field Detection of Near-Infrared Light Using Photoconductive Sampling

We demonstrate electric field detection of light using photoconductive sampling with a combination of ultrashort laser pulses of 5 fs duration and a DAST crystal. We successfully observed near-infrared component beyond 170 THz.

Electric field detection of coherent synchrotron radiation in a storage ring generated using laser bunch slicing

The electric field of coherent synchrotron radiation (CSR) generated by laser bunch slicing in a storage ring has been detected by an electro-optic sampling method. The gate pulses for sampling are sent through a large-mode-area photonic-crystal fiber. The observed electric field profile of the CSR is in good agreement with the spectrum of the CSR observed using Fourier transform far-infrared spectrometry, indicating good phase stability in the CSR. The longitudinal density profiles of electrons modulated by laser pulses were evaluated from the electric field profile.

Ultrabroadband electric field generation and detection from far infrared to optical communication frequency

We generated ultrabroadband coherent infrared wave with a frequency range of 0.1–200 THz using difference frequency generation in crystals of DAST, GaSe, and dipole radiation from a photoconductive antenna. Also we detected the wave by time domain spectroscopy with a photoconductive antenna.

Observation of Soft-Mode Hardening and Broadening in SrTiO 3 Thin Films by Broadband Terahertz Time-Domain Spectroscopy

Complex dielectric constants of SrTiO3 thin films have been measured using the broadband terahertz time-domain spectroscopy. The broad detection-bandwidth of the photoconductive antenna enables us to clarify soft-mode dispersions as well as the TO2 mode.

Coherent synchrotron terahertz radiation using electron bunch slicing

Coherent and strong terahertz wave is generated from a synchrotron light source using laser bunch slicing. The electric field is detected with the electro-optic sampling method using a Ti:sapphire oscillator for probe and a 24-m long large mode-area photonic crystal fiber for delivering it.