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2-(3-(4-Hydroxystyry1)-5,5-dimethylcyclohex-2-enylidene) malononitrile (OH1) is the only organic nonlinear optical (NLO) crystal that can be crystallized by physical vapour deposition (PVD) for terahertz (THz) wave generation. We report some optimizations of the growth temperature conditions of single-crystalline thin film by PVD. After transforming the setting temperature conditions from 90–120–180 °C to 90–145–180 °C, we observed that the temperature conditions influence the size of the OH1 single-crystalline thin film. Moreover, we found that, when the temperature gradient conditions were held at 90–135–180 °C during PVD for the growth of OH1 single-crystalline thin film, the single-crystalline thin films had longer b-axial extensions, which may be better-suited to nonlinear optics. The infrared transmission spectroscopy absorption peak positions of the OH1 single-crystalline thin film fabricated in this study were the same as those of bulk OH1 crystal. The crystallinity of the OH1 single-crystalline thin film was higher than that of bulk OH1 crystal, under all temperature conditions. [ABSTRACT FROM AUTHOR]

In 2003, we demonstrated a non-destructive terahertz spectroscopic imaging of illicit drugs hidden in envelopes using a widely tunable THz-wave parametric source, though its dynamic range at that time was less than four orders. Recently, we have realized more than nine orders of dynamic range with an evolved injection seeded THz-wave spectrometer. Now we can detect drugs under much thicker obstacles than before. In this report, we introduce the result of THz spectroscopic imaging of chemicals under thick envelopes and related topics; Enhanced tuning range of is-TPG up to 5 THz and >90 dB dynamic range THz spectroscopic system. [ABSTRACT FROM AUTHOR]

The hottest frequency region in terms of research currently lies in the 'frequency gap' region between microwaves and infrared: terahertz waves. Although new methods for generating terahertz radiation have been developed, most sources cannot generate high-brightness terahertz beams. Here we demonstrate the generation of ultrabright terahertz waves (brightness ∼0.2 GW/sr·cm2, brightness temperature of ∼1018 K, peak power of >50 kW) using parametric wavelength conversion in a nonlinear crystal; this is brighter than many specialized sources such as far-infrared free-electron lasers (∼1016 K, ∼2 kW). We revealed novel parametric wavelength conversion using stimulated Raman scattering in LiNbO3 without stimulated Brillouin scattering using recently-developed microchip laser. Furthermore, nonlinear up-conversion techniques allow the intense terahertz waves to be visualized and their frequency determined. These results are very promising for extending applied research into the terahertz region, and we expect that this source will open up new research fields such as nonlinear optics in the terahertz region. [ABSTRACT FROM AUTHOR]

Intense Terahertz (THz)-wave generation and highly sensitive THz-wave detection were obtained by wavelength conversion with nonlinear optical susceptibility χ of LiNbO crystals. Maximum peak output of about 50 kW (5 μJ/pulse) was demonstrated in an injection-seeded THz-wave parametric generator pumped by post-amplified emission from a microchip Nd:YAG laser. Using the sub-nanosecond pulse duration of the laser proposed herein provides effective mitigation of stimulated Brillouin scattering in LiNbO, producing higher gain for wavelength conversion between near-infrared (near-IR) pump light and THz waves. Monochromatic THz radiation was obtained in the continuous tuning range of 0.7-2.9 THz. Additionally, highly sensitive THz-wave detection was demonstrated based on up-conversion from THz waves to near-IR light as well as efficient THz-wave generation. The signal generated with non-collinear phase-matching condition showed spectroscopic detection on the screen apart from the LiNbO crystal. Highly sensitive detection with minimum energy of about 80 aJ/pulse (0.8 μW at peak) and a large dynamic range of more than 100 dB were achieved in this experiment. [ABSTRACT FROM AUTHOR]

We have obtained efficient terahertz (THz)-wave generation from surface-emitting or waveguide propagation using Cherenkov-type radiation with nonlinear optical (NLO) crystals. This approach presented the following advantages: 1) many crystals can be used as THz-wave emitters; 2) it is not necessary to satisfy the phase-matching condition inside the crystal; and 3) THz-wave generation is not suppressed by the absorption in the crystal. We demonstrated that the THz-wave generation was enhanced 50× by suppressing the phase mismatch with a surfing configuration for bulk lithium niobate (LiNbO3) crystals. Using the prism-coupled Cherenkov phase-matching method with organic crystal 4-dimethylamino-N-metyl-4-stilbazolium tosylate, we produced tunable THz radiation within ∼0.1–10 THz. There was no evidence of significant absorption in the crystal. To show the advantages of the waveguide emitter, we demonstrated THz generation using a ridge-type LiNbO3 waveguide with a thickness of 3.8 μm. We obtained THz-wave generation with an ideal temporal half-cycle pulse and a wide tuning range, which is applied to reflection tomography imaging. [ABSTRACT FROM PUBLISHER]

Abstract: We have suggested a wide range of real-life applications using novel terahertz imaging techniques. A high-resolution terahertz tomography has been demonstrated by ultra short terahertz pulses using optical fiber and a nonlinear organic crystal. We also describe a nondestructive inspection system that can monitor the soot distribution in a ceramic filter using millimeter-to-terahertz wave computed tomography. Further, we report on the thickness measurement of very thin films using high-sensitivity metal mesh filter. These techniques are directly applicable to the nondestructive testing in industries. [ABSTRACT FROM AUTHOR]

In this article, we discuss broadband-tunable terahertz-wave parametric generation (TPG) via stimulated polariton scattering and techniques for narrowing the output spectrum of sources based on this phenomenon. The TPG effect, which is observed when a LiNbO3 crystal is excited with nanosecond pulses from a Nd:YAG laser, has a gain bandwidth of over 500 GHz. After carrying out experiments aimed at converting the TPG effect into a high-power source of terahertz waves, we used our TPG light source for Fourier spectroscopy in the terahertz band. In addition, we were able to narrow the spectral bandwidth of the terahertz emission down to the Fourier limit (spectral purity Δν/ν∼10-4) by applying the method of optical injection seeding to the TPG using light from a wavelength-tunable semiconductor laser. When we used the light from this injection-seeded TPG source for the spectroscopy of water vapor in the terahertz region, we confirmed a resolution below 100 MHz (0.003 cm-1). Our final version of an injection-seeded TPG light source exhibited peak powers of over 300 mW (dynamic range > 106), and a frequency tunability of 0.7 to 2.4 THz. We anticipate that this compact nonlinear-optics-based terahertz wave light source, which can operate at ordinary temperatures and is structurally simple, can become an effective tool for scientific and technological research in the terahertz region. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(5): 52–65, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10047 [ABSTRACT FROM AUTHOR]

By using room-temperature parametric oscillation of LiNbO3 pumped by a Q-switched Nd:YAG laser, a tunable terahertz-wave source in the range between 1 and 2 THz has been realized with a simple configuration. Since the terahertz wave is strongly absorbed inside the crystal and is affected by total internal reflection at the crystal edge, terahertz radiation outside the crystal has been difficult. A grating coupler and a prism coupler have resulted in wide tunability, high efficiency, and high spatial coherency. In this paper, the basic configuration of the optical source, various radiation characteristics, and the terahertz spectroscopic system using the present source are described. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(7): 10–18, 1998 [ABSTRACT FROM AUTHOR]