Highly intense monocycle terahertz vortex generation by utilizing a Tsurupica spiral phase plate.

Optical vortex, possessing an annular intensity profile and an orbital angular momentum (characterized by an integer termed a topological charge) associated with a helical wavefront, has attracted great attention for diverse applications due to its unique properties. In particular for terahertz (THz) frequency range, several approaches for THz vortex generation, including molded phase plates consisting of metal slit antennas, achromatic polarization elements and binary-diffractive optical elements, have been recently proposed, however, they are typically designed for a specific frequency. Here, we demonstrate highly intense broadband monocycle vortex generation near 0.

Evaluation of polarized terahertz waves generated by Cherenkov phase matching.

We report terahertz (THz) wave generation by satisfying Cherenkov phase-matching condition in both s and p polarizations. A dual-wavelength optical parametric oscillator is constructed from two potassium titanium oxide phosphate crystals pumped by a frequency-doubled Nd:YAG laser. By rotating the orientation of both a lithium niobate crystal (LiNbO3) and the polarization of the pump waves, the polarization of the THz wave changes.

Broadband THz-wave generation by satisfying the noncollinear phase-matching condition with a reflected signal beam.

We demonstrated broadband terahertz (THz) wave generation by satisfying the noncollinear phase-matching condition with a reflected signal beam. We constructed a dual-wavelength optical parametric oscillator with two potassium titanium oxide phosphate crystals pumped by a frequency-doubled Nd:YAG laser. The collinear pump and signal waves were irradiated into a lithium niobate crystal.

THz-wave sensing via pump and signal wave detection interacted with evanescent THz waves.

We report a novel sensing technique that uses an evanescent terahertz (THz) wave, without detecting the THz wave directly. When a THz wave generated by Cherenkov phase matching via difference frequency generation undergoes total internal reflection, the evanescent THz wave is subject to a phase change and an amplitude decrease. The reflected THz wave, under the influence of the sample, interferes with the propagating THz wave and the changing electric field of the THz wave interacts with the electric field of the pump waves.

Entangled photon generation in two-period quasi-phase-matched parametric down-conversion.

We proposed and demonstrated a simple but deterministic scheme for generating polarization-entangled photon pairs at telecommunication wavelengths with type-II quasi-phase-matched spontaneous parametric down-conversion (QPM-SPDC) having two poling periods. We fabricated a LiNbO3 crystal having two poling periods so as to generate entangled photons at two wavelengths, i.e.

Prism-coupled Cherenkov phase-matched terahertz wave generation using a DAST crystal.

Terahertz (THz) wave generation based on nonlinear frequency conversion is a promising method for realizing a tunable monochromatic high-power THz-wave source. Unfortunately, many nonlinear crystals have strong absorption in the THz frequency region. This limits efficient and widely tunable THz-wave generation.

High-resolution time-of-flight terahertz tomography using a femtosecond fiber laser.

High-resolution tomographic imaging is demonstrated using a reflection-type terahertz time-domain spectroscopy. To realize a practical system for general use, a robust all-fiber laser was used as the pump light source. Broadband terahertz waves were generated with the combination of optical pulses compressed to 17 fs using optical fibers and a DAST crystal.

Cherenkov phase matched THz-wave generation with surfing configuration for bulk lithium nobate crystal.

We demonstrated a Cherenkov phase matched THz-wave generation with surfing configuration for bulk lithium niobate crystal. THz-wave output was enhanced about 50 times by suppressing phase mismatching for THz-wave propagation direction. The suppression was achieved by combining two pumping waves with dual wavelength with finite angle, and THz-frequency was controllable by changing the angle within 2.

Extremely frequency-widened terahertz wave generation using Cherenkov-type radiation.

Terahertz (THz) wave generation based on nonlinear frequency conversion is promising way for realizing a tunable monochromatic bright THz-wave source. Such a development of efficient and wide tunable THz-wave source depends on discovery of novel brilliant nonlinear crystal. Important factors of a nonlinear crystal for THz-wave generation are, 1.

Generation and detection of broadband coherent terahertz radiation using 17-fs ultrashort pulse fiber laser.

We describe the generation and detection of broadband terahertz radiation using an all-fiber laser. Optical pulses from a mode-locked fiber laser oscillator are compressed using nonlinear and dispersion effects induced in optical fibers, and 17-fs optical pulses with 170-kW peak power are generated at the wavelength region around 1.5 microm.

Cherenkov phase-matched monochromatic THzwave generation using difference frequency generation with a lithium niobate crystal.

We demonstrated a Cherenkov phase-matching method for monochromatic THz-wave generation using the difference frequency generation process with a lithium niobate crystal, which resulted in high conversion efficiency and wide tunability. We successfully generated monochromatic THz waves across the range 0.2-3.

Terahertz-wave generation in a conventional optical fiber.

We theoretically propose surface-emitted and collinear phase-matched terahertz (THz)-wave generation in a conventional optical fiber. The third-order nonlinear effect, four-wave mixing (FWM), is used to generate THz waves in an optical fiber. Surface-emitted THz-wave generation via FWM is realized using a single-mode fiber.

High-power terahertz-wave generation using DAST crystal and detection using mid-infrared powermeter.

The exact power output of a table-top-sized terahertz (THz)-wave source using a nonlinear optical process has not been clarified because detectors for these experiments [Si bolometer, deuterated triglycine sulfate (DTGS), etc.] are not calibrated well. On the other hand, powermeters for the mid-infrared (mid-IR) region are well established and calibrated.